Resistance to Trypanosoma cruzi induced by immunization with antigens isolated by affinity chromatography

The objective of this study was to determine whether antigens of Trypanosoma cruzi that are recognized by antibodies in sera of chronically infected animals and thus capable of being purified by affinity chromatography would be more efficient than non-purified antigens in inducing resistance against the parasite. Epimastigote stage antigens were isolated from a lysate of the organisms by affinity chromatography with IgG antibodies prepared from serum of rabbits chronically infected with T. cruzi. The antibodies strongly agglutinated epimastigotes, and mice passively transferred with them had lower parasitemia and longer survival times than controls. The presence of antigens in the fractions eluted from the antibody affinity column was demonstrated by an enzyme immunoassay. Mice were immunized with the isolated antigens either alone or mixed with Freund's incomplete adjuvant. All immunized animals formed antibodies to T. cruzi as demonstrated by the indirect immunofluorescent antibody test. Challenge with blood trypanosomes revealed that mice immunized with antigens mixed with Freund's incomplete adjuvant had lower parasitemia than mice immunized with antigens alone or controls. At 17 days of infection, mortality of controls was 100% vs 80% for mice immunized with affinity-isolated antigens in PBS and 45% for mice immunized with affinity-purified antigens mixed with Freund's incomplete adjuvant. Fifty-five percent of the mice immunized with affinity-purified antigens in incomplete Freund's adjuvant were still alive 45 days after infection, with no parasitemia detectable by microscopy. The immunization procedure, however, did not prevent multiplication and invasion of tissues by the parasites, since all immunized animals developed patent parasitemia and spleen parasitism at some point during the infection.