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.