Getting the bugs out of the immune system: do bacterial microbiota "fix" intestinal T cell responses?

Proinflammatory T helper 17 (Th17) cells control infections caused by microbial pathogens. Surprisingly, several recent reports now reveal that symbiotic gut bacteria modulate Th17 cell differentiation and function in the gastrointestinal tract. As various autoimmune and allergic disorders are mediated by uncontrolled T cell responses, immune regulation by the microbiota may have direct implications for human health.