Enhanced adhesive interactions of α₄-R/A^GFFKR splenocytes with VCAM-1 and MAdCAM-1 under shear stress. Splenocytes from wild-type (WT) and α₄-R/A^GFFKR (KI) mice were infused in 1 mM Mg²⁺/Ca²⁺ (A,B,E-J) or 1 mM Mn²⁺ (C,D) into a parallel wall flow chamber and allowed to accumulate on VCAM-1 (A,C,E,G,I) or MAdCAM-1 (B,D,F,H,J) substrates at 0.3 dyne/cm² for 45 seconds. Shear stress was incrementally increased every 10 seconds from 0.5 to 32 dyne/cm², and adhesive interactions of cells with the substrates were recorded and analyzed. In some experiments (E-J), cells were pretreated for 10 minutes at room temperature with blocking mAbs to α₄ (PS/2, 30 μg/mL), α₄β₇ (DATK32, 30 μg/mL), or β₁ (CBL 1333, 30 μg/mL) integrins or isotype control antibodies (IgG, 30 μg/mL). Data represent the mean plus or minus SEM of 3 independent experiments. P value less than .01 versus **KI in Mg²⁺/Ca²⁺ or *WT.