[Enhancement of the protective effect of SjC23 DNA vaccine against Schistosoma japonicum infection by immunostimulatory sequence].
OBJECTIVE
To investigate the effect of immunostimulatory sequence on SjC23 DNA vaccine against Schistosoma japonicum infection.


METHODS
SjC23 gene fragment was inserted into pcDNA3. 1-CpG to construct pcDNA3.1-SjC23/CpG. BALB/c mice in 4 groups were immunized intramuscularly 3 times at 2 week intervals, with 100 microg plasmid DNA per injection. Four weeks after the 3rd immunization, all mice were challenged with 45 +/- 1 cercariae of S. japonicum by abdominal skin penetration. After 45 days post-challenge, mice were perfused and the number of recovered worms and of eggs in liver was counted. Blood samples were collected from the tail vein of all mice 2 days before the 1st immunization and before challenge respectively. IgG, IgG1 and IgG2a in sera were detected. Three weeks after the 3rd inoculation, the spleen cells of 2 mice from each group were cultured and stimulated with ConA and recombinant peptide. The supernatant was collected to detect IL-2, IL-4 and IFN-gamma. Simultaneously, the cytotoxic activity was detected with 51Cr release assay in vitro.


RESULTS
The worm reduction rate in SjC23 group and SjC23/CpG group was 28.1% and 35.1%, the hepatic egg reduction rate was 21.6% and 26.5%, respectively, compared with the control group. The level of protection in SjC23/CpG group was higher than that in SjC23 group (P<0.05). ELISA results indicated that mice immunized with pcDNA3.1-SjC23 and SjC23/CpG produced specific IgG to rSjC23, while mice immunized with pcDNA3.1 and pcDNA3.1-CpG did not. Mice in SjC23 group and SjC23/CpG group also produced IgG1 and IgG2a antibody isotypes, with the ratio of IgG2a/IgG1 10.1 and 12.2, respectively. In comparison with the control, the level of IL-2 and IFN-gamma in mice immunized with pcDNA3.1-SjC23 and pcDNA3.1-SjC23/CpG was augmented. The cytotoxic activity of spleen cells from mice in SjC23/CpG group was augmented from 9.7% to 40.0% compared with that in SjC23 group.


CONCLUSIONS
The study indicates that immunostimulatory sequence appears to increase the level of protection induced by immunization with pcDNA3.1-SjC23 vaccine.
Zhao
Song
S
Jiangsu Institute of Parasitic Diseases, Wuxi 214064, China.
Zhu
Yin-chang
YC
Harn
Donald A
DA
Si
Jin
J
Ren
Jian-gong
JG
Yin
Xu-ren
XR
He
Wei
W
Liang
You-sheng
YS
Xu
Ming
M
Xu
Yong-liang
YL
D000276:Adjuvants, Immunologic; D000818:Animals; D000909:Antibodies, Helminth / Q000097:blood; D000947:Antigens, Helminth / Q000276:immunology*; D018899:CpG Islands / Q000276:immunology; D005260:Female; D015801:Helminth Proteins / Q000276:immunology*; D007074:Immunoglobulin G / Q000097:blood; D007376:Interleukin-2 / Q000097:blood; D008565:Membrane Proteins / Q000276:immunology*; D051379:Mice; D008807:Mice, Inbred BALB C; D012549:Schistosoma japonicum / Q000276:immunology*; D012554:Schistosomiasis japonica / Q000517:prevention & control; D013154:Spleen / Q000276:immunology; D019444:Vaccines, DNA / Q000276:immunology*
D000276:Adjuvants, Immunologic; D000909:Antibodies, Helminth; D000947:Antigens, Helminth; D015801:Helminth Proteins; D007074:Immunoglobulin G; D007376:Interleukin-2; D008565:Membrane Proteins; D019444:Vaccines, DNA; C072633:Sj23 antigen, Schistosoma japonicum