Department of Immunology, Institute of Microbiology, Federal University of Rio de Janeiro, “Dr. A. Castelan” Hospital and Institute of Regional Pathology, Northeast University, (UFRJ), Rio de Janeiro, Brazil
Anti-Trypanosoma cruzi agglutinins were studied by the direct agglutination test (DA) with or without previous treatment of the sera with 2-mercaptoethanol (2-ME) (DA and 2-MEDA, respectively), in serial serum samples obtained from 24 patients with acute Chagas' disease. Their agglutinin titers were compared with those found in 25 patients of similar age with other acute infections and 50 healthy children. All of the controls were negative by complement-fixation test for T. cruzi infection. All sera were also tested by indirect hemagglutination (IHA) and indirect immunofluorescence (IIF) tests, using anti-total human globulin (IIF-Ig) and anti-IgM human globulin (IIF-IgM). In the first serum sample obtained after infection from the chagasic patients, DA and 2-MEDA detected IgM antibodies in seven patients who were also positive by IIF-IgM. However, in 13 early sera from other patients antibodies were demonstrated by IIF-IgM only. Four patients were negative by both techniques. Early serum samples were usually negative in the IHA test. Further samples obtained from those patients in whom the infection became chronic were reactive in the IHA test. In these sera, agglutinin titers were usually not affected by 2-ME treatment, indicating a change in the class of Ig reactivity (from IgM to IgG). This observation was coincident with decreasing titers established by IIF-IgM, whereas antibody titers detected by IIF-Ig remained positive. However, in four patients IIF-IgM antibodies either persisted or reappeared following a period during which they were negative. During the follow-up of four patients in whom serologic reactivity became negative after treatment, antibodies were detected later. In two of these cases a positive IIF-IgM was observed.