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Differentiation‐inducing and cytotoxic effects of tumor necrosis factor and interferon‐gamma in myeloblastic ML‐1 cells

The effects of the tumor necrosis factor (TNF), and a second pleiotropic cytokine interferon‐gamma (IFN), were examined in a line of human myeloblastic leukemia cells (ML‐1). By itself, TNF causes ML‐1 to differentiate along the monocytic pathway. The cells exhibit an increase in Fc receptors and acquire the morphological characteristics of maturing phenotype. They remain viable and continue to proliferate (at ≥ 50% of the control growth rate) even with 102–104 units/ml TNF. IFN alone has similar effects, causing an increase in Fc receptors but little cytotoxicity. In contrast to either cytokine alone, the combination of TNF plus IFN causes a cessation of proliferation and extensive cell death. Cytotoxicity occurs in a synergistic fashion; it requires the simultaneous presence of both cytokines, occurring with concurrent but not sequential exposure. These different responses, differentiation (TNF alone) and cytotoxicity (TNF + IFN), occur with a similar range of doses (∼ 102–104 units/ml) and in a similar time frame (beginning on day 2). In other cell types, IFN can augment either the differentiation‐inducing or the cytotoxic effect of TNF. In ML‐1, the combined application of TNF plus IFN results in a shift from differentiation to cytotoxicity.