Signaling through FcγRIIA and the C5a-C5aR pathway mediates platelet hyperactivation in COVID-19

Apostolidis, Sokratis A.; Sarkar, Amrita; Giannini, Heather M.; Goel, Rishi R.; Mathew, Divij; Suzuki, Aae; Baxter, Amy E.; Greenplate, Allison R.; Alanio, Cécile; Abdel-Hakeem, Mohamed; Oldridge, Derek A.; Giles, Josephine; Wu, Jennifer E.; Chen, Zeyu; Huang, Yinghui Jane; Pattekar, Ajinkya; Manne, Sasikanth; Kuthuru, Oliva; Dougherty, Jeanette; Weiderhold, Brittany; Weisman, Ariel R.; Ittner, Caroline A. G.; Gouma, Sigrid; Dunbar, Debora; Frank, Ian; Huang, Alexander C.; Vella, Laura A.; Reilly, John P.; Hensley, Scott E.; Rauova, Lubica; Zhao, Liang; Meyer, Nuala J.; Poncz, Mortimer; Abrams, Charles S.; Wherry, E. John

Patients with COVID-19 present with a wide variety of clinical manifestations. Thromboembolic events constitute a significant cause of morbidity and mortality in patients infected with SARS-CoV-2. Severe COVID-19 has been associated with hyperinflammation and pre-existing cardiovascular disease. Platelets are important mediators and sensors of inflammation and are directly affected by cardiovascular stressors. In this report, we found that platelets from severely ill, hospitalized COVID-19 patients exhibit higher basal levels of activation measured by P-selectin surface expression, and have a poor functional reserve upon in vitro stimulation. Correlating clinical features to the ability of plasma from COVID-19 patients to stimulate control platelets identified ferritin as a pivotal clinical marker associated with platelet hyperactivation. The COVID-19 plasma-mediated effect on control platelets was highest for patients that subsequently developed inpatient thrombotic events. Proteomic analysis of plasma from COVID-19 patients identified key mediators of inflammation and cardiovascular disease that positively correlated with in vitro platelet activation. Mechanistically, blocking the signaling of the FcγRIIa-Syk and C5a-C5aR pathways on platelets, using antibody-mediated neutralization, IgG depletion or the Syk inhibitor fostamatinib, reversed this hyperactivity driven by COVID-19 plasma and prevented platelet aggregation in endothelial microfluidic chamber conditions, thus identifying these potentially actionable pathways as central for platelet activation and/or vascular complications in COVID-19 patients. In conclusion, we reveal a key role of platelet-mediated immunothrombosis in COVID-19 and identify distinct, clinically relevant, targetable signaling pathways that mediate this effect. These studies have implications for the role of platelet hyperactivation in complications associated with SARS-CoV-2 infection.