Presence of cells producing antiheart autoantibodies in the inflammatory infiltrate of chronic chagasic myocarditis

Etiological treatment of chronic Chagas disease: neglected 'evidence' by evidence-based medicine

No randomized clinical trials regarding the etiological treatment of chronic Chagas disease can be found in the medical literature. However, other 'evidence' sustaining the use of anti-Trypanosoma cruzi drugs for adult individuals with Chagas disease will be analyzed along with the limitations in evaluating the treatment efficacy. Today, the hypothesis of T. cruzi persistence in the target organs giving rise to the chronic inflammatory response is sustained. In addition, several experimental, pathological, nonrandomized clinical studies and studies based on the response or serological evolution (besides the clinical experience) demonstrate the role of T. cruzi in the pathogenesis of the chronic stage and the efficacy of etiological treatment to reduce the titers of antibodies and the progression of chronic Chagas heart disease. All of this supports the recommendation of treatment for every patient diagnosed with Chagas disease. The interpretation of this sum of evidence is not considered from the perspective of evidence-based medicine.

Experimental infection with Trypanosoma cruzi increases the population of CD8(+), but not CD4(+), immunoglobulin G Fc receptor-positive T lymphocytes

It is well established that activating-type Fc receptors for immunoglobulin G (FcgammaR), such as FcgammaRI and FcgammaRIII, are essential for inducing inflammatory responses. On the other hand, a unique inhibitory FcgammaR, FcgammaRIIB, inhibits intracellular signaling upon engagement of immunoglobulin G-immune complexes, suppressing inflammation and autoimmunity. The expression of FcgammaRIIB on B lymphocytes, natural killer cells, macrophages, mast cells, and a number of other cell types has been demonstrated for many years. However, the expression on T lymphocytes is probably restricted to activated cells in a narrow window of time. The controversy regarding the FcgammaR expression on T lymphocytes is attributable to considerable heterogeneity of cellular subpopulations and activation stages during immune responses in vivo. We addressed here this question by using mice experimentally infected with Trypanosoma cruzi, and we found an increase in the CD8(+) FcgammaR(+) population but not in the CD4(+) FcgammaR(+) population. Moreover, CD8(+) FcgammaR(+) T cells predominantly composed the cardiac inflammatory infiltration induced by the infection. These results indicate a novel pattern of FcgammaR expression on T cells in a pathological situation, and possible functional roles of this phenomenon are discussed.

Chagas' disease and the autoimmunity hypothesis

The notion that the pathology of Chagas' disease has an autoimmune component was initially based on the finding of circulating antibodies binding heart tissue antigens in patients and mice chronically infected with Trypanosoma cruzi. Later, T lymphocytes reactive with heart or nerve tissue antigens were found in chagasic mice and patients, extending the concept to include cell-mediated immunity. However, there is disagreement about whether the observed immunologic autoreactivities are triggered by T. cruzi epitopes and then affect host tissue antigens by virtue of molecular mimicry or are elicited by host antigens exposed to lymphocytes after tissue damage caused by the parasite. There is also disagreement about the relevance of immunologic autoreactivities to the pathogenesis of Chagas' disease because of the lack of reproducibility of some key reports supporting the autoimmunity hypothesis, conflicting data from independent laboratories, conclusions invalidated by advances in our understanding of the immunologic mechanisms underlying cell lysis, and, last but not least, a lack of direct, incontrovertible evidence that cross-reacting antibodies or autoreactive cells mediate the typical pathologic changes associated with human Chagas' disease. The data and views backing and questioning the autoimmunity hypothesis for Chagas' disease are summarized in this review.

Immunization with recombinant Trypanosoma cruzi ribosomal P2beta protein induces changes in the electrocardiogram of immunized mice

Molecular expression cloning techniques revealed that patients with severe chronic Chagas heart disease showed a strong humoral response against the cloned C-terminal portion of the Trypanosoma cruzi ribosomal P2beta protein, previously named JL5. The main linear epitope of this polypeptide was mapped to the 13 C-terminal amino acid sequence EEEDDDMGFGLFD (named R13), which is almost identical to the mammalian ribosomal P consensus sequence EESDDDMGFGLFD (named H13). Enzyme-linked immunosorbent assay measurements demonstrated that sera from patients with chronic Chagas heart disease presented a very specific anti-P humoral response with high anti-R13, but low H13 antibody levels. We attempted to develop an animal model that would reproduce, at least partially, two features of the human infection: (1) the serological pattern of the anti-P response, and (2) specific cardiac symptoms. To this effect, mice were immunized with T. cruzi P2beta recombinant protein. Immunization reproduced the typical anti-P antibody profile defined for chronic infections, but did not induce cardiac inflammatory lesions. However, it altered significantly the electrocardiograms of immunized mice. It is suggested that this assay represents a functional test for assessing the biological activity of antibodies against T. cruzi ribosomal P protein on cardiac muscle.

Human chagasic disease is not associated with an antiheart humoral response

An inflammatory cardiomyopathy occurs in humans with chronic Trypanosoma cruzi infection (Chagas' disease). This study finds that T. cruzi infection is not associated with the production of cardiac-specific autoantibodies in humans with cardiac manifestations.

Trypanosoma cruzi and mammalian heart cross-reactive antigens

Monoclonal antibodies produced against T. cruzi microsomal fraction (Mc) were used to investigate the presence of molecular mimicry between the parasite and mammalian tissues. A total of 42 cell lines secreting anti-Mc antibodies were characterized and selected by ELISA, dot blotting and Western blotting assays. Twenty seven supernatants reactive with Mc and/or parasite cytosol (CS) also reacted with human myocardial and/or skeletal muscle antigens by dot blotting assay. Twelve among those cross-reactive hybridomes, which happen to be all of the IgM isotype and to recognize structures on the surface and/or flagellum of the parasite, were selected for cell cloning. Western blotting analysis of these 12 monoclonal antibodies revealed that they mainly recognized bands of 65, 45, 34 and 27 kDa on myocardium and bands of 71, 59, 44 and 30-27 kDa on skeletal muscle. Moreover, seven among them, when assayed by immuno-histochemistry on human and hamster myocardium and skeletal muscle, recognized cytoplasmic antigens, although the monoclonal antibodies 5F2 and 5A9B11 did also bind to the vessel muscle layer. Competitive assays proved the specificity of tissue structures recognition by these monoclonal antibodies. Moreover, this reactivity resulted to be organ specific as they failed to react on lung, stomach and kidney samples. These results demonstrate the cross-reactivity of mammalian and parasite antigens, thus supporting the possibility that molecular mimicry plays a central role in the development of chagasic cardiomyopathy.