TGFB1 and pulmonary fibrosis: In contrast, myofibroblasts are also the main source of ROS in the process of pulmonary fibrosis, and the large amounts of ROS produced can induce the expression and secretion of various pro-fibrotic factors, including TGF-β, in a number of cells, which in turn forms a vicious circle and facilitates developing pulmonary fibrosis [27].