Abstract
Some human B-lymphoblastoid cell lines are shown to express at least two types of Ia-like antigens. One antigen is defined by alloantisera to HLA-DR, and the other antigen is defined by alloantisera and a monoclonal antibody to the specificities DC1, MT1 (MB1), and LB12, which are in linkage disequilibrium with HLA-DR. The subunits of the DC1 molecule differ from those of the DR molecule. The light chains of both molecules are structurally polymorphic.