TGFB1 and pulmonary fibrosis: Chen and colleagues suggested that epithelial cells could serve as a novel source of fibroblasts in pulmonary fibrosis through epithelial-mesenchymal transition (EMT) [22]: they demonstrated that MWCNT exposure induced pulmonary fibrosis and epithelial-derived fibroblasts via transforming growth factor-beta (TGF-β), one of the most potent EMT mediators [23, 24].