Bleeding and thrombosis defects in Jak2^Plt−/− mice. (A) Tail-bleeding time of Jak2^Plt+/+ and Jak2^Plt−/− mice. Results were estimated by the Kaplan-Meier method and were compared by using the log-rank test (n = 10 in each group; log-rank P = .0108). (B-C) Jak2^Plt+/+ and Jak2^Plt−/− mice were exposed to 10% FeCl₃ for 3 minutes, and arterial flow rates of the carotid artery were measured with a flow probe up to a maximum of 30 minutes to occlusion. (B) Time to occlusion after FeCl₃-induced injury. Results were estimated by the Kaplan-Meier method and were compared by using the log-rank test (n = 4 in each group; log-rank P = .0067). (C) Representative blood flow rate graphs. (D-F) Laser-induced injury of the cremaster muscle. Jak2^Plt+/+ and Jak2^Plt−/− mice were injected with anti-GPIbβ (red) and anti-fibrin (green) antibodies, and the cremaster arteries were interrogated with a 3i Ablate! laser during fluorescence, real-time, intravital video microscopy. (D) Representative still images at 0 to 3 minutes. Arrows represent blood flow direction. Bars represent 25 µm. Platelet (E) and fibrin (F) accumulation at the site of injury was measured by fluorescence intensity. Data are the mean ± standard error of the mean at each time point, compared by using the unpaired Student t test (n = 20 vessels in 4 Jak2^Plt+/+ mice and 28 vessels in 5 Jak2^Plt−/− mice; platelet and fibrin; P < .0001).