RORγt represses IL-10 production in Th17 cells to maintain their pathogenicity in inducing intestinal inflammation

The role of retinoid-related orphan receptor γ t (RORγt) in Th17 cell differentiation has been well established; however, how it regulates other T cell lineages is still not clearly understood. In this study, we report that in mice, while promoting Th17 cell differentiation, RORγt inhibited IL-10 production by T cells, thereby preserving the pathogenicity of Th17 cells. Treatment with RORγt-specific inhibitor suppressed Th17 cell signature cytokines, but promoted IL-10 production. RORγt inhibitor-treated Th17 cells induce less severe colitis compared with control Th17 cells. Mechanistically, the RORγt inhibitor induced T cell expression of Blimp-1 (encoded by Prdm1). Prdm1^-/- T cells produced significantly fewer IL-10 when treated with RORγt inhibitor compared with wild-type T cells. Furthermore, RORγt inhibitor-treated Prdm1^-/- Th17 cells induce more severe colitis compared with RORγt inhibitor-treated wild-type Th17 cells. Collectively, our studies reveal a novel mechanism by which RORγt drives and maintains pathogenic Th17 cell development by inhibiting IL-10 production.