ABSTRACT
Thrombosis is a prominent feature of coronavirus disease 2019 (COVID-19) and often occurs in patients who are critically ill; however, the mechanism is unclear. This COVID-19 associated coagulopathy (CAC) shares features with heparin-induced thrombocytopenia (HIT), including mild thrombocytopenia and thrombosis. We thus tested 10 CAC patients for anti-PF4/heparin antibodies and functional platelet activation. HIT was excluded in all samples based on anti-PF4/heparin antibody and serotonin release assay results. Of note, 6 CAC patients demonstrated platelet activation by the serotonin release assay that was inhibited by Fc{gamma}RIIA receptor blockade, confirming an IgG-specific immune complex (IC)-mediated reaction. Platelet activation was independent of heparin, but inhibitable by both therapeutic and high dose heparin. All 6 samples were positive for IgG-specific antibodies targeting the receptor binding domain (RBD) or the spike protein of the SARS-CoV-2 virus. These samples were additionally characterized by significant endothelial activation, shown by increased von Willebrand factor antigen and activity. ADAMTS13 activity was not severely reduced, and ADAMTS13 inhibitors were not present, ruling out thrombotic thrombocytopenic purpura. Our study thus identifies platelet-activating ICs as a mechanism that contributes to CAC thrombosis. Scientific CategoryThrombosis and Hemostasis Key PointsO_LIPatients with COVID-19 thrombosis have immune complexes that activate platelets through Fc{gamma}RIIA signalling C_LIO_LIPatients with COVID-19 thrombosis demonstrate increased VWF antigen and activity that is not related to severe ADAMTS13 reduction C_LI
ABSTRACT
Coronavirus Disease 2019 (COVID-19) is a global pandemic caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). While detection of SARS-CoV-2 by polymerase chain reaction with reverse transcription (RT-PCR) is currently used to diagnose acute COVID-19 infection, serological assays are needed to study the humoral immune response to SARS-CoV-2. SARS-CoV-2 IgG/A/M antibodies against SARS-CoV-2 spike (S) protein and its receptor-binding domain (RBD) were characterized using an enzyme-linked immunosorbent assay (ELISA) and assessed for their ability to neutralize live SARS-CoV-2 virus in recovered subjects who were RT-PCR-positive (n=153), RT-PCR-negative (n=55), and control samples collected pre-COVID-19 (n=520). Anti-SARS-CoV-2 antibodies were detected in 90.9% of resolved subjects up to 180 days post-symptom onset. Anti-S protein and anti-RBD IgG titers correlated (r= 0.5157 and r = 0.6010, respectively) with viral neutralization. Of the RT-PCR-positive subjects, 22 (14.3%) did not have anti-SARS-CoV-2 antibodies; and of those, 17 had RT-PCR cycle threshold (Ct) values >27, raising the possibility that these indeterminate results are from individuals who were not infected, or had mild infection that failed to elicit an antibody response. This study highlights the importance of serological surveys to determine population-level immunity based on infection numbers as determined by RT-PCR.
