Mother’s milk may provide targeted immunity but at gut health’s expense, pegs study

13 Jul 2022 --- More than just providing nutrition, a recent study has found that human breast milk may contain an entire immune system, including cells, proteins and antibodies curated to fight specific infectious diseases in growing babies. The trade-off is that it may attack gut flora as well, underscoring a key consideration for replicating its properties in substitutes such as baby formula.

“Our study differs from similar studies in that we used an in vitro challenge method to describe milk immune activity,” Dr. Katherine Wander, associate professor of anthropology, Binghamton University, tells NutritionInsight. “Our assay captures not only what is in milk, but what is happening in milk.”

Wander states that the study adds to the evidence that milk is complex and dynamic in ways that are both scientifically intriguing and integral to infant health.

“It continues to be important to find ways to support parents in breastfeeding and to learn as much as we can about milk so that we can improve milk substitutes like formula.”

Over the last year, the infant nutrition industry has made significant strides toward more closely replicating the functional properties of breast milk in newly developed baby formula – and closing the gap on this divide remains key for the sector.

Gut microbiome impacted by immunity?Mother’s milk appears to provide curated immunity against infectious disease.
The study also found that there may be a trade-off to be had for this acquired immunity. Infants who consumed milk with stronger immune responses were also found to have increased immunity to infectious diseases, especially common respiratory diseases like pneumonia. 

However, the milk’s immune system also attacked a benign strain of E. coli which is present in the intestinal tracts of most humans. 

This finding may show that the immune systems in breast milk may have an inappropriate action on infant gut flora, which the research team affirms plays a significant part in preventing diarrhea and other common infectious diseases. The researchers also acknowledge that this is expected as distinguishing between good and bad gut microbes is challenging, even for the immune systems of mature adults.

“Milk immune responses to inappropriate targets are not helpful to infants,” Wander stresses. “This approach is novel and, of course, needs to be replicated in other settings and expanded on before we can be sure it’s a robust finding.” 

A beneficial compromise?
During the study, the researchers tested the immune responses of the breast milk by combining it with the bacteria Salmonella and then measured the overnight production of interleukin-6, an immune cell molecule that stimulates inflammation responses. The researchers emphasize the importance of the gut microbiome but say the trade-off is stronger immunity. 

They then followed infants who were feeding from breast milk and found that milk which displayed stronger immune responses may even help to “train” the infants’ immune systems to attack dangerous bacteria.

“It’s not perfect – infants’ guts are not really similar to Petri dishes – but it gives us an idea of what the whole dynamic immune system of milk is capable of,” explains Wander. “And what we found suggests that the immune system of milk’s capabilities can reduce infants’ infectious disease risk, but only when it responds to appropriate targets, like Salmonella.”

The study included nearly 100 breastfeeding mothers and their infants living in rural Kilimanjaro, Tanzania. The study chose this area due to both high rates of breastfeeding among its population and the increased prevalence of infectious disease compared to other parts of East Africa.

Looking forward
The study posits that its applications may extend further than just infancy and breastfeeding. 

Understanding the mechanisms that help the immune system distinguish between “protection and harm” may help to identify other health problems such as autoimmune diseases like HIV and malnutrition.

Wander states: “Longer term, we also want to know how milk immune responses affect infant health beyond their infectious disease risk – through infant growth, intestinal microbial flora, and immune system development; those questions will take longer to answer, though.”

“Now that we know that milk immune responses are important for infant health, we need to look upstream at the maternal factors – like nutrition, chronic and infectious diseases, age and parity – that might affect milk immune responses.”

“We’re also looking at our longitudinal data to see if milk immune activity increased for infants who had an infectious disease during the data collection period,” concludes Wander.

By William Bradford Nichols