Biochemical dissection of DRw6 related epitopes using monoclonal antibodies

Three monoclonal antibodies (MoAbs) directed against polymorphic epitopes of Ia antigens were used as tools for a serological and biochemical dissection of the class II products encoded by the HLA-DRw6 haplotype. MoAb 16.23 defines an epitope common to DRw13 and DR3 haplotypes, MoAb S5 defines an epitope common to DRw13 and DR2 haplotypes, and MoAb S2 defines an epitope apparently restricted to DRw13. Not all DRw13 cells express these epitopes. Analysis of 16 DRw6 homozygous typing cells showed that expression of all three epitopes was restricted to those DRw13 cells that carried the Dw18 antigen, the DRw13 Dw19 cells being negative. The relationships among the molecules bearing these epitopes were investigated using sequential immunoprecipitation in lymphoblastoid cell lines derived from genetically characterized individuals. In both DRw13 and DR2 bearing cells, the DR2 + w13 epitope was localized to a population of DQ molecules which also carried the DQw1 specificity defined by MoAb Genox 3.53. The S5 epitope is therefore a private specificity that distinguishes the DQw1 antigens encoded by the DR2 and DRw13 haplotypes from the DQw1 antigens encoded by other haplotypes. The DRw13 and the DR3 + w13 epitopes were both shown to be expressed on DR molecules that also carried a DRw52-like specificity. In a DRw13 haplotype encoding both the S2 and 16.23 epitopes, the epitopes appeared to be located on separate molecules. The antibodies described here can distinguish between DRw13 cells which carry different Dw antigens, identify a private specificity on the DQw1 antigen, and define two distinct DR molecules encoded by some DRw13 haplotypes.