CalDAG-GEFI deficiency protects from platelet aggregation induced by antibodies to GPIX. (A) Aggregation of hFcR (black line), hFcR pretreated with 100μM 2-MeSAMP (light gray line), and hFcR/CDGI^−/− (dark gray line) platelets in response to 0.5 μg/mL anti-GPIX in combination with a threshold dose of U46619 (0.25μM). Aggregation responses of hFcR platelets to either 0.5 μg/mL anti-GPIX or 0.25μM U46619 alone are shown for comparison. (B) Rap1 activation in hFcR and hFcR/CDGI^−/− platelets at t = 15 minutes of stimulation with anti-GPIX (0.5 μg/mL) and/or U46619 (0.25μM) in the absence or presence of 100μM 2-MeSAMP. (Bottom panel) Total Rap1 as loading control. Representative of 3 independent experiments.