Soluble VCAM-1 delays the functional senescence of neutrophils. (A) Neutrophils were cultured in the presence or absence of soluble adhesion molecules for 18 hours at the concentrations stated (micrograms per milliliter). Apoptosis was measured by DiOC₆ staining. Results are expressed as the percentage of apoptotic neutrophils compared with neutrophils cultured in medium alone; mean ± SD of 3 separate experiments. (B) Neutrophils were cultured for 18 hours in the presence or absence of soluble adhesion molecules (VCAM-1, ICAM-1, PECAM-1 all at 10 μg/mL) or IFN-β (1000 U/mL). Apoptosis is evident in medium and ICAM-1- and PECAM-1-treated cells by the presence of small shrunken cells with condensed nuclei. (C) Neutrophils were cultured in the presence or absence of 10 μg/mL sVCAM-1, 1000 U/mL IFN-β, or both together and apoptosis measured by DiOC₆ staining. Each point is a single experiment. Bar is the mean; ^***P < .001. (D) Neutrophils were incubated with VCAM-1 in the presence or absence of the anti-VCAM antibody 1G11 (10 μg/mL). Cells were cultured alone (□) or in the presence of VCAM-1 (▪). An isotype-matched control antibody is shown. Apoptosis was measured by DiOC₆ staining. Data are the mean ± SD of 3 separate experiments. (E) VCAM-1 delays the functional senescence of neutrophils. Superoxide generation in response to PMA was determined by measuring oxidation of cytochrome c at the time of neutrophil isolation (t = 0) or following 18 hours of incubation with medium alone, 1000 U/mL IFN-β, 10 μg/mL sVCAM-1, or both together. Data are the mean ± SD of 3 separate experiments.