Functional analysis of HLA-DP polymorphism: a crucial role for DPbeta residues 9, 11, 35, 55, 56, 69 and 84-87 in T cell allorecognition and peptide binding.

The information available on the specific function of HLA-DP and the structure-function relationships is very limited. Here, single amino acid substitutions of HLA-DPB1*02012 have been used to analyze the role of polymorphic residues of the DPbeta1 domain on DP-mediated T cell allorecognition and peptide binding. Using a panel of specific anti-HLA-DP mAb, we identified the HLA-DP residues involved in the recognition by these mAb, with a crucial role for DPbeta56 for most of the mAb assayed. Individual substitutions at residues 9, 11, 35, 55, 56 and 69 completely abrogated T cell recognition mediated by two different HLA-DPw2-allospecific T cell clones (8.3 and 8.9). Interestingly single changes at positions 9, 11, 35 and 55 of HLA-DPbeta also altered the binding of peptides AAII(12-27) and IIP(53-65), natural ligands of the HLA-DPB1*02012 molecule. Individual changes at residues located in pocket 1 (84, 85, 86 and 87 from HLA-DPbeta) led to a partial reduction in cytotoxic T lymphocyte-mediated lysis and also partially affected peptide binding. However, the simultaneous substitution of these positions completely abolished both T cell allorecognition and peptide binding, suggesting a major role for polymorphisms at pocket 1 in HLA-DP function. Molecular modeling, used to predict changes induced by amino acid substitutions, supported the functional data. Taken together, these results strongly suggest that polymorphic residues 84, 85, 86 and 87 at pocket 1, residues 9, 35 and 55 at pocket 9, and residues 11 and 69 at pockets 6 and 4 respectively play a key role in HLA-DP function, probably by modifying the way the peptide is bound within the groove of HLA-DP2 and determining changes in the conformation of the MHC-peptide complex recognized by the TCR.