MPO and chronic obstructive pulmonary disease: Interestingly, neutrophil extracellular traps (NETs) formed by neutrophil elastase (NE), DNA, histones, and myeloperoxidase (MPO) (26) have been shown to mediate proinflammatory effects in vivo and in vitro and have served as useful biomarkers for a variety of diseases, including sepsis, acute lung injury, cystic fibrosis and COPD (27–29).