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Inflammatory bowel diseases (IBDs) such as Crohn's disease and ulcerative colitis are characterized by recurrent inflammation in the gastrointestinal tract. Infiltration of CD4+ lymphocytes and neutrophils is one of the predominant features of IBD.Recently, interleukin (IL)-23 and the downstream T cell-derived cytokine IL-17 have been found to be elevated in intestinal tissue and serum of IBD patients. However, the role of IL-17 and IL-17R signaling in gut inflammation is unknown. To examine this role, we investigated gut inflammation in wild-type or IL-17R knockout mice.Using a model of acute trinitrobenzenesulfonic acid (TNBS)-induced colitis, we found that IL-17 was produced in colon tissue at 24 and 48 hours and that IL-17R knockout mice were significantly protected against TNBS-induced weight loss, IL-6 production, colonic inflammation, and local macrophage inflammatory protein-2 induction. This protection occurred in the presence of equivalent induction of local IL-23 and higher levels of IL-12p70 and interferon-γ in IL-17R knockout mice compared with wild-type mice. Moreover, IL-17R knockout mice showed reduced tissue myeloperoxidase activity. Furthermore, overexpression of an IL-17R IgG1 fusion protein significantly attenuated colonic inflammation after acute TNBS.These results demonstrate that IL-17R signaling plays a critical role in the development of TNBS-induced colitis and may represent a target for therapeutic intervention for IBD.