How Breast Milk Shapes Gut Microbiome Signaling and Immunity

Jarvinen-Seppo turns to how breast milk and gut microbiota actually communicate with the developing immune system, an area she describes as still being actively explored. She explains that gut microbial metabolites appear to be central to this signaling. Bifidobacteria, and Bifidobacterium infantis in particular, are known to produce large amounts of lactate and acetate, metabolites that lower the pH of the infant gut.

That lower, more acidic pH makes the gut environment less hospitable to pathogens, giving bifidobacteria a role in protecting against certain infectious diseases. Jarvinen-Seppo describes this as one clear mechanism connecting bifidobacteria to immune benefit, but notes there are additional pathways as well. Other metabolites produced by gut bacteria appear to support production of specific immunoglobulins, the antibodies made by the immune system. Bacterial signals can also prompt immune cells to produce regulatory T cells, or Tregs — a subset of lymphocytes whose levels are shaped by the composition of the microbiota. Jarvinen-Seppo emphasizes that Tregs matter because they essentially instruct the immune system on whether to respond to signals from the environment, making them a key link between early microbial exposure and the balance between tolerance and immune reactivity later in life.

In the next episode, "Formula Feeding and the Gut Microbiome: Closing the Gap," Jarvinen-Seppo compares formula and mixed feeding to exclusive breastfeeding and explains how newer HMO-supplemented formulas try to narrow the gap.