Acute Gastrointestinal Infection Induces Long-Lived Microbiota-Specific T Cell Responses

In order to coexist peacefully, the billions of bacteria in our gut and our immune system have reached a detente. An intestinal mucosal firewall exists, so bacteria remain localized to the gut, where the immune system is tightly regulated so that these bacteria are tolerated. Enteric infections, however, lead to a breach in this mucosal firewall, resulting in exposure of the peripheral immune system to the intestinal bacterial contents. What is the result? Using oral Toxoplasma gondii infection in mice, Hand et al. (p. [1553][1], published online 23 August) show that, besides the T. gondii –specific T cell response, a commensal bacteria–specific T cell response is elicited. The CD4+ T cell–specific response was tracked to a commensal-derived flagellin, and these T cells expanded after T. gondii infection and formed long-lived memory cells able to respond to subsequent challenges. Thus, enteric infections can lead to the formation of commensal bacteria–specific, long-lived memory T cells that reside throughout the body—which may play a role in intestinal pathologies such as inflammatory bowel disease. [1]: /lookup/doi/10.1126/science.1220961