The immune system distinguishes self from non-self during viral and bacterial pathogenesis or from altered self in the recognition of tumor antigens through a ligand/receptor system comprised, in part, by the class I and class II antigen presenting molecules. The long-term goal of these studies is to determine the structural basis of these immune functions. This proposal focuses on the amino-terminal domains of these MHC glycoproteins, which have been associated with antigen presentation, alloantigenicity and MHC restriction. Variant MHC genes will be constructed by site-directed mutagenesis and by overlap extension. They will be introduced into cell lines and mice by DNA mediated gene transfer, and the resulting gene products will be assessed for antigen presentation and immune recognition properties using cellular immune response assays. Among the issues being addressed are: (1) a hypothesis suggesting that the position of amino acid side chains in and around the putative antigen binding site determines whether they influence functional properties; (2) whether the beta-sheet and alpha-helices of the putative antigen binding site interact to determine antigenic specificities recognized by T cells; (3) whether the loop regions of the amino-terminal domain of class I molecules influence antigen presentation; (4) the nature of intramolecular interactions within the amino-terminal domain that determine ability of class I molecules to present antigens; (5) to establish an MHC-free, murine cell line for gene transfer experiments to study the conserved properties of class I molecules that determine their antigen presenting capabilities, and (6) recent hypotheses that suggest class II molecules contain amino-terminal domains organized in a manner similar to class I molecules.
