SERPINE1 and COVID-19: These cytokines upregulate tissue factor expression, activate platelets, and inhibit fibrinolysis via increased plasminogen activator inhibitor-1 (PAI-1), collectively predisposing to a hypercoagulable state (103, 104) Recent studies have found that fibrin binds to the SARS-CoV-2 spike protein, forming a pro-inflammatory clot that leads to systemic thromboinflammation in COVID-19 (105).