Objective:To investigate the inhibitory effects and mechanism of budesonide on Th2-dominated immune response in a murine model of asthma. Methods:Twenty-four 6-week-old healthy BALB/c mice,SPF grade,were randomly divided into 3 groups,including the normal control group,the asthma group,and the budesonide group. Mice in the budesonide group were exposed to an aerosol of budesonide daily during ovalbumin(OVA) challenge. The murine asthma model was established by OVA sensitization and challenge. Twenty-four hours after the last airway provocation,acetylcholine (Ach) was administered via caudalis vein,and the airway resistance was measured by pulmonary function detector. The levels of IL-4 and IL-13 in branchoalveolar lavage fluid (BALF) and total IgE in serum were determined by enzyme-linked immunosorbent assay (ELISA). Total and differential cell counts in BALF were calculated by light microscopy. The airway inflammatory infiltration was detected by haematoxylin and eosin (HE) staining. The pulmonary thymic stromal lymphopoietin was determined by Western blot analysis. Results:As compared with the control group,the airway hyperreactivity,airway inflammation,cell count and eosinophil percentage in BALF,levels of total serum IgE and BALF IL-4 and IL-13,and thymic stromal lymphopoietin (TSLP) expression in the lung were significantly increased in the asthma group (P < 0.05). As compared with the asthma group,all the above indices mentioned in the budesonide group were decreased significantly(P < 0.05). Conclusion:Budesonide could reduce the allergen-induced airway inflammation and hyperreactivity by downregulating the expressions of pulmonary TSLP and Th2 cytokines,which may be an important mechanism of corticosteroids for the treatment of asthma.