NOS2 and pulmonary fibrosis: With further progression of pulmonary fibrosis, the expression of inducible nitric oxide synthase (iNOS) can accelerate the synthesis of endogenous free radical nitric oxide [28, 29], which can affect proteins, lipids, carbohydrates, and nucleic acids that are the main components of cells related to apoptosis, gene expression, signal transduction, and defense against pathogens.