Critical role of polymorphic residues from DPBI*02012 in T cell recognition and peptide binding

An important characteristic of HLA-DP molecules is that they are highly polymorphic. Most of the polymorphic residues in the DPβ chain are clustered into six regions (A: residues 8, 9, 11; B: 33, 35, 36; C: 55, 56; D: 65, 69; E: 76; and F: 84-87) and most of them located in the peptide binding region. To investigate the contribution of the individual polymorphic positions from the HLA-DPB1*02012 allele in allorecognition and peptide binding, thirteen DPB 1*02012 cDNAs were generated by site-directed mutagenesis changing polymorphic residues in this allele by the aminoacids present in other HLA-DP alleles. The functional involvement of these polymorphic positions in T-cell recognition was examined testing the ability of two HLA-DPw2 alloreactive CD4+ cytotoxic T-lymphocyte clones to lyse the panel B-LCL transfectant cells. Most of the substitutions prevented, total o partially, the recognition by these two CTLs clones, demonstrating the crucial role of these positions in allorecognition. Moreover, mutation on DPβ-84 affected the recognition mediated by one of the clones but not by the other, suggesting differences in the peptide-MHC complex recognised by each clone. The importance of HLA-DP polymorphism in peptide binding was also evaluated using synthetic peptides previously characterised as DP bounders. Peptide specificity was examined using B-LCLs expressing different HLA-DP alleles and the role of specific polymorphic residues on peptide binding assayed by flow cytometry using the panel of B cell transfectants described above. © 2001 Blackwell Science Ltd,.