Non-infectious forms of uveitis represent a significant cause of blindness and understanding the underlying mechanisms by which they occur is critical for their prevention and treatment. The long term objectives of this project are to better understand the mechanisms by which autoimmune uveitis occurs in a unique animal model that we have developed. Our model involves mice that are deficient for the Autoimmune Regulator (Aire) gene which has been shown to be the defective gene in the clinical disorder Autoimmune Polyglandular Syndrome Type 1 (APS1). Importantly, both APS1 patients and Aire-deficient mice have been demonstrated to spontaneously develop autoimmune uveitis. Thus, unraveling how a single gene defect in Aire can lead to uveitis can give us important clues into its pathogenesis. Aire appears to play a major role in controlling the promiscuous expression of a wide variety of self-antigens with the thymus, including several eye-specific antigens. We have recently developed novel reagents to further detect and measure eye-specific T cells that are negatively selected within the thymus in an Aire-dependent fashion. In addition, because the autoimmune response to the eye in our model appears to proceed in antigen-specific manner we are also interested in preventing uveitis with antigen-specific tolerance protocols. Three major goals are therefore envisioned: (1) understand mechanisms by which uveitogenic T cells are selected in the thymus in Aire-deficient mice; (2) preventing spontaneous uveitis with antigen-specific tolerance; (3) enforcing tolerance to the eye with extrathymic Aire-expressing cells. Because our animal model occurs spontaneously, it affords the opportunity to explore novel pathways that are involved in the induction of uveitis and also in the prevention and treatment of this disease. In addition, because many of the details on how Aire protects against autoimmunity remained to be unraveled our findings could also have broad implications for our understanding of immune tolerance. A significant case of blindness is caused by non-infectious forms of uveitis, many of which are thought to be autoimmune in nature. Autoimmune uveitis is thought to result from a defect in immune tolerance to the eye and understanding how tolerance to the eye is maintained is essential to treating and preventing the disease. In this proposal we will address the role of an important transcription factor called Aire (for Autoimmune Regulator) in controlling immune tolerance to the eye and its relevance to disease is clear as both humans and mice that have defects in Aire can develop uveitis.