DNA immunization with eukaryotic initiation factor-2α of Toxoplasma gondii induces protective immunity against acute and chronic toxoplasmosis in mice

• Vaccination with Toxoplasma gondii IF2α DNA vaccine induced specific humoral and cellular responses.
• Significant production of IFN-γ and IL-2 associated with Th1 type response was observed.
• Immunization resulted in a significantly prolonged survival time (15.9 ± 4.6 days) of immunized mice.
• Significant reduction in brain cyst reduction (44.1%) against chronic infection was observed.
• T. gondii IF2α is a potential vaccine candidate against both acute and chronic T. gondii infection.

Toxoplasma gondii infection is a serious health problem of humans and animals worldwide. T. gondii eukaryotic initiation factor-2α (TgIF2α) plays a crucial role in parasite viability and is an important virulence factor of T. gondii. To evaluate the vaccine potential of TgIF2α, we constructed a novel eukaryotic plasmid pVAX-IF2α expressing TgIF2α from the RH strain and validated expression and immunogenicity in vitro in the Marc145 cell expression system by indirect immunofluorescence (IFA). Administration of pVAX-IF2α intramuscularly induced specific humoral immune responses including high levels of specific TgIF2α IgG antibody and a mixed IgG1/IgG2a response with a predominance of IgG2a production. The cellular immune response was elicited, showing significant production of IFN-γ and IL-2 associated with Th1 type response, and thus strong cell-mediated cytotoxic activity with increased frequencies of IFN-γ parameters analyzed in both CD4+ and CD8+ T cell compartments (CD4+ IFN-γ+ T cells and CD8+ IFN-γ+ T cells). Immunization resulted in partial protection against acute and chronic toxoplamosis in outbred Kunming mice, demonstrated by a significantly prolonged survival time (15.9 ± 4.6 days) after challenge with the virulent RH strain and significant reduction in brain cysts (44.1%) against chronic infection with PRU cyst in contrast to control mice. Our data suggested that pVAX-IF2α could be used as a DNA vaccine candidate against both acute and chronic T. gondii infection by the activation of effective humoral and cellular immune responses.