Abstract: Objective To investigate the effect of intranasal immunization with different doses of the muscle larvae soluble antigen(MLSAg)of Trichinella spiralis on the protection of mice against T.spiralis infection.Methods Fifty adult C57BL/6J mice were randomly divided into five groups and were immunized intranasally with 5,10,20 or 30μg of MLSAg per mouse twice at interval of 2 weeks,and the mice receiving PBS were used as controls.On the 7th day after last immunization,all mice were infected with 150 T.spiralis larvae by gastric gavage.The health conditions of the infected mice were observed,and the body weight of mice was recorded every day after challenges.The infected mice were killed on the 28th day after challenges,and the levels of serum Ig G,IgA and Ig G,IgA in small intestinal juice were detected by ELISA.Meanwhile,the larvae in the tongue,masseter,diaphragma and the muscles of posterior limb were counted.Results The results showed that the body weight of the control mice gradually decreased after challenges,while those of mice immunized with different doses of MLSAg of T.spi ralis remained steadily growing.The levels of Ig G,IgA in intestinal juice and serum in all the immunized mice were higher than that of the control,especially in the 20μg dose immunized groups.In comparisison with the mice of 5μg dose immunized groups and the control group,the larvae loads in the muscles of tongue,masseter,diaphragma and posterior limb in the 10μg,20μg and 30μg dose immunized groups were significantly decreased.Conclusion It is evident that the intranasal immunization with different doses of MLSAg of T.spiralis can induce protective immune responses against the parasite,in which the protective effect induced with 20μg of soluble antigen were most significant.