Markers of differentiated B cell leukaemia: CD22 antibodies and FMC7 react with different molecules.

FMC7, a monoclonal antibody used extensively to characterize B cell leukaemias of differentiated phenotype (prolymphocytic, hairy cell, and similar leukaemias) was compared directly with antibodies of the CD22 cluster, which also react with B cells at a late stage in differentiation. Detailed comparison shows that the reaction spectrum, though similar, is not identical. Differences were particularly prominent in chronic lymphocytic leukaemia (CLL) and non-Hodgkin's lymphoma (NHL). Binding studies show that the antibodies react with different antigenic determinants, and immunochemical studies show that they react with different molecules. The FMC7 antigen, not previously characterized, was shown to be a protein of apparent molecular weight 105,000, by immunoblotting after electrophoresis of membrane extracts.