IRF8-deficient GPs yield more neutrophils and exhibit reduced apoptosis. (A) One thousand GPs (GMP-Ly6C⁺CD115^lo) isolated from the bone marrow of wild-type or IRF8^−/− mice were cultured in liquid media containing 50 ng/mL G-CSF for the indicated time points and neutrophil differentiation was monitored by flow cytometry (see supplemental Figure 2 for gating strategy). (B) GP apoptosis following 24-hour culture with G-CSF was assessed by Annexin V staining. Dotted line indicates starting GP number. All data are presented as mean plus standard deviation of independent cultures of GPs from 5 wild-type and 5 IRF8^−/− mice. Statistical significance was assessed by Student t test (*P < .05, **P < .01, ***P < .001).