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Major histocompatibility complex recognition by immune receptors: Differences among T cell receptor versus antibody interactions with the VSV8/H‐2Kb complex

The surface residues of the VSV8/Kb complex important for recognition by N15 and N26 αβ T cell receptors (TCR) were mapped by mutational analysis and compared to each other and with epitopes of well‐characterized Kb specific monoclonal antibodies (mAb). Three features of immune receptor recognition emerge. First, the footprints of the two TCR on VSV8/Kb are similar with more than 80% overlap between sites. Given that only 8 of 14 surface exposed VSV8/Kb 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 α1 and/or α2 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.