Inhibition of erythropoietin production in vitro by human interferon gamma

The effects of interferon-gamma (IFN-gamma), alone and in combination with IL-1, IL-6 and tumour necrosis factor-alpha (TNF-alpha), on in vitro erythropoietin (Epo) production by the human hepatoma Hep3B cell line were evaluated. The addition of IFN-gamma to either unstimulated or cobalt chloride (CoCl2)-treated Hep3B cells resulted in a dose-dependent inhibition of Epo release in the medium by as much as 70% at 1000 U/ml. Half-maximal inhibition was observed at around 50 U/ml. According to previous observations, IL-6 had a stimulatory effect on Epo production by CoCl2-treated Hep3B cells; however, the simultaneous addition of IFN-gamma and IL-6 resulted in a reversal of the stimulatory effects due to IL-6. IFN-gamma and IL-1 had an additive inhibitory effect, whereas IFN-gamma and TNF-alpha acted in a synergistic fashion in inhibiting Epo production by Hep3B cells. The inhibitory effect of IFN-gamma appeared to be due to a down-modulation of Epo mRNA levels in CoCl2-treated Hep3B cells, as shown by Northern blot analysis. These data indicate that Epo production by hepatoma cells in vitro is inhibited by IFN-gamma, and that a complex network of interacting cytokines may regulate Epo production in response to an hypoxic stimulus. Overall, these results also suggest that IFN-gamma might have a role in the defective Epo production observed in several inflammatory and immunemediated disorders characterized by relatively high IFN-gamma plasma levels.