SMAD3 and hypersensitivity pneumonitis: In summary, the result of our study concluded that YYYQ could alleviate the severity of alveolitis and fibrosis on BLM-induced pulmonary fibrosis in rats, inhibit the mRNA expression of TGF-β1 and its receptors, Smad3, α-SMA, and CTGF, enhance mRNA expression of Smad7 and E-cadherin, and reduce the mRNA expression of collagen such as laminin, collagen I, and hydroxyproline, but the effect on interleukin 18 was not obvious.