Circulatory exosomes from COVID-19 patients trigger NLRP3 inflammasome in endothelial cells

SARS-CoV-2 infection induces inflammatory response, cytokine storm, venous thromboembolism, coagulopathy, and multiple organ damage. Resting endothelial cells prevent coagulation, control blood flow and inhibit inflammation. However, it remains unknown how SARS-CoV-2 induces strong molecular signals in distant cells for immunopathogenesis. In this study, we examined the consequence of human endothelial cells (microvascular endothelial cells (HMEC-1) and liver endothelial cells (TMNK-1)) to exosomes from plasma of severe COVID-19 patients. We observed a significant induction of NLRP3, caspase-1 and IL-1β mRNA expression in the endothelial cells following exposure to exosomes from plasma of COVID-19 patients as compared to that of healthy donors. Activation of caspase-1 was noted in the endothelial cell culture medium following exposure to the COVID-19 exosomes. Further, COVID-19 exosomes significantly induced mature IL-1β secretion in the endothelial cell culture medium. Thus, our results demonstrated for the first time that exosomes from COVID-19 plasma trigger NLRP3 inflammasome in endothelial cells of distant organs.