Neutrophil extracellular traps and thrombosis in COVID-19

Here, we report on four patients whose hospitalizations for COVID-19 were complicated by venous thromboembolism ( VTE ). All demonstrated high levels of D-dimer as well as high neutrophil-to-lymphocyte ratios. For three patients, we were able to test sera for neutrophil extracellular trap ( NET ) remnants and found significantly elevated levels of cell-free DNA, myeloperoxidase-DNA complexes, and citrullinated histone H3. Neutrophil-derived S100A8/A9 (calprotectin) was also elevated. Given strong links between hyperactive neutrophils, NET release, and thrombosis in many inflammatory diseases, the potential relationship between NETs and VTE should be further investigated in COVID-19.