| Abstract: | In this study, we analyzed the effect of tumor necrosis factor (TNF) on retinoic acid (RA)-induced myeloid differentiation of the promyelocytic HL-60 leukemia cell line. We show that low concentrations of the two substances, almost inactive in inducing differentiation when used separately, induce differentiation when added simultaneously to the cell cultures. Cells simultaneously expressing both monocyte/macrophage phenotype (typically induced by TNF) and granulocyte characteristics (typically induced by RA) are induced by a combination of the two factors, indicating that TNF and RA potentiate each other's activity. The results obtained using immune interferon (IFN-gamma) in combination with the two inducers suggest that the mechanism of action of TNF and IFN-gamma are possibly different. The inhibitory effect of RA on the expression of HLA class I antigens and of the high-affinity Fc receptor is potentiated by TNF but completely reversed by rIFN-gamma. |
