Neutrophils recruited to the lung in patients with COVID-19 pneumonia have inflammasome activation and are predisposed to NETosis. Smears of tracheal aspirates were costained with DAPI (blue), an anti-CD66b antibody (neutrophil marker, green) and an anti-ASC antibody (red), or with an anti-H3cit antibody (red). Nonspecific staining corresponds to immunostaining performed without primary antibodies. (A) Representative images from widefield microscopy of tracheal aspirates from severe COVID-19 patients. White arrows indicate the presence of the ASC speck. Scale bar, 10 µm. (B) Quantification of CD66b⁺ neutrophils in tracheal aspirates. (C) Quantification of ASC speck–positive neutrophils in tracheal aspirates. (D) Quantification of H3cit⁺ neutrophils in tracheal aspirates. (E) A nonparametric Spearman correlation test was computed. SEM, standard error of the mean.