The effects of interferon on granulopoiesis in vitro.

Colony formation by myeloid progenitor cells (CFU-c) in agar was inhibited to the same extent by heterogeneous human leucocyte IFN (IFN-Le) and 2 different cloned IFN-a2 preparations, but ∼10 times less by cloned IFN-α1; cluster formation remained unaffected by any of the interferons. An antiproliferative effect is suggested by both lower cell yield and DNA synthesis in IFN containing liquid cultures. Incubation of cells with IFN for 18 h prior to plating with colony stimulating factor (CSF) reduced colony formation, indicating an altered responsiveness of CFU-c to CSF. In IFN treated cultures no consistent block of morphological differentiation occurred, but granulocyte alkaline phosphatase activity was reduced. Thus, IFN may play a modulatory role on functional markers. Our results indicate that the effects observed with heterogeneous preparations are due to IFN and not to impurities and that various differentiation parameters are unequally affected by IFN.