Analysis of HLA-DR antigens by using monoclonal antibodies: recognition of conformational differences in biosynthetic intermediates.

The monoclonal antibodies L203 and L227 were used to characterize Ia-like antigens on human B cell lines. The antibodies appear to recognize subsets of HLA-DR molecules on the cell line Raji, which is heterozygous for HLA-DR. However, by using L203 and L227, more than 1 DR-like molecule could not be clearly identified on the DRw8 homozygous cell line MADURA. The 2 antibodies did display different affinities for different forms of the same DR molecule. On DRw8 and cell lines of other DR types, L227 had a greater affinity than L203 for the biosynthetic intermediates of the DR heavy and light chains. L203 displayed a greater affinity than L227 for the mature forms of the DR subunits. The antibody L227 immunoprecipitated the denatured DR light chain, but not the heavy chain, suggesting that the antigenic determinant is on the light chain. The L203 and L227 determinants are not on the N-linked oligosaccharides, since both antibodies recognized nonglycosylated DR antigens from cells treated with tunicamycin. In contrast to the DRw8 homozygous cell line, it was found that DRw6 homozygous B cell lines express at least 2 DR light chains. A xeno anti-HLA-DR (anti-p23,30) serum and L203 recognized both light chains, whereas L227 precipitated only 1 of the 2. A model depicting the expression of the L203 and L227 antigenic determinants on the DRw8 molecule is discussed.