Expression of CD40 on murine mast cells following IL-3 nutrient withdrawal

CD40 is a 45 kDa cell surface glycoprotein of the tumor necrosis factor (TNF-alpha) gene family. Expression of CD40 has been reported on different hematopoeitic cell types. We observed that CD40 is also present on IL-3 dependent mast cell lines and bone marrow-derived mast cells (BMMC) by FACS analysis with MAb anti-CD40 (HM40-3). CD40 was upregulated on the surface of mast cells treated with PMA plus ionomycin, or incubated with GM-CSF and IFN-gamma. On the other hand, surface CD40 was also present on cells entering early or late phase of apoptosis, 24 hr following IL-3 withdrawal, as determined by uptake of annexin V and/or 7aaD, a viable dye. Recombinant CD40L further upregulated CD40 expression in IL-3 depleted cultures. Two molecular species of CD40 exhibiting Mr 40K and 45K were demonstrated by immunoblot in cell lysates prepared from IL-3 depleted cultures. These observations suggest that cell surface expression of CD40 may play a role in the maintenance of mast cells in vitro and/or their persistence in inflammatory infiltrates in vivo.