Sodium dodecyl sulfate-resistant HLA-DR "superdimer" bands are in some cases class II heterodimers bound to antibody

The detection of diners of diners in MHC class II crystals has excited spec ulation about their possible functions in T cell Ag recognition. Biochemica l evidence for the existence of DR superdimers falls short of proof and is controversial, To monitor B lymphoma cells for high m.w. complexes of HLA-D R molecules, membrane preparations and cell lysates mere screened by one-an d two-dimensional Western blotting. Under these conditions, in which DR alp ha beta heterodimers were readily detected, no DR complexes with an (alpha beta)(2)-chain composition could be identified. Two mAbs (L243 and D1-12) i mmunoprecipitated high m.w. DR complexes suspected to be superdimers. Howev er, biochemical analysis revealed that, rather than superdimers, these were SDS-stable complexes of DR in combination with the Abs, Thus, previous obs ervations of HLA-DR superdimer bands mag also reflect complexes of DR molec ules with bound Ab.