Major histocompatibility complex recognition by immune receptors: Differences among T cell receptor versus antibody interactions with the VSV8/H-2K(b) complex

The surface residues of the VSV8/K-b complex important for recognition by N15 and N26 alpha beta T cell receptors (TCR) were mapped by mutational analysis and compared to each other and with epitopes of well-characterized K-b specific monoclonal antibodies (mAb). Three features of immune receptor recognition emerge. First, the footprints of the two TCR on VSV8/K-b are similar with more than 80% overlap between sites. Given that only 8 of 14 surface exposed VSV8/K-b residues identified as critical for TCR interaction are in common, the chemical basis of the N15 and N26 interactions is nevertheless distinct. Second, the cognate peptide is a major focus of TCR recognition: mutation at any of the three exposed side chains (at p1, p4 or p6) abrogates interaction of both TCR as measured by functional T cell activation. Third, in contrast to TCR, mAb bind to discrete segments on the periphery of the alpha 1 and/or alpha 2 helices without orientational restriction. These findings suggest that unlike soluble antibodies, surface membrane receptor-ligand interactions on opposing cells (i.e. TCR-peptide/MHC, CD8-MHC) limit the orientational freedom of the TCR in the immune recognition process.