Platelets Can Associate With SARS-CoV-2 RNA and Are Hyperactivated in COVID-19

To evaluate the contribution of platelets to inflammation and thrombosis in patients with COVID-19. Methods and Results: Blood was collected from 115 consecutive patients with COVID-19 presenting nonsevere (n=71) and severe (n=44) respiratory symptoms. We document the presence of severe acute respiratory syndrome coronavirus 2 RNA associated with platelets of patients with COVID-19. Exhaustive assessment of cytokines in plasma and in platelets revealed the modulation of platelet-associated cytokine levels in both patients with nonsevere and severe COVID-19, pointing to a direct contribution of platelets to the plasmatic cytokine load. Moreover, we demonstrate that platelets release their alpha- and dense-granule contents in both nonsevere and severe forms of COVID-19. In comparison to concentrations measured in healthy volunteers, phosphatidylserine-exposing platelet extracellular vesicles were increased in nonsevere, but not in severe cases of COVID-19. Levels of D-dimers, a marker of thrombosis, failed to correlate with any measured indicators of platelet activation. Functionally, platelets were hyperactivated in COVID-19 subjects presenting nonsevere and severe symptoms, with aggregation occurring at suboptimal thrombin concentrations. Furthermore, platelets adhered more efficiently onto collagen-coated surfaces under flow conditions.

Taken together, the data suggest that platelets are at the frontline of COVID-19 pathogenesis, as they release various sets of molecules through the different stages of the disease. Platelets may thus have the potential to contribute to the overwhelming thrombo-inflammation in COVID-19, and the inhibition of pathways related to platelet activation may improve the outcomes during COVID-19.