Control neutrophils stimulated with asthma exacerbation serum release neutrophil extracellular traps (NETs) expressing interleukin (IL)-17A. (A) Levels of IL-17A in asthma serum compared to healthy individuals (controls) (n = 29 subjects per group). (B) Correlation between H3Cit, representing NET release, and IL-17A levels in asthma serum. Spearman’s r2 values are shown. (C) IL-17A mRNA expression in control neutrophils treated with asthma serum, as assessed via qPCR (n = 6 independent experiments). (D) Fluorescence microscopy images showing IL-17A/NE staining (blue, DAPI; green, IL-17A; red, NE; original magnification, 400×) in control neutrophils incubated with asthma serum. For (C,D), untreated condition refers to control neutrophils stimulated with serum from healthy subjects (control serum). (E) IL-17A levels in in vitro-generated NET structures (n = 6 independent experiments). NETs were obtained via control neutrophils incubated with asthma serum (asthma NETs) or serum from healthy subjects (control NETs). For (A,C,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).