Immunopathological characteristics of COVID-19 patients. (A) Doublet cells were excluded by forward scatter height (FSC-H) and forward scatter area (FSC-A) gating for all flow cytometry analysis. Viable cells were identified using fixable viability stain and side scatter area (SSC-A) gating. Neutrophils were identified as cells stained for CD15⁺CD16⁺ among CD14⁻CD19⁻ cells.(B) Flow cytometry analyses of living cells from the whole blood of healthy controls (H.Control) or COVID-19 patients.(C) Frequency and absolute numbers of CD15⁺CD16⁺ neutrophils gated on CD14⁻CD19⁻ live cells from whole blood from healthy controls (n = 7) or COVID-19 patients (n = 7). (D) CT of the chest of one patient who died from COVID-19. Images from apical to basal segments (I to IV) show multiple consolidations with air bronchograms in a peripheral and peribronchovascular distribution, more evident in the lower lobes, associated with ground-glass opacities. (E) Representative pulmonary histological findings in 10 cases, autopsied by ultrasound-guided, minimally invasive autopsy. I: The area with interstitial and alveolar neutrophilic pneumonia with diffuse alveolar damage and hyaline membranes in the alveolar space (black arrows). Septal vessel with margination of leukocytes and an intraluminal early fibrin thrombus (green star). II: Area with neutrophilic pneumonia (red arrow), septal thickening, epithelial desquamation, and squamous metaplasia (black arrows). I and II: H&E. Scale bar indicates 50 µm. Data are representative of at least two independent experiments one experiment and are shown as mean ± SEM. P value was determined by two-tailed unpaired Student t test (C).