IFN-γ produced on immune activation in WT mice suppresses eosinophil development. (A) Representative plots of Siglec-F staining on blood of WT and IFN-γ^−/− mice, showing eosinophils as SSC^hiSiglec-F⁺ cells (percentages are shown) 4 days after the first injection of αCD40 or control IgG. Numbers of eosinophils in (B) blood and (C) bone marrow (total from 2 femurs and 2 tibiae). (D) Numbers of EoPs in the bone marrow of these mice. (E) Representative plots of Siglec-F staining on blood of WT and IFN-γ^−/− mice showing eosinophils as SSC^hiSiglec-F⁺ cells (percentages are shown) 8 days after infection with LCMV-Armstrong. Numbers of eosinophils in (F) blood and (G) bone marrow (total from one femur and one tibia). (A-D) Data are from 5 mice per group. (E-G) Data are from 5 or 6 mice per infected group and 3 or 4 mice per control group. Both experiments have been performed twice with comparable outcome. Data are mean ± SEM. *P < .05; **P < .01; ***P < .001.