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High resolution of Trypanosoma cruzi amastigote antigen in serodiagnosis of different clinical forms of Chagas' disease.

Department of Immunology and Serology, Institute Adolfo Lutz, São Paulo University, Brazil.

ABSTRACT

The serodiagnosis of Chagas' disease, a highly prevalent disorder in South American countries, is usually made by the detection of antibodies to Trypanosoma cruzi epimastigote antigen. In this study, we assess the diagnostic performance of the immunofluorescence test with T. cruzi (Y strain) amastigote antigen from an LLC-MK2-infected cell supernatant in comparison with a test with the conventional epimastigote antigen. A total of 238 serum samples from patients in the acute and chronic phases of the disease, with the chronic indeterminate, cardiac, and digestive forms, and from nonchagasic individuals were tested for the presence of immunoglobulin G (IgG), IgM, and IgA antibodies. The reactivity of the amastigote antigen in terms of geometric mean titers was 2 to 4 times higher than that of the epimastigote antigen. Clear-cut results were obtained with the amastigote antigen, with no overlapping of true and false positives. IgG antibodies to amastigotes were found in all patients with Chagas' disease, whereas all sera from nonchagasic patients were negative, except for those from patients with visceral leishmaniasis, in which 63% cross-reactivity was observed. IgM antibodies to amastigotes were detected in 100% of sera from patients with acute Chagas' disease and in 7.5% of sera from patients with chronic Chagas' disease, whereas IgA antibodies were found in 60% of sera from patients in the acute phase and in 33% of sera from patients in the chronic phase. Despite the cross-reactivity observed with sera from visceral leishmaniasis patients, the IgG immunofluorescence test with the amastigote antigen had the highest sensitivity, specificity, and efficiency. No relationship was observed between the class-specific antibodies or their titers and the clinical forms of patients in the chronic phase. Amastigotes from the cell culture supernatant proved to be useful as an alternative antigen to epimastigotes because of their high resolution in the serodiagnosis of Chagas' disease.

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