Analysis of monoclonal antibodies specific for unique and shared determinants on HLA-DR4 molecules

The specificities for seven mAbs to HLA-DR4 were determined initially using homozygous BCLs and L-cell transfectants expressing wild-type DR molecules. Three antibodies (NFLD.D1, NFLD.M1, and NFLD.D7) bound all DR4 molecules, but only one was specific for DR4. Four antibodies (NFLD.D2, NFLD.D3, NFLD.D8, and NFLD.D10) reacted with some but not all DR4 subtypes and had extra reactions, particularly with DR gene products associated with susceptibility to RA. To localize the antibody-binding epitopes on DR4 molecules, the antibodies were then analyzed on transfectants expressing hybrid genes, which were generated by exon shuffling of DRB1*0403 and DRB1*0701. Two of the pan-DR4 antibodies bound epitopes that require the beta 2 domain while the third mapped primarily to the HVR-I region. One antibody NFLD.D10 to subtypes of DR4 mapped to residues 40-97 on DR beta 1*0403 chains. Comparison of reaction patterns with amino acid sequences suggest that the antibodies against subtypes of DR4 are specific primarily for a region containing sequences postulated to determine susceptibility to RA.