Use of antigen preparations of the amastigote stage of Trypanosoma cruzi in the serology of Chagas' disease.

Antigens derived from the amastigote or the epimastigote stages of Trypanosoma cruzi and prepared by sonication or formalinization were examined and compared in the immunofluorescent antibody (IFA) test and enzyme-linked immunosorbent assay (ELISA) for the detection of antibodies to the parasite in sera of infected humans. The results revealed that antigens derived of amastigotes from cell cultures can be used for the detection of antibodies to T. cruzi in both tests. In the IFA test, 46.3% of the sera had higher titers with amastigote antigens, 41.5% had equal titers with antigens from both stages, and 12.2% had higher titers with epimastigote antigens. In the ELISA, 43.9% had higher titers with amastigote antigens, 43.9% had equal titers with antigens of both stages and 12.2% had higher titers with the epimastigote antigens. The differences in titers, however, were not of a magnitude sufficient to indicate a higher sensitivity for the amastigote antigens. The ELISA was performed successfully with formalinized or sonicated organisms of both stages. The use of formalinized parasites introduces a new advantage over previously reported ELISA methods. Formalinized antigens are easier to prepare and can be stored for prolonged periods of time at 4 degrees C. The reason for the higher titers with amastigote antigens was examined by using 125I-labeled antigens to determine the binding of antigens to the plastic solid-phase used in the ELISA and to compare the antigens of each stage that could be immunoprecipitated by antibodies to T. cruzi. The ability of amastigote antigens to bind to the plastic solid phase appeared to be slightly higher than that of epimastigote antigens although the differences were not statistically significant. On the other hand, the amount of antigens in the amastigote preparation immunoprecipitated by antibodies in 6 of 10 sera examined was higher than the amount of antigens in the epimastigote preparation immunoprecipitated by antibodies in the same sera. In two sera the amount was similar, and in the remainder more antigens in the epimastigote antigen preparation were immunoprecipitated. These results are of interest and may suggest clinical implications.