Protective efficacy of Toxoplasma gondii bivalent MAG1 and SAG1 DNA vaccine against acute toxoplasmosis in BALB/c mice

Background: Toxoplasma gondii is capable of infecting a wide range of warm-blooded animals, causing a worldwide epidemic of zoonotic toxoplasmosis. SAG1 protein is expressed at the proliferative tachyzoite stage, whereas MAG1 is expressed at the bradyzoite and tachyzoite stages. These two proteins display protective roles in previous studies, however, there synergetic protective efficacy as a DNA vaccine against toxoplasmosis has not been clarified. Methods: : In this study, we amplified TgMAG1 and TgSAG1 genes and inserted into eukaryotic expression vector pcDNA3.1(+). The pcDNA3.1(+)-TgMAG1 (pMAG1), pcDNA3.1(+)-TgSAG1 (pSAG1), pcDNA3.1(+)-TgMAG1-TgSAG1 (pMAG1-SAG1) plasmids were transfected into HEK-293 cells and each protein was verified in vitro through western blot. Then, mice were intramuscularly immunized with pMAG1, pSGA1 or pMAG1-SGA1, and anti- T. gondii IgG levels were measured in the serum. Cytokines levels of IL-4, IL-10 and IFN-γ in mice splenocytes culturing supernatants were measured using commercial ELISA kits. Immunized mice were challenged with T. gondii tachyzoites with lethal doses followed by determination of mortality, whereas mice infected with low dose tachyzoites followed by monitoring the parameters of survival rate and parasites burden analysis of brains and livers. Results: : The pMAG1, pSGA1 or pMAG1-SGA1 exhibited well reactogenicity with expected band sizes of 17.843 kDa, 15.572 kDa, 33.415 kDa, respectively. The immunized mice triggered significantly high levels of anti- T. gondii IgG antibodies in comparison with that in the negative control groups, moreover pMAG1-SGA1 immune achieved the highest levels. The DNA vaccines also led to obvious IFN-γ release from splenocytes culturing supernatants, whereas had no role in the IL-4 and IL-10. The protective efficacy results showed that DNA vaccines immunization prolonged the acute infection mice survival time to 14 d, 16 d, 32 d. Consistently, the liver and brain parasites in each immunization group were significantly reduced comparing with PBS control group. Conclusions: : This study revealed that bivalent TgMAG1 and TgSAG1 DNA vaccine displayed excellent protective immunity against toxoplasmosis in mice. These data provide new sight into the development of Toxoplasma gondii vaccines.