G-CSF responsiveness of d715 G-CSFR progenitors. (A) Mice (n = 4-5, each genotype) were treated with G-CSF (10 μg/kg/d for 7 days). Neutrophil number in the blood was quantified at baseline and on day 7. (B) The number of CFU-Gs per femur was determined in untreated mice (n = 4-5, each genotype; ^*P < .05 compared with wild-type mice). (C) c-Kit⁺ Lin^- cells were isolated from mice (n = 3-8, for each genotype) and cultured in media containing G-CSF and kit ligand for 7 days in the presence of 1 μM PP2 or vehicle alone (DMSO). The fold increase in cell number on day 7 is shown. Data represent the mean ± SEM. ^*P < .05 compared with DMSO-treated mice of the same genotype.