A state of immunothrombosis has been reported in COVID-19. Platelets actively participate in this process. Platelet-rich plasma (PRP) was incubated with spike full-length protein and the RBD domain in independent assays. Researchers evaluated platelet activation through the expression of P-selectin and activation of glycoprotein IIbIIIa (GP IIbIIIa), determined by flow cytometry and the ability of the proteins to induce platelet aggregation.