The PM2.5-stimulated group, MXD treatment group underwent PM2.5 stimulation while the control group and intervention group underwent the same surgical procedure without the transtracheal instillation. (A) Observation of pathological changes in lung tissues by naked eye after normal saline infusion. (B) Representative HE staining images of rat lung tissues (magnification, ×200). (C) Lung histologic injury score. Data are shown as mean ± S.D. n=6/group, **P<0.01 compared with PM2.5-stimulated group; ^##P<0.01 PM2.5-stimulated group compared with control group. Con, control group; Int, intervention group; PM2.5, PM2.5-stimulated group.