Evaluation Of Protective Immune Responses Induced By DNA Vaccines Encoding Toxoplasma Gondii Surface Antigen1(SAG1) And14-3-3Protein In BALB/c Mice

Toxoplasmosis, caused by an obligate intracellular protozoan parasite Toxoplasma gondii, has been a serious clinical and veterinary problem. Effective DNA vaccines against T. gondii can prevent and control the spread of toxoplasmosis, which is important for both human health and the farming industry. There was10-20million people infected with T. gondii in the world. T. gondii infection is usually asymptomatic, which can cause obsessive-compulsive disorder (OCD), schizophrenia, depression, Alzheimer’s disease, Parkinson’s disease, etc. In recent years, DNA vaccines against T. gondii have been well developed and received considerable attention and are a good option for this ubiquitous parasite. The T. gondii14-3-3protein has been proved to be antigenic and immunogenic and was a potential vaccine candidate against toxoplasmosis. In this study, we evaluated the immune responses induced by recombinant plasmids encoding T. gondii surface antigen1(SAG1) and14-3-3protein by immunizing BALB/c mice intramuscularly.Objective: In this study, we constructed three eukaryotic plasmids,pBudCE4.1-SAG1, pBudCE4.1-14-3-3and pBudCE4.1-SAG1/14-3-3, to examine humoral and cellular immune responses elicited by14-3-3and SAG1protein in BALB/c mice. The aim of this study was to evaluate the potential of T. gondii14-3-3protein as a vaccine candidate antigen, demonstrate the immune protective efficacy elicited by SAG1gene and compare the immunological effect between single-gene and multi-gene vaccines. Methods:In the present study, BALB/c mice were randomly divided into five groups, including three experimental groups (pSAG1,p14-3-3and pSAG1/14-3-3) and two control groups (PBS and pBudCE4.1), and were immunized intramuscularly three times. The levels of IgG antibodies and cytokine production in mouse sera were determined by enzyme-linked immunosorbent assays (ELISA). Two weeks after the last immunization, all mice were challenged intraperitoneally (i.p.) with1×104tachyzoites of T. gondii and the survival time of mice was observed and recorded everyday.Results: Mice vaccinated with pSAG1, p14-3-3or pSAG1/14-3-3developed high levels of IgG2a and gamma interferon (IFN-γ) and low levels of interleukin-4(IL-4) and interleukin-10(IL-10) compared to control groups (PBS or pBudCE4.1), which suggested a modulated Thl type immune response (P<0.05). After intraperitoneal challenge with1×104tachyzoites of T. gondii (RH strain), the survival time of mice in experimental groups was longer than control groups (P<0.05). Mouse immunized with pSAG1/14-3-3induced a higher level of IgG antibody response and significantly prolonged the survival time when compared with pSAGl or p14-3-3(P<0.05).Conclusions: The study suggested that T. gondii14-3-3protein can induce effective immune responses in BALB/c mice and was a novel DNA vaccine candidate against toxoplasmosis, and the immune protective efficacy elicited by SAG1gene was also demonstrated. Our results also showed multi-gene vaccine significantly enhanced immune responses and protective efficacy and was superior to the single-gene vaccine.