Abstract: Objective To study the protective efficacy of co-immunization with Schistosoma japonicum glutathione S-transferase (Sj26) DNA and recombinant Sj26 protein (rSj26 GST) vaccine against Schistosoma japonicum in BALB/c mice. Methods The Sj26 gene was cloned into eukaryotic expression vector pEGFP-N3 with enhanced green fluorescence protein. The recombinant plasmid pEGFP-Sj26 was transfected into baby hamster kidney (BHK) cells, fluorescent microscope and Western blotting were employed to identify the expressed products. Each mouse in co-immunization group was primed with plasmid pEGFP-Sj26, boosted 2 weeks later and immunized with rSj26 GST 4 weeks later. While each mouse in pEGFP-Sj26 group and rSj26 GST group was primed and boosted with pEGFP-Sj26 or rSj26 GST independently. Two weeks after last immunization, each mouse was challenged with 40±1 cercariae of S.japonicum Chinese strain. At the 45th day post-infection, mice were sacrificed and the worms were perfused from portal vein and the number of worms and eggs in liver tissue were counted. Results In BHK cells transfected with the recombinant plasmid pEGFP-Sj26,the expression of Sj26-EGFP fusion protein was confirmed by fluorescent microcopy and Western blotting. The worm reduction rate in co-immunized group was 50.8%, significantly higher than that in pEGFP-Sj26 group (28.0%,P<0.01) and rSj26 GST group (25.5%, P<0.01). Liver egg reduction rate in co-immunized group, pEGFP-Sj26 group and rSj26 GST group were 32.7%, 20.6% and 33^0% respectively. The number of eggs per female in liver of co-immunized mice and rSj26 GST group were significantly higher than that in control group (P<0.01). Conclusion Compared to the immunization with pEGFP-Sj26 or rSj26 GST alone,the co-immunization with pEGFP-Sj26 and rSj26 GST can enhance protective efficacy in BALB/c mice.

Key words: Schistosoma japonicum, Glutathione S-transferase, DNA vaccine, Recombinant protein vaccine, Co-immunization