The goal of this proposal is to further understand how the neuropeptide alpha-melanocyte stimulating hormone (α-MSH) regulates immunity, and how it can be used to suppress uveitis to reestablish immune privilege. Previously published work, and the progress of our past grant-period demonstrated that α-MSH-treatment during uveitis can restore immunosuppressive activity of retinal pigment epithelial cells (RPE). In addition, we have demonstrated that part of immune privilege is suppression of the phagocytic/antigen-processing pathway within macrophages by healthy RPE. This suppression is mediated by α-MSH produced by RPE and is dependent on expression of the α-MSH-receptor, melanocortin 5 receptor (MC5r), in the retina. Therefore, suppression of EAU, and the induction of regulatory T cells by α-MSH-therapy is possibly associated with regulating antigen presenting cell activity within the uveitic eye. This would be mediated through α-MSH binding specific melanocortin-receptors on the RPE and APC of the retina. Therefore, we hypothesize that α- MSH regulates the processing and presentation of antigen within the immune privileged microenvironment, and that α-MSH-therapy acts through this mechanism to suppress autoimmune uveitis. We will demonstrate this regulation by assessing the role of α-MSH to regulate the phagocytic pathway in macrophages and microglial cells; by determining the ability of α-MSH-treated APC to antigen-activate effector T cells; and assess the potential for α-MSH to mediate innate-immune memory tolerance in macrophages. The α-MSH- therapy will involve treating EAU with whole neuropeptide and specific melanocortin-receptor-agonists. The regulation of antigen uptake, processing, and presentation will be assayed on both tissue macrophages, and retinal microglial cells. Also, we will examine retinal microglial cells and α-MSH-treated macrophages for expression of markers and activity associated with innate-immune memory tolerance. We will examine changes in this regulation in the initial stages of EAU as suggested by our preliminary data. Our proposed work will have a meaningful impact, because the results will provide new information about the molecular mechanisms of uveitis, and α-MSH anti-inflammatory-activity. Also, it will define how melanocortin-based therapy can regulate antigen presentation and T cell activation by suppressing the central drivers of autoimmune disease.