Reduced thrombus formation of Jak2^Plt−/− platelets at arterial shear rates. PPACK-anticoagulated whole blood from Jak2^Plt+/+ and Jak2^Plt−/− mice was labeled and perfused on a type 1 collagen–immobilized surface at an arterial shear rate of 1500 s⁻¹. (A) Representative still images at 3 minutes. Bars represent 100 µm. (B) Fluorescence intensity at 3 minutes. Results represent mean ± SD and were compared by using the unpaired Student t test (n = 3 in each group; *P = .0317). (C) Dwell time of individual Jak2^Plt+/+ and Jak2^Plt−/− platelets. Results were estimated by the Kaplan-Meier method and were compared by using the log-rank test (n = 60 Jak2^Plt+/+ and 97 Jak2^Plt−/− platelets; log-rank P = .141). Plasma VWFpp (D) and VWF (E) levels and VWFpp/VWF ratio (F) in Jak2^Plt+/+ and Jak2^Plt−/− mice. Results are the mean ± SD and were compared by using the unpaired Student t test (n = 16 Jak2^Plt+/+ and 4 Jak2^Plt−/− mice; VWFpp, P = .223; VWF, P = .0868; VWFpp/VWF, P = .865). (G) Jak2^Plt+/+ and Jak2^Plt−/− platelets were activated for 5 minutes at 37°C with 4 µg/mL botrocetin, incubated with FITC-labeled anti-mouse VWF antibody, and analyzed by flow cytometry. Results are the mean ± SD and are compared by 2-way ANOVA (n = 6 in each group; control, P = .96; botrocetin, P = .89).