Immune responses against Schistosoma japonicum after vaccinating mice with a multivalent DNA vaccine encoding integrated membrane protein Sj23 and cytokine interleukin-12.
BACKGROUND
The vaccination of mice with DNA encoding single candidate antigens has failed to induce significant protection against Schistosoma japonicum (S. japonicum) challenge infections. In this study, we evaluated the feasibility of using a multivalent DNA vaccine which co-expressed S. japonicum integral membrane protein Sj23 and murine cytokine IL-12 to induce protective immune responses.


METHODS
The plasmid pVIVO2-IL12-Sj23, a eukaryotic expression vector expressing Sj23 and murine IL-12 simultaneously, was constructed, identified, and tested for expression in vitro. Its ability to protect against S. japonicum challenge infections was analyzed according to worm reduction rate and egg reduction rate after vaccination of BALB/c mice. The serum levels of specific IgG antibody were determined by enzyme-linked-immuno sorbent assay (ELISA) and Western blot analysis. Using cultured spleen cells, IFN-gamma and IL-4 post-stimulation were quantified by ELISA. The phenotypes of splenocyte populations were analyzed by flow cytometry (FCM).


RESULTS
The plasmid DNA pVIVO2-IL12-Sj23 was proven to express well in vitro by transient transfection of HEK-293 cells. Immunization resulted in a worm reduction rate of 45.53% and egg reduction rate of 58.35%. ELISA and Western blot analysis indicated that immunized mice generated specific IgG against Sj23. Spleen cells showed significant increases in IFN-gamma but decreases in IL-4. No significant differences in CD4+ and CD8+ subgroup ratios were observed after the challenges.


CONCLUSIONS
The multivalent DNA vaccine pVIVO2-IL12-Sj23 is sufficient to elicit moderate but highly significant levels of protective immunity against challenge infections. Cytokine IL-12, as a gene adjuvant, was able to enhance the Th1 responses and, hence, the protective immunity.
Gan
Yan
Y
Department of Parasitology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China.
Shi
You-en
YE
Bu
Ling-yi
LY
Zhu
Xiao-hua
XH
Ning
Chang-xiu
CX
Zhu
Hong-gang
HG
D000818:Animals; D000909:Antibodies, Helminth / Q000097:blood*; D000947:Antigens, Helminth / Q000235:genetics* / Q000276:immunology; D016516:CD4-CD8 Ratio; D016207:Cytokines / Q000096:biosynthesis; D015801:Helminth Proteins / Q000235:genetics* / Q000276:immunology; D018664:Interleukin-12 / Q000235:genetics* / Q000276:immunology; D008297:Male; D008565:Membrane Proteins / Q000235:genetics* / Q000276:immunology; D051379:Mice; D008807:Mice, Inbred BALB C; D012549:Schistosoma japonicum / Q000276:immunology*; D018417:Th1 Cells / Q000276:immunology; D014611:Vaccination; D019444:Vaccines, DNA / Q000276:immunology*
D000909:Antibodies, Helminth; D000947:Antigens, Helminth; D016207:Cytokines; D015801:Helminth Proteins; D008565:Membrane Proteins; D019444:Vaccines, DNA; C072633:Sj23 antigen, Schistosoma japonicum; D018664:Interleukin-12