TGFB1 and pulmonary fibrosis: Connective tissue growth factor (CTGF), another profibrogenic cytokine, plays an important role in the formation of pulmonary fibrosis under tissue damage (Robinson et al. 2012); it is expressed at extremely low concentrations under normal conditions and is overexpressed by specific stimuli (e.g., hypoxia or TGF-β) (Yang et al. 2014; Han et al. 2008).