The role of I-A(g7) β chain in peptide binding and antigen recognition by T cells

We examine here how the β chain of the class II MHC molecule I-A(g7) influences T cell recognition. Three sets of T cell clones were identified. The first set recognizes peptides bound to I-A(g7), I-A(d) and I-A(g7) mutant in which the allele-specific residues His and Ser at position 56 and 57 were changed to the Pro at residue 56 and to non-polymorphic Asp at residue 57. The second set responds to the antigen presented only by I-A(g7) and does not recognize the peptides bound to the other class II molecules. The third set is also specific for I-A(g7) as a result of the poor binding of the peptide to I-A(d) and the mutant I-A(g7). These results indicate that positions 56 and 57 of the I-A(g7) class II MHC β chain play a role in both T cell recognition of the MHC-peptide complex and peptide binding to MHC. These two different functions may be involved in I-A(g7)-restricted β cell antigen recognition by diabetogenic T cell clones.