Adhesion of both platelets and leukocytes is impaired after injection of activated Cd40l^−/−Apoe^−/− platelets. Intravital microscopy of the endothelial wall of carotid arteries in 17-week-old Apoe^−/− mice shows an impaired adhesion of intravenously administered calcein-labeled Cd40l^−/−Apoe^−/− platelets (green) (A). Subsequent rhodamine 6G injection shows a decreased adhesion of leukocytes (red) in Apoe^−/− mice injected with Cd40l^−/−Apoe^−/− platelets compared with mice injected with Cd40l^+/+Apoe^−/− platelets (B) (n = 6). *P < .05. (C-D) Representative images of the external carotid artery. Scale bars represent 100 μm.