ROLE OF POLYMORPHIC RESIDUES OF HUMAN-LEUKOCYTE ANTIGEN-DR MOLECULES ON THE BINDING OF HUMAN-IMMUNODEFICIENCY-VIRUS PEPTIDES

A study was made of the binding properties of 96 human immunodeficienc y virus peptides to human leucocyte antigen (HLA)-DR1 and HLA-DR103 mo lecules, which differ by three amino acids at positions 67, 70 and 71 in the beta chains. The affinity of the peptides was characterized by their inhibitory concentrations in competitive binding assays which di splace half of the labelled influenza haemagglutinin peptide HA306-318 (IC50). Among the high-affinity peptides (IC50 less than or equal to 1 mu M), seven bound to DR1, three to DR103 and five equally well to b oth alleles (promiscuous peptides). Thirty-two other peptides showed m edium or low affinity for DR molecules. The role of polymorphic residu es was analysed using six mutated DR molecules, intermediates between DR1 and DR103 and differing by one or two substitutions at positions 6 7, 70 or 71. We reached the same conclusions when using DR1-specific o r DR103-specific peptides: modification of residue 70 had no effect on peptide affinity, but single substitution at positions 67 or 71 decre ased the allele specificity of the peptides while double substitution at 67 and 71 completely reversed the peptide specificity. In functiona l assays, DR-binding peptides are able to outcompete specific T-cell p roliferation. Furthermore, modification at position 67 or 70 significa ntly affects the T-cell response and mutation at position 71 abolishes completely the T-cell proliferation. Thus, the polymorphic positions 67 and 71 contributed to the peptide binding with direct effects on T- cell receptor (TCR) recognition while position 70 seems to be mostly e ngaged in TCR interactions. Furthermore, our results suggest that poly morphic residues may select allele-specific peptides and also influenc e the conformation of promiscuous peptides.