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)‐γ 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‐γ increased but IL‐4 decreased. The results indicate that 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. Edited by Changde LU