Chagas' disease: polyspecificity of antibodies against Trypanosoma cruzi acidic antigens

The aim of this work was to study the reactivity of chagasic patient sera against a panel of natural antigens and its relationship with the immune response against T. cruzi acidic antigens. The presence of IgG and IgM antibodies reactive with myosin, myoglobin, actin and thyroglobulin was investigated in sera with positive serology for Chagas' disease classified into groups (G) I, n = 7, with normal electrocardiogram (ECG) and no signs or symptoms of the disease; GII, n = 7, with ECG abnormalities but without cardiomegaly and GIII, n = 7, with cardiomegaly and congestive heart failure. Healthy individual sera were analyzed in parallel as controls. In the three groups of chagasic patients, a high proportion of sera exhibited an enhancement of IgG response anti actin ranging from 71 to 100%. IgM against this antigen was found positive in GI, 21%; GII and GIII, 57%. The antibodies binding to myosin and myoglobin were mainly of IgM type. When myosin was assayed, the frequency of reactive sera was gradually diminished as heart involvement increased: GI 57%, GII 28% and GIII 14%. Only IgG antibodies against thyroglobulin were detected in the three groups of chagasic patients ranging from 43 to 86%. IgG natural antibodies showed to be polyreactive, since a diminished reactivity against each one of the natural antigens assayed and against T. cruzi acidic antigens (FIV) was observed in the sera absorbed with any of the selected antigens irrespective of the absorbing ones. Moreover, the antibodies against FIV parasite's antigens purified by immunoabsorption showed a similar reactivity with FIV, myosin and actin, and a slight lower reactivity with thyroglobulin. These results indicate that in chagasic patients, the specific humoral response against FIV is associated with an increase of the natural autoantibodies along with their polyspecificity.