TGF-β and its canonical downstream signalling molecule Smad3 are central to the development and progression of fibrosis as elevated levels of TGF-β are sufficient to reproduce organ fibrosis in animal models, stimulate fibroblast differentiation and epithelial-to-mesenchymal transformation, and the observation that Smad3-deficiency confers resistance in mouse models of IPF (Bonniaud et al, 2004; Zhao et al, 2002). This evidence concerns the gene SMAD3 and idiopathic pulmonary fibrosis.