Protective effects of immunization with a recombinant cyst antigen in mouse models of infection with Toxoplasma gondii tissue cysts.

A portion of the major Toxoplasma gondii tissue cyst antigen (MAG1) was expressed in bacteria as a fusion to glutathione S-transferase (GST) and the purified fusion protein (rMAG1) was used to immunize mice in an attempt to induce protective immunity against challenge with live cysts from the T. gondii ME49 strain. Sixty percent of mice immunized with rMAG1 and challenged with 500 cysts of the T. gondii ME49 strain survived, while only 20% of mice immunized with GST alone survived, suggesting a protective effect specific to the MAG1 portion of the recombinant protein. In a model of chronic infection with ME49 cysts, rMAG1-immunized mice had significantly fewer cerebral cysts and reduced inflammation in the brain compared with mice immunized with GST alone.