IFNγ induces monopoiesis over granulopoiesis in vivo and in vitro. M:N ratios in the BM (A) and peripheral blood (B) of WT, CD70TG, IFNγ^−/−, and CD70TGxIFNγ^−/− mice were measured by dividing the number of monocytes by the number of neutrophils. Data in panels A and B represent means ± SD from at least 3 mice per group. (C) M:N ratios in BM of CD27^−/− and CD70TGxCD27^−/− control mice and 3 weeks after transfer of WT or IFNγ^−/− T cells. (D) M:N ratios in BM of WT and IFNγ^−/− mice 4 days after the first injection of αCD40 or control IgG. Data in panels C and D represent means ± SD from 5 mice per group. (E) Type of colonies derived from total WT BM (left; means ± SD from 6 mice per group) or from 250 purified GMPs (right; means ± SD from 4 mice per group) cultured for 8 days in semisolid medium with or without IFNγ. M indicates monocyte/macrophage; G, granulocyte; and GM, mixed monocyte/macrophage and granulocyte. All experiments were performed at least 2 times with similar results. *P < .05; **P < .01; ***P < .001.