CXCR4 blockade decreases localization of infused labeled peripheral blood neutrophils. To examine the effects of CXCR4 blockade on circulating neutrophil retention, mice were treated with either 40 μg/mouse blocking antibody (▪) or control immunoglobulin (□) intravenously 30 minutes before indium-labeled isolated peripheral neutrophils were infused. The mice were then bled and dissected 4 hours after cell infusion, and these tissues were assayed by gamma counting. Data points are the means of 3 to 7 separate mice (± SEM). ^*Significantly different when compared with control-treated animals, P < .01. ns indicates not significant.