Abstract: 　Objective To compare the protective immunity against challenge infection and the characteristics of immune response induced by nucleic acid vaccine encoding full length paramyosin of Chinese S. japonicum (Sjc97 DNA ) and ultraviolet attenuated cercariae vaccine(UVC). Methods C57BL/6 mice were vaccinated intramuscularly with the Sjc97 DNA twice at interval of wk 0 and wk 3, and challenged in three weeks after immunization with Sjc97 DNA (Sjc97 DNA group). C57BL/6 mice in UVC group were challenged with non attenuated cercariae five weeks post immunization with UVC. Another two groups of mice were vaccinated with blank plasmid and infected with non attenuated cercariae without immunization respectively to serve as control. Seven weeks after challenge infection the mice were perfused to obtain worm burden and the number of eggs in the liver tissue. The specific anti SEA and AWA IgG, IgA and IgG subclasses in sera of the mice and cytokines secreted by splenocytes exposed to mitogen Con A for 96 h at pro and post challenge were determined by ELISA test. Results C57BL/6 mice immunized with Sjc97 DNA or UVC before challenge infection produced predominantly cytokines of IL 2, IFN γ and antibodies of IgG2a, IgG2b and IgA. The levels of above cytokines and antibodies were higher in UVC group significantly than that in Sjc97 DNA group. The mice immunized with Sjc97 DNA showed a worm reduction rate of 36.3 % and egg reduction rate of 42.4 % in the liver, and in the UVC group, 66.9 % worm reduction rate and 75.6 % egg reduction rate in the liver. At the seventh week after challenge infection with non attenuated cercariae, the immune responses of Th1 type in the mice of two vaccine groups were still predominant, although Th2 type responses increased slightly; and Th2 type responses of the mice in the blank vector and infection control groups were predominant. Conclusion The nucleic acid vaccine, Sjc97 DNA, and UV attenuated cercariae could all induce protective immunity in C57BL/6 mice significantly. The protective immunity induced by UVC is stronger significantly than that by Sjc97 DNA, and is obviously correlated with Th1 type responses.

Key words: Schistosoma japonicum, paramyosin, nucleic acid vaccine, UV attenuated cercariae, immunity