How bile acids help defend against pathogens
doi:10.1038/nindia.2019.161 Published online 6 December 2019
A team of biologists has found how bile acids modulate the functions of specific immune cells that help kill pathogens1. The findings, they say, may help devise ways for treating immune-related disorders.
Bile acids help digest fat, form defences against bacteria and even aid in glucose metabolism. Bacteria residing in the gut transform bile acids to secondary bile acids that possibly modify immune response. However, it remains largely unknown how bile acids modulate the activity of immune cells.
To find out, an international research team, including a scientist from the Birla Institute of Technology and Science in Hyderabad, India, screened 30 compounds that include bile acids and secondary bile acids.
They narrowed their search to two compounds that are secondary bile acids. When cultured with specific mice-derived immune cells, the secondary bile acids substantially enhanced the differentiation of some of the immune cells. These acids even suppressed the activity of some of the immune cells.
The experiments reveal additional anti-inflammatory roles of the secondary bile acids that are usually found in humans and mice. Both acids are present in the stool samples of patients with inflamed colons as well as in the caeca of mice.
Remarkably, both bile acids are completely absent in germ-free mice, suggesting that specific gut-residing bacteria may contribute to the production of these acids.
The researchers say that this study may provide leads for the development of strategies for controlling immune cell function, which goes haywire in autoimmune and other inflammatory diseases.
1. Hang, S. et al. Bile acid metabolites control TH17 and Treg cell differentiation. Nature (2019) doi:10.1038/s41586-019-1785-z