VWF strings attach to HUVECs by discrete adhesion sites. (A) HUVECs were stimulated with histamine and exposed to laminar flow at a shear stress of 2.5 dyne/cm². After 5 minutes, flow direction was reversed and images were captured every 30 seconds. indicate the initial flow direction (start) and the reversed flow direction (0-120 s). indicate anchorage sites for VWF strings. Bars represent 20 μm. (B) Electron micrographs of immunogold-labeled VWF strings. Samples were prepared as described in “Immunoelectron microscopy.” Arrows indicate cell extrusions in direct contact with VWF strings. Bars represent 500 nm.