PROS1 and endothelial dysfunction: We have recently shown that S protein stimulation of endothelial cells leads to marked elevation in intracellular superoxide production to induce endothelial dysfunction, which is also characterized by activation of inflammatory signaling, including production of cytokines and chemokines such as IL-6 (one of the key cytokines mediating cytokine storm during the pathogenesis of COVID-19) and MCP-1 (23).