Platelet activation and aggregation upon binding of an influenza virus. (A) Virus NA-dependent desialylation of platelets from human platelets determined by lectin (ECL-FITC) binding. Mean (n = 6); error bars, SD; Tukey’s multiple-comparisons test, *P < .0001; OSC (100 µM). (B) Virus activation of platelets in human plasma. Positive control (ADP; 10 µM). Final virus concentration 50 pM. OSC 100 µM. Mean (6 donors); error bars, SD; Tukey’s multiple-comparisons test, *P < .05; **P < .01. (C) Dose-dependent activation of platelets in plasma by influenza A/PR/8/34 virus. Error bars, SD; Tukey’s multiple-comparisons test, ****P < .0001. (D) Aggregation of platelets by influenza virus subtypes in 3 donors. Positive control (ADP; 10 μM). Final virus concentration (50 pM).