Before the discovery of NETosis (controlled neutrophil cell death with the release of NETs), necrosis was generally considered to be the primary source of neutrophil DNA in the lungs of patients with CF; however, this was subsequently revealed not to be the case, as NETosis was shown to be responsible for the release of myeloperoxidase (MPO), heparin-binding protein (HBP), DNA and NE in CF sputum and bronchoalveolar lavage fluid (BALF) [132–135]. The gene discussed is MPO; the disease is cystic fibrosis.