Protective Efficacy Induced by Virus-like Particles Expressing Dense Granule Protein 5 of Toxoplasma gondii

<b>Background:</b><i>Toxoplasma gondii</i> (<i>T. gondii</i>) causes severe disease in immunocompromised individuals and pregnant women, underscoring the urgent need for effective vaccines against toxoplasmosis. The dense granule protein 5 (GRA5) of <i>T. gondii</i> plays a key role in parasitic cyst formation. <b>Methods:</b> This study evaluated the protective immune responses induced by a virus-like particle (VLP) vaccine expressing the <i>T. gondii</i>-derived antigen GRA5 in a mouse model challenged with the ME49 strain of <i>T. gondii</i>. GRA5 VLPs were generated using a baculovirus expression system, and VLP formation was confirmed by Western blotting and visualized using transmission electron microscopy. Mice were intranasally immunized with GRA5 VLPs three times at 4-week intervals to induce immune responses, followed by infection with <i>T. gondii</i> ME49. <b>Results:</b> Intranasal immunization with GRA5 VLPs induced parasite-specific IgG antibody responses in the serum and both IgG and IgA antibody responses in the brain. Compared to the non-immunized group, immunized mice exhibited significantly higher levels of germinal center B cells and antibody-secreting cell responses. Moreover, the VLP vaccine suppressed the production of IFN-γ and IL-6 cytokines, leading to a significant reduction in brain inflammation and decreased cyst counts following lethal challenge with <i>T. gondii</i> ME49 infection. <b>Conclusion:</b> These findings suggest that the GRA5 VLP vaccine derived from <i>T. gondii</i> elicits a protective immune response, highlighting its potential as an effective vaccine candidate against toxoplasmosis.