Fig. 1: Comparison of platelet morphology with and without SARS-CoV-2 S protein.

A DIC images of platelets without (Control) and pre-incubated with 20 µg/ml S protein (Spike) on a collagen I support. * indicates collagen I fibers. B DIC images of platelets without and pre-incubated with S on a poly-L-lysine support. C DIC images of platelets without and pre-incubated with S protein on a fibronectin support. Scale bar: 5 µm (A–C). D Quantification of the aspect ratio of platelets (major axis/minor axis) on different coated surfaces, without and in the presence of S protein. The median aspect ratio is shown below the corresponding violin plot. The significance was determined by two-tailed Mann–Whitney U test. Number of platelets (collagen control: 442, collagen spike: 391, Poly-L-lysine control: 343, Poly-L-lysine spike: 430, Fibronectin control: 505, Fibronectin spike: 446) examined over at least three independent experiments from different donors. Each dot represents the value from a single platelet. E Quantification of the circularity of platelets on different coated surfaces, without and in the presence of S protein. The median circularity is shown below the corresponding violin plot. The significance was determined by two-tailed Mann–Whitney U test. Number of platelets (collagen control: 442, collagen spike: 391, Poly-L-lysine control: 343, Poly-L-lysine spike: 430, Fibronectin control: 505, Fibronectin spike: 446) examined over at least 3 independent experiments from different donors. Each dot represents the value from a single platelet. F Comparison of platelet activation, incubated with and without S protein, on Poly-L-Lysine (left), and on Fibronectin (right) Platelets with amoeba-like morphologies were defined as activated platelets. The median percentage of the activation is shown below the corresponding dot plot. The significance was determined by two-tailed Mann–Whitney U test. Number of platelets (collagen control: 442, collagen spike: 391, Poly-L-lysine control: 343, Poly-L-lysine spike: 430, Fibronectin control: 505, Fibronectin spike: 446) examined over at least three independent experiments from different donors. Each dot represents the value from a series of experiment. G Sandwich ELISA assay detecting PF4 release in the absence and presence of S protein. The mean ± SD is shown below the corresponding dot plot. The significance was determined by two-tailed Mann–Whitney U test. n = 3 independent experiments from n = 3 different donors. Source data are available as a Source Data file.