Neutrophil mobilization by G-CSF or GROβ is abrogated in MKO mice. (A) Mice (n = 5 per group) were given a single subcutaneous injection of G-CSF (125 μg/kg) and the absolute neutrophil count measured at the indicated times. †P < .05 compared with time 0. (B) Representative histograms showing cell surface CXCR4 expression on blood neutrophils from control (CTL) or MKO mice at baseline and 65 minutes after a single dose of G-CSF (+G). (C) Mice (n = 8-11 per group) were treated with G-CSF (125 μg/kg per day, twice daily injections) for 5 days, and neutrophils in the bone marrow and blood were quantified. The calculated neutrophil distribution index is shown in the far right panel. *P < .05 compared with control mice at the same time point; #P < .05 compared with untreated mice of the same genotype. (D) Mice (n = 9-12 per group) were given a single subcutaneous injection of GROβ (100 μg/kg), and the absolute neutrophil count was determined at the indicated times. †P < .05 compared with time 0. (E) CXCR4 cell-surface expression on peripheral blood neutrophils from control mice was determined by flow cytometry at baseline and at the time of peak mobilization, 30 minutes after GROβ administration. **P < .001. Data represent the mean ± SEM.