A differentiation antigen expressed selectively by a proportion of human blood cells: detection with a monoclonal antibody.

A monoclonal antibody, FMC 8, has been prepared after immunization with a cell line of the non-T-non-B type acute lymphoblastic leukaemia (ALL). The antigen detected by this antibody consists of a single polypeptide chain with an apparent molecular weight of 24,000 d. The antigen is absent from T cells but appears after mitogen stimulation. It is found on the majority of normal circulating B cells but is absent in most chronic lymphocytic leukaemias. All cells of the non-T-non-B type express the antigen, whereas T-ALL cells generally do not. Granulocytes, monocytes and platelets react with the antibody, but erythrocytes do not. The wide but selective distribution of the antigen renders FMC 8 potentially useful, together with other monoclonal antibodies, in the delineation of differentiation pathways and in phenotypic analysis of leukaemia and lymphoma cells.