This application is for a period of training intended to bridge the gap between working as a postdoctoral fellow and becoming an independent investigator. It is planned so that the work involved achieves a mix between pursuing a proven area of productive research and allowing the PI to develop expertise in new areas, including molecular biology and transcriptional regulation of cytokine genes, that will allow him to develop sufficient technical experience to become an independent investigator. During the period of post-doctoral research, the PI studied the immune response to the immunodominant epitope of myelin proteolipid protein (PLP 139-151, HSLGKWLGHPDKF) that induces experimental autoimmune encephalomyelitis (EAE) in SJL mice. It was clear that various altered peptides (also called altered peptide ligands or APLs) generated by a single amino acid substitution in the TCR contact residue of the encephalitogenic peptide regulated EAE and induced cross-reactive T cells. We hypothesize that cross-reactive interactions may be particularly important in the generation, regulation and propagation of organ specific autoimmune disease. APLs can be used as tools to dissect the effects of cross-reactivity on the autoimmune responses in vivo. APLs may have direct effects on autopathogenic cells, they may expand cross-reactive repertoires which are autoantigen reactive, or they may initiate a breakdown in tolerance by promoting a pro-inflammatory environment in the target organ. To investigate these possibilities we have generated a number of tools in the laboratory. We have produced a panel of T cell clones specific for the cognate ligand and altered peptides derived from the cognate ligand, and identified heteroclitic peptide ligands ( superagonists ) which induce proinflammatory cytokines (IFN-gamma and TNF-alpha) from Th2/Th0 cells. We have characterized several panels of cross-reactive clones, generated autoantigen specific TCR transgenic mice and obtained mice in which the autoantigen has been genetically deleted. These tools will allow us to undertake the following specific aims: 1) Determine if interactions with APLs alter the pathogenic potential of naive and differentiated autoantigen specific T cells; 2) Determine if cross-reactive T cells have different properties when they are activated and differentiated by restimulation with an autoantigen or a cross-reactive foreign antigen or APL; and 3) Determine whether superagonist ligands can induce unique signals that induce production of proinflammatory cytokines from an otherwise non-inflammatory T cell that may play a role in initiating autoimmune disease. Together these aims should identify the role of APLs in organ specific autoimmune disease, and define the mechanisms by which these ligands have effects in vivo.