Protective immunity induced by a native Toxoplasma gondii antigen against Toxoplasma infection in Balb/c mice

The vaccine development towards Toxoplasma gondii, a parasitic protozoan is an elusive goal. Our objective was to investigate the immunogenic and protective effects of a native T. gondii antigen in BALB/c mice. Balb/c mice were immunized by injecting T. gondii native antigen subcutaneously three times, one-week interval between each injection. The serum levels of anti-T. gondii IgG, IgG subclass antibodies, IFN-γ, and IL-10 were quantified using ELISA. In a challenge, immunized mice with target antigen were given a lethal dose of RH strain of T. gondii tachyzoites; the number of surviving mice was counted. The target antigen was identified in tachyzoite antigenic extract at 44-kDa molecular mass using western blotting. The 44-kDa antigen was isolated and partial characterized as protein. The immunized mice exhibited significant (p < 0.05) elevated levels of specific anti-T. gondii IgG, IgG1 and IgG2a antibodies compared to control groups. Furthermore, the 44-kDa antigen significantly (p < 0.001) stimulates the synthesis of IFN-γ, as well as IL-10 indicating the native antigen might elicit immune responses of both Th1 and Th2 types. Furthermore, immunized BALB/c mice displayed prolonged survival time up to 12 days against lethal challenge with T. gondii RH strain in comparison with non-immunized controls. In conclusion, immunization of BALB/c mice with 44-kDa native antigen generates immunoprotective responses against T. gondii infection and increases survival time. The 44-kDa antigen may have the potential as a promising candidate vaccine against T. gondii infection and further investigations based on recombinant target protein will be performed.