Quantitative expression of epitopes defined by murine monoclonal antibodies on DR molecules from different HLA haplotypes

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Abstract
Monoclonal antibodies 50D6 and 2Ir5, reactive with human class II molecules, were analyzed quantitatively by flow cytometry and cellular radioimmunoassay for their binding to cells of different HLA-DR types. Monoclonal antibody 50D6 bound equally to cells of all DR types tested except DR7, where no reactivity was observed. Monoclonal antibody 2Ir5 was reactive with all cells. However, the percentage of DR molecules at the cell surface expressing 2Ir5 epitope varied with the DR type and increased as follows: DR3 = DR7 < DR2 < DR5 < DR4 < DR1. MAb 50D6 reacted with an epitope spatially related to but distinct from the 2lw4 epitope present on all DR molecules. The 50D6 epitope was shown to be present on isolated DR1 molecules.