L-CELLS EXPRESSING DQ MOLECULES OF THE DR3 AND DR4 HAPLOTYPES - REACTIVITY PATTERNS WITH MABS

cDNAs coding for the HLA class II DR and DQ alpha and beta chains of t he diabetogenic haplotypes DR3 and DR4 were introduced into a mammalia n expression vector and transfected into L-cell mouse fibroblasts to p roduce cells expressing individual human class Il molecules. Stable L transfectants were generated expressing each of the DR or DQ isotypes of the cis-encoded alpha and beta chains of the DR3 or DR4 haplotypes, as well as the trans-encoded a and beta chains of the DQ molecules of the two haplotypes, However, isotype mismatched combinations (DR alph a/DQ beta or DQ alpha/DR beta) did not result in any stable transfecta nts. The stable DQ L-cell transfectants obtained, along with homozygou s B-cell lines expressing the DQ2 and DQ8 specificities, were tested a gainst a large panel of twentyone anti-HLA class II monoclonal antibod ies (mAbs), Their unusual reactivity patterns are described including the failure of most ''pan-DQ'' mAbs to react with all DQ expressing L- cell transfectants, Interestingly, some mAbs react with certain ap het erodimers expressed on B-LCL but fail to recognize the same heterodime rs expressed on the transfectants. This is suggestive of minor structu ral modifications that class II molecules undergo depending on the cel ls they are expressed on.