SSAO activity is important for VAP-1-dependent rolling of PMNs on HUVECs under shear. (A) Two video frames taken 3 seconds apart showing rolling and stably adherent PMNs on VAP-1-transfected HUVECs (t = 0 is by definition the moment when infused leukocytes appear on the endothelial cells in the microscopic field). The open arrows point to 2 rolling cells (nos. 1 and 2; their rolling path during the 3-second interval is indicated by the dotted arrow), and some of the firmly adherent cells are pointed out by thin black arrows (nos. 3-6). The shear was 1.0 dyn/cm². Bar, 20 μm. (B) The SSAO inhibitors (BTT = BTT-2027, SC + HA = semicarbazide + hydroxylamine) block rolling of PMNs on VAP-1-transfected HUVECs, but have no effect on rolling on VAP-1Y471F-transfected cells. The number of rolling PMNs was counted after each treatment and compared with that seen in the vehicle-treated capillaries. The results are mean ± SEM from 3 to 5 independent experiments using HUVECs and PMNs isolated from different individuals. (C) The effect of anti-VAP-1 mAb on PMNs rolling on VAP-1- and VAP-1Y471F-transfected HUVECs was analyzed as described in panel B in the presence of control (HB116) and anti-VAP-1 (TK8-14) mAbs. The results are mean ± SEM (n = 3-4). ^*P < .05; ^**P < .01. Endoth. indicates endothelial cells; pretreat., pretreated; and vehic, vehicle.