Fig. 1

Phenotypic and functional characterization of circulating neutrophils from COVID-19 patients. a, b Surface expression of CD62L (a) and CD11b (b) on resting neutrophils (PMNs) was studied in whole-blood samples maintained at 4 °C and stained with specific monoclonal antibodies. Results are expressed as mean fluorescence intensity (MFI). c Production of ROS by unstimulated neutrophils was studied with dihydroethidium (DHE) oxidation after treatment of whole-blood samples for 50 min with PBS; results are expressed as MFI. d–f Analysis of neutrophil-platelet aggregates (NPA). d Gating strategy and representative dot plots of flow cytometry analysis. e NPA levels, expressed as percentage of neutrophils that bind platelets. f Correlation of the percentage of NPA with CD11b expression at the neutrophil surface. g, h Analysis of capacity for L-selectin shedding (g) and neutrophil degranulation (h) in response to stimulation. CD62L and CD11b expression were analyzed after incubation of whole-blood samples for 45 min with PBS or fMLP (10⁻⁶ M). Results are expressed as a stimulation index (SI; MFI of stimulated sample/MFI of unstimulated sample). i, j ROS production by stimulated neutrophils was measured after pretreatment of whole-blood samples for 45 min with PBS, TNF-α (TNF, 5 ng/mL) or LPS (TLR4 agonist, 10 ng/mL). One histogram representative of ROS production by LPS-primed samples from a control (white), a CAP patient (grey) and a COVID-19 patient (black) (i). Results are expressed as SI (j). Samples came from age-matched healthy controls (HCs) (n = 38), CAP patients (n = 22) and COVID-19 patients at day 1 (n = 53), day 3 (n = 49) and day 7 (n = 40). Values are means ± SEM. *P < 0.05, **P < 0.01, ***P < 0.001, adjusted for age