Functional defects of Jak2^Plt−/− platelets downstream of GPVI and CLEC-2.Jak2^Plt+/+ and Jak2^Plt−/− platelets were activated for 2 minutes at 37°C with CRP (A,E), rhodocytin (B,F), thrombin (C,G), or ADP and U46619 (D,H); incubated with FITC-labeled anti-mouse CD62P antibody (A-D), Oregon Green 488-labeled fibrinogen (E-G), or anti-active αIIbβ3 antibody JON/A (H); and analyzed by flow cytometry. Results are expressed as a percentage of positive platelets (A-G) or mean fluorescence intensity (MFI) (H). Results represent mean ± SD of 5 (CRP), 4 (rhodocytin), 6 (thrombin), and 4 (ADP and U46619) independent experiments and were compared by 2-way ANOVA. *P < .05; **P < .01; ***P < .001. Aggregation of Jak2^Plt+/+ and Jak2^Plt−/− platelets was determined by light transmission under stirring conditions at 37°C in response to 2.5 (I), 5 (J), or 10 (K) µg/mL collagen; 1 (L), 2.5 (M), or 5 (N) µg/mL CRP; or 0.05 (O) or 0.1 (P) U/mL thrombin. Graphs are representative of 4 independent experiments.