Partially purified antigen preparations of Toxoplasma gondii protect against lethal infection in mice.

Antigens of Toxoplasma gondii eluted from polyacrylamide gels after electrophoresis under reducing conditions were examined for their capacity to react with antibodies from infected humans, to induce antibody formation, and to protect mice against T. gondii. Antigens with approximate molecular weights of 35,000 and 14,000 strongly reacted in an enzyme-linked immunosorbent assay of human immunoglobulin M (IgM) and IgG antibodies to T. gondii. Mice injected with the eluted antigen preparations formed antibodies that reacted differently in four serological tests for Toxoplasma antibodies. All mice formed antibodies that reacted in the IgG and IgM enzyme-linked immunosorbent assay. Antibodies reacting in the conventional indirect immunofluorescent antibody test were detected in all mice except those injected with low-molecular-weight (14,000 or less) antigens. Sabin-Feldman dye test antibodies were not detected in any of the mice. Antibodies reacting in the latex agglutination test were detected mainly in mice injected with antigens with an approximate molecular weight of 66,000. Challenge of the injected mice with a lethal inoculum of T. gondii revealed that the highest survival rate was in animals that received antigens with approximate molecular weights of 35,000 and 14,000.