A new study reveals new protective benefit of breast milk

An immune component of breast milk known as the complement system shapes the gut environment of infant mice in ways that make them less susceptible to certain disease-causing bacteria, according to a study led by researchers at the Johns Hopkins Bloomberg School of Public Health.

The researchers found that mouse pups that nursed from lactating mice whose breast milk lacked a key complement protein had different gut microbe populations than pups that nursed on standard mouse breast milk, making them highly vulnerable to Citrobacter rodentium, a bacterium that infects the guts of mice. Citrobacter rodentium is similar to certain types of diarrhea-causing E. coli that can infect humans but not mice.

The study was published online in the journal Cell.

The researchers’ experiments suggest that mouse breast milk’s complement components boost mouse infant health by directly eliminating some types of gut-dwelling bacteria. This reshaping of the gut microbiota leaves the infant mice far less susceptible to Citrobacter rodentium infection, thus protecting the young from certain infectious threats. The reshaping activity is not dependent on antibodies, in contrast to the way complement components are thought to typically work.

The researchers also confirmed in separate in vitro analyses that human breast milk contains these complement components, which demonstrated similar activity in targeting specific bacteria.

Taken together, these findings shed light on the mechanisms of how breast milk functions to provide protection from certain bacterial infections.

”These findings reveal a critical role for breast milk complement proteins in shaping offspring’s gut microbe compositions and protecting against bacterial infection in the gut in early life,” says study senior author Fengyi Wan, PhD, a professor in the Bloomberg School’s Department of Biochemistry and Molecular Biology. “This represents an important expansion of our understanding of breast milk’s protective mechanisms.”

Reference: Study in mice uncovers new protective benefit of breast milk; Cell; DOI: 10.1016/j.cell.2023.12.019