Both MC5r and A2Ar Are Required for Protective Regulatory Immunity in the Spleen of Post-Experimental Autoimmune Uveitis in Mice

The ocular microenvironment uses a poorly defined melanocortin 5 receptor (MC5r)-dependent pathway to recover immune tolerance following intraocular inflammation. This dependency is seen in experimental autoimmune uveoretinitis (EAU), a mouse model of endogenous human autoimmune uveitis, with the emergence of autoantigen-specific regulatory immunity in the spleen that protects the mice from recurrence of EAU. In this study, we found that the MC5r-dependent regulatory immunity increased CD11b(+)F4/80(+)Ly-6C(low)Ly-6G(+)CD39(+)CD73(+) APCs in the spleen of post-EAU mice. These MC5r-dependent APCs require adenosine 2A receptor expression on T cells to activate EAU-suppressing CD25(+)CD4(+)Foxp3(+) regulatory T cells. Therefore, in the recovery from autoimmune disease, the ocular microenvironment induces tolerance through a melanocortin-mediated expansion of Ly-6G(+) regulatory APCs in the spleen that use the adenosinergic pathway to promote activation of autoantigen-specific regulatory T cells.