Impaired KC-induced VLA-4 and β₂ integrin functional regulation in β-arr 2–depleted cells. (A-C) Effect of either β-arr isoform depletion on frequency and strength of tethers mediated by CXCR2⁺ RBL-2H3 cells with (A) low (0.025 μg/mL), (B) medium (0.05 μg/mL), or (C) high (0.2 μg/mL) concentrations of VCAM-1/Fc coimmobilized with heat-inactivated (−) or functional (+) KC (2 μg/mL), determined at a shear stress of 0.75 dyn/cm². Data are expressed as mean plus or minus the range of 2 experimental fields. Results are representative of 3 independent experiments (*P < .05 relative to control cells for each adhesive category). (D) Effect of either β-arr isoform depletion on resistance to detachment by incremental shear stresses of CXCR2⁺ RBL-2H3 cells. Cells were accumulated on a medium VCAM-1/Fc concentration (0.05 μg/mL) coimmobilized with heat-inactivated or functional KC (2 μg/mL) for 1 minute under a shear stress of 0.75 dyn/cm² and then subjected to the indicated shear stresses, incremented at 5-second intervals. The percentage of cells resisting detachment by the indicated shear stresses is shown. Results are expressed as mean ± SEM of 4 experimental fields in 2 independent experiments (*P < .05 for β-arr 2–depleted vs control RBL-2H3 cells). (E) Representative immunoblot analysis of endogenous expression of β-arr 1 and β-arr 2 in CXCR2⁺ RBL-2H3 cells transfected with either control, β-arr 1 or β-arr 2 siRNAs. Whole cell lysates were immunoblotted with a β-arr–specific antibody. Expression of β-actin was used as protein loading control. (F-K) Effect of either β-arr isoform depletion on KC-stimulated adhesion of differentiated 32D cells to (F,I) low (0.1 μg/mL), (G,J) medium (0.5 μg/mL), or (H,K) high (1 μg/mL) concentrations of ICAM-1/Fc under flow. Data are expressed as mean plus or minus the standard deviation (± SD) of 8 to 12 experimental fields in 3 independent experiments (*P < .02, **P < .001 relative to control cells; paired 2-tailed Student t test). (L) Representative immunoblot analysis of endogenous expression of β-arr 1 and β-arr 2 in differentiated 32 D cells transfected with either control, β-arr 1, or β-arr 2 siRNAs. Whole cell lysates were immunoblotted with a β-arr–specific antibody. Expression of β-actin was used as protein loading control.