Inflammatory T cells express receptors (TCR) that recognize foreign molecules, but may also be misdirected to react against self molecules, eg. myelin proteins, causing autoimmune diseases such as multiple sclerosis (MS). One natural regulatory mechanism that limits this process involves a second set of T cells that recognizes the TCR expressed by the inflammatory T cells. These regulatory "TCR reactive" T cells can be readily boosted in vivo with recombinant TCR proteins or peptides that correspond to variable (V) region genes that are over expressed by the pathogenic self reactive T cells. After activation with defined TCR sequences, TCR reactive T cells secrete inhibitory factors (cytokines) that can locally inhibit both the target pathogenic T cells as well as bystander inflammatory T cells that may express a different TCR directed at different myelin antigens. Treatment with TCR proteins has been shown to be highly effective at preventing and treating rodent models of MS, called experimental autoimmune encephalomyelitis (EAE). These studies have provided crucial data for treating patients with MS, where trials are currently in progress. Recent studies in mice that express a transgenic TCR BV chain for myelin basic protein (MBP) have demonstrated that TCR-reactive T cells develop through rearrangement of non-transgenic AV genes that pair mainly with the transgenic BV chain. Other groups have demonstrated the critical importance of newly rearranged CD4+ TCR alpha/beta+ regulatory T cells in preventing spontaneous EAE in TCR double transgenic mice that cannot produce regulatory T cells. It is thus hypothesized that TCR reactive T cells constitute the major portion of this important regulatory T cell population that thus far has not been characterized for antigen specificity. Two specific aims are proposed: Aim 1. Contribution of TCR-specific regulatory CD4+ T cells to EAE resistance. CD4+ T cells specific for TCR AV and BV determinants will be functionally evaluated in TCR double transgenic B10.PL mice specific for MBP-Ac1-11, where TCR-reactive T cells are naturally enriched, and in double transgenic mice backcrossed onto the RAG&#8209;1-/- background, where TCR-reactive T cells cannot be positively selected. Defined TCR reactive T cell populations will be used to transfer protection to recipient mice susceptible to spontaneous or induced EAE. Aim 2. Contribution of cytokines, chemokines, and chemokine receptors to TCR mechanism. Intact and knockout B6 mice with MOG-induced EAE will be vaccinated with BV8S2 protein to assess the role of selected cytokines, chemokines, and chemokine receptors that have been implicated in the protective TCR mechanism. In knockout mice where TCR protection is lost, wild type T cell populations will be added back to confirm efficacy. These proposed studies will provide new and definitive insights into the biological importance and function of TCR-reactive T ceils in preventing and treating spontaneous and induced EAE, and will guide further human studies.