Histologic analysis of time-dependent re-endothelialization in murine carotid artery. Typical observations of endothelial cells stained by anti-VWF antibodies in the carotid artery of α2-AP^-/- (B,D,F,H; original magnification, × 400) and in α2-AP^+/+ mice (A,C,E,G; original magnification, × 400). Before the initiation of injury, an intact endothelial cell layer was observed (A-B). Endothelial cells were removed by the injury (C-D). Regenerated endothelial cells (arrows) only partly covered the injured area in wild-type mice (E); however, an obvious compact endothelial cell layer (arrows) developed on the injured surface in α2-AP^-/- mice (F) 2 days after injury. Four weeks after injury, a neointimal thickening (^*) had developed in the injured area. A regenerated endothelial cell layer (arrows) was observed on the neointima in wild-type mice (G) and in α2-AP^-/- mice, in which the endothelial cell layer (arrows), however, was thicker (G). Scanning electron photomicrographs of regeneration of endothelial cells in the injured carotid artery 48 hours after injury in α2-AP^+/+ mice (I,K) and in α2-AP^-/- mice (J,L) showed prompt and intense re-endothelialization in α2-AP^-/- mice. The white bar represents 10 μm.