The monoclonal antibody AC1.59 defines a new polymorphic determinant on HLA-DR molecules.

2-dimensional gel electrophoresis analysis and sequential immunoprecipitation studies have shown that the monoclonal antibody (MoAb) AC1.59 recognizes a gene product of the HLA-DR locus. The determinant defined by the MoAb AC-1.59 has an unusual distribution on HLA-DR allospecificities, since it is expressed by HLA-DR1, DRw8, DRw9 antigens and by subtypes of HLA-DRw6 and HLA-DR4 antigens. In the latter allospecificity the expression of the MoAb AC1.59 defined determinant correlates with the cellularly defined HLA-Dw4 alloantigen. The present investigation provides evidence of serological heterogeneity within HLA-DR alloantigens. Furthermore these results suggest that monoclonal antibodies can sharpen the discriminatory power of serological assays to dissect the heterogeneity and complexity of HLA-DR alloantigens.