The autoimmune disease process underlying insulin dependent diabetes (IDD) relies upon interactions between genetic susceptibility genes located both inside and outside of the major histocompatibility complex (MHC) and multiple components of the immune system (i.e., antigen presenting cells, T-cells). Whereas previous studies have demonstrated that individuals with or at increased-risk for IDD (i.e., islet cell autoantibody positive relatives) display a number of immune abnormalities, the contribution of IDD susceptibility genes to these processes are poorly understood. The goal of this program project is to examine the immune system of individuals at varying risks for IDD in order to elucidate the mechanisms by which IDD susceptibility genes interact with antigen presenting cells and T-cells to engender the autoimmune destruction of pancreatic beta cells. This program will examine this question through three separate projects: Project 1 - The Roles of CTLA-4 and CD28 in IDDM Pathogenesis; Project 2 - PGS2 in the Pathogenesis of IDD in Humans and NOD Mice; and Project 3 - Immune Function and Genetic Susceptibility for IDD. Project I is designed to characterize the recently identified IDDM12 gene using a combination of genetic and functional analyses. This project will further define the genomic interval for IDDM12, and evaluate CTLA4 & CD28 as candidate genes for this disease susceptibility interval. With preliminary evidence that NOD mice and humans at increased-risk for IDD display abnormally high-levels of prostaglandin synthase-2 (PGS-2), project 2 will seek to identify a role for this molecule in the pathogenesis of IDD. Specifically, this project will define a genetic basis for the aberrant PGS-2 expression, and identify the effects of PGS-2 expression on monocyte/macrophage function, T-cell activation, and peripheral tolerance mechanisms. Project 3 will prospectively monitor a number of cellular immune activities (i.e., blastogenesis/cytokine production to beta cell antigens, expression of immunoregulatory molecules, class Il peptide binding of beta cell autoantigens) in individuals at very high- risk, low-risk, or extremely low-risk for IDD. Additional studies will monitor these immunological parameters in persons divergent in non-MHC linked susceptibility genes (i.e., IDDM2, IDDM12). These projects will be supported by three core facilities; A-Administration; B-Mouse Facility; C-Laboratory). The successful completion of this study will be beneficial to improve our understanding of events critical to the natural history of progression to IDD, identify genetic/immunologic screening tools for the disease, and develop selective immunotherapies for the prevention of IDD.