[Studies on the protective effect of the mutant of Sj23 DNA vaccine against schistosomiasis].

OBJECTIVE: To investigate the protective immunity of the vaccine against schistosomiasis, a mutant of Mr 23 000 membrane protein DNA (Sj23DNA) without the homologous sequence of ME491. METHODS: The mutant of Sj23 DNA with no homologous sequence of ME491 on the cell membrane of human melanoma was obtained by overlap PCR. The mutant was transfected into human embryonic kidney cells of the line HEK293. Indirect fluorescent antibody test (IFAT) was used to detect the expressed protein. Expression of the mutant of Sj23DNA in muscular cells of mice was conducted through vaccinating the mouse with 100 microg purified plasmids by injecting them into the quadriceps muscle of thigh. Four weeks after the immunization, the quadriceps muscles were taken and cryostat sections were prepared for detecting the expression by IFAT. Forty BALB/c mice were randomly divided into four groups and injected with the mutant of pcDNA3-Sj23 plasmid DNA, pcDNA3-Sj23 plasmid DNA, pcDNA3 blank plasmid (100 microg per mouse) and sterile saline (30 microl per mouse) respectively. Four weeks after the immunization, mice were challenged with cercariae (40+/-2 cercariae per mouse) by abdominal skin penetration. Mice were then killed 6 weeks later, perfusion and squash methods were carried out to collect the adult worms and the number of eggs per gram of liver tissue was calculated. Worm and egg reduction rates were used to evaluate the protective immunity. RESULTS: Specific fluorescence was demonstrated in muscular cells of mice vaccinated with the mutant of pcDNA3-Sj23. The worm reduction rate and egg reduction rate were 40.3% and 42.8% respectively in the mutant of pcDNA3-Sj23 group, which were higher than those in the pcDNA3-Sj23 plasmid group (33.1% and 28.9% respectively). The difference between these two groups was significant (P<0.05). CONCLUSION: The modified Sj23DNA without the homologous sequence of ME491 induces higher protection against Schistosoma japonicum infection in mice than that of Sj23DNA.