It turns out the gut bacteria have plenty of other functions. A new study reveals that the bacteria in the intestines also regulate its host's immune system.

A team of researchers from Brown University found that the microbiome prevents an overactive immune system from attacking the so-called good bacteria. The findings can aid in understanding and treating autoimmune and inflammatory diseases.

The study was published in the journal Immunity.

Gut Bacteria Regulates Immune System

The role that the microbiome plays in regulating the immune system involves moderating the levels of protein that convert vitamin A into its active form, retinoic acid. The researchers found that Firmicutes which, together with Bacteroidetes, comprise the majority of the gut bacteria in both humans and mice reduce the expression of a protein called retinol dehydrogenase 7 (Rdh7) within the cell that lines the walls of the intestines.

In an experiment, the lab mice that were genetically engineered to not have Rdh7 in their intestinal cells were found to have less retinoic acid. The mice also had fewer immune cells responsible for the creation of IL-22 which is, in turn, responsible for coordinating the antimicrobial response of the body against good bacteria.

The researchers do not exactly how the microbiome suppresses the Rdh7. They hope to explore whether the suppression will lead to inflammation or autoimmune disease to the genetically-engineered mice.

The Gut Bacteria, Vitamin A, And Immune System

The researchers explained that their findings could be the key to understanding disorders like Crohn's, an inflammatory bowel disease. Previous clinical studies have found that inflammation of the bowel is a result of the disruption of the interaction between the body and the microbiome.

"The role of vitamin A in inflammation is context-dependent and is very hard to tease apart," stated Shipra Vaishnava, an assistant professor of molecular microbiology and immunology at Brown University. "A change in vitamin A status and vitamin A metabolic genes coincides with inflammatory bowel diseases, but we don't know if this promotes inflammation or not."

The researchers also hope that their findings could help enlighten the field about the role of the microbiome in treating vitamin A deficiency, which is common in children in Africa and Southeast Asia.