Evaluation of immunogenicity and protective effect of DNA vaccine encoding surface antigenl (SAG1) of Toxoplasma gondii and TLR-5 ligand as a genetic adjuvant against acute toxoplasmosis in BALB/c mice

Aims: Toxoplasma gondii is an obligate intracellular, protozoan that causes a high incidence of serious zoonotic parasitic disease in humans. In the present study the immune-protective efficacy of a DNA vaccine encoding SAG1 in combination with a gene sequence encoding FliC of Salmonella typhimurium (Toll-like receptor 5 agonist) was evaluated against acute T. gondii infection in mice. Methods and results: Ninety-nine female inbred BALB/c mice were divided into nine groups of 11 mice and were immunized intramuscularly three times at three-week intervals (days 0, 21 and 42) and challenged with virulent T. gondii RH strain 4 weeks later. The immunization of pVAX1-SAG1 administered with pVAX1-fliC in mice indicated specific humoral responses, with higher IgG antibody titers and a mixed IgG1/IgG2a response than in other groups (with a predominance of IgG2a over IgG2b and IgG1). Also, the cellular immune response elicited high levels of IFN-gamma and IL-12 cytokines and low levels of IL-4 production compared to traditional adjuvants. Furthermore, the mice vaccinated with pVAX1-SAG1+pVAX1-fliC survived for slightly longer after the last immunization and challenge with the T. gondii. Conclusion: This investigation indicated that cocktail DNA vaccine encoded SAG1 gene of T. gondii and FliC can protect against acute toxoplasmosis.