Abstract: Objective To investigate the enhancement effect of IL-4 expression plasmid on cathepsin B DNA vaccine of Schistosoma japonicum (Sj) in mice. Methods The recombinant IL-4 plasmid constructed by cloning PCR amplified product of murine IL-4 gene into eukaryotic expression vector pcDNA3.1 was co-injected intramuscularly with Sj cathepsin B expression plasmid DNA to mice as the test group. The other three groups of mice were set up as control including IL-4 expression plasmid, Sj cathepsin B expression plasmid and two vacant vector plasmids. The expression of IL-4 and cathepsin B was visualized by immunohistochemistry. Challenge infection in mice was carried out 3 weeks after the last vaccination and immune protection was assessed by worm and egg reduction rates. Results The recombinant mIL-4 plasmid and cathepsin B DNA vaccine were expressed in muscular cells of the vaccinated mice. Immunization with cathepsin B DNA plus recombinant mIL-4 plasmid yielded a 43.2 % of worm reduction rate and a 76.6% of egg reduction rate, showing a significant difference（P<0.01, P<0.05） compared with that of cathepsin B DNA vaccine alone. Conclusion As an adjuvant, IL-4 DNA can improve the protective effect of cathepsin B DNA vaccine in mice against S. japonicum infection.

Key words: Schistosoma japonicum, DNA vaccine, Cathepsins, Recombinant IL-4, Immunoprotection