<h2>Summary</h2> Interleukin-23 (IL-23) is an inflammatory cytokine that plays a key role in the pathogenesis of several autoimmune and inflammatory diseases. It orchestrates innate and T cell-mediated inflammatory pathways and can promote T helper 17 (Th17) cell responses. Utilizing a T cell transfer model, we showed that IL-23-dependent colitis did not require IL-17 secretion by T cells. Furthermore, IL-23-independent intestinal inflammation could develop if immunosuppressive pathways were reduced. The frequency of naive T cell-derived Foxp3<sup>+</sup> cells in the colon increased in the absence of IL-23, indicating a role for IL-23 in controlling regulatory T cell induction. Foxp3-deficient T cells induced colitis when transferred into recipients lacking IL-23p19, showing that IL-23 was not essential for intestinal inflammation in the absence of Foxp3. Taken together, our data indicate that overriding immunosuppressive pathways is an important function of IL-23 in the intestine and could influence not only Th17 cell activity but also other types of immune responses.

Interleukin-23 Restrains Regulatory T Cell Activity to Drive T Cell-Dependent Colitis