Leukocyte rolling in Peyer's Patch (PP) high endothelial venules (HEV) occurs at different characteristic velocites in L-selectin- and β₇ integrin-deficient mice

Both L-selectin and β₇ integrins have been implicated in lymphocyte homing to Peyer's Patches in vivo. In order to understand the contributions of both L-selectin and β₇ integrins to leukocyte rolling in PP, we have measured the leukocyte rolling flux fraction and rolling velocity in hemodynamically similar PP HEV using in vivo epiluminescence intravital microscopy in wild-type, L-selectin-deficient (L -/-), and β₇ integrin-deficient (β₇ -/-) mice. Intravascular leukocytes were stained using acridine red and average blood flow velocities in PP HEV were measured using fluorescent beads. The rolling flux fractions in wild-type (98±15%) and β₇ -/- (85±10%) mice were not statistically different. In both wild-type and β₇ -/- mice, the rolling flux fraction was reduced by 80-90% with the blocking L-selectin mAb MEL-14 (p<0.01). Conversely, in L -/- mice, the rolling flux fraction was only 19±6% (p<0.01 vs. wild-type and β₇ -/- mice). The rolling velocity distribution in wild-type mice was bimodal, with peaks around 30 and 95 μm/s. β₇ -/- mice had a velocity distribution with one peak at ∼85 μm/s. Conversely, L -/- mice had a unimodal velocity distribution with the peak at ∼25 μm/s. Together, these data highlight a role for β₇ integrins in mediating leukocyte rolling in PP HEV in vivo.