ICOS-mediated phosphoinositide 3-kinase signaling controls induction and maintenance of collagen-induced arthritis

Abstract The inducible T-cell costimulator (ICOS) is a key costimulatory receptor facilitating differentiation and function of follicular helper T cells and inflammatory T cells. Rheumatoid arthritis patients were shown to have elevated levels of ICOS+ T cells in the synovial fluid suggesting a potential role of ICOS-mediated T cell costimulation in autoimmune joint inflammation. In this study, using ICOS knockout and knockin mouse models, we found that ICOS-mediated phosphoinositide 3-kinase (PI3K) signaling is required for the induction and maintenance of collagen-induced arthritis (CIA), a murine model of rheumatoid arthritis. For the initiation of CIA, ICOS-mediated PI3K signaling was critical for antibody production and expansion of inflammatory T cells. Further, we found that ICOS-PI3K signaling is important for maintenance of CIA in an antibody independent manner. Importantly, we found that a small molecule inhibitor of glycolysis, 3-bromopyruvate, ameliorates established CIA suggesting a potential link between ICOS-PI3K signaling and glucose metabolism. Thus, we identified ICOS-PI3K axis as a key signaling pathway that controls induction and maintenance of CIA and provide evidence that T cell glycolytic pathways can be potential therapeutic targets for rheumatoid arthritis.