MICROVARIATION CREATES SIGNIFICANT FUNCTIONAL DIFFERENCES IN THE DR3 MOLECULES

Two DR3 molecules differ by four amino acids whose side chains point i nto the DR antigen-binding groove. To begin to assess the role of micr ovariation on DR3 function, DRB1()0302 residues were replaced with DR B1()0301 residues at beta-chain positions 26, 47, 86, and 47 plus 86. Murine fibroblast cell lines expressing DR(alpha,beta 1()0301), DR(a lpha,beta 1()0302), and the four mutant 0302 molecules were examined for alloproliferative DR(alpha,beta 1()0302)-specific TLC stimulation and peptide binding. Changing position 26 had the most profound effec t on T-cell recognition (seven of nine TLCs did not respond). Two TLCs did not respond to the mutant 0302V86 molecule and four TLCs that did respond to this mutant lost responsiveness when positions 47 and 86 w ere mutated together. These data suggest that each of these variant re sidues, including position 47, influence T-cell recognition. Surprisin gly, none of the mutations had an effect on the absolute binding of HA 307-319 (DR[alpha,beta 1()0302] specific) and HSP 3-13 (DR[alpha,bet a 1()0301] specific); however, the mutant 0302 molecules changed at p osition 86 (glycine to valine) consistently bound HA 307-319 at signif icantly higher levels than DR(alpha,beta()0302). These data for posit ion 86 are in contrast to other DR molecules and indicate that peptide contact residues for a specific DR molecule cannot be predicted based on binding results obtained with other DR molecules. These data sugge st that each of these variant groove residues, although not accessible to the TCR, contribute to the significant functional differences betw een the DR3 microvariants through subtle influences on the DR3-peptide complex.