αIIbβ3 integrin signaling and actin cytoskeletal remodeling are required for stabilization of developing thrombi in vivo. (A) Numbers of platelets attached to the vessel wall 10 seconds after laser/ROS-induced injury in L746A KI mice and their wild-type (WT) littermates (n = 30 vessels from 5 animals in each group). (B) Calculated numbers of platelets within developing thrombi 0 seconds, 10 seconds, and 20 seconds after laser/ROS-induced injury. (C) Representative in vivo imaging after laser injury (n = 30 vessels from 5 animals in each group). Scale bar is 10 μm. Asterisks indicate statistical significance (P < .05). (D-F) Thrombus formation in Y747A KI mice and their WT littermates. The experimental protocols were the same as in panels A-C. Note that thrombus formation is more severely impaired in Y747A KI mice than L746A KI mice. (G) Representative curve showing the numbers of platelets in a developing thrombus after laser/ROS-induced injury in wild-type (WT, black line), TNF-α KO (gray line), and Y747A KI (dotted line) mice. Arrows in each line show the time of initial platelet attachment to the endothelium. (H-J) Impaired thrombus formation in Pf4-Rac1 KO mice. Platelet attachment (H) and thrombus development (I) after laser/ROS-induced injury was quantified, and in vivo images are shown (J). Horizontal lines denote median values (B,E,I).