Human medullary thymocyte p80 antigen and In(Lu)-related p80 antigen reside on the same protein.

Study of human T lymphocyte differentiation antigens with monoclonal antibodies has led to the identification of two antigens shared by erythrocytes and leukocytes. The protein (p80) defined by A1G3 antibody has previously been shown to be acquired during human intrathymic T-cell maturation. The antigen defined by A3D8 antibody has been demonstrated also to reside on an 80 kd protein; expression of the A3D8 antigen on erythrocytes and a subset of leukocytes is regulated by the rare In(Lu) gene. In this study, we demonstrate that the antigens defined by the A1G3 and A3D8 antibodies reside on the same protein and represent closely related but nonidentical epitopes on the p80 molecule. Expression of the A1G3 antigen on erythrocytes and a subset of leukocytes is also down-regulated by the In(Lu) gene. The possible role of the In(Lu) gene in thymocyte differentiation is discussed.