The Characterization of Cardiac Explants Reveals Unique Fibrosis Patterns and a Predominance of CD8+ T Cell Subpopulations in Patients with Chronic Chagas Cardiomyopathy

Abstract

Aim: The present study aimed to characterize the histopathological findings and the phenotype of inflammatory cells in the myocardial tissue of patients with end-stage heart failure (ESHF) secondary to CCC in comparison with ESHF secondary to non-Chagas cardiomyopathies (NCC).

Methods: A total of 32 explanted hearts were collected from transplanted patients between 2014 and 2017. Of these, 21 were classified as CCC and 11 as other NCC. A macroscopic analysis followed by a microscopic analysis were performed. Finally, the phenotypes of the inflammatory infiltrates were characterized using flow cytometry.

Results: Microscopic analysis revealed more extensive fibrotic involvement in patients with CCC, with more frequent foci of fibrosis, collagen deposits, and degeneration of myocardial fibers, in addition to identifying foci of inflammatory infiltrate of greater magnitude. Finally, cell phenotyping identified more memory T cells, mainly CD8+CD45RO+ T cells, and fewer transitioning T cells (CD45RA+/CD45RO+) in patients with CCC compared with the NCC group.

Conclusions: CCC represents a unique form of myocardial involvement characterized by abundant inflammatory infiltrates, severe interstitial fibrosis, extensive collagen deposits, and marked cardiomyocyte degeneration. The structural myocardial changes observed in late-stage Chagas cardiomyopathy appear to be closely related to the presence of cardiac fibrosis and the colocalization of collagen fibers and inflammatory cells, a finding that serves as a basis for the generation of new hypotheses aimed at better understanding the role of inflammation and fibrogenesis in the progression of CCC. Finally, the predominance of memory T cells in CCC compared with NCC hearts highlights the critical role of the parasite-specific lymphocytic response in the course of the infection.

Keywords: chagas disease; chronic chagas cardiomyopathy; histopathology; immunophenotyping.

Figure 1

Macroscopic inspection of explanted hearts highlighting (A) globoid appearance of a heart affected by chronic Chagas cardiomyopathy compared with a (B) non-Chagas cardiomyopathy explant with a more preserved anatomical shape. (C) Highlights the marked dilatation and thinning of the left ventricular walls as well as the presence of extensive replacement of healthy myocardial tissue by fibrosis in the heart affected by CCC compared with the explant with NCC (D). The arrow in (C) indicates the presence of a left ventricular aneurysm, typical of advanced-stage CCC.

Figure 2

Histological section of myocardium stained with hematoxylin-eosin. The images in the left column (A,C,E) correspond to cardiac tissue from the CCC group, while those in the right column (B,D,F) correspond to the non-chagasic group. (A,B) Interstitial fibrosis, highlighting in the CCC group prominent lymphohistiocytic inflammatory infiltrate diffusely distributed. (C,D) The yellow arrows indicate perivascular fibrosis. Scale bars are 100 μm for (A–D). (E,F) Cardiomyocyte hypertrophy and areas of necrosis in both groups (CCC and NCC). The two-way horizontal arrow in both figures indicates increased fiber diameter. The unidirectional straight arrow in both figures indicates the presence of large, irregularly shaped nuclei. Finally, the presence of eosinophils in the CCC group is indicated by the curved arrow. Scale bars are 20 μm for (E,F).

Figure 3

Comparison of inflammatory infiltrate type (focal vs. diffuse) according to the evaluated structure of patients with chronic Chagas cardiomyopathy (CCC) and non-Chagas cardiomyopathy (NCC). Bars represent the raw proportion of patients in which the mentioned alteration was present. Statistical significance: * p < 0.05; ** p ≤ 0.01. Abbreviations: RA: right atrium; LA: left atrium; RV: right ventricle; LV: left ventricle.

Figure 4

Histopathological findings in patients with chronic Chagas cardiomyopathy (CCC) and non-Chagas cardiomyopathy (NCC). The scale indicates the severity of the abnormal histopathological finding: 0: absent, 1: mild, 2: moderate, and 3: severe. Each bar represents the raw proportion of patients in each category. Statistical significance: ** p ≤ 0.01; *** p ≤ 0.001. Abbreviations: RA: right atrium. LA: left atrium. RV: right ventricle. RL: left ventricle.

Figure 5

Masson’s trichrome stain showing extensive myocardial fibrosis in patients with CCC. (A) Extensive interstitial fibrosis represented by thick bands of fibroconnective tissue with extensive deposition of extracellular collagen matrix. The arrangement of the fibrous tissue separates the muscle fibers into small aggregates that give the appearance of islets. (B) Perivascular fibrosis. (C) Interstitial fibrosis in greater detail. (D) Colocalization of abundant inflammatory infiltrate and high degree of fibrosis with lymphocytes closely adhering to or in the vicinity of the sarcolemma.

Figure 6

Type IV and XIV collagen immunohistochemical staining of cardiac tissue from patients with end-stage heart failure secondary to chronic Chagas cardiomyopathy. (A) Type IV collagen. Abundant immunoreactivity of type IV collagen, distributed in basement membranes and areas of interstitial fibrosis. (B) Type XIV collagen immunoreactivity shows cardiomyocytes with parallel fibrils directed longitudinally and the presence of a transverse pattern. The nuclei of the cardiomyocytes are shown in blue.

Figure 7

Immunophenotypic characterization of the T CD4+ and CD8+ cells composing the inflammatory infiltrate in explants with chronic Chagas cardiomyopathy (CCC) vs. non-Chagas cardiomyopathy (NCC). The median for each group is highlighted in red.