IL-33 has also been implicated in the formation of neutrophil extracellular traps during virus-induced asthma exacerbation.58 Similarly, neutrophil priming with GM-CSF might promote the production of neutrophil extracellular traps.59 By releasing neutrophil elastase and other proteinases, neutrophil extracellular traps could in turn cleave and further activate IL-33. These pathways might be relevant in patients with critical COVID-19, since neutrophilia and the neutrophil-to-lymphocyte ratio are associated with poor prognosis, and high concentrations of neutrophil extracellular traps have been detected in patients with COVID-19 admitted to hospital and receiving mechanical ventilation.60