Identification of the MT3 molecule from HLA-DR4, 7, and w9 homozygous cell lines.

Human B lymphoblastoid cell lines are known to express several class II antigens. The MT3 specificity defined by alloantisera is in linkage disequilibrium with DR4, DR7, and DRw9, and is called a "supertypic" specificity. To identify the MT3 molecule, immunoprecipitates of HLA-DR and MT3 antigens from extracts of three metabolically labeled HLA-DR homozygous cell lines (Wa;DR4, L-Pi-tot;DR7, L-KT12;DRw9) were analyzed by two-dimensional gel electrophoresis. The light chains of the MT3 antigens from DR4, DR7, and DRw9 homozygous cell lines were indistinguishable from one another in charge and m.w. The light chains of the MT3 antigens differed from those of DR4, DR7, and DRw9 antigens, whereas the heavy chains of the MT3 and DR antigens were indistinguishable. The MT3 antigen appears to share the same heavy chain as the DR antigens. However, this antigen would constitute a new human class II molecule distinct from the DR antigen. These data also raised the possibility that the light chains of the MT3 molecules may be the products of a new locus different from the DR locus.