Many of major autoimmune diseases are sexually dimorphic. Systemic Lupus Erythematosus (SLE), scleroderma, multiple sclerosis, Sjogren’s syndrome, and some forms of Type 1 diabetes (T1D) are primarily occurring in females. It has been attributed to multiple factors including expression of the genes encoded by sex chromosomes, hormonal regulation of gene expression, and lately to unexpected regulation by commensal microbiota. Thus, understanding of sexual dimorphism of diseases requires that the problem be approached by a combination of different strategies. In this proposal, we take advantage of our abilities to perform state of the art experiments using genetically modified and gnotobiotic animals with original and constantly developing computational methods. Our preliminary data demonstrates the efficiency of such an integrative approach to the problem. We have suggested a ‘dual signal’ model of autoimmunity involving regulation by microbes and sex hormones. Accordingly, hormonal and microbial influences do not have to be simultaneous: they may be important at different stages of development or disease progression. We are focusing on T cell-intrinsic and T- cell-extrinsic effects of Androgen Receptor (AR) and the mechanisms of microbiota’s effect on T1D development. Given the complexity of the problem, we plan to pursue several carefully selected goals that will continue to lay foundation for the future expansion of research in this important area. Specific Aim 1. Determine the input of T cell-intrinsic and T cell-extrinsic mechanisms in the sexual dimorphism of T1D. 1.1. Determine whether all cells involved in AR-mediated protection from T1D are of bone marrow origin; 1.2. Define the role of myeloid cells in male protection from T1D; 1.3. Test the contribution of myeloid cells in T cell transfer experiments; 1.4. Test a role that transcription factor AIRE plays in sexual dimorphism of T1D. Specific Aim 2. Investigate the influence of AR signaling on T cell selection and function 2.1. Determine the influence of AR on the TCR repertoires; 2.2. Determine how the properties of the TCR affect the influence of AR on repertoire selection; 2.3. Study the role of AR in regulation of interferon gamma (IFNg) related to autoimmunity; 2.4. Study the role of AR in regulation of the IFNg locus; Specific Aim 3. Determine where and when the microbiota amplifies AR effects on T1D development. 3.1. Test T1D development in GF animals with conditional AR deficiencies; 3.2. Determine whether microbes contribute to changes in immune cells properties during their development; 3.3. Establish the timeline to imprinting males to become resistant to T1D by the microbiota; 3.4. Determine which immune-related pathways are affected by the microbiota.