Breastfeeding may be an ancient practice but we are learning new things about it all the time. My colleagues and I, for instance, have recently found that the lactating breast has the amazing ability to help fight infections affecting the mother as well as those experienced by the baby.
This protects babies from infections at a time when their own immune system is still immature. Protective agents in breast milk include antibodies and a mix of proteins, such as lactoferrin and lysozyme, which have strong antibacterial properties.
In addition to these protective molecules that the mother provides to the baby via breastfeeding, we now know that breast milk also contains immune cells that pass into the milk from the mother’s bloodstream.
What we found
Previous studies have examined immune cells predominantly in colostrum, the milk produced by the mother in the first few days after birth. Colostrum contains a high proportion of immune cells compared to other cells.
The main function of breast milk at this stage is to protect the baby from infections immediately after birth. But very few studies have looked at how many immune cells there are in mature breast milk, which is what the baby receives most of the time it is breastfed.
In a study recently published in Clinical and Translational Immunology, my colleagues and I examined both colostrum and mature breast milk.
We found a dramatic decrease in the proportion of immune cells within the first two weeks of birth. The number of immune cells dropped from as high as 70% in colostrum to less than 2% in mature breast milk.
This low level of breast milk immune cells is maintained throughout lactation (even up to two years), as long as the mother and baby are healthy. But when either the mother or the baby has an infection, the proportion of immune cells increases dramatically.
Upon recovery, immune cell proportion returns to the baseline of 2% or less.
The greatest increases in immune cells occur with severe infections of the breast, such as mastitis, during which the proportion of immune cells in breast milk can increase up to 94%.
Mastitis is a devastating condition during which mothers experience severe pain, often as intense as childbirth, in the infected breast. When not resolved quickly, it can lead to giving up breastfeeding early.
Our work has exciting implications for treating this infection as it provides a tool for early and rapid diagnosis based on breast milk immune cells. This could facilitate timely treatment, resulting in continued breastfeeding, which would benefit both mother and child.
The baby’s infections also result in a marked increase in the immune cell proportion, even when the mother doesn’t manifest any symptoms. We don’t know whether the increase is there to protect the mother or the baby, or both.
Still, the changes in breast milk highlight its unique, dynamic nature and reiterate the importance of breastfeeding for protecting babies against infection.
Even the baseline of 2% or less of immune cells when mother and baby are healthy corresponds to hundreds or thousands of immune cells being ingested daily. This helps prevent infection and when the child is infected, it increases to provide extra support to fight illness.
Helping the needy
The baseline level of immune cells in breast milk under healthy conditions is higher for babies who are exclusively breastfed. This is another good reason for exclusive breastfeeding for the first six months of life, as is recommended by the World Health Organization.
The implications of our study are particularly significant for mothers and children in developing countries. There, due to limited access to medicine, the immune response of the breast to infections (affecting both mothers and babies) has a greater impact on health. Breastfeeding can surely be life-saving in such situations.
Our research also generates new diagnostic opportunities to assess the health of both the mother and the baby. These findings may be used as a diagnostic tool to assess the health status of the lactating breast.
As we accumulate evidence for the protective effects of breastfeeding, we’re developing a deeper appreciation of how amazing breast milk really is.