Fingerprints are an exclusive characteristic of each human being that allows to identify a person without margin of error. Now, a group of scientists has verified that each woman’s breast milk is also different, since it contains a unique set of antibodies that remains stable during pregnancy and lactation. This conclusion has been reached by a new study conducted by researchers at the University of Pittsburgh School of Medicine, which has been published in the Journal of Experimental Medicine.
Babies’ immune systems are not fully developed when they are born, so it is the antibodies that are transferred through the placenta and breast milk that protect them against harmful bacteria. These antibodies bind to the bacteria in the intestine and prevent them from invading the host. Thus, the findings help to understand why some babies are more protected than others against various infections and why some develop necrotizing enterocolitis (NEC), a serious inflammatory bowel disease that affects preterm infants primarily and can lead to death.
“While each donor milk in our study had very different antibody profiles from each other, we found that the antibodies from the same donor were quite similar over time, even over months,” said Timothy Hand, associate professor of pediatrics and immunology at Pitt Medical School and UPMC Children’s Hospital of Pittsburgh and lead author. “This means that if a baby’s parents lack particular antibodies, such as those that prevent NEC, they will never receive that immunity. This could help explain why some babies develop NEC and others don’t.”
“Different women have different microbiomes and have dealt with different infections, so it makes perfect sense that breast milk antibodies reflect that variability.”
Necrotizing enterocolitis has been linked to a family of bacteria called Enterobacteriaceae and is two to four times more common in formula-fed babies than in breast-fed babies. In a previous study, Hand and his team found that Enterobacteriaceae in fecal samples from healthy infants primarily bound to maternal antibodies, while infants who developed NEC had more bacteria that prevented this binding. Hand suspected that the variation in the immunity of babies with NEC was due to each mother passing on different antibodies, and the new study supports this hypothesis.
Same amount and diversity of antibodies in case of preterm birth
The researchers analyzed breast milk from donors at the Human Milk Science Institute and Biobank in Pittsburgh and Mommy’s Milk Human Milk Research Biorepository in San Diego, using a variety of different bacteria to measure which strains each donor’s antibodies bound to.
“The antibody profiles of individual donors looked completely different, which is what we expected, but we were able to show for the first time,” Hand said. “During pregnancy, B cells travel from the intestine to the mammary gland, where they begin to produce antibodies. The mom is trying to protect the baby from her by using antibodies that she uses to protect her own gut. Different women have led different lives, have different microbiomes, and have dealt with different infections, so it makes perfect sense that breast milk antibodies reflect that variability.”
During the lactation period, breast milk changes from highly concentrated protein-rich colostrum to mature milk. To find out if the composition of the antibodies also changes, Hand and his team compared breast milk from the same donors over time, observing the same donors during multiple pregnancies.
“The antibodies were not only similar in the donors during a pregnancy, but they were also remarkably stable between the babies,” Hand says. “This suggests that when B cells reach breast tissue, they don’t leave. This is important for understanding how babies acquire immunity and how they deal with infections.”
The researchers also looked at whether breast milk antibodies were different if a donor had a preterm birth. “Some B cells move to the mammary gland during the third trimester, so we wonder if a person gives birth before the end of this trimester, their milk will have fewer antibodies,” Hand says. “The good news was that we found no difference: people who deliver preterm have the same amount of antibodies and the same diversity as those who deliver at term.”
Other studies have shown that feeding a premature baby his mother’s milk was the best way to lower the chances that he will develop NEC, but if it is not available, donor milk is an important substitute or supplement. This milk is sterilized to kill bacteria, but whether this process also affects antibodies has not been proven.
The authors of the new study found that pasteurization reduced antibody levels in donor milk. While this likely means that babies fed donor milk receive fewer antibodies than those breastfed by their mothers, Hand said more research is needed to learn what antibody levels protect against diseases such as NEC. Determining which specific bacteria pose the greatest danger to premature babies at risk of NEC would help scientists develop antibodies that could be added to formula or breast milk to boost their immunity.
.
