SUBSTITUTIONS IN THE HLA-DR-ALPHA CHAIN DIFFERENTIALLY AFFECT DR7-RESTRICTED T-CELL RECOGNITION OF RABIES VIRUS-ANTIGEN

To investigate the functional roles of DR alpha residues in T-cell rec ognition, 20 mutants of the DR alpha chain were constructed by site-di rected mutagenesis. These DR alpha mutants were expressed with WT DR(b eta 10701) on mouse L cells and used as APC for four DR7-restricted T -cell clones specific for rabies virus antigens. The results indicate that the DR<alpha residues are differentially involved in recognition of rabies virus antigen by different T-cell clones. Mutations in the f loor of the antigen-binding groove (positions 9, 11, 22, and 24), on t he alpha-helix (47, 55, 65, 66, and 72), and surprisingly on the outer loop(15, 18, and 19), abrogated recognition by ac least one T-cell cl one. Most of these residues appear to be involved in either peptide or TCR contact, based on the DR1 crystal structure. The involvement in T -cell recognition of DR alpha residues located in the outer loop outsi de the binding groove suggests that these residues may directly contac t TCR, or indirectly contribute to the conformation of peptide sitting in the groove.