SARS-CoV-2 induces platelet activation partially through its receptor-binding domain, and integrin αIIbβ3 interaction

COVID-19 is a multisystem inflammatory disease associated with an increased risk of thrombotic events. Platelet activation is a key mechanism involved in COVID-19-associated hypercoagulability. SARS-CoV-2 binding and entry into host cells occurs predominantly through the interaction between the Spike protein and the angiotensin-converting enzyme 2 (ACE2) receptor, mediated by the receptor-binding domain (RBD). However, ACE2 expression on platelets remains controversial, and the mechanisms underlying virus–platelet interactions are not fully understood. This study aimed to evaluate mechanisms of SARS-CoV-2-induced platelet activation involving receptor binding. Platelets were isolated from healthy donors (IRB: 85978925.4.1001.5147) and stimulated in vitro with SARS-CoV-2 at multiplicities of infection (MOI) of 0.05 and 0.5 (n=8–9), or with recombinant Spike protein or its domains (2 µg/mL; n=7). A competition assay was performed between SARS-CoV-2 and recombinant RBD. Additionally, neutralizing antibodies were used to investigate the involvement of platelet receptors. Platelet activation was assessed by CD62P, CD63, and PAC-1 expression using flow cytometry, and inflammatory mediator secretion. Recombinant Spike and S1 proteins alone did not induce platelet activation. In contrast, SARS-CoV-2 at both MOIs increased CD62P, CD63, and PAC-1 expression. SARS-CoV-2–RBD competition reduced platelet activation, decreasing CD63 and CD62P expression at MOI 0.5 and MIF secretion at MOI 0.05, indicating that virus–platelet interaction occurs, at least in part, through the Spike RBD. Inhibition of integrin αIIbβ3, but not CLEC2, DC-SIGN, or CD62P, reduced SARS-CoV-2-induced platelet activation, suggesting that integrin αIIbβ3 contributes to SARS-CoV-2 binding and signaling to platelets. These findings support a potential role for the Spike RBD and integrin αIIbβ3 in SARS-CoV-2-induced platelet activation.