New mouse study reveals protective power of breast milk

Breast milk complement alters gut microbiota for infant health.


Breast milk’s immune part, the complement system, shapes the gut of baby mice. A study from Johns Hopkins University shows that when lactating mice lack a specific complement protein in their milk, their pups have different gut microbes. These mice become more prone to a bacterium, Citrobacter rodentium, similar to some E. coli, causing diarrhea in humans but not in mice.

Mouse breast milk’s complement components boost infant health by eliminating certain gut bacteria. This reshapes the gut microbiota, making infant mice less vulnerable to Citrobacter rodentium infection. Unlike typical complement functions relying on antibodies, this activity doesn’t require them.

The study also found similar complement components in human breast milk, suggesting a shared protective mechanism. Published in Cell, these findings provide insights into how breast milk protects against bacterial infections.

Study senior author Fengyi Wan, Ph.D., a professor in the Bloomberg School’s Department of Biochemistry and Molecular Biology, said, “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. This represents an important expansion of our understanding of breast milk’s protective mechanisms.”

Dongqing Xu, Ph.D., an assistant scientist, led a study on the benefits of breastfeeding. Breast milk provides excellent nutrition, protects against illnesses, and helps fend off infections through antibodies and white blood cells.

Using mice without crucial complement genes, the study discovered that milk lacking complement proteins left mouse pups vulnerable to severe colitis from Citrobacter rodentium. In contrast, dogs fed regular milk with complement proteins showed minor signs of gut infection. This highlights the crucial role of complement proteins in breast milk.

The team found that breast milk complements protein protection by shaping infant gut microbiota. These proteins eliminate specific bacteria, creating an environment where harmful inflammation is less likely in the presence of Citrobacter rodentium.

Breast milk complement proteins are crucial in establishing a protective gut microbiota, promoting infant health, and defending against pathogens. This study also advances basic immunology by revealing that breast milk complement activity against bacteria doesn’t need antibodies, operating as a nonspecific immune response.

Wan said, “This opens the door to a lot of new investigations, for example, elucidating the specific complement biology in breast milk and comparing that to complement biology in the blood and assessing the role of complement beyond the antibody-dependent specific immune system.”

This study provides valuable insights into the protective mechanisms of breast milk, showcasing its role in shaping infant gut microbiota and defending against infections. The findings highlight the importance of breast milk in promoting infant health and contribute to advancing our understanding of basic immunology.

Journal reference:

  1. Dongqing Xu, Siyu Zhou, et al., Complement in breast milk modifies offspring gut microbiota to promote infant health. Cell. DOI: 10.1016/j.cell.2023.12.019.


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