Abstract
BackgroundToxoplasmosis caused by the intracellular parasite Toxoplasma gondii (T. gondii) is a global epidemic parasitic disease. DNA vaccines play an important role in preventing the spread of toxoplasmosis. SAG family genes encoding particular surface proteins of T. gondii are the best candidates of DNA vaccine. As a member of SAG family genes, SAG5 gene has been proved to have better antigenic than SAG1. In addition, alpha-Galactosylceramide (α-GalCer) was used to be an adjuvant in malaria vaccine and received positive results. In this study, the effect of the DNA vaccine enhanced by α-GalCer was evaluated by immunizing BALB/c mice.MethodsIn the present study, SAG5D gene of T. gondii was cloned, sequenced, and biologically characterized. BALB/c mice were randomly divided into five groups, including three experimental groups (pEGFP-C1-SAG5D, α-GalCer and α-GalCer/pEGFP-C1-SAG5D) and two control groups (PBS and pEGFP-C1), and were immunized intramuscularly three times. The levels of IgG antibodies and cytokine productions in mouse sera were determined by enzyme-linked immunosorbent assays (ELISA). Two weeks after the last immunization, all mice were challenged intraperitoneally with 1 × 104 tachyzoites of T. gondii and the survival time of mice was recorded.ResultsA significant level of increase of IgG response against the soluble tachyzoite antigens (STAg) was detected by ELISA in experimental group. It revealed relatively high level of IFN-γ production by the spleen cells. There were higher productions of interleukin-4 (IL-4) in α-GalCer treated groups compared to control groups. Challenge experiment showed a longer survival period (11 days compared with 5 days in control) in SAG5D DNA vaccinated mice was found after a lethal challenge with T. gondii RH strain.ConclusionsThe present study suggested that T. gondii SAG5D was a novel and positive DNA vaccine candidate against toxoplasmosis. In addition, the adjuvant (α-GalCer) enhanced the body’s cellular immune response and prolonged the survival time of mice after challenge.Electronic supplementary materialThe online version of this article (doi:10.1186/s12879-014-0706-x) contains supplementary material, which is available to authorized users.
Highlights
Toxoplasmosis caused by the intracellular parasite Toxoplasma gondii (T. gondii) is a global epidemic parasitic disease
Toxoplasmosis caused by the intracellular parasite T. gondii is a global epidemic parasitic disease, and one in three people worldwide were infected by T. gondii in different degrees [1]
ASplenocytes from 4 mice per group two weeks after the final immunization. bValues for IFN-γ at 96 hr, IL-4 at 24 hr, IL-10 at 72 hr are expressed as mean ± SD. *Compared with PBS or pEGFP-C1 group, P < 0.05; #compared with pEGFP
Summary
Toxoplasmosis caused by the intracellular parasite Toxoplasma gondii (T. gondii) is a global epidemic parasitic disease. SAG family genes encoding particular surface proteins of T. gondii are the best candidates of DNA vaccine. As a member of SAG family genes, SAG5 gene has been proved to have better antigenic than SAG1. The effect of the DNA vaccine enhanced by α-GalCer was evaluated by immunizing BALB/c mice. Toxoplasmosis caused by the intracellular parasite T. gondii is a global epidemic parasitic disease, and one in three people worldwide were infected by T. gondii in different degrees [1]. The other three SAG5 subtypes can express corresponding proteins in tachyzoites [18]. As a member of SAG family genes, SAG5 gene may have excellent immunogenicity like SAG1. It is necessary and interesting to construct a SAG5 gene vaccine and examine its immunization
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