NOS2 and idiopathic pulmonary fibrosis: Several studies have demonstrated that the DDAH/iNOS pathway is pathologically involved in a number of pulmonary disorders including asthma (Trifilieff et al., 2000; Batra et al., 2007), IPF (Pullamsetti et al., 2011), and COPD (Seimetz et al., 2011).