Reduced KC-triggered rapid arrest and shear-resistant adhesion to VCAM-1 of Rap1-depleted cells. (A) Representative immunoblot analysis of endogenous expression of Rap1A and Rap1B in CXCR2⁺ RBL-2H3 cells transfected with either control, Rap1A, Rap1B, or both siRNAs. Whole cell lysates were immunoblotted with total Rap1A/B- and Rap1B-specific antibodies. Expression of β-actin was used as protein loading control. (B) Effect of either or both Rap1 isoform depletion on frequency and strength of tethers mediated by CXCR2⁺ RBL-2H3 cells with a medium concentration (0.05 μg/mL) of VCAM-1/Fc coimmobilized with heat-inactivated (data not shown) or functional KC (2 μg/mL) under flow conditions. Data are expressed as mean ± SD of 4 experimental fields in 2 independent experiments (*P < .05 relative to control cells for the arrest fraction). Results are representative of 3 independent experiments. (C) Effect of either or both Rap1 isoform depletion on KC-induced shear-resistant adhesion of CXCR2⁺ RBL-2H3 cells to a medium VCAM-1/Fc concentration (0.05 μg/mL), determined as described in the legend to Figure 2D. Results are expressed as mean ± SEM of 4 experimental fields in 2 independent experiments (*P < .05 for either or both Rap1 isoform–depleted vs control RBL-2H3 cells).