Virus phagocytosis by platelets is dependent on the presence of SAs. (A) Virus uptake over time by human platelets. Original magnification ×25 000. Red arrows: internalized viruses. (B) Quantification of membrane-bound and internalized viruses in ultrathin-sliced platelet sections (n = 100; 50 nm) fixed after 1, 5, 10, 20, 30, and 60 minutes of incubation with influenza A/PR/8/34 virus. Error bars, standard error of the mean. (C) Temperature-dependent virus uptake. Mean (n = 5); error bars, SD. (D) Platelet desialylation with exogenous NA abolishes virus uptake. Control (+) and sialidase-treated (−) platelets. Mean (n = 3); error bars, SD. (E) Virus uptake is independent of DC-SIGN. Uptake in the absence (−) or presence (+) of αDC-SIGN receptor blocking antibody. Mean (n = 4); error bars, SD. ****P < .0001, n.s., nonsignificant, by Student t test.