Immunization with Trypanosoma cruzi epimastigote antigens incorporated into iscoms protects against lethal challenge in mice.

An immunoglobulin G3 monoclonal antibody obtained by immunizing mice with a cell membrane preparation of epimastigotes of Trypanosoma cruzi was shown to agglutinate live epimastigotes, lyse blood-form trypanosomes, and partially protect mice by passive transfer. The main antigens recognized by the monoclonal antibody were located in the flagella of epimastigotes and blood-form trypanosomes. Antigens of epimastigotes, purified by affinity chromatography with the monoclonal antibody, were shown to be highly glycosylated and revealed a wide band with an Mr between 45,000 and 68,000 in sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting. Immunization of mice with a small concentration of the affinity purified antigens incorporated into an antigen delivery system prepared with Quil A (Isotec AB, Lulea, Sweden), a saponin derivative, induced strong antibody and cell-mediated immune responses and protected 100% of the immunized animals against death due to challenge with 100 100% lethal doses of blood form trypanosomes. Protection was due to the use of the antigen delivery system, since mice immunized with equal concentrations of antigens alone or in combination with saponin had 100% mortality. The results suggest that small concentrations of epimastigote antigens obtained by biochemical methods and incorporated into the proper antigen delivery system may serve as a vaccine against Chagas' disease.