G-CSF blocks the retention of neutrophils by SDF-1α. Freshly isolated murine bone marrow neutrophils were used in a chemotaxis assay and then placed on top of the chemotaxis plate in the presence or absence of G-CSF (10 nM) as indicated. Neutrophils were preincubated in the presence or absence of SDF-1α (50 nM) for 15 minutes at 37°C. KC (1 nM) was added to the bottom chamber as indicated. Migration of neutrophils is expressed as the mean number of cells counted per bottom well, mean plus or minus SD. A representative figure of 4 independent experiments is shown (n = 3). **P < .01 (1-way ANOVA and Dunnett test).