Gamma interferon (IFN gamma) and IFN alpha/beta suppress murine myeloid colony formation (CFU-C)N: magnitude of suppression is dependent upon level of colony-stimulating factor (CSF).

The effect of different types of interferon (IFN) on macrophage and granulocyte colony formation (CFU-C) in vitro was studied using bone marrow cells from C57BL/6 mice. CFU-C formation was measured at 7 days using a standard methylcellulose culture system with L-cell conditioned medium (LCCM) as a source of colony-stimulating factor activity (CSF), IFN gamma was obtained from staphylococcal enterotoxin A- (SEA) stimulated mouse spleen cells and was partially purified (50-fold) using affinity chromatography. IFN alpha/beta was obtained from Newcastle disease virus-infected mouse L-cells and was partially purified (286-fold) using an AcA 202 column. IFN gamma inhibited CFU-C formation in a dose-dependent manner and was 100 times more inhibitory than IFN alpha/beta. IFN gamma completely suppressed CFU-C formation with as little as 15 units of antiviral activity. In contrast, 1000 to 2000 units of antiviral activity of IFN alpha/beta was required for complete suppression of CFU-C formation. The ability of IFN gamma to inhibit CFU-C formation was completely abolished after pH 2 treatment (24 hr), heat treatment (60 degrees C, 2 hr), or treatment with a specific antiserum against IFN gamma, which indicated that IFN gamma was the mediator of CFU-C inhibition. When IFN gamma and IFN alpha/beta were mixed together and added to bone marrow cells, they had a synergistic effect on the suppression of CFU-C formation. The level of inhibition mediated by both IFN gamma and IFN alpha/beta was totally dependent upon the amount of CSF present in the culture system; increasing the level of CSF could completely overcome the IFN suppressive effect. These results suggest that IFN gamma and IFN alpha/beta may have regulatory roles in hematopoiesis.