Breastfeeding is encouraged because it provides many benefits to both mothers and infants. Breastmilk is nutritious, and some research has found that there are positive emotional impacts as well. Children that breastfeed may be at lower risk for metabolic disorders like type 2 diabetes and obesity, and a variety of immune related disorders as well, including asthma, and allergies. New research has shown that infants get an immune boost from breastmilk that can prevent infectious disease. It has also illustrated how complex the relationship between breastmilk and immunity can be, however. The work has been reported in Evolution, Medicine, and Public Health.
People may link breastmilk with immunity because of maternal antibodies that are known to be transferred from mom to infant, and while that is “probably very important," it also seems that a lot more is happening too, noted corresponding study author Katherine Wander, a Binghamton University Associate Professor of Anthropology. "The immune system of milk is a whole system, capable of mounting immune responses. We’re only beginning to understand the full extent and role of the immune system of milk.”
In this study, the researchers focused on a group of nearly 100 pairs of moms and infants in rural Kilimanjaro, where both prolonged breastfeeding and infections in infancy are particularly common.
Breastmilk contains a host of molecules and cells that can mount an immune response on their own. Warner suggested that while these substances come from the mother's immune system, they seem to be carefully chosen, and not randomly selected. It's not clear how that selection happens, however.
In this study, the researchers collected breastmilk from the study volunteers to test how it reacted to a pathogen, by combining it with a bit of Salmonella bacteria. This mixture was incubated overnight, then the scientists measured the levels of an inflammatory signaling molecule called interleukin-6.
The researchers also noted which infants were receiving milk that had a stronger immune response in the lab tests; they found that those infants were also less likely to get an infectious disease. The breastmilk that reacted more strongly to Salmonella also seemed to reduce an infant's chance of getting an infect, especially respiratory infections like pneumonia.
There was another observation, however. When milk had a strong response to Salmonella, it also tended to react strongly to a harmless strain of E. coli too. Nonpathogenic strains of E. coli are a normal part of digestive flora. But when infants had a strong reaction to the benign E. coli, they were more likely to get a gastrointestinal infection. Thus, some breastmilk might mount an incorrect immune response that has the potential to cause problems.
The researchers were surprised to identify this confounding factor. “With so much at stake, we really expected the immune system of milk to be very finely tuned to protecting infants against infection,” Wander said.
Immune systems have to learn how to differentiate between beneficial microbes, and those that cause trouble. Immune responses also have to attack pathogens without harming healthy tissue, then turn off when the job is complete. This can be tough even for adult immune systems, and the researchers found that infants deal with these physiological issues too. Breastmilk may help train the infant immune system to deal with bacteria, but more work will be needed to understand the process.
“We need to understand how milk immune responses are affected by things we can design public health programs around, like HIV infection or malnutrition," said study co-author Blandina Mmbaga of the Kilimanjaro Clinical Research Institute.
Sources: Binghamton University, Evolution, Medicine, and Public Health