Surface expression of CXCR4 decreases with neutrophil maturation and activation. Isolated bone marrow, peripheral, and exudate neutrophils were stained with biotinylated anti-CXCR4 or isotype control antibodies followed by streptavidin-phycoerythrin and were analyzed by flow cytometry. Results are expressed as a ratio of the mean fluorescence intensity of cells stained with CXCR4 antibody versus isotype control antibody. Data points are the means of 3 to 5 separate experiments performed for each analyzed population of neutrophils (± SEM). Expression significantly different when compared with each other, ^*P < .001, ^**P < .02.