Interactions between integrin α9 and VCAM-1 promote neutrophil hyperactivation, mediate neutrophil adhesion at venous shear rate, and enhance endothelial cell apoptosis. (A) Schematic of experimental design. (B) Elastase and (C) MPO levels in cell-culture media 6 hours after stimulation. (D) Experimental design. (E) Representative images of the neutrophil adhesion to the VCAM-1 coated slides at venous shear rate (left); magnification, 20×; scale bar, 50 μm; and qualification (right). (F) Representative cross-sectional immunofluorescence image of terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling-positive mouse endothelial cells incubated with cell supernatant of stimulated neutrophils from α9^fl/fl and α9^fl/flMrp8Cre^+/− mice (left); and quantification (right); magnification, 10×; scale bar, 100 μm. Data are mean ± SEM and analyzed by repeated measures ANOVA followed by the corrected method of Benjamini and Yekutieli (B-C) or the Mann-Whitney test (E-F); n = 5 (B-C); n = 5 (E); and n = 5 (F).