Induction of CD40 in promyelocytic HL60 cells cultured with retinoic acid and/or various cytokines.

The antigenic protein CD40 on the surface of B lymphocytes plays an important role in their proliferation, immunoglobulin class switching, and rescue from apoptosis in the germinal center through interaction with T lymphocytes expressing CD40 ligand. The protein is also found on the cell surface of other antigen-presenting cells such as monocytes, dendritic cells, and thymic epithelium cells, but its presence in other myeloid cells has not been reported. We show here that CD40 protein is induced in promyelocytic HL60 cells, when cultured with retinoic acid, a vitamin that converts them to granulocyte-like cells. The cultured cells also expressed CD15, a marker for granulocytes, and cytochrome b(558), an essential component of the superoxide-generating system in phagocytes, on their surface. No detectable amount of mRNA for CD40 was found in naive HL60 cells, whereas a large amount of the message was induced in the cells cultured with the vitamin. Although CD40 expression was enhanced when the cells were further cultured with GM-CSF or IFN-gamma, expression of CD14, a marker for monocytes, was also enhanced. HL60 cells, therefore, express CD40 protein during differentiation not only toward monocytes but also toward granulocytes, at least transiently.