CD72 antigen is a member of the type II integral membrane glycoproteins which includes other related cell surface molecules such as the asialoglycoprotein receptors, CD23 and the Kupffer cell receptor. The function of CD72 is unknown but the exposure of B cells to CD72 antibodies activates a variety of signaling pathways and can induce MHC class II expression and B cell proliferation. CD72 antigen is expressed on all cells of B cell lineage with the exception of plasma cells and weakly on human tissue macrophages.