A cell-intrinsic glucocorticoid biosynthesis and sensing circuit maintains a homeostatic Th17 cell state.

T helper 17 (Th17) cells are heterogeneous: homeostatic Th17 (Th17Hom) cells maintain tissue homeostasis, and pro-inflammatory Th17 (Th17Inf) cells drive autoimmune inflammation. IL-23 drives Th17Inf, but the signals that maintain Th17Hom remain unclear. Here, we found that differential glucocorticoid (GC) production downstream of CYP11A1, a critical enzyme for steroidogenesis, distinguished Th17Hom cells from Th17Inf cells. Although TCR signaling opened the Cyp11a1 locus, TGF-β1 and IL-6, key cytokines for Th17Hom cell differentiation, maintained and amplified Cyp11a1. Th17Hom cell-derived GC signaled through the glucocorticoid receptor (GR), which was higher in Th17Hom cells compared with Th17Inf cells, thereby forming a circuit that maintained the homeostatic state. Integration of multi-omics data from CYP11A1- and GR-deficient Th17Hom cells revealed a gene network underlying this circuit. TGF-β1, a key node in the network, restored GC sensing to Th17Inf. We thus identify a GC signaling circuit that maintains Th17 homeostasis with implications for treating Th17-mediated autoimmunity.