Antibodies in Breast Milk Prime the Baby's Gut to Handle Mom's Invading Microbes

Breastfeeding moms give their babies antibodies, too
New research suggests that breast-feeding moms give their babies antibodies along with microbes to build a healthy gut immune response. Fredy Builes/Reuters

Breast milk is amazing. It is packed with infection-fighting microbes to bolster a baby's barely-there immune system and aid in digestion, and it can even change its immunological composition according to what the baby needs, based on receptors in the mammary gland that can "read" the infant's saliva.

But the breast milk is also loaded with microbes, which means a brand-new baby's gut is subject to a full-on invasion of tiny, foreign animals from the moment he or she starts feeding. The infant's immune system, rather than attack these foreign organisms like an immune system is designed to do, instead sits back and lets them invade. And now we know a bit more about why: In a study published Thursday in the journal Cell, researchers from the University of California Berkeley found that in addition to all those microbes, mother's milk is loaded up with antibodies to the very same microbes it contains. In other words, the milk contains both the beneficial microbes and what the body needs to be able to accept them.

The researchers also found that the immunoglobulin G (IgG) antibodies in breast milk "teach" the body to respond appropriately to gut microbes. It was previously thought that those antibodies were only responsible for fighting pathogens in the baby's system, but, as Berkeley immunologist Meghan Koch explained in a statement, her team's findings "show that the antibody response to the gut microbiota is more complex than previously appreciated and reveal a broader function for maternal IgG antibodies in helping to establish proper immune function early in life."

Koch and her team looked at the antibodies infant mice acquired from their mothers in the first two weeks of their life, and they found that the IgG antibodies effectively braced the body to accept a far broader spectrum of bacteria than do another class of antibodies in the milk, called IgA antibodies, which could change the way researchers think about immune response more generally. For example, disorders like Crohn's disease and ulcerative colitis are the result of the body's immune system responding improperly to gut microbes. Studying IgG antibodies may open new avenues for researchers to approach those diseases.

"This information could then be used to assess an individual's risk for inflammatory intestinal disorders and to implement therapeutic interventions at early disease stages," Gregory Barton, another author on the paper and an immunologist at Berkeley, said in a statement.