Neutrophil inflammation is common in CTEPH. (A) Circulating blood neutrophil counts: control (n = 60), CTEPH (n = 109); (B) plasma concentrations of MPO: control (n = 60), CTEPH (n = 96), (C) total MMP-9: control (n = 60), CTEPH (n = 46), (D) active MMP-9: control (n = 60), CTEPH (n = 67), (E) extracellular dsDNA: control (n = 60), CTEPH (n = 63), (F) DNase activity: control (n = 57), CTEPH (n = 103), and (G) circulating CitH3: control (n = 60), CTEPH (n = 77). (H) Macroscopic view of thrombus excised during pulmonary endarterectomy representing fresh (red; circle) and organized (white; arrow) material. (I) Immunofluorescence staining for CitH3 in fresh red CTEPH thrombus (scale bars, 50 µm). Data in panels A-G are shown as median and interquartile ranges. (J) Ex vivo NET formation in healthy controls (n = 5) and in patients with CTEPH (n = 6) after coincubation with S aureus. Data are shown as mean ± SEM. *P < .05; ***P < .001 (unpaired Student t test); ****P < .0001 (Mann-Whitney U test). US, unstimulated.