Proliferative index in vivo. Cell proliferation (n = 4, for each time point) measured as the BrdU index (percentage) of recovered endothelial cells (□) and SMCs in media (•) following vascular injury in α2-AP^+/+ (A) or α2-AP^-/- mice (B). Data represents mean ± SEM. Typical observations of BrdU-positive cells in the injured carotid artery of α2-AP^-/- (C) and in α2-AP^+/+ mice (D). Twenty-four hours after injury, BrdU-positive cells (arrows) were clearly observed in the recovered endothelial layer in α2-AP^-/- mice (C). However, BrdU-positive cells were present mainly in media (SMCs) in α2-AP^+/+ mice (D). Original magnification, × 400.