Vaccination against Schistosoma japonicum infection by DNA vaccine encoding Sj22.7 antigen

To observe the in vitro expression of DNA vaccine pcDNA3-Sj22.7 and its immunological effect in mice, the recombinant plasmid pcDNA3-Sj22.7 was used to transfect HeLa cells with liposome-mediated method and the expression of Sj22.7 mRNA and protein was examined using reverse transcription-polymerase chain reaction, sodium dodecylsulfate-polyacrylamide gel electrophoresis and Western blot. Then, the ability of pcDNA3-Sj22.7 to protect against Schistosoma japonicum challenge infections was analyzed according to worm reduction rate and egg reduction rate after vaccination of mice. The serum levels of specific IgG antibody and T lymphocyte proliferation response were also determined. After the challenge infection, Sj22.7-driven interferon (IFN)-gamma and interleukin (IL)-4 was also quantified. Results showed that pcDNA3-Sj22.7 could express Sj22.7 mRNA and protein in vitro. Immunization resulted in a worm reduction rate of 29.70%, egg reduction rate of 47.25% (liver) and 51.73% (intestine), and egg reduction rate of 25.90% (eggs per female), suggesting induction of significant anti-fecundity in the pcDNA3-Sj22.7 group. Enzyme-linked immunosorbent assay and Western blot analysis indicated that immunized mice generated specific IgG against Sj22.7. T lymphocytes from mice immunized with pcDNA3-Sj22.7 showed a significant proliferation response to rSj22.7. The culture of spleen cells showed that secretion of IFN-gamma increased but IL-4 decreased. The results indicate hat DNA vaccination by pcDNA3-Sj22.7 is sufficient to elicit significant levels of protective immunity against S. japonicum infection. The DNA vaccine could induce significant cellular and humoral immune response, and display predominant T helper cell type 1 type immune responses, which contribute to the protective immunity against challenge infection in mice.