CLEC-2 deficiency impairs GPIbα-mediated integrin αIIbβ3 activation. Aggregation of washed WT and CLEC-2–deficient platelets in response to 10 μg/mL of VWF and 2 μg/mL of botrocetin, which facilitates VWF binding to GPIbα, in the absence (A) or presence (C) of GR144053 trihydrochloride (GR). (B and D) Quantification of platelet aggregation shown in (A) and (C), respectively. (E) Flow cytometry analysis of binding of mAb Jon/A, which specifically binds to activated integrin αIIbβ3, to platelets. Washed platelets were stimulated with 2 μg/mL of botrocetin (Botro) in the presence or absence of 10 μg/mL of VWF from human plasma. After that, platelets were immediately incubated with mAb Jon/A, and mAb Jon/A binding was analyzed with flow cytometry. The data are representative of 5 independent experiments, and data represent mean ± standard deviation (SD). *P < .05.