Antibodies against human CD63 activate transfected rat basophilic leukemia (RBL-2H3) cells

CD63 is a widely expressed glycoprotein member of the transmembrane 4 superfamily (TM4SF) that is present on activated platelets, monocytes and macrophages and many non-lymphoid cells. It has been proposed that CD63 and other members of the TM4SF couple to intracellular signal transduction pathways and may have a role in cellular adhesion, proliferation and activation. We have investigated the functions of human CD63 by expression in the rat basophilic leukemia cell line, RBL-2H3, which has previously been reported to respond to antibodies against the rat homolog of CD63. Using a panel of antibodies against human CD63 we have shown that high levels of granular secretion from transfected RBL cells can be stimulated by some, but not all, of the antibodies. The specificity of this response suggests that these activating antibodies may be mimicking a natural ligand for CD63. The secretory response to crosslinking of the high affinity IgE receptor and also that to non-receptor stimuli (phorbol ester and calcium ionophore) is inhibited by an antibody that appears to recognise both human and rat homologs of CD63. These results suggest that stimulus-secretion coupling can occur through human CD63 and that RBL cells transfected with this protein will constitute a valuable tool in elucidating its function.