Abstract
BackgroundIntracellular parasites, such as T. gondii, present a plurality of antigens because of the complexity of its life cycle. Compound DNA vaccines bring a new approach and hope for the treatment of toxoplasmosis. In this study, a DNA vaccine encoding two major surface antigens SAG1, SAG3 from T. gondii, with A2/B subunit of cholera toxin as a genetic adjuvant was constructed.MethodsBALB/c mice were immunized intramuscularly with PBS, pcDNA3.1, pSAG1, pSAG1/SAG3 and pSAG1/SAG3-CTXA2/B three times separately. Immunized mice were tested for IgG antibody and IFN-γ and IL-4 production by ELISA. The proliferation of T cells was measured by DNA synthesis assay and the lymphocyte subsets of spleen cells by flow cytometry. All the immunized mice were challenged with 103 highly virulent RH tachyzoites of Toxoplasma gondii intraperitoneally and the survival times were recorded.ResultsAn enhanced production of IgG antibodies, antigen-specific lymphocyte proliferation and IFN-γ production from splenic cells were induced in mice immunized with pSAG1/SAG3 compared to mice immunized with pSAG1 (P<0.05). Introduction of CTXA2/B further enhanced the Th1 cell-mediated immunity with higher levels of IFN-γ, lymphocyte proliferation activity and percentage of CD8+ T-cells. When challenged with lethal doses of T. gondii (1×103), all control mice (PBS and empty plasmid group) died within 6 days. Mice immunized with pSAG1 died within 8 days. While 20% and 40% survival rate were achieved from mice immunized with pSAG1/SAG3 and pSAG1/SAG3-CTXA2/B.ConclusionsThis study indicates the compound DNA vaccine encoding T. gondii antigens SAG1, SAG3 with CTXA2/B gene was a promising DNA vaccine candidate against toxoplasmosis, which could effectively enhance the humoral and cellular immune response and prolong survival time in vaccinated mice.
Highlights
Intracellular parasites, such as T. gondii, present a plurality of antigens because of the complexity of its life cycle
Plasmid construction and in vitro expression of compound genes The recombinant plasmids pSAG1, pSAG1/SAG3 and pSAG1/SAG3-CTXA2/B with the correct insert orientation were detected by restriction enzyme analysis and PCR
PSAG1, pSAG1/SAG3 and pSAG1/SAG3-CTXA2/B plasmids transfection bands were at 786bp, 1278bp, 1790bp respectively, which proved all the genes could be expressed in HeLa cells
Summary
Intracellular parasites, such as T. gondii, present a plurality of antigens because of the complexity of its life cycle. Prevalence of T. gondii infection increased by 7% during the past ten years in China [1]. This parasite is of major medical importance, being a cause of congenital disease and abortion [2]. Compound polyvalent DNA vaccines bring about a new approach and hope for T. gondii. Because complex intracellular parasites, such as T. gondii, present a plurality of antigens and as the antigen presentation capability varies widely among different individuals, immunization with a vaccine that includes a broad array of antigens is likely to be more efficacious than a single antigen
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