The FMC7 antibody detects a glycoprotein of 105 kD found on circulating B-lymphocytes. Studies on normal lymphocytes, leukaemic cells and cell lines indicate that FMC7 is marker for a limited segment of the B cell maturation pathway. This glycoprotein is expressed in varying degrees on normal circulating B-cells, chronic B-cell leukaemia (B-CLL), prolymphocytic leukaemia (PLL) and other B cell neoplasias. It labels the same population as CD22 antibodies but reacts with a different antigen. Stain peripheral blood B lymphocytes and tonsil B lymphocytes. No reaction with granulocytes, monocytes, platelets, erythrocytes, T lymphocytes or null cells. React with HRIK and Raji cell lines. 

CD23 reacts with a B cell differentiation antigen, a 45 kDa type II integral membrane glycoprotein. The antigen acts as a low affinity IgE receptor (FcER2). It is expressed mainly on mature B cells, mantle zone B cells, and follicular dendritic cells, but not on proliferating cells in the germinal centres. CD23 is also expressed by monocytes and eosinophyls. 

The CD19 antigen (90 kDa) is expressed from the earliest stages of B-progenitor development, on all peripheral B cells including germinal centre B cells and all B cell lines and B cell leukaemias tested. T cell and monocytic cell lines are negative. The antigen is a type I integral membrane glycoprotein whose in vitro inhibition will influence B cell activation and proliferation.