The effect of mutations in the MHC class I peptide binding groove on the cytotoxic T lymphocyte recognition of the K^b‐restricted ovalbumin determinant

The H‐2K^b‐restricted cytotoxic T lymphocyte (CTL) response directed against ovalbumin (OVA) is specific for a region contained within the sequence OVA_253‐276. In this study we have characterized this response by examining the class I‐restricted presentation of OVA peptides by the naturally occurring K^b mutant (K^bm) glycoproteins K^bm1, K^bm3, K^bm5, K^bm8, K^bm10, K^bm11 and K^bm23. To facilitate this study we derived a series of somatic cell hybrid targets expressing the various K^bm class I molecules. Experiments using bulk OVA‐specific CTL from C57BL/6 mice demonstrated that all the K^bm molecules except for K^bm1 and K^bm8 could present OVA peptides for effective T cell recognition. Clonal analysis revealed a more complex and relatively diverse pattern of CTL recognition of the K^bm/peptide combinations. This diversity is unlikely to result from the existence of multiple, independent K^b‐restricted T cell determinants within OVA, since all CTL tested were specific for a single region between residues 259 and 273. Examination of the fine specificity of K^bm presentation identified individual changes at residues 77, 80 and 116 which affected T cell recognition. The results imply that these changes do not inhibit peptide binding since some clones could recognize peptide presented by a particular K^bm molecule, while other clones could not. All three residues reside within the peptide‐binding cleft of the class I protein and are not expected to directly contact the T cell receptor. Although we did not formally demonstrate that OVA binding by K^bm vs. K^b is quantitatively identical, our results are best explained by postulating that the changes at residues 77, 80 and 116 indirectly affect T cell recognition by altering peptide conformation. Taken together our results suggest that changes within the class I binding site can profoundly modify peptide presentation without significantly inhibiting peptide‐class I association.