TGFB1 and pulmonary fibrosis: Considering TGF-β/Smad signaling is implicated in fibrosis-related lung diseases and PM2.5-initiated pulmonary fibrosis is partly TGF-β dependent, we hypothesized that MXD prevented lung fibrosis via suppressing TGF-β-mediated EMT process and examined the regulatory effect of MXD on the TGF-β/Smad signal pathway [81].