In the first two years of this grant, we have demonstrated that while normal epithelial cells stimulate antigen non-specific suppressor cells in antigen specific and mixed lymphocyte cultures, epithelial cells from patients with inflammatory bowel disease (IBD) preferentially activate potent T helper cells in vitro. This failure to generate suppression in the GI tract may account for the chronic inflammation seen in these disorders. The current proposal seeks to specifically identify the consequences of T cell activation in this disease, by measuring spontaneous and induced cytokine secretion by T cell subpopulations in the lamina propria. Several approaches will be used to identify the profile of cytokines produced including bioassay of supernatants generated from mitogen or anti-CD3 stimulated T cells, growth of T cell lines from mucosal biopsies, and in situ hybridization using specific riboprobes. In addition we plan to assess the effects of this T cell activation on the function of local cell populations including epithelial cells (measuring accessory cell function and cytokine production) and B cells (measuring changes in B cell subpopulations with emphasis on CD5+ B cells as a source of autoantibodies). Finally, we plan to dissect out the mechanism of the failure of epithelial cells to stimulate CD8+ T cells with a focus on identifying alterations of the CD8 ligand apparently present on normal epithelial cells. The results of these studies should help provide a clearer understanding of the pathogenetic mechanisms of IBD and potentially pave the way for novel therapies in these disorders.