Dear Editor, Complex interactions between various processes have arisen as key elements underlying the pathophysiology of coronavirus disease 2019 (COVID-19). First, immunothrombosis and neutrophil extracellular trap (NET) release contribute to inflammation-associated lung damage and thrombosis, and second, endothelial cell dysfunction participates in the disease-associated coagulopathy. 1,2 In addition, cytokine release syndrome (CRS) dictates adverse clinical outcomes, with interleukin (IL)-6 playing a central role. 3 However, the sequence of events leading to a vicious cycle of synergistic pathways causing unchecked immune activation and thrombus formation have to date not been clearly defined. Here, we investigated the role of NETs, endotheliopathy, hemostatic imbalance, and interleukin-6 (IL-6) release in the severity of the disease, as well as their synergy in patient outcomes. For this purpose, we recruited 142 hospitalized COVID-19 patients from March to May 2020. Infection was confirmed by qRT-PCR testing. Healthy controls (HC, N = 50) were also included. Clinical and demographical variables are reported in Table S1, and biochemical analytical data and cell counts in Table S2. To address whether NETs and von Willebrand factor (VWF)/a disintegrin-like and metalloprotease with thrombospondin type 1 motif 13 (ADAMTS13) axis are associated and contribute to the prognosis of COVID-19 patients, we analyzed plasma cell-free DNA (cfDNA), citrullinated histone H3-DNA (citH3-DNA) complexes (surrogated NET marker), von Willebrand factor antigen (VWF:Ag), von Willebrand factor collagen binding (VWF:CB), ADAMTS13 activity, IL-6 levels, clinical scores, and outcomes. Analysis of NETosis and endotheliopathy markers in the first available sample confirmed a coagulation imbalance in COVID-19 patients versus HC (Figure S1A-F). In addition, NETs and VWF:Ag correlated with neutrophil count, neutrophil/lymphocyte ratio, and with acute-phase reactants and coagulation parameters (Table S3). Importantly, NETs and VWF:Ag/ADAMTS13 This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.