ACIDIC RESIDUES IN THE DR-BETA CHAIN 3RD HYPERVARIABLE REGION ARE REQUIRED FOR STIMULATION OF A DR(ALPHA,BETA-1-ASTERISK-0402)-RESTRICTED T-CELL CLONE

We investigated the minimal requirements for stimulation of an antigen -specific HLA-DR(alpha,beta 10402)-restricted T-cell clone (Een217) b y using transfectants expressing mutant DR beta chains as APCs. Antige n-specific stimulation of Een217 was induced with transfectants expres sing DR(alpha,beta 10402) and DR(alpha,beta 1*0403) but not other DR4 subtypes that also bind the peptide recognized by this clone. Analysi s of the effects of single amino acid substitutions in the beta chains of each of the DR4 subtypes revealed a requirement for acidic residue s in the third HVR, particularly amino acid 71, in stimulation of clon e Een217. Functional class II mutants were generated from nonstimulato ry DR4 subtype beta chains by acidic residue substitutions within the third HVR. These data define the requirement for negatively charged re sidues in this region for peptide-induced stimulation of this T-cell c lone. The required acidic residues can be located at either position 7 0, 71, or 74 in the DR beta chain. The negative charge in this segment of the DR beta chain alpha-helix may be required for direct interacti ons with the T-cell receptor of Een217 or may affect peptide conformat ion.