How bile acids and the microbiota interact to shape host immunity

Bile acids are increasingly appearing in the spotlight owing to their novel impacts on various host processes. Similarly, there is growing attention on members of the microbiota that are responsible for bile acid modifications. With recent advances in technology enabling the discovery and continued identification of microbially conjugated bile acids, the chemical complexity of the bile acid landscape in the body is increasing at a rapid pace. In this Review, we summarize our current understanding of how bile acids and the gut microbiota interact to modulate immune responses during homeostasis and disease, with a particular focus on the gut. Here, Raffatellu and co-workers discuss our growing understanding of how primary bile acids (which are cholesterol-derived molecules synthesized in the liver) and secondary bile acids (which are primary bile acids that have been microbially modified) shape immune responses in health and disease, with a particular focus on bile acids and intestinal immunity.