Abstract: Objective To detect the protection in mice induced by DNA vaccine encoding SjIR3 against Schistosoma japonicum（Sj）. Methods SjIR3 was amplified by PCR with specific primers and linked to T vector. The reconstructed plasmid was digested by XhoⅠand BamHⅠ. The target segments were collected and inserted into pcDNA3.0 to construct DNA vaccine SjIR3/pC. Fifty-four female mice were divided into 3 groups: groups A and B received normal saline and pcDNA3.0 respectively as controls, and group C was immunized with SjIR3/pC. All the mice were injected three times with an interval of two weeks. Sera were collected before each inoculation and before challenge infection. Six mice from each group were sacrificed 2 weeks after the final inoculation and spleen cells were collected. Serum IgG was detected by ELISA and the proliferation activity of spleen T lymphocytes induced by ConA or rSjIR3 was detected by MTT assay. The remaining mice were infected by （40±1） Sj cercariae per mouse 2 weeks after the final inoculation. Forty-five days later, mice were sacrificed and perfused, numbers of adult worms and of eggs in liver tissue were counted. Results ELISA showed no significant change of serum IgG level in groups A and B, but considerable increase in group C （0.78±0.05）（P<0.01）. The proliferation activity of spleen T lymphocytes increased with the induction of ConA or recombinant protein rSjIR3 after the final inoculation. The A₅₇₀ was 0.57±0.02 and 0.68±0.01 respectively, showing a significant difference in comparison to the groups A and B （P<0.01）. The worm reduction rate and the egg reduction rate in group C were 29.42% and 36.56% respectively. Conclusion DNA vaccine encoding SjIR3 induces humoral and cell-mediated immune response, and shows partial immune protection against Schistosoma japonicum.

Key words: Schistosoma japonicum, SjIR3, DNA vaccine, Mouse, Immune protection