Baby Receives Unique Breast Milk Antibodies from Mom

According to a new Journal of Experimental Medicine study from the University of Pittsburgh School of Medicine, each individual’s breast milk has a unique assemblage of antibodies that are unexpectedly persistent throughout breastfeeding and throughout pregnancies.

Because antibodies from breast milk drive a baby’s early immunity, the new study sheds light on why infants’ protection against different infections differs and why some suffer necrotizing enterocolitis (NEC), a potentially fatal gut condition.

“While each milk donor in our study had very different antibody profiles from one another, we found that antibodies from the same donor were quite similar over time — even across the span of months,” said senior author Timothy Hand, Ph.D., associate professor of pediatrics and immunology at Pitt’s School of Medicine and UPMC Children’s Hospital of Pittsburgh. “This means that if a baby’s parent happens to lack particular antibodies — such as those that fend off NEC — they’re never going to receive that immunity. This could help explain why some babies get NEC and others don’t.”

Hand describes NEC as a terrible inflammatory gastrointestinal disease that primarily affects premature infants. NEC, which has been linked to the Enterobacteriaceae family of bacteria, is around two to four times more common in formula-fed babies than in breast-fed babies.

Babies are protected from dangerous microorganisms by antibodies given through the mother’s placenta and breast milk before their immune systems mature. These antibodies bind to bacteria in the colon and prevent them from infiltrating the host.

Hand and his colleagues discovered previously that Enterobacteriaceae in fecal samples of healthy newborns were predominantly bound by maternal antibodies. Infants who went on to develop NEC, on the other hand, had more bacteria that avoided being bound. Hand suspected that diversity in kids’ NEC immunity was due to various moms passing along different antibodies, and the new study backs up this theory.

Hand and his colleagues examined donor breast milk from Pittsburgh’s Human Milk Science Institute and Biobank and San Diego’s Mommy’s Milk Human Milk Research Biorepository. They evaluated which bacterium strains each donor’s antibodies linked to using an array of various bacteria.

“Individual donors’ antibody profiles looked completely different, which is what we had expected but were able to show for the first time,” said Hand. “During pregnancy, B cells travel from the intestine to the mammary gland, where they start making antibodies. The mom is trying to protect her infant using antibodies that she uses to protect her own intestine. Different women have led different lives, have different microbiomes and have encountered different infections, so it makes perfect sense that breast milk antibodies would reflect that variability.”

During breastfeeding, a mother’s milk transforms from extremely concentrated protein-rich colostrum to mature milk. Hand and his colleagues studied breast milk from the same donors over time to see if antibody composition changed as well. They also examined the same donors throughout numerous pregnancies.

“Not only were antibodies similar in donors across one pregnancy, they were also remarkably stable between infants,” said Hand. “This suggests that when B cells arrive in the breast tissue, they don’t leave. This is important for understanding how babies acquire immunity and how they deal with infections.”

The researchers also wanted to know if there were any differences in breast milk antibodies if the donor gave birth prematurely.

“Some B cells move to the mammary gland during the third trimester, so we wondered if a person delivers before this trimester is complete, would their milk have fewer antibodies,” said Hand. “The good news was that we found no difference: Individuals who deliver preterm have just as many antibodies and the same diversity as those who deliver full-term.”

Other research indicates that mother’s milk is the best food for minimizing a premature baby’s risk of having NEC, although donor milk is an important substitute or supplement if that isn’t available. This milk is sterilized to destroy microorganisms, but it has not been studied to see if this technique affects antibodies.

Pasteurization, according to Hand and his colleagues, lowered antibody levels in donor milk. While data suggests that newborns receiving donor milk have fewer antibodies than those who receive milk from their mother, Hand believes that further research is needed to determine whether levels of antibodies are protective against disorders like NEC.

In the future, researchers may be able to develop antibodies that may be given to formula or breast milk to improve protection by better knowing the specific bacteria that are most hazardous for preterm infants at risk of NEC.

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