Markers of neutrophil extracellular traps (NETs) in the circulation of patients with asthma exacerbation and control neutrophils stimulated with asthma exacerbation serum. Levels of (A) circulating DNA and (B) H3Cit representing NET release in asthma serum compared to healthy individuals (controls) (n = 29 subjects per group). (C) Correlation between circulating DNA and H3Cit levels. Spearman’s r2 values are shown. (D) Fluorescence microscopy images showing NE/H3Cit staining (blue, DAPI; green, NE; red, H3Cit; original magnification, 400×) and (E) percentage of NET release (n = 6 independent experiments), as assessed via immunofluorescence, in control neutrophils incubated with asthma serum. Untreated condition refers to control neutrophils stimulated with sera from healthy subjects (control serum). For (A,B,E), data are shown as mean ± SD, Mann–Whitney U test (2 tailed). For (D), a representative example of 6 independent experiments is shown. All conditions were compared to controls/untreated (statistically significant: p < 0.05).