The indeterminate phase of Chagas' disease: ultrastructural characterization of cardiac changes in the canine model.

The indeterminate phase of Chagas' disease is defined as the prolonged period of clinically silent infection that follows the phase of acute primary infection with Trypanosoma cruzi. The dog is the only experimental animal model in which the indeterminate phase progresses to the late phase of severe, chronic myocarditis. This report describes the cardiac histologic and ultrastructural findings in dogs that survived the acute phase of infection with T. cruzi, becoming clinically and electrocardiographically normal for up to 3.5 years, while maintaining positive serologic test results during this period of time. Most of the myocardium appeared morphologically normal; however, small foci of mild, chronic myocarditis were present, with interstitial edema, mild fibrosis, and infiltration by lymphocytes, macrophages, and plasma cells. No microvascular lesions and no areas of close contact between immune effector cells and endothelial cells or cardiac myocytes were present. These findings were in sharp contrast to those observed in the canine model during the acute infection with T. cruzi. In this model, acute myocyte damage and lesions in the microcirculation, including fibrin microthrombi, were associated with close contacts between immune effector cells and myocytes or endothelial cells. Focally inflamed interstitial tissue showed increased deposition of amorphous and collagenous extracellular matrix as well as evidence of breakdown of collagen. The features of the inflammatory cells in the indeterminate phase of Chagas' disease were interpreted as indicating a self-limited cycle of focal inflammatory changes, with modulation and suppression of cell-mediated immune responses. Thus, we consider the indeterminate phase of Chagas' disease to be a stage of host-parasite equilibrium rather than a process of progressive damage.

Morphological aspects of the myocarditis and myositis in Calomys callosus experimentally infected with Trypanosoma cruzi: fibrogenesis and spontaneous regression of fibrosis.

Calomys callosus a wild rodent, is a natural host of Trypanosoma cruzi. Twelve C. callosus were infected with 10(5) trypomastigotes of the F strain (a myotropic strain) of T. cruzi. Parasitemia decreased on the 21st day becoming negative around the 40th day of infection. All animals survived but had positive parasitological tests, until the end of the experiment. The infected animals developed severe inflammation in the myocardium and skeletal muscle. This process was pronounced from the 26th to the 30th day and gradually subsided from the 50th day becoming absent or residual on the 64th day after infection. Collagen was identified by the picro Sirius red method. Fibrogenesis developed early, but regression of fibrosis occurred between the 50th and 64th day. Ultrastructural study disclosed a predominance of macrophages and fibroblasts in the inflammatory infiltrates, with small numbers of lymphocytes. Macrophages had active phagocytosis and showed points of contact with altered muscle cells. Different degrees of matrix expansion were present, with granular and fibrillar deposits and collagen bundles. These alterations subsided by the 64th days. Macrophages seem to be the main immune effector cell in the C. callosus model of infection with T. cruzi. The mechanisms involved in the rapid fibrogenesis and its regression deserve further investigation.

Myocardial changes in acute Trypanosoma cruzi infection. Ultrastructural evidence of immune damage and the role of microangiopathy.

Histological and ultrastructural studies of the hearts of dogs sacrificed 18 to 26 days after intraperitoneal inoculation with 4 x 10(5) blood forms of the 12 SF strain of Trypanosoma cruzi/kg of body weight disclosed myocarditis characterized by parasitic invasion of some myocytes, damage and necrosis of nonparasitized myocytes, and interstitial infiltration by mononuclear cells. Nonparasitized myocytes showed alterations ranging from mild edema to severe myocytolysis. These changes often were accompanied by contacts of myocytes with lymphocytes (both granular and agranular) and macrophages. These contacts were characterized by focal loss of the myocyte basement membrane and close approximation of the plasma membranes of the two cells. Contacts between lymphocytes and capillary endothelial cells were also frequent. Platelet aggregates and fibrin microthrombi were observed in some capillaries. Our findings suggest that immune effector cells play a major role in the pathogenesis of the myocyte damage and the microangiopathy in acute Chagas' disease.

Antibodies to laminin and immunohistochemical localization of laminin in chronic chagasic cardiomyopathy: a review.

Antibodies against laminin were determined by ELISA in forty six patients suffering from Chagas' disease and twenty healthy persons (control group). The patients were divided into three groups according to the severity of clinical, electrocardiographic and echocardiographic studies. Histologic, ultrastructural and immunohistochemical studies were made of endomyocardial biopsy specimens from 10 of these patients with chronic Chagasic cardiomyopathy. Antibodies to laminin were detected in 50% of the patients in each of the three groups. However analysis of the data did not allow us to determine any significant correlation among the severity of the different clinical and non-invasive studies and the level of circulating antibodies to laminin. The highest titers of antilaminin antibodies were detected in the group with severe cardiological alterations (37% of the patients). Histological and electron microscopic observation of myocardial biopsies disclosed marked thickening of the basement membranes of the myocytes, endothelial cells and vascular smooth muscle cells. Light (peroxidase-labeled antibodies) and electron (gold-conjugated antibody) microscopic immunohistochemical methods revealed a positive reaction for laminin in these thickened basement membranes. This thickening may develop as a consequence of: a) an immunologic reaction which is triggered by the presence of a laminin-like molecule on the surfaces of T. cruzi amastigotes and trypomastigotes; b) an immunologic response to direct injury of basement membranes causing some of their components to become antigenic; c) myocardial fibrosis, with synthesis of new connective tissue components, and d) a combination of the preceding factors. The relationship of these changes to antilaminin antibodies remains unclear.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunohistochemical localization of laminin in the hearts of patients with chronic chagasic cardiomyopathy: relationship to thickening of basement membranes.

Histologic, ultrastructural, and immunohistochemical studies were made of endomyocardial biopsy specimens from 10 patients with chronic chagasic cardiomyopathy. Histologic and electron microscopic observation disclosed marked thickening of the basement membranes of the myocytes, endothelial cells, and vascular smooth muscle cells in all patients. Light (peroxidase-labeled antibodies) and electron (gold-conjugated antibody) microscopic immunohistochemical methods revealed a positive reaction for laminin in these thickened basement membranes. This thickening of basement membranes may develop as a consequence of: (1) an immunologic reaction that is triggered by the presence of a laminin-like molecule on the surfaces of Trypanosoma cruzi amastigotes and trypomastigotes; (2) an immunologic response to direct injury of basement membranes causing some of their components to become antigenic; (3) myocardial fibrosis, with synthesis of new connective tissue components; and (4) a combination of the preceding factors. The relationship of these changes to antilaminin antibodies requires clarification.

Endomyocardial biopsies in chronic chagasic cardiomyopathy. Immunohistochemical and ultrastructural findings.

Mononuclear cellular infiltrates and extensive fibrosis, with or without apical ventricular aneurysms, are the usual morphological findings in chronic chagasic cardiomyopathy. These lesions are thought to be mediated by immune phenomena rather than by continuing parasitic invasion of the heart. In the present report, we correlated clinical, immunohistochemical and ultrastructural findings in 30 endomyocardial biopsies from patients with chronic chagasic cardiomyopathy. In 12 of these biopsies, immunocytochemical techniques were used to identify and count leukocytes (common leukocyte antigen, CLA), T lymphocytes (UCHL-1 antibody) and B lymphocytes (L-26 antibody). The biopsy specimens showed variable degrees of myocardial hypertrophy and mononuclear infiltrates. No tissue forms of trypanosomes were found. The endocardium averaged 24 +/- 12.6 microns (mean +/- SD) in thickness. The mean myocyte diameter was 20 +/- 7.33 microns. The hearts were severely fibrotic containing a mean of 24.1 +/- 12.8% of fibrous tissue (range 8.2-49%), mast cells were scarce. Mononuclear cell infiltrates were found in 25 of the 30 biopsies. In 12 biopsies, immunohistochemical studies showed that the majority of the lymphocytes were T lymphocytes and associated with necrotic or degenerating myocytes. 10 of the 12 biopsy samples showed 5 or more CLA-positive mononuclear cells/high power field. In these 10 patients, T and B lymphocytes represented 32 and 13% of the total mononuclear infiltrating cells, respectively. The remaining cells were monocytes and macrophages.

Electrophysiologic-structural correlations in chagasic aneurysms causing malignant arrhythmias.

We studied the structure and ultrastructure of three chagasic aneurysms, the excision of which abolished malignant arrhythmias. Chronic recurrent ventricular tachycardia often occurs in patients with chagasic aneurysms, and ventricular mapping indicates that these arrhythmias originate in regions adjacent to those aneurysms. In our patients, ventricular tachycardia had been refractory to medical treatment. During surgery, epicardial and endocardial mapping showed abnormal potentials. Sutures were placed in the areas of resection, their sizes approximating those of earliest activation so that these sites could be identified. The myocardium showed chronic inflammatory reaction, myocytolysis and fibrosis. The presence of "islets" was common (normal, "early" damaged or "established" necrotic myocytes surrounded by fibrous tissue). The "early" lesions were predominant at the previously identified areas of arrhythmogenic activity. The ultrastructural studies showed hypertrophy of myocytes and partial or complete loss of myofibrils, swelling of mitochondria and disruption of mitochondrial cristae, accumulation of lipofuscin granules, and intracellular oedema. A most striking alteration was the thickening of the basement membranes of myocytes and vascular endothelial and smooth muscle cells. The interlaced fronts of respectively healthy (fast conducting) and "early" damaged (slow conducting) myocytes seen in serial sectioning produced an ideal configuration for reentry circuits. The final proof that the arrhythmias originated in these endocardial regions was their abolition by resection of the aneurysm.