The molecular reaction patterns of the DRw52-specific mouse monoclonal antibodies UL-52 and 7.3.19.1 were investigated. Upon immunoprecipitation and two-dimensional IEF-SDS polyacrylamide gel electrophoresis analysis (2D-PAGE) mAb UL-52 selectively isolated DR beta 1 molecules from DRw52-positive cell lines, whereas mAb 7.3.19.1 predominantly precipitated DR beta 3 molecules. Reduced mAb UL-52 binding affinity was observed to DRw8- and DRw12-positive cells, potentially resulting from structural modifications within the antibody binding site. Comparison of mAb UL-52 reactivity with published DR beta chain amino acid sequences demonstrates that the amino acid residues -S- in positions 11 and 13 on DR beta 1 molecules essentially contribute to the formation of the antibody binding site. mAb 7.3.19.1 reactivity, on the other hand, correlates with the expression of DR beta 3 chain amino acid residues K, G and N, in positions 71, 73 and 77, respectively. In contrast to other DRw52 monoclonal antibodies described so far, mAb UL-52 demonstrates a similar reactivity to DRw52 allosera, suggesting that mAb UL-52 and DRw52 allosera possibly recognize the same or a similar determinant on DR beta 1 molecules.
