HPC mobilization by IL-8 or G-CSF in MMP-9–deficient mice. (A) Wild-type (WT; ♦) or MMP-9–deficient mice (KO; □) were treated with a single intraperitoneal injection of 30 μg human recombinant IL-8 at time zero, and the number of colony-forming cells (CFU-Cs) in the blood was quantified at the indicated time points. A minimum of 3 mice were analyzed at each time point. (B) Wild-type or MMP-9–deficient mice were treated with saline alone (□; n = 4) or with G-CSF (▪; 250 μg/kg per day for 5 days; n = 10), and the number of CFU-Cs in the bone marrow, blood, and spleen was quantified 4 hours after the last injection. Data represent the mean ± SD.