Induction of retinal neovascularization containing human endothelial cells. (Top) Mice that received xenotransplants were perfused with anti-human CD31 (FITC) followed by 2 wash perfusions. Flat mounts of the retina were examined by confocal fluorescence microscopy. Panels show fluorescence micrographs of noninjured control retinas versus injured ischemic retinas isolated from the same animal. Only injured eyes stained positive (green) for human CD31. Original magnification for control and ischemic retina 1, × 10; for control and ischemic retina 2, × 20. (Bottom) Immunohistochemistry staining for human CD31 and human LAMP-1 was performed on human uterus as a positive control (original magnification, × 64), noninjured retinas from the same animal that received xenotransplants served as negative controls (control eye, original magnification × 64), and injured ischemic retinas (original magnification, × 64). Human endothelial cells (brown stained cells demarcated with a bracket) were detected only in the injured retinas. Some of the new vessels were formed within the vitreous of the injured eyes. In those sections the retina is annotated with an arrow and the vitreous in clearly labeled.