MICROHETEROGENEITY IN HLA-B35 ALLELES INFLUENCES PEPTIDE-DEPENDENT ALLORECOGNITION BY CYTOTOXIC T-CELLS BUT NOT BINDING OF A PEPTIDE-RESTRICTED MONOCLONAL-ANTIBODY

Strong peptide dependency of HLA-B3501-specific alloreactive T-cell c lones was observed in the recognition of cells bearing closely related B35 variants. The single amino acid exchange in the beta-pleated shee t of B3503 completely abolished the responses of all clones, whereas an amino acid exchange in the alpha(2) helix of the newest B35 member (B3508) only altered allorecognition of one T-cell clone, demonstrati ng the differential impact of these positions on peptide binding to B3 5 molecules. In contrast to T cells, a mAb (TU 165) recognizing the B3 5 specificity in a peptide-dependent manner bound to the B35 variants irrespective of their sequence heterogeneity. However, quantitative bi nding differences were detected with cells bearing the same B35 allele s. This is most likely due to variations in the amount of peptide(s) t hat associates with B35 and forms the ligand seen by this mAb. These r esults reveal how naturally occurring single amino acid substitutions have led to generation of functionally distinct molecules of another m ultimember HLA class I cluster.