Fig. 4.
Ligation of ICAM-1 by rolling neutrophils regulates Ps in unstimulated microvessels. To test the role of rolling neutrophils in Ps regulation, circulating neutrophils were depleted (Depl) using anti-GR-1 Ab (RGB-8C5, 200 μg/mouse ip injection 12 h before microcirculatory measurements), and Ps was measured in unstimulated arterioles and venules in the absence of neutrophils. In separate experiments in neutrophil-depleted animals, Ps was measured in unstimulated arterioles and venules following ligation (Ligx1) of ICAM-1 with an anti-ICAM-1 mAb (YN/1.7.4, 50 μg/ml iv). Ps measurements were performed 20 min post-Ab ligation. Neutrophil depletion had no effect on baseline Ps in unstimulated arterioles (as expected, because unstimulated arterioles do not support leukocyte rolling interactions); however, Ps in venules was significantly decreased (below basal level as indicated by dashed line and presented in Fig. 2B). Ligation with ICAM-1 Ab significantly increased Ps in both vessel types: to a value not significantly different from Ps measured in activated arterioles (Fig. 1) and unactivated venules (Fig. 2), both of which characteristically support rolling interactions. *Significantly different from each other (P < 0.05). ^Significantly different from Ps value in unstimulated venules (Fig. 2B). For all groups the measurements were made in n = 7–10 vessels from 2–4 mice.