SARS-CoV-2 activates platelets in a TF pathway and thrombin-dependent manner. Platelet responses to β-propiolactone–inactivated SARS-CoV-2 (CoV2) obtained from human A549 (ACE2) cell infection or conditioned media (C.Med) solution (A549 [ACE2] cell culture supernatant obtained after 4 days of culture and treatment with β-propiolactone [1:1000 vol/vol]). (A) Platelets were stimulated with C.Med or CoV2 (1:25 vol/vol) in the presence of platelet-free plasma (0.5%) deficient in individual coagulation factors. The heatmap indicates the mean platelet activation by CoV2 stimulation. The statistical significance symbols indicate comparisons of CoV2 with C.Med-stimulated platelets. N = 5. (B) Platelet stimulation with CoV2 (1:25 vol/vol) in the presence of PFP (0.5%) and in the presence of d-phenylalanyl-prolyl-arginyl chloromethyl ketone (PPACK) (0/10 µM). CoV2 was preincubated for 15 minutes with PPACK before incubation with PFP. N = 4. (C) Platelets were preincubated for 15 minutes with vorapaxar (20 µM) and BMS-9861200 (20 µM), a PAR-1 and PAR-4 inhibitor, respectively, or DMSO (0.45%). Thereafter, platelets were stimulated with CoV2 (1:25 vol/vol) in the presence of PFP (0.5%). N = 5. Data are represented as mean ± SD. Statistical analysis: (A) Ordinary two-way ANOVA followed by Sidak’s multiple comparison test. (B) Paired t-test. (C) Ordinary one-way ANOVA followed by Dunnett’s multiple comparison test. *P < .05, **P < .01, ***P < .001, and ****P < .0001. ns, not significant.