RORγt+Foxp3+ regulatory T cells in the regulation of autoimmune arthritis.

RORγt+Foxp3+regulatory T (Treg) cells, known as T regulatory 17 cells (Tr17 cells), are a novel subset of Treg cells, which have the potential to regulate the development of experimental autoimmune encephalomyelitis (EAE) thorough a specific repression of T helper 17 (Th17) cell-mediated inflammation. However, the function of Tr17 cells the development of other autoimmune diseases such as autoimmune arthritis remains unclear. Collagen-induced arthritis (CIA) was found to be prolonged in Foxp3creRORγtfl/fl mice, in which Tr17 cells were deleted, compared with Foxp3wtRORγtfl/fl mice. Tr17 cells were significantly increased in ankle joints (AJ) compared with draining lymph nodes after the onset of arthritis. CC chemokine receptor 6 (CCR6) was up-regulated on Tr17 cells compared to RORγt negative Treg cells. CD25, cytotoxic T-lymphocyte antigen 4 (CTLA-4), glucocorticoid-induced TNF-receptor (GITR), and inducible T-cell co-stimulator (ICOS) expression was also up-regulated on Tr17 cells compared to RORγt negative Treg cells. IL-10-producing cells and Blimp-1+ and T-bet+ cells were increased in Tr17 cells compared to RORγt-negative Treg cells. Tr17-enriched Treg cells significantly suppressed proliferation of conventional T cells through IL-10 compared with CCR6-Treg cells. Tr17 cells increased during the clinical course of CIA and accumulated in inflamed joints. Taken together, it appears that Tr17 cells play a crucial role in the regulation of autoimmune arthritis.

T-bet represses collagen-induced arthritis by suppressing Th17 lineage commitment through inhibition of RORγt expression and function.

T-bet is a key transcription factor for the T helper 1 lineage and its expression level is negatively correlated to inflammation in patients with rheumatoid arthritis (RA). Our previous study using T-bet transgenic mice revealed over-expression of T-bet completely suppressed collagen-induced arthritis (CIA), a murine model of RA, indicating a potential suppressive role of T-bet in the pathogenesis of autoimmune arthritis. Here, we show T-bet-deficiency exacerbated CIA. T-bet in CD4 + T cells, but not in CD11c + dendritic cells, was critical for regulating the production of IL-17A, IL-17F, IL-22, and TNFα from CD4 + T cells. T-bet-deficient CD4 + T cells showed higher RORγt expression and increased IL-17A production in RORγt-positive cells after CII immunization. In addition, T-bet-deficient naïve CD4 + T cells showed accelerated Th17 differentiation in vitro. CIA induced in CD4-Cre T-betfl/fl (cKO) mice was more severe and T-bet-deficient CD4 + T cells in the arthritic joints of cKO mice showed higher RORγt expression and increased IL-17A production. Transcriptome analysis of T-bet-deficient CD4 + T cells revealed that expression levels of Th17-related genes were selectively increased. Our results indicate that T-bet in CD4 + T cells repressed RORγt expression and function resulting in suppression of arthritogenic Th17 cells and CIA.