Assessment of the immunogenicity and protective efficiency of a novel dual-promoter DNA vaccine, harboring SAG1 and GRA7 genes, from RH strain of Toxoplasma gondii in BALB/c mice

摘要

Background: Toxoplasmosis, a protozoan parasitic disease caused by Toxoplasma gondii , has been a serious human and veterinary medicine problem with global distribution. In the current study, we assessed immunogenicity and protective efficiency of a novel dual-promoter DNA vaccine, harboring SAG1 and GRA7 genes, from RH strain of Toxoplasma gondii ( T. gondii ) with or without CpG-ODN as adjuvant in a murine model. Methods: BALB/c mice were immunized intramuscularly with pVitro-SAG1-GRA7 alone and pVitro-SAG1-GRA7 with CpG-ODN three times at three-week intervals. Enzyme-linked immunosorbent assay (ELISA) was used to assess total IgG, IgG1 and IgG2a antibodies and gamma interferon (IFN-γ) and interleukin-10 (IL-10) cytokines in mice sera. Four weeks post final vaccination, MTT assay and lethal challenge-infection with 1×10sup3/sup tachyzoites of T. gondii RH strain were carried out to assess stimulation index (SI) and mice survival time, respectively. Results: The IgG levels in mice immunized with multicomponent vaccines, including pVitro-SAG1–GRA7 alone and pVitro-SAG1–GRA7 with CpG-ODN, were significantly higher than those in control mice or single-gene DNA-vaccinated ones ( P 0.05). Furthermore, level of IgG2a in mice receiving pVitro-SAG1–GRA7 with CpG-ODN was significantly higher than that in mice receiving pVitro-SAG1-GRA7 alone ( P 0.05). The Toxoplasma lysate antigen (TLA)-stimulated lymphocytes from pVitro-SAG1-GRA7 with CpG-ODN group responded more dramatically than those from control groups or single-gene DNA-vaccinated groups ( P 0.001). The pVitro-SAG1-GRA7 with CpG-ODN-vaccinated mice developed high levels of IgG2a and IFN-γ ( P 0.001) and low levels of IgG1 and IL-10, compared to control groups, suggesting a modulated immune response type Th1. In addition, survival time of the mice immunized with pVitro-SAG1-GRA7 with CpG-ODN was significantly extended, compared to controls ( P 0.05); however, all mice died. Conclusion: The multivalent pVitro-SAG1-GRA7 DNA vaccine with CpG-ODN adjuvant is a promising vaccine candidate against toxoplasmosis.