9407894 Fink The discovery that tolerance to self antigens encountered in the lymphoid periphery can be induced by rendering self- reactive T cells immunoincompetent has stimulated the analysis of the signaling machinery in these anergic populations. The experiments described in this proposal are aimed at understanding the nature of the signaling defects in a subpopulation of murine T cells that has been rendered refractory to normally stimulatory signals. These T cells are derived from mice that are transgenic for a T cell receptor (TCR) chain gene whose expression mediates the recognition of a self antigen. Encounter of the T cell with this self antigen is unusual in that it results in the downregulation of the cell surface expression of both the TCR and its CD8 coreceptor, and renders these cells immunoincompetent, even upon stimulation by signals not thought to be affected by receptor density. These studies are designed to localize the impairment in signaling in anergic cells by analyzing: (1) their ability to mobilize internal calcium stores in response to antibody-mediated crosslinking of surface TCR molecules (2) their patterns of tyrosine phosphorylation before and after TCR crosslinking (3) the mobility shift of the CD8-associated nonreceptor protein tyrosine kinase p56lck upon cell activation (4) the activity of mitogen-activated protein kinase upon TCR crosslinking, and (5) the transcriptional activity of the genes encoding the transcription factors c-fos and c-jun upon activation. %%% The lymphocyte effector arm of the immune system is divided into two main compartments, B and T Cells. While B cells make antibody molecules that can recognize soluble foreign substances or antigens, T cells concentrate on cell-bound antigens using a two chain surface receptor (the T cell receptor or TCR). Much of T cell differentiation takes place in the thymus, including the induction of self tolerance, a process that often resu lts in the deletion of thymocytes whose TCRs recognize self proteins. This distinction between "self" and "nonself" is critical to the functioning of a healthy immune system. T cell tolerance to antigens expressed outside the thymus can be induced and maintained by mechanisms in addition to clonal deletion. Encounter of self-reactive T cells with antigens in the lymphoid periphery can render these cells nonfunctional or "anergic" frequently resulting in their elimination. This investigator has defined a population of relatively long- lived anergic T cells that can purified from murine blood on the basis of an unusual surface antigen phenotype. Using this system, she will define the aspects of the complicated pathways of signaling that lead inward from the TCR on the cell surface that are altered in anergic relative to immunocompetent cells. These studies are aimed at understanding this nondeletional mechanism for maintaining self tolerance, and why it occasionally fails. ***
