Protective immunity against Toxoplasma gondii in mice induced by the SAG2 internal image of anti-idiotype antibody

A monoclonal antibody TGCM5 (isotype G, subclass 1, κ light chain) against SAG2, a major surface antigen of Toxoplasma gondii tachyzoites, was produced in quantity and its Fab-containing idiotype (Id) was injected into rabbits for production of rabbit anti-Id sera. The rabbit anti-Id IgG (aId-IgG) with a SAG2 internal image was obtained by purification with a protein A column. Significant lymphocyte proliferation induced by tachyzoite lysate antigen was observed in BALB/c mice that received two injections of aId-IgG, but not in non-immunized control mice. Large amounts of γ interferon were detected in supernatants of splenocyte cultures prepared from mice immunized with aId-IgG. Of the mice immunized with aId-IgG, 75–87.5% survived at least 28 days after a lethal challenge of 1×103 live tachyzoites, which killed all non-immunized control mice within 10 days. The results showed that the SAG2 internal image presented by aId-IgG indeed elicited a protection against the infection of T. gondii in mice.