tag:theconversation.com,2011:/au/topics/innate-immune-response-12501/articlesInnate immune response – The Conversation2023-07-31T01:25:32Ztag:theconversation.com,2011:article/2095212023-07-31T01:25:32Z2023-07-31T01:25:32ZWhat is food protein-induced enterocolitis syndrome or FPIES? And are more babies getting it?<figure><img src="https://images.theconversation.com/files/537971/original/file-20230718-27-ju6ir8.jpg?ixlib=rb-1.1.0&rect=17%2C11%2C3817%2C2144&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/adorable-sad-caucasian-baby-crying-high-2054346290">Shutterstock</a></span></figcaption></figure><p>Parents, carers and childcare settings are much more aware of <a href="https://www.healthdirect.gov.au/partners/national-allergy-strategy">food allergies</a> than they once were. Precautions are taken and emergency plans can be developed for each child at risk of a reaction. But fewer people have heard of food protein-induced enterocolitis syndrome (FPIES). </p>
<p>FPIES is a poorly understood food allergy that mostly affects infants. It can be caused by a variety of foods including some not usually associated with food allergies like rice, oats and vegetables. Other causes are more typical of food allergies, like cow’s milk and <a href="https://onlinelibrary.wiley.com/doi/abs/10.5694/mja2.12071">egg</a>. The most common symptom is profuse, repetitive vomiting one to four hours after <a href="https://www.allergy.org.au/patients/food-other-adverse-reactions/food-protein-induced-enterocolitis-syndrome-fpies">eating the food</a>. </p>
<p>Reactions can be dramatic and worrying for parents, with infants becoming pale, lethargic (sleepy) and floppy. In severe cases, infants develop dehydration and low blood pressure. The diagnosis is often not made the first time a reaction occurs, because of the wide range of diseases which can cause these symptoms and the time delay between when a trigger food is ingested and the onset of symptoms. </p>
<p>Until recently, FPIES was thought to be rare, but new evidence suggests it is <a href="https://onlinelibrary.wiley.com/doi/abs/10.5694/mja2.12071">more common than previously thought</a>. The past decade has also seen significant research efforts trying to identify what part of the immune system is responsible for causing FPIES reactions, to identify better tests for diagnosis and management.</p>
<h2>What is it that causes symptoms?</h2>
<p>We don’t currently know much about the immune dysregulation that causes FPIES. </p>
<p>FPIES is classified as a <a href="https://www.rch.org.au/uploadedFiles/Main/Content/allergy/Non%20IgE%20Food%20Allergy.pdf">non-IgE mediated food allergy</a>, differing from other types of more common food allergy like peanut allergy, where reactions are caused by <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6640697/">allergy antibodies</a> that can be detected in the blood. </p>
<p>That also means medications used for treatment of these types of allergies (such as EpiPens and antihistamine) do not work in FPIES. <a href="https://pubmed.ncbi.nlm.nih.gov/33548465/">Recent studies</a> suggest another part of the immune system, called the innate system might be involved. This system is the body’s <a href="https://www.hopkinsmedicine.org/health/conditions-and-diseases/the-immune-system">first line of defence</a> against potential invaders. It <a href="https://www.ncbi.nlm.nih.gov/books/NBK279396/">includes</a> bacteria that fights off bugs or injuries, rather than cells that adapt to respond to threats.</p>
<h2>Missed cases?</h2>
<p>Symptoms of FPIES can be mistaken for other conditions such as gastroenteritis (“gastro”), twisted bowel or serious blood infections. This can delay diagnosis.</p>
<p>Unlike most other types of food allergies, which have reactions caused by allergy antibodies, there is no blood test to diagnose FPIES. Diagnosis relies on careful clinical history and may require a specialised <a href="https://www.allergy.org.au/patients/food-other-adverse-reactions/food-protein-induced-enterocolitis-syndrome-fpies">oral food challenge</a>. This can involve removing foods suspected of causing a reaction from the diet and then reintroducing them one-by-one in planned stages under medical supervision. </p>
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Read more:
<a href="https://theconversation.com/i-think-my-child-has-outgrown-their-food-allergy-how-can-i-be-sure-130455">I think my child has outgrown their food allergy. How can I be sure?</a>
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<h2>How common is FPIES and is it becoming more common?</h2>
<p>Because it is under-recognised and difficult to diagnose, estimates of FPIES prevalence <a href="https://www.jaci-inpractice.org/article/S2213-2198(19)30727-5/fulltext">vary considerably</a> – between 0.015% to 0.7% of infants.</p>
<p>Although data is sparse, some studies report an increase in rates of FPIES. A study of Australian and New Zealand hospital data reported <a href="https://onlinelibrary.wiley.com/doi/10.1111/jpc.13767">hospital admissions had tripled</a> for infants with symptoms consistent with potential FPIES between 1998 and 2014. </p>
<p>An increasing awareness of FPIES, as well as improvements in diagnosis, mean FPIES diagnoses may increase without a true increase in the condition. Different estimates of FPIES rates <a href="https://pubmed.ncbi.nlm.nih.gov/31950904/">between countries</a> (for example 0.15% in Australia and 0.7% in Spain) may be due to true differences or variations in diagnosis and reporting. More research is needed to understand these differences.</p>
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<a href="https://images.theconversation.com/files/537967/original/file-20230718-29-qyquvs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="parent feeds child by spoon at table" src="https://images.theconversation.com/files/537967/original/file-20230718-29-qyquvs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/537967/original/file-20230718-29-qyquvs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/537967/original/file-20230718-29-qyquvs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/537967/original/file-20230718-29-qyquvs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/537967/original/file-20230718-29-qyquvs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/537967/original/file-20230718-29-qyquvs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/537967/original/file-20230718-29-qyquvs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Infants may outgrow their allergies.</span>
<span class="attribution"><a class="source" href="https://images.unsplash.com/photo-1563263427-708318a97183?ixlib=rb-4.0.3&ixid=M3wxMjA3fDB8MHxwaG90by1wYWdlfHx8fGVufDB8fHx8fA%3D%3D&auto=format&fit=crop&w=1744&q=80">Unsplash</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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<h2>What foods trigger FPIES?</h2>
<p>Different foods appear to commonly cause FPIES in different countries. In Australia, rice is the most <a href="https://onlinelibrary.wiley.com/doi/10.1111/pai.13448">reported FPIES trigger</a>, with cow’s milk, soy and eggs also common. Cow’s milk is the most common reported trigger in the <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10273880/">United States and Europe</a>. Fish is a common trigger reported in Mediterranean <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10273880/">countries</a>, and increasingly reported as a cause of FPIES in older children and <a href="https://pubmed.ncbi.nlm.nih.gov/35753669/">adults</a>. It is unclear what causes these differences, which may only be partially explained by differences in infant feeding and weaning practices between countries. </p>
<p>Reactions often occur for the first time in infancy with the introduction of a new food, either on the first exposure or after the first few exposures. Most affected babies only react to a single food, although some foods cross-react. This means infants have a <a href="https://onlinelibrary.wiley.com/doi/abs/10.5694/mja2.12071">similar response</a> to related foods such as with grains (rice and oats); cow’s milk and soy; fish and shellfish. Those with FPIES need to avoid the foods that trigger FPIES reactions, but there is often no need to avoid other non-related foods. </p>
<p>Most children will outgrow FPIES in their first few years of life. There appear to be differences in how quickly FPIES resolves depending on the trigger food, with cow’s milk and grains FPIES <a href="https://onlinelibrary.wiley.com/doi/abs/10.5694/mja2.12071">resolving more quickly</a> than egg and seafood FPIES. Adults can also develop FPIES, however this is <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9234874/">less common</a>.</p>
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Read more:
<a href="https://theconversation.com/can-i-prevent-food-allergies-in-my-kids-88873">Can I prevent food allergies in my kids?</a>
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<h2>What to do if you suspect you or your child has FPIES</h2>
<p>If you think that you or your child may have FPIES, talk to your doctor. They may recommend a referral to an allergist for assessment. </p>
<p>The next step may be developing an <a href="https://www.allergy.org.au/patients/food-other-adverse-reactions/fpies-action-plan">action plan</a> for a FPIES reaction. For severe reactions, such as when an infant becomes dehydrated or floppy after vomiting or diarrhoea, seek specialist care at your closest hospital emergency department. </p>
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Read more:
<a href="https://theconversation.com/early-exposure-to-infections-doesnt-protect-against-allergies-but-getting-into-nature-might-126603">Early exposure to infections doesn't protect against allergies, but getting into nature might</a>
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<p class="fine-print"><em><span>Dianne Campbell receives part-time salary from DBV Technologies and reports grants from the National Health and Medical Research Council of Australia and received advisory board fees from Allergenis Technologies and Westmead Fertility Centre. She is affiliated with Sydney University and the Sydney Children’s Hospitals Network. </span></em></p><p class="fine-print"><em><span>Eric Lee and Jennifer Koplin do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>You can’t test for this little-known food allergy that usually affects infants – and the symptoms can be very worrying.Jennifer Koplin, Group Leader, Childhood Allergy & Epidemiology, The University of QueenslandDianne Campbell, Professor, Child and Adolescent Health, Faculty of Medicine and Health,, University of SydneyEric Lee, Department of Allergy & Immunology at the Children's Hospital at Westmead, University of SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1687082021-11-03T11:23:09Z2021-11-03T11:23:09ZWhy vaccine doses differ for babies, kids, teens and adults – an immunologist explains how your immune system changes as you mature<figure><img src="https://images.theconversation.com/files/429805/original/file-20211102-19-1cqiw40.jpg?ixlib=rb-1.1.0&rect=0%2C896%2C5503%2C4032&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Many vaccine formulations are tweaked for patients of different ages.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/student-andy-melgar-checks-in-with-emt-alfonso-deza-after-news-photo/1327357664">Mario Tama via Getty Images</a></span></figcaption></figure><p>Human beings are born pretty helpless, with a lot of developing to do. And just as you must learn such skills as how to walk, so must your immune system learn to defend against infections. As time passes, your immune system matures through different stages, much the way you advanced from crawling to standing, walking and running.</p>
<p>This process is one of the reasons scientists study the immune response to a vaccine in different age groups, and why, for example, the COVID-19 vaccines need to be tested separately in children ages 5-11 and those 12-16. Doctors want to use the vaccine dose that provides the best protection with the fewest side effects. And that’s going to depend on how the immune system is working based on how developed it is – something you can’t really tell from the outside.</p>
<p><a href="https://directory.hsc.wvu.edu/Profile/56680">I’m an immunologist</a>, and here’s the way I explain to my pediatric and adult patients how vaccines work in people of all different ages. </p>
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<a href="https://images.theconversation.com/files/429806/original/file-20211102-29191-vtodoe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="baby at mother's breast" src="https://images.theconversation.com/files/429806/original/file-20211102-29191-vtodoe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/429806/original/file-20211102-29191-vtodoe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=454&fit=crop&dpr=1 600w, https://images.theconversation.com/files/429806/original/file-20211102-29191-vtodoe.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=454&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/429806/original/file-20211102-29191-vtodoe.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=454&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/429806/original/file-20211102-29191-vtodoe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=571&fit=crop&dpr=1 754w, https://images.theconversation.com/files/429806/original/file-20211102-29191-vtodoe.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=571&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/429806/original/file-20211102-29191-vtodoe.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=571&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">A newborn’s immune system still has a lot to learn and relies on supports from mom.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/close-up-of-mother-breastfeeding-baby-boy-while-royalty-free-image/1203911366?adppopup=true">Paulo Sousa/EyeEm via Getty Images</a></span>
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<h2>Two halves of the immune system</h2>
<p>The immune maturing process starts shortly after birth.</p>
<p>When you’re born, your main immune protection comes via antibodies your mother shared through the placenta and breast milk. They provide what’s called passive immunity. <a href="https://doi.org/10.3389/fimmu.2020.595297">Newborns’ adaptive immune system</a> – the part of your immune system that will make your own antibodies – isn’t really up and running yet. The process gets started right away, but it can take years for the adaptive immune system to reach full maturity.</p>
<p>Luckily you’re also born with what’s called the <a href="https://www.ncbi.nlm.nih.gov/books/NBK279396/">innate immune system</a> – and it lasts throughout your life. It doesn’t need to learn in order to fight off infections and promote health as the adaptive immune system does. Without the innate immune system people would get sick a lot faster and more often.</p>
<p>The innate immune system starts with your skin and mucous membranes. Should any germs get past those physical barriers, it has enzymes just waiting to break down foreign organisms. Beyond that there are specialized cells looking for anything that is not you in order to kill intruders, while other cells called phagocytes gobble up invaders.</p>
<p>So the innate immune system is <a href="https://www.forbes.com/sites/fionamcmillan/2019/02/26/the-immune-systems-first-responders-are-smarter-than-we-thought/?sh=5fdc40261d82">your body’s first responder</a>. It buys you a bit of time. Then your adaptive immune system comes in and joins the fight.</p>
<p>When you become immunized via a vaccine or infection, your adaptive immune system starts actively making antibodies of your own. They’re proteins that act like suction cups and stick to viruses or bacteria to help the body get rid of the germs faster and prevent the infection from spreading. Antibodies are specialized to recognize and take down a particular intruder.</p>
<p>The adaptive immune system can learn a new infection or recall one that it has not seen in a long time.</p>
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<a href="https://images.theconversation.com/files/429808/original/file-20211102-29670-eqps6i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="frozen vaccine vials" src="https://images.theconversation.com/files/429808/original/file-20211102-29670-eqps6i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/429808/original/file-20211102-29670-eqps6i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/429808/original/file-20211102-29670-eqps6i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/429808/original/file-20211102-29670-eqps6i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/429808/original/file-20211102-29670-eqps6i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/429808/original/file-20211102-29670-eqps6i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/429808/original/file-20211102-29670-eqps6i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">The dose that works for adults might not be appropriate for youngsters of different ages.</span>
<span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/VirusOutbreakBiden/d89b46b600de4f7d9f834aa4901fb24c/photo?boardId=d7f2514f50804466b15dfb81ed00d9cd&st=boards&mediaType=audio,photo,video,graphic&sortBy=&dateRange=Anytime&totalCount=52&currentItemNo=0">AP Photo/Francisco Seco</a></span>
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<h2>Vaccines account for immune development</h2>
<p>In the same way an infant will learn to walk even if you don’t secure the stairways and pool areas for them, your immune system can learn to squelch an invading virus without a vaccine – but the chance of injury is much greater. </p>
<p>Vaccines work by triggering the creation of antibodies that will recognize a specific germ and work to fight it off in a safer manner than getting the infection for the first time without it. How well a vaccine works is a combination of how many antibodies you produce in response to it, how effective they are and the safety of the vaccine.</p>
<p>When researchers work to fine-tune the dosage of a vaccine for different age groups, they need to be aware of what parts of the immune system are online and what parts aren’t fully active in people at each developmental stage. This is part of the reason some vaccines – <a href="https://theconversation.com/kids-arent-just-littler-adults-heres-why-they-need-their-own-clinical-trials-for-a-covid-19-vaccine-162821">such as for COVID-19</a> – <a href="https://theconversation.com/the-fda-authorizes-pfizers-covid-19-vaccine-for-children-ages-5-to-11-a-pediatrician-explains-how-the-drug-was-tested-for-safety-and-efficacy-169907">get tested and approved on different schedules</a> for adults, teens, kids and babies.</p>
<p>A number of vaccines for infants are given as a series – meaning they get the same kind of shot several times over the course of a few months. A baby’s adaptive immune system is prone to being forgetful or not listening at this age – the same way a baby falters as it tries to stand and walk. With each exposure, every aspect of the immune system <a href="https://doi.org/10.1038/cr.2009.139">gets stronger and better</a> at defending against the would-be infection.</p>
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<a href="https://images.theconversation.com/files/429732/original/file-20211102-54176-3uy4s0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="chart listing vaccination schedule for young children" src="https://images.theconversation.com/files/429732/original/file-20211102-54176-3uy4s0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/429732/original/file-20211102-54176-3uy4s0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/429732/original/file-20211102-54176-3uy4s0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/429732/original/file-20211102-54176-3uy4s0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/429732/original/file-20211102-54176-3uy4s0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=369&fit=crop&dpr=1 754w, https://images.theconversation.com/files/429732/original/file-20211102-54176-3uy4s0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=369&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/429732/original/file-20211102-54176-3uy4s0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=369&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Some vaccines need to be given multiple times.</span>
<span class="attribution"><a class="source" href="https://www.cdc.gov/vaccines/schedules/easy-to-read/child-easyread.html">CDC National Center for Immunization and Respiratory Diseases</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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<p>After 4 years of age and through younger adult life, your immune system tends to be <a href="https://doi.org/10.1016/j.jaci.2018.02.017">more responsive and less prone to forgetting</a>. It’s not a coincidence that this is when people tend to <a href="https://www.uhhospitals.org/Healthy-at-UH/articles/2018/04/allergies-and-age">gain most of their allergies</a>. For the COVID-19 Pfizer vaccine, researchers found that kids ages 5 to 11 had a similar immune and safety response at <a href="https://www.pfizer.com/news/press-release/press-release-detail/pfizer-and-biontech-announce-positive-topline-results">one-third the dose</a> used for those ages 12 and up.</p>
<p>Scientists tend to start with patients between ages 18 and 55 years old when studying vaccines. Their adult immune systems have matured and they can be counted on to reliably report any adverse reactions. Seeing what happens in the adult age group also helps physicians predict what might occur when a vaccine is administered to others and be on the lookout for these side effects in the younger age groups.</p>
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<p>Around age 55 or so, the adaptive immune system <a href="https://doi.org/10.1098/rspb.2014.3085">starts to become weaker again and forgetful</a>, in some ways more like the infant’s developing system. Luckily vaccine boosters can provide a quick refresher for these older patients – like helping protect them from accidental falls after a lifetime having mastered walking and running.</p>
<p>In the end, vaccines provide the safest environment for the immune system to learn, and tweaking the dosages for different age groups helps ensure that each patient gets just what’s necessary to get the job done.</p><img src="https://counter.theconversation.com/content/168708/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Brian Peppers does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>First CDC signed off on a COVID-19 vaccine for adults, then teens. Now US children ages 5 to 11 are officially eligible for shots. Here’s the science on why each group needs to be considered separately.Brian Peppers, Assistant Professor of Pediatric and Adult Allergy/Immunology, West Virginia UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1587282021-04-19T12:26:18Z2021-04-19T12:26:18ZNo, vaccine side effects don’t tell you how well your immune system will protect you from COVID-19<figure><img src="https://images.theconversation.com/files/395509/original/file-20210416-15-4ygaa1.jpg?ixlib=rb-1.1.0&rect=856%2C297%2C6838%2C4899&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">It's not a bad sign if you feel fine after your COVID-19 shot.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/woman-proud-to-have-received-vaccine-royalty-free-image/1298099790">Luis Alvarez/DigitalVision via Getty Images</a></span></figcaption></figure><p><em>If someone gets a headache or feels a bit under the weather after receiving a COVID-19 vaccine, it’s become common to hear them say something like “Oh, it just means my immune system is really working hard.” On the flip side, when people don’t notice any side effects, they sometimes worry the shot isn’t doing its job or their immune system isn’t reacting at all.</em></p>
<p><em>Is there any link between <a href="https://www.cdc.gov/coronavirus/2019-ncov/vaccines/pdfs/321466-A_FS_What_Expect_COVID-19_Vax_Final_12.13.20.pdf">what you can notice after a vaccine</a> and what’s happening on the cellular level inside your body? <a href="https://www.umassmed.edu/news/news-archives/2020/12/robert-finberg-named-distinguished-professor-of-medicine/">Robert Finberg</a> is a physician who specializes in infectious diseases and immunology at the Medical School at the University of Massachusetts. He explains how this perception doesn’t match the reality of how vaccines work.</em></p>
<h2>What does your body do when you get a vaccine?</h2>
<p>Your immune system responds to the foreign molecules that make up any vaccine via two different systems.</p>
<p>The initial response is due to what’s called the <a href="https://www.ncbi.nlm.nih.gov/books/NBK26846/">innate immune response</a>. This system is activated as soon as your cells notice you’ve been exposed to any foreign material, from a splinter to a virus. Its goal is to eliminate the invader. White blood cells called neutrophils and macrophages travel to the intruder and work to destroy it.</p>
<p>This first line of defense is relatively short-lived, lasting hours or days.</p>
<p>The second line of defense takes days to weeks to get up and running. This is the long-lasting <a href="https://doi.org/10.1111/j.1600-065X.2008.00731.x">adaptive immune response</a>. <a href="https://doi.org/10.1101/2021.03.03.21252872">It relies on your immune system’s T and B cells</a> that learn to recognize particular invaders, such as a protein from the coronavirus. If the invader is encountered again, months or even years in the future, it’s these immune cells that will recognize the old enemy and start generating the antibodies that will take it down.</p>
<p>In the case of the SARS-CoV-2 vaccines, it takes approximately two weeks to develop the adaptive response that brings long-lasting protection against the virus.</p>
<p><a href="https://doi.org/10.1016/j.anai.2020.01.025">When you get the vaccine shot</a>, what you’re noticing in the first day or two is part of the innate immune response: your body’s inflammatory reaction, aimed at quickly clearing the foreign molecules that breached your body’s perimeter. </p>
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<p>It varies from person to person, but how dramatic the initial response is does not necessarily relate to the long-term response. In the case of the two mRNA COVID-19 vaccines, <a href="https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines/Moderna.html">well over 90% of people immunized</a> <a href="https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines/Pfizer-BioNTech.html">developed the protective adaptive immune response</a> while fewer than 50% <a href="http://dx.doi.org/10.15585/mmwr.mm7008e3">developed any side effects</a>, and most were mild. </p>
<p>You may never know how strongly your body’s adaptive immune response is gearing up.</p>
<p>The bottom line is you can’t gauge how well the vaccine is working within your body based on what you can detect from the outside. Different people do mount stronger or weaker immune responses to a vaccine, but post-shot side effects won’t tell you which you are. It’s the second, adaptive immune response that <a href="https://doi.org/10.1038/s41577-020-00479-7">helps your body gain vaccine immunity</a>, not the inflammatory response that triggers those early aches and pains.</p>
<h2>What are side effects, anyway?</h2>
<p>Side effects are normal responses to the injection of a foreign substance. They include things like fever, muscle pain and discomfort at the injection site, and are mediated by the innate immune response.</p>
<p>Neutrophils or macrophages in your body notice the vaccine molecules and produce cytokines – molecular signals that cause fever, chills, fatigue and muscle pain. Doctors expect this cytokine reaction to happen any time a foreign substance is injected into the body.</p>
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<span class="caption">You might not notice any symptoms at all after your COVID-19 vaccine.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/man-removes-his-hat-for-a-temperature-check-as-he-arrives-news-photo/1231819773">SOPA Images/LightRocket via Getty Images</a></span>
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<p>In studies where neither recipients nor researchers knew which individuals were getting the mRNA vaccine or a placebo, approximately <a href="https://doi.org/10.1056/NEJMoa2034577">half of people aged 16 to 55 who received a SARS-CoV-2 vaccine</a> developed a headache after the second dose. This reaction may relate to the vaccine – but a quarter of people who received just a placebo also developed a headache. So in the case of very common symptoms, it can be quite difficult to attribute them to the vaccine with any certainty.</p>
<p>Researchers anticipate some reports of side effects. <a href="https://www.pharmacytimes.com/view/adverse-event-not-the-same-as-side-effect">Adverse events</a>, on the other hand, are things that physicians do not expect to happen as a result of the vaccine. They would include organ failure or serious damage to any part of the body.</p>
<p>The blood clots that triggered the U.S. to <a href="https://theconversation.com/johnson-and-johnson-vaccine-suspension-a-doctor-explains-what-this-means-for-you-158923">pause distribution of the Johnson & Johnson vaccine</a> are a very rare event, apparently happening with one-in-a-million frequency. Whether they are definitely caused by the vaccine is still under investigation – but if scientists conclude they are, blood clots would be an extremely rare side effect. </p>
<h2>What component in the shot causes side effects?</h2>
<p>The only “active ingredient” <a href="https://doi.org/10.1056/NEJMoa2034577">in the Pfizer</a> and <a href="https://doi.org/10.1056/nejmoa2035389">Moderna vaccines</a> is the <a href="https://theconversation.com/what-is-mrna-the-messenger-molecule-thats-been-in-every-living-cell-for-billions-of-years-is-the-key-ingredient-in-some-covid-19-vaccines-158511">mRNA instructions that tell the recipient’s cells</a> to build a viral protein. But the shots have other components that help the mRNA travel inside your body.</p>
<p>To get the vaccine’s mRNA into the vaccinated person’s cells where it can do its job, it must evade enzymes in the body that would naturally destroy it. Researchers protected the mRNA in the vaccine by wrapping it in a bubble of lipids that help it avoid destruction. Other ingredients in the shots – like polyethylene glycol, which is part of this lipid envelope – could cause allergic responses.</p>
<h2>If I feel sick after my shot, does that signal strong immunity?</h2>
<p>Scientists haven’t identified any relationship between the initial inflammatory reaction and the long-term response that leads to protection. There’s no scientific proof that someone with more obvious side effects from the vaccine is then better protected from COVID-19. And there’s no reason that having an exaggerated innate response would make your adaptive response any better. </p>
<p><a href="https://doi.org/10.1056/NEJMoa2035389">Both the authorized</a> <a href="https://doi.org/10.1056/NEJMoa2034577">mRNA vaccines</a> provided protective immunity to over 90% of recipients, but fewer than 50% reported any reaction to the vaccine and far fewer had severe reactions.</p>
<p>[<em>Insight, in your inbox each day.</em> <a href="https://theconversation.com/us/newsletters/the-daily-3?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=insight">You can get it with The Conversation’s email newsletter</a>.]</p><img src="https://counter.theconversation.com/content/158728/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Robert Finberg receives funding from Pfizer for COVID-19 vaccine studies. He serves on the governor's vaccine advisory board for the state of Massachusetts. </span></em></p>It’s normal for different people to mount stronger or weaker immune responses to a vaccine, but post-shot side effects won’t tell you which you are.Robert Finberg, Professor of Medicine, UMass Chan Medical SchoolLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1555552021-02-18T07:30:07Z2021-02-18T07:30:07ZWhy do kids tend to have milder COVID? This new study gives us a clue<figure><img src="https://images.theconversation.com/files/384941/original/file-20210218-22-jyn87n.jpg?ixlib=rb-1.1.0&rect=0%2C1%2C1000%2C664&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/little-girl-hospital-child-doll-wearing-1681446460">from www.shutterstock.com</a></span></figcaption></figure><p>A new Australian study, <a href="https://www.nature.com/articles/s41467-021-21414-x">published overnight in Nature Communications</a>, gives an insight into how kids’ immune systems respond to infection with SARS-CoV-2, the virus that causes COVID-19.</p>
<p>It’s the first study, to my knowledge, that directly compares children and adults with mild COVID.</p>
<p>Children are less likely to become infected, and when they are, they are more likely to be asymptomatic. This is in contrast to other viral and respiratory infections that are more prevalent among young people.</p>
<p>This new research helps explain how kids’ immune systems work when confronted with the coronavirus — and gives us clues as to why they generally seem to fare better than adults.</p>
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Read more:
<a href="https://theconversation.com/worried-about-your-child-getting-coronavirus-heres-what-you-need-to-know-131909">Worried about your child getting coronavirus? Here's what you need to know</a>
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<h2>The kids (immune systems) are alright</h2>
<p>The researchers studied 48 kids, mostly in primary school, across 28 households during Melbourne’s second wave. All children were exposed to the coronavirus in their households by infected parents.</p>
<p>This study focused on the “innate” immune response in children, which forms the early part of the immune system’s attack on a virus (or bacteria, or other pathogens). The innate immune system plays an important role in viral protection before the body raises antibodies.</p>
<p>The study found there were dynamic changes in kids’ early immune responses, compared with coronavirus-infected adults. </p>
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Read more:
<a href="https://theconversation.com/explainer-what-is-the-immune-system-19240">Explainer: what is the immune system?</a>
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<p>One key innate immune cell that was elevated in children exposed to the virus was a type of white blood cell called “neutrophils”. These cells patrol the body for infections. When they discover a pathogen, they have a unique ability to respond by trapping and killing the invading pathogen (in this case, the coronavirus).</p>
<p>This role may ensure the virus is not able to infect more cells. This potentially decreases the “viral load”, basically the amount of virus in your body.</p>
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<a href="https://images.theconversation.com/files/384942/original/file-20210218-24-qinmbe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Neutrophil, shown in white, among red blood cells" src="https://images.theconversation.com/files/384942/original/file-20210218-24-qinmbe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/384942/original/file-20210218-24-qinmbe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/384942/original/file-20210218-24-qinmbe.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/384942/original/file-20210218-24-qinmbe.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/384942/original/file-20210218-24-qinmbe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/384942/original/file-20210218-24-qinmbe.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/384942/original/file-20210218-24-qinmbe.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">The researchers looked at neutrophils, a type of white blood cell.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/neutrophil-white-blood-cell-3d-illustration-1184857141">from www.shutterstock.com</a></span>
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<p>For some of the kids in the study, the early immune responses kept the viral load so low that they never returned a positive test, despite being tested throughout the study and having been exposed to coronavirus.</p>
<p>One strength of this study is that it was “longitudinal”, meaning it studied families over time, rather than simply at one point in time. The researchers looked at immune responses of the families just after their exposure to the virus, and returned more than 30 days later to see what had changed. This allowed them to identify the key changes induced because of the exposure to the virus.</p>
<h2>Kids vs adults</h2>
<p>A key question arising from this research is: why did the kids show such strong immune responses, resulting in few or no symptoms, while their parents were very ill?</p>
<p>It’s a difficult question to answer, at least so far. But the key differences in responses are likely to lie in the early responses of the immune system.</p>
<p>There is some previous research that might give some clues. </p>
<p><a href="https://www.pnas.org/content/117/40/24620">One theory</a> surrounds the fact that children have less of the receptors called “ACE2” in their respiratory tract. These receptors are the pathway of entry for the virus into our cells. In theory, less ACE2 receptors mean less chance for the virus to break in and infect our cells. Virus’ don’t survive for very long outside a cell. With less ACE2 receptors, it may give more time for the innate immune cells to control the virus as much as it can while waiting for other immune cells to come along and help.</p>
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<a href="https://theconversation.com/ace2-the-molecule-that-helps-coronavirus-invade-your-cells-138369">ACE2: the molecule that helps coronavirus invade your cells</a>
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<p>Another possibility relates to “interferons”, which are alert signals released by cells to tell the body there’s a virus around. <a href="https://immunology.sciencemag.org/content/5/49/eabd1554">Researchers think</a> higher levels of interferons during the early phase of an infection are very important for controlling coronavirus. Potentially, interferons may help promote the increased neutrophils that were seen in children, compared with lower numbers observed in adults. </p>
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<p>The wide range of symptoms in COVID are intriguing and frustrating at the same time. Conventional wisdom was that kids are more prone to getting sick with respiratory illnesses than adults — just ask any parent! But with COVID it seems to be the opposite. </p>
<p>Often when we think we’ve nailed down a specific mechanism as to how this new virus works and how our bodies respond to it, it turns out such a mechanism is different across different people. We can see this in the huge range of symptoms that different people display — some get a runny nose, others get a cough, and others suffer extreme exhaustion and respiratory distress or develop “long COVID”, in which symptoms drag on for months.</p>
<p>Coronavirus is still keeping immunologists on their toes. Studies like this one help solve some of the puzzle in understanding who’s at most at risk of severe disease and why.</p>
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Read more:
<a href="https://theconversation.com/five-life-lessons-from-your-immune-system-103425">Five life lessons from your immune system</a>
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<img src="https://counter.theconversation.com/content/155555/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Joanna Groom receives funding from NHMRC. </span></em></p>Children in the study seemed to display a very strong “innate” immune response.Joanna Groom, Laboratory Head, Walter and Eliza Hall InstituteLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1473912020-10-02T14:02:45Z2020-10-02T14:02:45ZOlder people like President Trump are at more risk from COVID-19 because of how the immune system ages<figure><img src="https://images.theconversation.com/files/361389/original/file-20201002-22-1i0nzfk.jpg?ixlib=rb-1.1.0&rect=391%2C270%2C4173%2C2891&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Masking up is one way to cut down on risk of COVID-19 infection.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/president-donald-trump-wears-a-face-mask-while-he-pays-his-news-photo/1228685397">Alex Brandon/Getty Images News via Getty Images</a></span></figcaption></figure><p>President Donald Trump’s announcement that <a href="https://twitter.com/realDonaldTrump/status/1311892190680014849">he’s tested positive for COVID-19</a> is especially concerning because of his age. At 74 years old, Trump is solidly within an age group that’s been hit hard during the coronavirus pandemic.</p>
<p>People of all ages can get sick from SARS-CoV-2, the virus that causes COVID-19. But the severity of the illness tends to worsen the older the patient is. Through the end of September, <a href="https://www.cdc.gov/nchs/nvss/vsrr/covid_weekly/index.htm#AgeAndSex">79% of COVID-19 deaths</a> in the United States had been in patients over 65. These statistics are <a href="https://doi.org/10.3855/jidc.12600">broadly similar</a> <a href="https://ourworldindata.org/coronavirus">in countries around the world</a>.</p>
<p>What is it that puts older people at increased risk from viruses like SARS-CoV-2? Scientists think it’s primarily due to changes in the human immune system as we age.</p>
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<h2>Your body’s tools to fight off virus infections</h2>
<p>As you go about your life, your body is constantly bombarded by pathogens – the bacteria, fungi and viruses that can make you sick. A human body is a great place for these organisms to grow and thrive, providing a nice warm environment with plenty of nutrients.</p>
<p>That’s where your immune system comes in. It’s your body’s defense system against these kinds of invaders. Before you’re even born, your body starts producing specialized B-cells and T-cells – types of white blood cells that can recognize pathogens and help block their growth.</p>
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<a href="https://images.theconversation.com/files/321468/original/file-20200319-126300-18zc0vh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/321468/original/file-20200319-126300-18zc0vh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/321468/original/file-20200319-126300-18zc0vh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/321468/original/file-20200319-126300-18zc0vh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/321468/original/file-20200319-126300-18zc0vh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/321468/original/file-20200319-126300-18zc0vh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/321468/original/file-20200319-126300-18zc0vh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/321468/original/file-20200319-126300-18zc0vh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">An artist’s rendering of the white blood cells that help recognize and fight off invaders.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/lymphocytes-illustration-royalty-free-illustration/685027719">Kateryna Kon/Science Photo Library via Getty Images</a></span>
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<p>During an infection, your B-cells can proliferate and produce antibodies that grab onto pathogens and block their ability to spread within your body. T-cells work by recognizing infected cells and killing them. Together they make up what scientists call your “adaptive” immune system.</p>
<p>Maybe your physician has checked your white blood cell levels. That’s a measurement of whether you have more B-cells and T-cells in your blood than usual, presumably because they’re fighting infection.</p>
<p>When you’re very young, you don’t have a lot of these B- or T-cells. It can be a challenge for your body to control infection because it’s simply not used to the job. As you mature, your adaptive immune system learns to recognize pathogens and handle these constant invasions, allowing you to fight off infection quickly and effectively.</p>
<p>While white blood cells are powerful people-protectors, they’re not enough on their own. Luckily, your immune system has another layer, what’s called your <a href="https://doi.org/10.1159/000453397">“innate” immune response</a>. Every cell has its own little immune system that allows it to directly respond to pathogens quicker than it takes to mobilize the adaptive response.</p>
<p>The innate immune response is tuned to pounce on types of molecules that are commonly found on bacteria and viruses but not in human cells. When a cell detects these invader molecules, it triggers production of an antiviral interferon protein. Interferon triggers the infected cell to die, limiting infection. </p>
<p>Another type of innate immune cell, called a monocyte, acts as a sort of cellular bouncer, getting rid of any infected cells it finds and signaling the adaptive immune response to shift into gear.</p>
<p>The innate and adaptive immune systems can act together as a fine-tuned machine to detect and clear out pathogens.</p>
<p><iframe id="tjyf5" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/tjyf5/1/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<h2>Older immune systems are weaker</h2>
<p>When a pathogen invades, the difference between illness and health is a race between how fast the pathogen can spread within you and how fast your immune response can react without causing too much collateral damage.</p>
<p>As people age, their innate and adaptive immune responses change, shifting this balance.</p>
<p><a href="https://doi.org/10.1016/j.humimm.2009.07.005">Monocytes from older individuals</a> <a href="https://doi.org/10.1093/infdis/jir048">produce less interferon</a> in response to viral infections. They have a harder time killing infected cells and signaling the adaptive immune response to get going.</p>
<p>Low-grade chronic inflammation in individuals that commonly occurs during aging can also <a href="https://doi.org/10.1111/j.1749-6632.2000.tb06651.x">dull the ability of the innate and adaptive immune responses</a> to react to pathogens. It’s similar to becoming used to an annoying sound over time.</p>
<p>As you age, the reduced “attention span” of your innate and adaptive immune responses make it harder for the body to respond to viral infection, giving the virus the upper hand. Viruses can take advantage of your immune system’s slow start and quickly overwhelm you, resulting in serious disease and death.</p>
<h2>Social distancing is vital</h2>
<p>Everyone, no matter their age, needs to protect themselves from infection, not just to keep themselves healthy but also to help protect the most vulnerable. Given the difficulty older individuals have in controlling viral infection, the best option is for these individuals to avoid becoming infected by viruses in the first place.</p>
<p>This is where washing hands, avoiding touching your face, self-isolation and <a href="https://theconversation.com/social-distancing-what-it-is-and-why-its-the-best-tool-we-have-to-fight-the-coronavirus-133581">social distancing</a> all become important, <a href="https://www.cdc.gov/coronavirus/2019-ncov/prepare/prevention.html">especially for COVID-19</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/321445/original/file-20200318-1905-pndn5q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/321445/original/file-20200318-1905-pndn5q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/321445/original/file-20200318-1905-pndn5q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=378&fit=crop&dpr=1 600w, https://images.theconversation.com/files/321445/original/file-20200318-1905-pndn5q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=378&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/321445/original/file-20200318-1905-pndn5q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=378&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/321445/original/file-20200318-1905-pndn5q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=475&fit=crop&dpr=1 754w, https://images.theconversation.com/files/321445/original/file-20200318-1905-pndn5q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=475&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/321445/original/file-20200318-1905-pndn5q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=475&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The mist ejected by a sneeze can launch viruses airborne, so other people can inhale them.</span>
<span class="attribution"><a class="source" href="https://phil.cdc.gov/Details.aspx?pid=11161">James Gathany</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>COVID-19 is caused by a respiratory virus, which can spread via tiny virus-containing droplets. Larger droplets fall to the ground quickly; very small droplets dry up. Mid-range droplets are of most concern because they can <a href="https://www.medscape.com/viewarticle/741245_3">float in the air for a few feet</a> before drying. These droplets can be inhaled into the lungs.</p>
<p>Keeping at least 6 feet away from other people helps significantly reduce your chance of being <a href="https://doi.org/10.1186/s12879-019-3707-y">infected by these aerosol droplets</a>. But there’s still the <a href="https://theconversation.com/viruses-live-on-doorknobs-and-phones-and-can-get-you-sick-smart-cleaning-and-good-habits-can-help-protect-you-133054">possibility for virus to contaminate surfaces</a> that infected people have touched or coughed on. Therefore, the best way to protect vulnerable older and immunocompromised people is to stay away from them until there is no longer a risk. By stopping the spread of SARS-CoV-2 throughout the whole population, we help protect those who have a harder time fighting infection.</p>
<p><em>This article draws on material from <a href="https://theconversation.com/older-people-are-at-more-risk-from-covid-19-because-of-how-the-immune-system-ages-133899">an article originally published</a> on March 19, 2020.</em></p><img src="https://counter.theconversation.com/content/147391/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Brian Geiss receives funding from the National Institutes of Health.</span></em></p>Older coronavirus patients face grimmer outlooks. A virologist explains the aging-related changes in how immune systems work that are to blame.Brian Geiss, Associate Professor of Microbiology, Immunology & Pathology, Colorado State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1433232020-08-26T12:22:26Z2020-08-26T12:22:26ZDeclining antibodies and immunity to COVID-19 – why the worry?<figure><img src="https://images.theconversation.com/files/350678/original/file-20200731-25-14azhjx.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C6540%2C4442&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An artist's impression of antibodies (red and blue) responding to an infection with the new coronavirus SARS-CoV-2 (purple). </span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/antibodies-responding-to-covid-19-royalty-free-illustration/1227513276?adppopup=true">KTSDESIGN/SCIENCE PHOTO LIBRARY / Getty Images</a></span></figcaption></figure><p>Most people are aware that testing for antibodies in a person’s blood can show if someone has had a specific disease, such as COVID-19. Those antibodies provide protection from getting the disease again.</p>
<p>But in a <a href="https://www.nejm.org/doi/full/10.1056/NEJMc2025179">paper published in the New England Journal of Medicine</a>, researchers found that antibody levels decline in individuals who have recovered from COVID-19, dropping by half every 36 days. Does that mean people who have recovered from COVID-19 have lost their immunity? </p>
<p><a href="https://scholar.google.com/citations?user=VMa6rFgAAAAJ&hl=en">I am a geneticist</a> interested in innate immune response – the part of the immune system that we have at birth – and how the innate immune cells “educate” antibody-producing cells about a pathogen and how to identify and destroy it. As I’ll explain, antibodies are important for immunity, but they aren’t the only factor that counts.</p>
<h2>Two arms of the immune system</h2>
<p>The immune system is made up of two parts: innate immunity and adaptive – or acquired – immunity. </p>
<p><a href="https://www.ncbi.nlm.nih.gov/books/NBK279396/">The innate immune system</a>, which includes white blood cells called dendritic cells, monocytes and neutrophils, is present at birth and responds instantly to invaders. This group of white blood cells bombard pathogens with destructive chemicals and swallow and destroy viruses and bacteria. The innate immune system provides an instantaneous reaction to a pathogen. The problem is that it’s a blunt instrument – it responds the same way to all perceived threats. </p>
<p>The adaptive immune system, which is made up of B cells and T cells, must learn about a pathogen and its characteristics from the innate immune cells. This system takes longer to kick in, but the up side is that it is very specific and in many cases lasts a lifetime.</p>
<h2>The immune system’s memory</h2>
<p>The history of pathogen exposure is carried in so-called memory T cells and memory B cells. When an infection is defeated and gone, these cells reside in the peripheral tissues of the body such as lymph nodes or spleen and serve as a memory of the disease-causing virus. This immunological memory is responsible for the host defense and kicks into action in case of the second wave or attack of the pathogen. </p>
<p>It is normal for <a href="https://www.scientificamerican.com/article/concerns-about-waning-covid-19-immunity-are-likely-overblown/">antibody levels to decline</a> after a person has recovered from a disease. But the New England Journal of Medicine paper <a href="https://www.cidrap.umn.edu/news-perspective/2020/07/study-covid-19-antibodies-decay-quickly-after-mild-illness">raised concerns</a> because it suggests that we are losing our immunological memory – which is as bad as losing a real memory.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/351399/original/file-20200805-237-1wd13k0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/351399/original/file-20200805-237-1wd13k0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/351399/original/file-20200805-237-1wd13k0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=472&fit=crop&dpr=1 600w, https://images.theconversation.com/files/351399/original/file-20200805-237-1wd13k0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=472&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/351399/original/file-20200805-237-1wd13k0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=472&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/351399/original/file-20200805-237-1wd13k0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=593&fit=crop&dpr=1 754w, https://images.theconversation.com/files/351399/original/file-20200805-237-1wd13k0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=593&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/351399/original/file-20200805-237-1wd13k0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=593&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Basophils, Neurophils, Eosinophils and Monocytes (left) make up the innate immune system. B cells and T cells are part of the adaptive immune system.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/vector-types-of-blood-cells-erythrocytes-royalty-free-illustration/1216602031?adppopup=true">Vitalii Dumma / Getty Images</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>What role do T cells play in immunity?</h2>
<p>B cells and antibodies are only part of the immune response. T cells help B cells produce antibodies – which are proteins that can bind to a specific pathogen and destroy it.</p>
<p>The way this happens is that first the B cells swallow the virus and start producing antibodies. </p>
<p>T cells cannot swallow the virus. But a type of white blood cell called an antigen-presenting cell can. After it does, it “shows” different parts of the virus to the T cells. The T cells then learn about the virus which they can now seek and destroy. </p>
<p>T cells also stick to the B cells and send them the activation signals that help B cells ramp up antibody production.</p>
<h2>If antibodies decline, what does this mean for COVID-19 immunity?</h2>
<p>It suggests that when there are fewer antibodies in the blood, there is a greater chance that a number of individual virus particles, called virions, will survive and escape destruction. Therefore, the remaining virions will continue to proliferate and cause disease.</p>
<p>[<em>Deep knowledge, daily.</em> <a href="https://theconversation.com/us/newsletters/the-daily-3?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=deepknowledge">Sign up for The Conversation’s newsletter</a>.]</p>
<h2>What do declining antibody levels mean for establishing herd immunity?</h2>
<p>Herd immunity refers to a population and occurs when a sufficiently high number of people within a community are immune to the virus and incapable of transmitting it. That provides protection for those who are still vulnerable. For example, if 60% of people are protected against COVID – because they have survived the infection and carry antibodies – it might protect (via less frequent interactions) the remaining 40% from getting sick. </p>
<p>But the results in the New England Journal of Medicine suggest that people with lower levels of antibody may still have the virus and may not have symptoms of the disease. </p>
<p>That means that if these people with low antibody levels hang around healthy, uninfected people, they present a danger to them because they can transmit the virus. </p>
<h2>When antibody levels fall, does immunity disappear?</h2>
<p>In general, the answer is no. If the virus attempts to cause a second infection, the memory B and T cells are able to recognize it, multiply million of times and defend the body against the virus, preventing it from triggering another full-blown infection. </p>
<p>The protection provided by memory T and B cells is the reason that vaccine-based protection works.</p>
<p>However, there are exceptions. A lifelong vaccine against the flu does not work because flu’s genetic code changes rapidly, altering the appearance of the flu, and therefore requires a new vaccine every season. </p>
<p>But with SARS-CoV-2, the problem as I see it, seems to be that those <a href="https://doi.org/10.1038/s41467-020-17292-4">memory T cells </a><a href="https://doi.org/10.1038/s41591-020-1038-6">and B cells</a> seem to be wiped out. </p>
<p>Antibodies are proteins and last for only between three and four weeks in the blood circulation. To keep antibody levels high, B cells need to replenish them with a fresh supply. But in COVID-19, the declining antibody levels suggest that the cells that produce these antibodies are not present in sufficient numbers, which would explain the drop in antibody levels. Studies of how long immunity from COVID-19 last may shed more light, but for now we do not know the reason why.</p><img src="https://counter.theconversation.com/content/143323/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Alexander (Sasha) Poltorak does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>If antibody levels drop dramatically after an infection, what does that mean for immunity? An expert explains how B and T cells contribute to immunity and why antibodies don’t tell the full story.Alexander (Sasha) Poltorak, Professor of Immunology, Tufts UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1441762020-08-21T18:09:51Z2020-08-21T18:09:51ZIBD: How a class of killer T cells goes rogue in inflammatory bowel disease<figure><img src="https://images.theconversation.com/files/353234/original/file-20200817-18-1fz4mrb.jpg?ixlib=rb-1.1.0&rect=18%2C28%2C6211%2C4119&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">There are currently no permanent treatments for most patients with inflammatory bowel disease.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/woman-having-painful-stomach-ache-royalty-free-image/1188226212?adppopup=true">PokPak05/iStock/Getty Images Plus</a></span></figcaption></figure><p>Between <a href="https://doi.org/10.1016/S2468-1253(19)30333-4">6 and 8 million people worldwide</a> suffer from inflammatory bowel disease, a group of chronic intestinal disorders that can cause belly pain, urgent and frequent bowel movements, bloody stools and weight loss. New research suggests that a malfunctioning member of the patient’s own immune system called a killer T cell may be one of the culprits. This discovery may provide a new target for IBD medicines.</p>
<p>The two main types of IBD are <a href="http://doi.org/10.1016/S0140-6736(16)32126-2">ulcerative colitis,</a> which mainly affects the colon, and <a href="https://doi.org/10.1016/S0140-6736(16)31711-1">Crohn’s disease,</a> which can affect the entire digestive tract. Researchers currently believe that IBD is triggered when an <a href="https://www.nejm.org/doi/full/10.1056/nejmra0804647">overactive immune system attacks harmless bacteria in the intestines</a>. Although there are many treatments for IBD, <a href="https://doi.org/10.1097/mog.0000000000000536">for as many as 75% of individuals with IBD</a> there are no effective long-term treatments. This leaves many patients without good options. </p>
<p>I am a <a href="https://changlab.ucsd.edu">physician-scientist</a> conducting research in immunology and IBD and in a <a href="http://immunology.sciencemag.org/lookup/doi/10.1126/sciimmunol.abb4432">new study</a>, <a href="https://medschool.ucsd.edu/som/medicine/research/labs/chang-lab/people/Pages/default.aspx">my team</a> and our colleagues specializing in <a href="https://goldrathlab.com/">immunology</a>, <a href="https://health.ucsd.edu/specialties/gastro/areas-expertise/ibd-center/Pages/default.aspx">gastroenterology</a> and <a href="https://yeolab.github.io/">genomics</a> examined immune cells from the blood and intestines of healthy individuals and compared them with those collected from patients with ulcerative colitis to gain a better understanding of how the immune system malfunctions in IBD. There are many reasons why current treatments aren’t permanent, but one reason is that scientists don’t fully understand how the immune system is involved in IBD. It is our hope that closing the current knowledge gap about how the immune system is involved in this disorder will eventually lead to new durable treatments for IBD that target the right immune cells.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/353284/original/file-20200817-16-1titleg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/353284/original/file-20200817-16-1titleg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/353284/original/file-20200817-16-1titleg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/353284/original/file-20200817-16-1titleg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/353284/original/file-20200817-16-1titleg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/353284/original/file-20200817-16-1titleg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/353284/original/file-20200817-16-1titleg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/353284/original/file-20200817-16-1titleg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Ulcerative colitis is a type of inflammatory bowel disease that results in chronic inflammation and damage to the large intestine.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/ulcerative-colitis-royalty-free-illustration/1143632545?adppopup=true">Graphic_BKK1979/iStock via Getty Images</a></span>
</figcaption>
</figure>
<h2>Immunology 101</h2>
<p>The immune system can be divided into <a href="https://www.youtube.com/watch?v=jeN8v5I5VNA">innate and adaptive branches</a>. The innate branch is our first line of defense and acts quickly – within minutes to hours. But this system senses changes caused by microbes generally. It does not mount a targeted response against a specific pathogen, which means that some invaders can be overlooked. </p>
<p>The adaptive branch is designed to detect specific threats, but is slower and takes a couple of days to get going. T cells are a part of the adaptive immune system and can be further subdivided into <a href="https://theconversation.com/coronavirus-b-cells-and-t-cells-explained-141888">CD4⁺ and CD8⁺ T cells</a>. </p>
<p>CD4⁺ T cells are helpers that aid other immune cells by releasing soluble molecules called cytokines that can induce inflammation.</p>
<p>CD8⁺ T cells can also release cytokines, but their main function is to kill cells infected by microbial invaders. This is why CD8⁺ T cells are often referred to as serial killers. </p>
<p>After the infection is cleared and the pathogen has been destroyed, cells called memory T cells remain. These memory T cells “remember” the pathogen they’ve just encountered and if they see it again, they mount a stronger and faster response than the first time. They and their descendants can also live for a long time, even decades in the case of certain infections like <a href="https://doi.org/10.1099/0022-1317-81-5-1313">measles</a>. </p>
<p>The goal of a <a href="https://www.nytimes.com/interactive/2020/science/coronavirus-vaccine-tracker.html">vaccine</a> is to provide a preview of the microbe so that the immune system can build an army of memory cells against an infectious agent, such as SARS-CoV-2, the virus that causes COVID-19. That way, <a href="https://www.theatlantic.com/health/archive/2020/08/covid-19-immunity-is-the-pandemics-central-mystery/614956/">if the virus attacks</a>, the memory T cells will spring into action and activate an immune response including the <a href="https://www.nature.com/articles/s41467-017-00843-7">production of antibodies from B cells</a>.</p>
<h2>Memory T cells that reside in organs</h2>
<p>Immunologists further subdivide <a href="https://doi.org/10.1038/ni.3031">memory T cells</a> into different classes depending on if and where they travel in the body. Circulating memory T cells are scouts that look for signs of infection by patrolling the blood, lymph nodes and spleen. </p>
<p><a href="https://doi.org/10.1016/j.coi.2018.03.017">Tissue-resident memory cells</a>, abbreviated TRM, are sentries stationed at key ports of entry into the human body – including the skin, lungs, and intestines – and act rapidly to counter an infectious threat. Intestinal TRM also function as peacekeepers and do not tend to overreact against the many harmless microbes living in the intestines.</p>
<p>In the <a href="http://immunology.sciencemag.org/lookup/doi/10.1126/sciimmunol.abb4432">new study</a>, our team analyzed blood and intestinal samples to discover that intestinal CD8⁺ TRM come in at least four different varieties, each with unique features and functions. </p>
<p>We noticed that individuals with ulcerative colitis had higher numbers and proportions of cells belonging to one of these four varieties. This particular variety, which we’ll call inflammatory TRM here, carried instructions to make very large amounts of cytokines and other protein factors that allow them to kill other cells. High levels of certain cytokines can cause inflammation and tissue damage in the body.</p>
<p>[<em>Deep knowledge, daily.</em> <a href="https://theconversation.com/us/newsletters/the-daily-3?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=deepknowledge">Sign up for The Conversation’s newsletter</a>.]</p>
<p>It seems that in individuals with ulcerative colitis, the balance of memory cells is shifted in favor of this rogue population of inflammatory TRM that may become part of the problem by causing persistent inflammation and tissue damage.</p>
<p>We also found evidence consistent with the possibility that these inflammatory TRM might be exiting the intestinal tissue and entering the blood. Other studies in <a href="https://doi.org/10.1038/s41590-020-0607-7">mice</a> and <a href="https://doi.org/10.1126/sciimmunol.aav8995">people</a> have shown that TRM, despite being called “tissue-resident,” can leave tissues in certain circumstances. </p>
<p>By leaving the tissue and entering the blood, inflammatory TRM may be able to travel to other parts of the body and cause damage. This possibility may explain why autoimmune diseases that start in one organ, like <a href="https://doi.org/10.1007/s11894-019-0698-1">IBD</a> in the digestive tract or <a href="https://www.emjreviews.com/dermatology/article/psoriasis-beyond-the-skin/">psoriasis</a> in the skin, often affect other parts of the body.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/353248/original/file-20200817-22-1e2ytlu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/353248/original/file-20200817-22-1e2ytlu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/353248/original/file-20200817-22-1e2ytlu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/353248/original/file-20200817-22-1e2ytlu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/353248/original/file-20200817-22-1e2ytlu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/353248/original/file-20200817-22-1e2ytlu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/353248/original/file-20200817-22-1e2ytlu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The balance of memory T cell subtypes changes in individuals with ulcerative colitis. Illustrations created with BioRender.com.</span>
<span class="attribution"><span class="source">John Chang</span></span>
</figcaption>
</figure>
<h2>IBD and other autoimmune diseases as a memory problem</h2>
<p>The very features that make memory T cells so desirable for vaccines – their capacity to live for such a long time and mount a stronger response when they encounter a microbial invader for the second time – may explain why autoimmune diseases are chronic and lifelong.</p>
<p>It is important to point out that none of the current drug treatments for IBD specifically target long-lived memory cells, which might be a reason why these therapies don’t work long-term in many individuals. One therapeutic approach might be to target inflammatory TRM for destruction, but this could result in side effects like suppression of the immune system and increased infections.</p>
<p>Our findings build on previous studies showing that <a href="https://doi.org/10.1053/j.gastro.2017.07.047">different TRM varieties</a>, like the <a href="https://doi.org/10.1038/s41590-018-0298-5">CD4⁺ subtype</a>, may also be involved in IBD, while other studies show that TRM play a role in autoimmune diseases affecting other organs like the <a href="https://doi.org/10.1126/scitranslmed.3010641">skin</a> and <a href="https://doi.org/10.1126/sciimmunol.aba4163">kidneys</a>.</p>
<p>The possibility that T cell memory is co-opted in IBD is exciting, but there is much that we still don’t understand about TRM. Can we selectively target inflammatory TRM for destruction? Would this be an effective treatment for IBD? Can we do so without causing major side effects? Further research will be needed to answer these important questions and to strengthen the link between TRM and IBD.</p><img src="https://counter.theconversation.com/content/144176/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>John Chang receives research grant funding from the National Institutes of Health, the Kenneth Rainin Foundation, Takeda, and Eli Lilly.</span></em></p>Researchers discover clues to the origin of inflammatory bowel disease and a possible strategy for treatment.John Chang, Professor of Medicine, University of California, San DiegoLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1338992020-03-19T12:06:52Z2020-03-19T12:06:52ZOlder people are at more risk from COVID-19 because of how the immune system ages<figure><img src="https://images.theconversation.com/files/321466/original/file-20200319-126270-1h2b5un.jpg?ixlib=rb-1.1.0&rect=207%2C39%2C3367%2C2441&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A nursing home resident who tested positive for the virus visits through the window with her daughter.</span> <span class="attribution"><a class="source" href="http://www.apimages.com/metadata/Index/Virus-Outbreak-US/ad2fd7eca51e46b5a390af76f9d8aa7e/2/0">AP Photo/Ted S. Warren</a></span></figcaption></figure><p><em>An updated version of this article was published on Oct. 2, 2020. <a href="https://theconversation.com/older-people-like-president-trump-are-at-more-risk-from-covid-19-because-of-how-the-immune-system-ages-147391">Read it here</a>.</em></p>
<p>The rapidly spreading coronavirus pandemic is taking a particularly harsh toll on older people.</p>
<p><a href="https://doi.org/10.3855/jidc.12600">Data from the initial outbreak in China and then Italy</a> show that infected people under the age of 60 are at low – but not no – risk of dying from COVID-19. More recent data from the U.S. suggest that a <a href="https://www.cdc.gov/mmwr/volumes/69/wr/mm6912e2.htm?s_cid=mm6912e2_w">higher rate of people in their 30s and 40s</a> have experienced severe illness and even death than previously thought. Curiously, <a href="https://www.washingtonpost.com/health/2020/03/17/coronavirus-looks-different-kids-than-adults/">young children</a> do not appear to be at increased risk of serious COVID-19 complications, in contrast to what happens with other viruses, <a href="https://www.cdc.gov/flu/highrisk/children.htm">like the seasonal flu</a>. </p>
<p>However, the statistics get <a href="https://doi.org/10.3855/jidc.12600">grimmer as the patients get older</a>. Whereas people in their 60s have a 0.4% chance of dying, people in their 70s have a 1.3% chance of dying, and people over 80 have a 3.6% chance of dying. While this may not sound like a high chance of death, during the current outbreak in Italy, <a href="https://doi.org/10.1016/S0140-6736(20)30627-9">83% of those who succumbed to COVID-19</a> infection were over the age of 60.</p>
<p>The new coronavirus SARS-CoV-2, which causes COVID-19, is therefore a <a href="https://www.cdc.gov/mmwr/volumes/69/wr/mm6912e2.htm">very serious pathogen for people over 60</a>. As it continues to spread, this older age group will continue to be at risk for serious disease and death.</p>
<p>What is it that puts older people at increased risk from viruses like this? It’s primarily thought to be due to changes in the human immune system as we age.</p>
<h2>Your body’s tools to fight off virus infections</h2>
<p>As you go about your life, your body is constantly bombarded by pathogens – the bacteria, fungi and viruses that can make you sick. A human body is a great place for these organisms to grow and thrive, providing a nice warm environment with plenty of nutrients.</p>
<p>That’s where your immune system comes in. It’s your body’s defense system against these kinds of invaders. Before you’re even born, your body starts producing specialized B-cells and T-cells – types of white blood cells that can recognize pathogens and help block their growth.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/321468/original/file-20200319-126300-18zc0vh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/321468/original/file-20200319-126300-18zc0vh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/321468/original/file-20200319-126300-18zc0vh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/321468/original/file-20200319-126300-18zc0vh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/321468/original/file-20200319-126300-18zc0vh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/321468/original/file-20200319-126300-18zc0vh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/321468/original/file-20200319-126300-18zc0vh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/321468/original/file-20200319-126300-18zc0vh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An artist’s rendering of the white blood cells that help recognize and fight off invaders.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/lymphocytes-illustration-royalty-free-illustration/685027719">KATERYNA KON/Science Photo Library via Getty Images</a></span>
</figcaption>
</figure>
<p>During an infection, your B-cells can proliferate and produce antibodies that grab onto pathogens and block their ability to spread within your body. T-cells work by recognizing infected cells and killing them. Together they make up what scientists call your “adaptive” immune system.</p>
<p>Maybe your physician has checked your white blood cell levels. That’s a measurement of whether you have more B-cells and T-cells in your blood than usual, presumably because they’re fighting infection.</p>
<p>When you’re very young, you don’t have a lot of these B- or T-cells. It can be a challenge for your body to control infection because it’s simply not used to the job. As you mature, your adaptive immune system learns to recognize pathogens and handle these constant invasions, allowing you to fight off infection quickly and effectively.</p>
<p>While white blood cells are powerful people protectors, they’re not enough on their own. Luckily, your immune system has another layer, what’s called your <a href="https://doi.org/10.1159/000453397">“innate” immune response</a>. Every cell has its own little immune system that allows it to directly respond to pathogens quicker than it takes to mobilize the adaptive response.</p>
<p>The innate immune response is tuned to pounce on types of molecules that are commonly found on bacteria and viruses but not in human cells. When a cell detects these invader molecules, it triggers production of an antiviral interferon protein. Interferon triggers the infected cell to die, limiting infection. </p>
<p>Another type of innate immune cell, called a monocyte, acts as a sort of cellular bouncer, getting rid of any infected cells it finds and signaling the adaptive immune response to shift into gear.</p>
<p>The innate and adaptive immune systems can act together as a fine-tuned machine to detect and clear out pathogens.</p>
<h2>Older immune systems are weaker</h2>
<p>When a pathogen invades, the difference between illness and health is a race between how fast the pathogen can spread within you and how fast your immune response can react without causing too much collateral damage.</p>
<p>As people age, their innate and adaptive immune responses change, shifting this balance.</p>
<p><a href="https://doi.org/10.1016/j.humimm.2009.07.005">Monocytes from older individuals</a> <a href="https://doi.org/10.1093/infdis/jir048">produce less interferon</a> in response to viral infection. They have a harder time killing infected cells and signaling the adaptive immune response to get going.</p>
<p>Low-grade chronic inflammation in individuals that commonly occurs during aging can also <a href="https://doi.org/10.1111/j.1749-6632.2000.tb06651.x">dull the ability of the innate and adaptive immune responses</a> to react to pathogens. It’s similar to becoming used to an annoying sound over time.</p>
<p>As you age, the reduced “attention span” of your innate and adaptive immune responses make it harder for the body to respond to viral infection, giving the virus the upper hand. Viruses can take advantage of your immune system’s slow start and quickly overwhelm you, resulting in serious disease and death.</p>
<h2>Social distancing is vital</h2>
<p>Everyone, no matter their age, needs to protect themselves from infection, not just to keep themselves healthy but also to help protect the most vulnerable. Given the difficulty older individuals have in controlling viral infection, the best option is for these individuals to avoid becoming infected by viruses in the first place.</p>
<p>This is where washing hands, avoiding touching your face, self-isolation and <a href="https://theconversation.com/social-distancing-what-it-is-and-why-its-the-best-tool-we-have-to-fight-the-coronavirus-133581">social distancing</a> all become important, <a href="https://www.cdc.gov/coronavirus/2019-ncov/prepare/prevention.html">especially for COVID-19</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/321445/original/file-20200318-1905-pndn5q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/321445/original/file-20200318-1905-pndn5q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/321445/original/file-20200318-1905-pndn5q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=378&fit=crop&dpr=1 600w, https://images.theconversation.com/files/321445/original/file-20200318-1905-pndn5q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=378&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/321445/original/file-20200318-1905-pndn5q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=378&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/321445/original/file-20200318-1905-pndn5q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=475&fit=crop&dpr=1 754w, https://images.theconversation.com/files/321445/original/file-20200318-1905-pndn5q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=475&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/321445/original/file-20200318-1905-pndn5q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=475&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The mist ejected by a sneeze can launch viruses airborne, so other people can inhale them.</span>
<span class="attribution"><a class="source" href="https://phil.cdc.gov/Details.aspx?pid=11161">James Gathany</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>COVID-19 is caused by a respiratory virus, which can spread via tiny virus-containing droplets. Larger droplets fall to the ground quickly; very small droplets dry up. Mid-range droplets are of most concern because they can <a href="https://www.medscape.com/viewarticle/741245_3">float in the air for a few feet</a> before drying. These droplets can be inhaled into the lungs.</p>
<p>Keeping at least 6 feet away from other people helps significantly reduce your chance of being <a href="https://doi.org/10.1186/s12879-019-3707-y">infected by these aerosol droplets</a>. But there’s still the <a href="https://theconversation.com/viruses-live-on-doorknobs-and-phones-and-can-get-you-sick-smart-cleaning-and-good-habits-can-help-protect-you-133054">possibility for virus to contaminate surfaces</a> that infected people have touched or coughed on. Therefore, the best way to protect vulnerable older and immunocompromised people is to stay away from them until there is no longer a risk. By stopping the spread of SARS-CoV-2 throughout the whole population, we help protect those who have a harder time fighting infection.</p>
<p><em>This article has been updated to clarify that people of all ages are at risk of coming down with COVID-19.</em></p><img src="https://counter.theconversation.com/content/133899/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Brian Geiss receives funding from the National Institutes of Health. </span></em></p>Different demographics are more or less vulnerable to serious complications from the coronavirus. A virologist explains the aging-related changes in how immune systems work that are to blame.Brian Geiss, Associate Professor of Microbiology, Immunology & Pathology, Colorado State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/805322017-07-23T22:34:14Z2017-07-23T22:34:14ZExplainer: How the human body first fights off pathogens<p>People constantly encounter viruses, bacteria or parasites. Fortunately, our skin, the specialized lining of our guts and other parts of our body that are exposed to the outside world prevent them from entering. When a pathogen breaches this barrier, our body’s defences come into play.</p>
<p>Those defences, which we also call the human immune system, have two branches — <a href="https://dx.doi.org/10.1016/S0140-6736(00)04904-7">innate and adaptive</a>. Our innate immune system is our first line of defence. It has special molecules that recognize “fingerprints” or patterns in proteins or genetic material that are only present in pathogens. These molecules signal the presence of a pathogen to the cellular genetic machinery, which then produces effector molecules called <a href="https://dx.doi.org/10.1097%2FAIA.0b013e318034194e">cytokines</a>. </p>
<p>The effector molecules initiate a process to eliminate the pathogen. The adaptive immune response kicks in at a later stage. Its job is to mount a much more robust defence by destroying cells infected with a virus or by neutralizing the virus or toxins produced by bacterial pathogens. </p>
<p>The adaptive system also has a memory and activates very rapidly if it encounters the same pathogen again. The innate and adaptive immune systems are linked and the innate system primes the adaptive branch of immunity for a more robust immune response. </p>
<h2>Response against invaders</h2>
<p>The innate immune system is primitive and probably evolved earlier in invertebrates and lower vertebrates. Although innate immune response has systemic effects on the entire human body, every cell can be considered a factory housing some components of the innate immune response. </p>
<p><a href="https://dx.doi.org/10.1146/annurev.immunol.20.083001.084359">Innate immunity</a> starts at the cellular level through conserved pathogen sensing proteins in the cell that sense a pathogen, such as a virus. During virus infection, sensors in human cells recognize viral proteins and nucleic acids to activate genes, such as interferons that inhibit viral replication. </p>
<p>Once infected cells have sensed an invading pathogen, they secrete molecules called cytokines and <a href="https://dx.doi.org/10.1177/10454411950060020101">chemokines</a>. Cytokines such as <a href="https://dx.doi.org/10.1128%2FCMR.14.4.778-809.2001">interferons</a> are molecules that signal neighbouring cells and induce an antiviral state in them. These cells are then primed to resist an infection with the invading virus. Cytokines such as interferons activate anti-viral genes in the infected and neighbouring cells. These genes are called <a href="https://dx.doi.org/10.1016%2Fj.coviro.2011.10.008">interferon stimulated genes</a> (ISGs) since they are only made in the presence of interferons. ISGs impede virus replication in the cells. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/179067/original/file-20170720-23980-1ib9ynb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/179067/original/file-20170720-23980-1ib9ynb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=392&fit=crop&dpr=1 600w, https://images.theconversation.com/files/179067/original/file-20170720-23980-1ib9ynb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=392&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/179067/original/file-20170720-23980-1ib9ynb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=392&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/179067/original/file-20170720-23980-1ib9ynb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=493&fit=crop&dpr=1 754w, https://images.theconversation.com/files/179067/original/file-20170720-23980-1ib9ynb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=493&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/179067/original/file-20170720-23980-1ib9ynb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=493&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Thermal scanner in use at Manila’s International Airport during a MERS outbreak in 2014.</span>
<span class="attribution"><span class="source">(AP Photo/Aaron Favila)</span></span>
</figcaption>
</figure>
<p>At the tissue level, an infection usually manifests itself in the form of an inflammation. Typical signs of inflammation include redness, swelling, pain, heat and loss of function. This is an area of intense battle between the invading microbe and the body’s immune system. Each cell within this area is like a soldier and several cell types together form an army against the microbes. </p>
<p>Chemokines are molecules that attract specialized immune cells to this site of infection. These include cells that “eat” pathogens and dead cells such as <a href="https://www.nature.com/nri/focus/macrophages/index.html?WT.ec_id=SLBU_COMMS">macrophages</a>. In the battlefield, chemokines are like “radio calls.” </p>
<p>Macrophages respond to these calls and invade the site of infection, consuming any cell-free or cell-associated pathogen. These pathogens are then destroyed by internal mechanisms in the macrophages. Macrophages are also like the medics in a battle zone. They help remove damaged cells (“wounded soldiers”) and clear the area. </p>
<p>White blood cells such as <a href="https://www.ncbi.nlm.nih.gov/pubmedhealth/PMHT0022058/">neutrophils</a> respond to chemokines by migrating to the site of infection. These cells secrete powerful inflammatory molecules and <a href="https://dx.doi.org/10.1007%2Fs00418-008-0461-4">reactive oxygen species</a> that aid in getting rid of the pathogen. </p>
<p>Neutrophils, just like macrophages, can also ingest microorganisms or particles. Neutrophils are cells that have internal granules that house powerful chemicals. When neutrophils accumulate at the site of infection, they release these chemicals that have bactericidal properties. </p>
<h2>An evolutionary battle</h2>
<p>Pathogens continue to evolve new mechanisms to evade the body’s immune response. Charles Darwin’s <a href="https://theconversation.com/explainer-theory-of-evolution-2276">theory of evolution</a> and survival of the fittest are relevant for microbes as well. Just like bacteria evolve to become resistant to antibiotics, viruses evolve ways to evade the immune responses. </p>
<p><a href="https://theconversation.com/explainer-what-exactly-is-coronavirus-35456?sg=d80c4e6d-7852-42f9-8222-761299f18fab&sp=1&sr=2">Coronaviruses</a> have evolved mechanisms to shut down cytokine production. In the absence of cytokines, the cell has no way to communicate with other cells about the viral infection. The virus can then multiply to higher levels, causing significant infection and even death in humans. This has been observed both in <a href="https://dx.doi.org/10.1038/nrmicro.2016.81">severe acute respiratory syndrome (SARS) and Middle-East respiratory syndrome (MERS)</a>. </p>
<p>It’s therefore very important to identify the mechanisms employed by these viruses to shut down host defences. Drugs can then be designed to inhibit these viral mechanisms and boost human innate immune responses. </p>
<p>The innate immune system has <a href="https://dx.doi.org/10.1016/j.immuni.2013.06.010">control mechanisms</a> to inhibit damage to the human body by excessive secretion of cytokines. Cytokines are deemed necessary for controlling virus replication, but excessive production of cytokines leads to tissue damage. Excessive cytokine production, a phenomenon called <a href="https://dx.doi.org/10.1128%2FMMBR.05015-11">“cytokine storm”</a> in SARS patients has been associated with lung damage. So a timely balance between inflammatory and anti-inflammatory processes is ideal to tackle infections. </p>
<p>The innate immune response is really the sentinel of the human body; standing at the doors to detect invading pathogens. These sentinels fight off an invading organism while alerting the adaptive immune response (“the cannons”) about the threat.</p><img src="https://counter.theconversation.com/content/80532/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Arinjay Banerjee receives funding from the Saskatchewan Innovation and Opportunity Scholarship. </span></em></p><p class="fine-print"><em><span>Vikram Misra receives funding from Natural Sciences and Engineering Research Council (NSERC) of Canada through its Discovery and Collaborative Research and Training Enterprise (CREATE) funding programs.</span></em></p>We’ve all endured infections. Here’s how it works when our bodies are attacked by viruses, bacteria or parasites, and our innate immune system becomes the first line of defence.Arinjay Banerjee, PhD Candidate in Veterinary Microbiology, University of SaskatchewanVikram Misra, Professor of Veterinary Microbiology, University of SaskatchewanLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/372852015-09-22T03:18:11Z2015-09-22T03:18:11ZExplainer: how does the immune system learn?<figure><img src="https://images.theconversation.com/files/93851/original/image-20150904-16782-1d3aqpf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The only thing standing between invaders such as bacteria, viruses, parasites and fungi and our devastation is our immune system.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/kurtxio/2280690723/">kurtxio/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>We’re outnumbered by bacteria, viruses, parasites and fungi that can make us ill. And the only thing standing between them and our devastation is our <a href="https://theconversation.com/explainer-how-does-the-immune-system-work-27163">immune system</a>. </p>
<p>The immune system does such a good job most of the time that we only really think about it when things go wrong. But to provide such excellent protection against a whole host of pathogens, our immune system must constantly learn.</p>
<h2>Parts of the whole</h2>
<p>The immune system is made up of two equally important parts: <a href="http://www.garlandscience.com/res/pdf/9780815342434_ch02.pdf">innate immunity</a> and <a href="http://www.ncbi.nlm.nih.gov/books/NBK21070/">adaptive immunity</a>. </p>
<p><strong>Innate immunity</strong> rapidly responds to invaders; innate immunity cells deal with more than 90% of infections, removing them within hours or days. These cells recognise invaders by looking for broad shared patterns, such as common molecules on the surface of most bacteria. They might look for lipopolysaccharides (LPS), for instance, a molecule found in many bacterial cell walls. </p>
<p>When the innate response fails to fend off an invasion, the invaders are handled by <strong>adaptive immunity</strong>. Instead of broad patterns, each adaptive cell sees a very specific pattern. This could be one particular protein on the surface of a virus or bacteria.</p>
<p>But because the adaptive immune system doesn’t know what invaders it may meet, it makes millions of different cells, each of which is created to recognise a random different pattern. One adaptive cell may recognise only the flu virus, for instance, while another may recognise only a single type of bacteria.</p>
<p>When adaptive immune cells recognise an invader, they replicate so they form an army to kill it. This very specialised process can take a week the first time we’re infected by a new invader. If we’re exposed to a flu virus, for instance, only the small number of adaptive cells that can randomly recognise flu viruses are activated to remove infection, which is why it takes time to fight it off.</p>
<p>After an invader is removed, the adaptive cells that recognised it are kept, as specialised “memory cells”. If we see the same invader again, those cells can respond before we get ill. This is how the adaptive immune system learns. </p>
<h2>Always learning</h2>
<p>The traditional understanding of the immune system was that <a href="http://www.garlandscience.com/res/pdf/9780815342434_ch02.pdf">innate immune cells couldn’t learn</a>; that they dealt with each invader the same way every time. But <a href="http://www.the-scientist.com/?articles.view/articleNo/41992/title/Thanks-for-the-Memories/">new evidence</a> suggests innate responses are changed by previous infections or vaccination, through “<a href="http://www.the-scientist.com/?articles.view/articleNo/41992/title/Thanks-for-the-Memories/">innate learning</a>” or “<a href="http://www.sciencedirect.com/science/article/pii/S1931312811001284">trained immunity</a>”. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/93852/original/image-20150904-16745-1tfc3ha.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/93852/original/image-20150904-16745-1tfc3ha.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/93852/original/image-20150904-16745-1tfc3ha.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/93852/original/image-20150904-16745-1tfc3ha.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/93852/original/image-20150904-16745-1tfc3ha.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/93852/original/image-20150904-16745-1tfc3ha.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/93852/original/image-20150904-16745-1tfc3ha.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Only the small numbers of adaptive cells that recognise flu viruses are activated to remove infection, which is why it takes time to fight off the flu.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/julishannon/5530622078/">Juli/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
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<p>Because innate learning changes innate immune cells, it has broad effects on how the immune system deals with infections. That means infection by one invader can cause changes in how the immune system deals with a completely different invader. In contrast, adaptive learning leads to very specific protection against repeat infection by the same invader.</p>
<p>Innate learning can have unexpected effects on how our immune system deals with secondary infections (infections that occur during or after a different infection). Here’s an example: the “bacille Calmette-Guerin” (BCG) vaccine is designed to protect against tuberculosis, and does a good job at protecting from tuberculosis as expected. But it also protects <a href="http://www.pnas.org/content/109/43/17537.full">against infection</a> by a completely unrelated invader, <em>Candida albicans</em>. </p>
<p><em>Candida albicans</em> infection causes “<a href="http://www.webmd.com/skin-problems-and-treatments/guide/candidiasis-yeast-infection">candidiasis</a>”, more commonly known as thrush or yeast infection. Studies of BCG-vaccinated patients had previously suggested that vaccination <a href="http://www.sciencedirect.com/science/article/pii/S0264410X03001816">protects against infections</a> other than tuberculosis. But how this happened wasn’t understood. </p>
<p>Then researchers showed protection from yeast infection happened through an <a href="http://www.pnas.org/content/109/43/17537.full">improved innate response</a>. The innate immune cells “learn” from the vaccine and protect from yeast infection for up to three months afterwards. And this is just one of a growing number of studies showing that innate immune cells can learn. </p>
<p>These studies extend to primitive invertebrates, including <a href="http://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.0030026">flies</a> and <a href="http://www.sciencemag.org/content/329/5997/1353">mosquitoes</a>. Invertebrates completely lack adaptive immune cells, so any immune memory responses they have are from innate learning. </p>
<p>In mice, herpesvirus infections <a href="http://www.nature.com/nature/journal/v447/n7142/full/nature05762.html">can protect from completely</a> different bacterial infections. Rather than responding the same way to every invader, innate learning changes our immune responses based on previous experiences.</p>
<p><a href="http://www.scientificamerican.com/article/your-immune-system-is-made-not-born/?WT.mc_id=SA_WR_20150204">Recent evidence</a> also suggests immune learning is strongly affected by environmental factors, including diet, lifestyle, our surroundings and previous infections. </p>
<p>Immune responses to the yearly flu vaccine, for example, are impacted <a href="http://www.cell.com/cell/abstract/S0092-8674%2814%2901590-6">more by environmental factors</a> than genetic differences. This suggests we can improve our immune responses by altering life experiences. </p>
<p>Rather that being stuck with the immune system we genetically inherit, research is showing that immune responses are shaped by life experiences. It provides hope that we can improve immunity and reduce disease through changes in lifestyle and our environment.</p><img src="https://counter.theconversation.com/content/37285/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Steven Maltby receives funding from The Canadian Institutes of Health Research (CIHR), The University of Newcastle and the Hunter Medical Research Institute (HMRI). He works for the University of Newcastle and the HMRI.</span></em></p>The immune system does such a good job most of the time that we only really think about it when things go wrong. But to provide such excellent protection, it must constantly learn.Steven Maltby, Post-doctoral Fellow in Immunology & Genetics / Research Academic for Centre of Excellence in Severe Asthma, University of NewcastleLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/271632014-09-30T04:02:01Z2014-09-30T04:02:01ZExplainer: how does the immune system work?<figure><img src="https://images.theconversation.com/files/59882/original/45sfn8sg-1411540985.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The innate immune response causes the common signs of inflammation including swelling, pain, heat, redness and loss of function. </span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/bdu/3543903974">Brandon Daniel/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>The immune system is critical for protecting against illness-causing organisms, such as viruses, bacteria and fungi, which are collectively known as pathogens. Without it, we would quickly become infected, sicken, and die. </p>
<p>Immune cells are constantly on the lookout for pathogens, patrolling the blood by moving around in the blood. Around half your blood volume is fluid known as plasma; the remainder is made up of millions of different types of cells. </p>
<p>The majority of cells are red blood cells that transport oxygen around. A minority are white blood cells, or <a href="https://theconversation.com/explainer-what-is-the-immune-system-19240">immune cells</a> that act as the body’s army. The immune system produces many different types of these white blood cells, each with a specific role. </p>
<h2>The factory</h2>
<p>All blood cells start their life in the bone marrow, which is the hollow part of the bones; every cell type originally comes from <a href="http://vimeo.com/74878202">blood stem cells</a>. While blood stem cells produce all of our blood cells, other types of stem cells in the bone marrow produce organs, the bone itself and so on. </p>
<p>Stem cells are able to replace themselves, but must also constantly produce new cells to replace old ones. Red blood cells are replaced after several months, while different immune cell lifespans range from days to years. </p>
<p>When the bone marrow doesn’t produce enough blood cells, it can result in anemia (reduced red blood cells) or cytopenia (low cell numbers). These conditions cause low energy or “immuno-deficiency”, which means the body fails to produce a strong immune response, leaving the person more susceptible to infection and illness.</p>
<p>Producing too many blood cells, on the other hand, can result in blood proliferative disorders or blood cancers. People with myeloproliferative disorders, for instance, start with minor symptoms but can end up having difficulty breathing, high blood pressure and heart attack or stroke. And constant high levels of blood cells can lead to a diagnosis of leukemia (white blood cell cancer).</p>
<h2>The army</h2>
<p>After immune cells are produced in the bone marrow, they quickly enter the blood stream. Many then enter tissues, especially those lining our skin, lungs, and gut, where they wait for pathogens or invaders. Others patrol the body until they encounter invaders.</p>
<p>These cells serve as the first line of defence against invaders that would make us sick; they’re called the “innate” immune response. </p>
<p>Innate immune response deals with the majority of invaders that enter our body. The cells involved respond to very broad signals that are shared by many types of invaders. The signals they look out for include essential components of bacterial cell walls or molecules present on the surface of viruses.</p>
<p>When they detect an invader, immune cells sound an alarm, calling more immune cells to the area from the blood. The innate immune response causes the common signs of inflammation including swelling, pain, heat, redness and loss of function. </p>
<p>When the cells respond to harmless signals, they can cause conditions including allergic rhinitis (hayfever), <a href="http://www.asthmaaustralia.org.au/">asthma</a> and <a href="http://www.allergy.org.au/patients/food-allergy/food-allergy">food allergies</a>.</p>
<h2>Getting educated</h2>
<p>If the innate response fails to control an infection, the body will have to activate the “adaptive” immune response. Adaptive immunity develops a specific response for each invader.</p>
<p>Adaptive immune cells go through an extensive education before they can fight invaders. One type of cells (T cells), move to a specialised organ near the heart, called the thymus, for their education. Another type (B cells), remain in the bone marrow.</p>
<p>During their education, these cell types must pass two quality-control steps. The first step ensures that each cell is capable of making a response if they encounter their particular invader. This makes sure no further energy is wasted on keeping non-responsive cells alive, or expanding these cell populations.</p>
<p>The second step ensures the cells won’t respond against the body. Any such cell must be removed so it doesn’t cause damage. Failure to remove these “self-reactive” cells can result in <a href="https://theconversation.com/explainer-what-are-autoimmune-diseases-22577">autoimmune diseases</a>, such as diabetes, multiple sclerosis and autoimmune arthritis.</p>
<p>Once educated, the cells move through the body, visiting lymph nodes to monitor for invaders. Lymph nodes, which are located throughout the body, are the swollen areas we can feel in our armpits or throat when we’re getting sick. </p>
<p>Each adaptive immune cell can only respond to one type of invader, so the body must generate a huge number of these cells to respond to the numerous invaders it may encounter. </p>
<p>When they encounter an invader they recognise, adaptive immune cells replicate and attack it. This requires time and is the reason why it can take a week of illness before an infection is cleared. </p>
<p>Once an infection is cleared, the immune cells that fought it stay alive so they can rapidly respond if they ever encounter the same invader again. This is called a memory response and it’s the reason vaccination works. </p>
<p><a href="http://www.vaccines.gov/">Vaccines</a> activate our adaptive immune response, without the risk of making us sick because they only expose us to a portion of the invader or an inactive part of it. The immune cells become educated to recognise this part of the invader and this creates a strong memory response if that invader is ever encountered again.</p>
<p>The immune system produces millions of specialised cells everyday to keep bodies healthy. What’s really amazing about the complex process behind it is that when it’s working properly, we don’t even notice it’s there at all.</p><img src="https://counter.theconversation.com/content/27163/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Steven Maltby receives funding from The University of Newcastle and the Canadian Institutes of Health Research (CIHR). He is affiliated with The University of Newcastle.</span></em></p><p class="fine-print"><em><span>Vicki Maltby receives funding from The Multiple Sclerosis Society of Australia (MSRA) and the Canadian Institutes of Health Research (CIHR). She is affiliated with The University of Newcastle.</span></em></p>The immune system is critical for protecting against illness-causing organisms, such as viruses, bacteria and fungi, which are collectively known as pathogens. Without it, we would quickly become infected…Steven Maltby, Post-doctoral Fellow in Immunology & Genetics, University of NewcastleVicki Maltby, Post-doctoral fellow, University of NewcastleLicensed as Creative Commons – attribution, no derivatives.