The protective immunity produced in infected C57BL/6 mice of a DNA vaccine encoding Schistosoma japonicum Chinese strain triose-phosphate isomerase

The development of a SjCTPI DNA vaccine for Schistosoma japonicum and the detection of the immune responses to and the protective efficacy of immunization were performed and challenged in C57BL/6 mice. According to the gene sequence of SjCTPI and murine IL-12, three pairs of primers were designed. The full length cDNA encoding SjCTPI and P35, P40 amplified from pUC19-SjCTPI and murine IL-12 by PCR were subcloned into an eukaryotic expression vector (pcDNA3.1). Forty-five female C57BL/6 mice were divided into three groups; each mouse of the control group was injected with 100 pg of pcDNA3.1 by i.m. route; the TPI group was injected with 100 microg of pcDNA3. 1-SjCTPI; the TPI+IL- 12 group was injected with 100 microg of pcDNA3.1-SjCTPI and 100 pg of mixture of pcDNA3.1-P35 and pcDNA3.1-P40. Each mouse was immunized at weeks 1 and 5 and challenged with 45 cercariae of Schistosoma japonicum Chinese strain at week 9. The mice were killed and perfused 45 days after challenge; the numbers of recovered worms and hepatic eggs were counted. The expression of SjCTPI in muscle tissue was determined by an immunohistochemical method. Culture of spleen cells showed the production of IL-2, IL-4, IL-10 and IFN-gamma with the stimulation of specific antigen before and after challenge. Sera were collected from each group before immunization, before challenge and two weeks post challenge; ELISA and Western-blot tests were performed for detection of anti-rTPI antibodies. The antigen of SjCTPI was expressed in the membrane and plasma of the muscle cells of C57BL/6 mice. The obvious rising of IL-2 in TPI group and TPI+IL-12 group before and after challenge was seen. The anti-rTPI antibody detection with Western-blot showed that ten serum samples from the control group were negative; nine of ten serum samples from the TPI group were weakly positive, eight of ten from the TPI+IL-12 group were weakly positive. The worm and egg reduction rates of TPI group and TPI+IL- 12 group were 27.9% and 13.7%, 31.9% and 18.6% respectively in comparison with the pcDNA group. pcDNA3.1-TPI DNA vaccine could confer partial protection against a subsequent challenge of Schistosoma japonicum in C57BL/6 mice and might therefore be a potential DNA vaccine.