immunogenicity of gamma-irradiated toxoplasma gondii tachyzoites in mice

the immunogenicity of γ-irradiated tachyzoites of a highly virulent strain of toxoplasma gondii (rh strain) was investigated. immunized mice survived challenge infection and displayed increased interferon gamma (inf-γ ) production. on the other hand, nonimmunized controls died after 10 days and displayed a significantly decreased lymphoproliferative response to concanavalin a (con a). no tachyzoites were detected in peritoneal exudates of the immunized mice 10 days after challenge. these results indicate that the vaccination with γ-irradiated tachyzoites not only protects the mice against challenge infection, but may circumvent the danger of the vaccine being life-threatening because of remaining tachyzoites inside macrophages posing as a latent infection.