Treatment with oral polymyxin B reduces cytokine-induced stem cell mobilization, while treatment with ciprofloxacin has no effect on IL-8– or G-CSF–induced mobilization. (A) Mice were treated with 100 mg/L polymyxin B and 20 mg/L saccharose added to their drinking water for 1 week. Mice were then mobilized with either a single intraperitoneal injection of 30 μg IL-8 (n = 13) or 5 μg G-CSF (n = 15) per day for 5 days. At 20 minutes after the IL-8 injection and 24 hours after the injection with G-CSF, mice were killed and blood was harvested. Results are expressed as means ± SD. *P < .05 compared with the controls (n = 6-8). (B) Mice were treated with 125 mg/L ciprofloxacin and 20 mg/L saccharose added to their drinking water for 1 week. The control mice received normal drinking water. Antibiotic treatment was continued when mice were mobilized with either a single injection of 30 μg IL-8 (controls: n = 6, treatment group: n = 9) or 5 μg G-CSF (controls: n = 4, treatment group: n = 10) per day for 5 days. At 20 minutes after the IL-8 injection and 24 hours after the injection with G-CSF, the mice were killed and blood was harvested. Results are expressed as means ± SD.