Abstract: Abstract: Objective To explore the protective effcets of Schisandra chinensis extract (SCE) in paraquat (PQ)-induced pulmonary fibrosis in mice，and its intrinsic molecular mechanisms thereof. Methods A total of 108 mice were randomly allocated into six groups (n=18): control group, model group, low concentration of SCE group (200 mg/kg), medium concentration of SCE group (400 mg/kg), high concentration of SCE group (800 mg/kg) and vitamin C group (100 mg/kg). Except control group, mice were given by intragastric administration with PQ (100 mg/kg) and administered with SCE and Vitamin C once per 24 h after PQ modeling. Mice were sacrificed at 7, 14 and 21 d after modeling. Six mice were executed at different time points. The degree of lung tissue inflammation and fibrosis were observed by HE staining and Masson staining. The mRNA and protein expression levels of transforming growth (TGF)-β1, interleukin (IL)-6 and IL-17 in lung tissue were determined by RT-PCR and ELISA respectively. Results (1) Compared with control group, the lung tissue of model group showed a large number of inflammatory cell infiltration, space congestion, and its inflammation scores increased at 7 and 14 days after modeling (P < 0.05). At the same time, compared with model group and vitamin C group, inflammation scores were significantly decreased in medium concentration of SCE group and high concentration of SCE group (P < 0.05). (2) Compared with control group, collagen fibersand the degree of fibrosis were significantly increased in model group， while pulmonary fibrosis were decreased in medium concentration of SCE group and high concentration of SCE group at 14 and 21 days after modeling (P < 0.05). (3) With the extension of modeling time, both mRNA and protein expressions of TGF-β1 were obviously elevated, IL-6 decreased and IL- 17 reduced after the first increase in PQ group. Compared with PQ group, levels of three cytokines mRNA and protein expression in medium concentration of SCE group and high concentration of SCE group changed as follows: IL-6 level was markedly decreased at 7 and 14 days after modeling; TGF-β1 level was markedly increased at 14 and 21 days after modeling. However, IL-17 level was markedly decrease at three time points（P < 0.05） . Conclusion SCE can relieve PQ-induced lung inflammation and fibrosis by suppressing TGF-β1, IL-6, and IL-17 expressions.

Key words: Schisandra chinensis, Paraquat, pulmonary fibrosis, transforming growth factor-β1, interleukin-6, interleu? kin-17