Infant Immunity

Infant Immunity

The following is a student blog post by Jennifer Wood

When an infant is born, they do not have a complete immune system. Some of the mother’s immune cells can cross the placenta into the baby, however the majority of the infant’s immunity comes from its mother’s breast milk. The first few days after giving birth, the mother produces a “pre-milk” secretion known as colostrum. This fluid is different from milk, and contains an extremely high number of leukocytes, T cells and macrophages, in an even greater concentration than in the mother’s blood. The leukocyte content of colostrum “varies from ~13.2% to 70.4%”** . This benefits the newborn’s immature immune system greatly, and since the immunity is specific to the mother’s environment, the baby now is also specifically prepared for the environment it is born into.
After a few days, the actual milk comes in, and the amount of antibodies in the milk drop, as other types of nutrition and fats begin to change the composition of the breast milk. The Leucocyte count drops to about “2%, if both mother and infant are healthy”**. However, when the mother or infant become ill, the quantity of antibodies in the breast milk increase exponentially, “as high as 45%”**, even when the mother is asymptomatic.


These illnesses can be caused by any number of infections, viral, bacterial, and even fungal. Scientists have come to realize that when an ill infant is nursing, a little bit of saliva is sucked back into the nipple as “backwash”. This backwash triggers a specific reaction in the mother’s body, which allows it to create a perfect, customized immune response to the infant’s illness. Scientists have come to find secretory “IgA, IgM, IgG, lactoferrin, lysozyme, and cytokines”** in breast milk. Much more than just the macrophages previously assumed to be the main line of defense. It has also been discovered that the macrophages and other cells are much more motile in the breast milk than in the bloodstream, meaning they can get to the nursing infant and begin fighting infection much more efficiently. The breast milk, along with all of these immune cells assist in supporting the infants developing immune system by offering prebiotics, building the intestinal mucosal lining (IgA), and other passive antibodies to illnesses that the mother has experienced in the past. These breast milk antibodies do not just staying the digestive tract of the infant, but move into the bloodstream and provide the additional building blocks and support for the infants own individual maturing immune system.
Immune Cell–Mediated Protection of the Mammary Gland and the Infant during Breastfeeding1–4 Foteini Hassiotou* and Donna T Geddes School of Chemistry and Biochemistry, Faculty of Scienc
e, The University of Western Australia, Crawley, Australia
Breast Milk: Proactive Immunomodulation and Mucosal Protection against Viruses and Other Pathogens Chiara Cerini; Grace M Aldrovandi Future Virology. 2013;8(11):1127-1134. 

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