Segmented filamentous bacteria, Th17 inducers and helpers in a hostile world.

The Th17 cell composition in the murine gut is strikingly dependent on the presence of the commensal segmented filamentous bacteria (SFB). SFB potently stimulates innate and adaptive immune responses and protects the host from pathogens both in and outside of the gut, partly due to its unique ability to promote a Th17-fostering environment. Recent work has highlighted the role of the tight adherence of SFB to the intestinal surface in mediating the potent immunostimulatory potential of SFB. Progress has also been made in our understanding of how SFB fosters this protective immune environment on the cellular and molecular level. This review focuses on the ability of SFB to specifically stimulate Th17 immunity.