DIFFERENT REGIONS OF THE N-TERMINAL DOMAINS OF HLA-DR1 INFLUENCE RECOGNITION OF INDIVIDUAL PEPTIDE-DR1 COMPLEXES

The contributions of individual amino acids in the polymorphic beta ch ain and the conserved or chain of HLA-DR1 to influenza HA-specific DR1 -restricted and anti-DR1 allospecific T-cell recognition were analyzed . The genes encoding HLA-DR1 were subjected to site-directed mutagenes is in order to introduce single amino acid substitutions at 12 positio ns in the beta(1) domain and 11 positions in the or, domain. The beta( 1)-domain substitutions were all at polymorphic positions and introduc ed residues that are found in DR4 alleles. The amino acids introduced into the DR alpha(1) domain were based on the sequences of other human and mouse class II alpha chains. The responses of 12 DR1-restricted T -cell clones specific for two peptides of HA and seven anti-DR1 allosp ecific clones were studied. Substitutions at positions that point up f rom and into the peptide-binding site in the third variable region of the beta(1)-domain alpha-helix caused substantial reduction in the res ponses of all of the clones. Substitutions at multiple positions in th e beta(1)-domain floor and in the alpha(1) domain influenced the anti- DR1 responses of the alloreactive and of the HA100-115-specific T-cell clones. In contrast, very few changes outside of the beta(1) domain t hird variable region affected the responses of the HA30G-324-specific DR1-restricted T-cell clones. These results suggest that a surprisingl y limited region of the HLA-DR1 molecule is critically involved in T-c ell recognition of HA306-324 by DR1-restricted T cells. However, the s usceptibility of the HA100-115-specific and the anti-DR1 allospecific T-cell clones to substitutions at multiple positions in both N-termina l domains shows that the response to DR1-HA306-324 is unusual and may reflect the promiscuity with which this peptide binds to HLA-DR molecu les.