Enhancement of protective immune response to recombinant Toxoplasma gondii ROP18 antigen by ginsenoside Re

Toxoplasma gondii, the etiological agent of toxoplasmosis, is an obligate intracellular protozoan parasite that infects a variety of mammals including humans. In an attempt to find new antigen-adjuvant combinations that enhance the immunogenicity of antigen candidates for toxoplasma vaccines, we analyzed the potent protection in mice immunized with recombinant protein ROP18 when co-administered with ginsenoside Re, a most important component isolated from Panax ginseng. All immunized mice produced specific anti-rROP18 immunoglobulins, with high levels of IgG antibody and a mixed IgG1/IgG2a response, with predominance of IgG1 production. The cellular and humoral immune responses were associated with the production of IFN-γ and IL-4 cytokines respectively. Vaccinated mice displayed a significantly increased survival time compared with control mice which died within 6 days of challenge with RH strain. Our data demonstrate that by addition of ginsenoside Re, the rROP18 triggered a stronger humoral and cellular response against T. gondii, and that Re is a promising vaccine adjuvant against toxoplasmosis, deserves further evaluation and development.