Myocardial inflammatory infiltrate in human chronic chagasic cardiomyopathy: Immunohistochemical findings

Mast cells: a novel therapeutic avenue for cardiovascular diseases?

Mast cells are tissue-resident immune cells strategically located in different compartments of the normal human heart (the myocardium, pericardium, aortic valve, and close to nerves) as well as in atherosclerotic plaques. Cardiac mast cells produce a broad spectrum of vasoactive and proinflammatory mediators, which have potential roles in inflammation, angiogenesis, lymphangiogenesis, tissue remodelling, and fibrosis. Mast cells release preformed mediators (e.g. histamine, tryptase, and chymase) and de novo synthesized mediators (e.g. cysteinyl leukotriene C4 and prostaglandin D2), as well as cytokines and chemokines, which can activate different resident immune cells (e.g. macrophages) and structural cells (e.g. fibroblasts and endothelial cells) in the human heart and aorta. The transcriptional profiles of various mast cell populations highlight their potential heterogeneity and distinct gene and proteome expression. Mast cell plasticity and heterogeneity enable these cells the potential for performing different, even opposite, functions in response to changing tissue contexts. Human cardiac mast cells display significant differences compared with mast cells isolated from other organs. These characteristics make cardiac mast cells intriguing, given their dichotomous potential roles of inducing or protecting against cardiovascular diseases. Identification of cardiac mast cell subpopulations represents a prerequisite for understanding their potential multifaceted roles in health and disease. Several new drugs specifically targeting human mast cell activation are under development or in clinical trials. Mast cells and/or their subpopulations can potentially represent novel therapeutic targets for cardiovascular disorders.

Immunomodulation of Myocardial Fibrosis

Immunotherapy is a potential cornerstone in the treatment of myocardial fibrosis. During a myocardial insult or heart failure, danger signals stimulate innate immune cells to produce chemokines and profibrotic cytokines, which initiate self-escalating inflammatory processes by attracting and stimulating adaptive immune cells. Stimulation of fibroblasts by inflammatory processes and the need to replace damaged cardiomyocytes fosters reshaping of the cardiac fibroblast landscape. In this review, we discuss new immunomodulatory strategies that manipulate and direct cardiac fibroblast activation and differentiation. In particular, we highlight immunomodulatory strategies that target fibroblasts such as chimeric antigen receptor T cells, interleukin-11, and invariant natural killer T-cells. Moreover, we discuss the potential of manipulating both innate and adaptive immune system components for the translation into clinical validation. Clearly, multiple pathways should be considered to develop innovative approaches to ameliorate myocardial fibrosis and hence to reduce the risk of heart failure.

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

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.

Increased mast cell density is associated with decreased fibrosis in human atrial tissue

Fibrotic remodelling of the atria is poorly understood and can be regulated by myocardial immune cell populations after injury. Mast cells are resident immune sentinel cells present in the heart that respond to tissue damage and have been linked to fibrosis in other settings. The role of cardiac mast cells in fibrotic remodelling in response to human myocardial injury is controversial. In this study, we sought to determine the association between mast cells, atrial fibrosis, and outcomes in a heterogeneous population of cardiac surgical patients, including a substantial proportion of coronary artery bypass grafting patients. Atrial appendage from patients was assessed for collagen and mast cell density by histology and by droplet digital polymerase chain reaction (ddPCR) for mast cell associated transcripts. Clinical variables and outcomes were also followed. Mast cells were detected in human atrial tissue at varying densities. Histological and ddPCR assessment of mast cells in atrial tissue were closely correlated. Patients with high mast cell density had less fibrosis and lower severity of heart failure classification or incidence mortality than patients with low mast cell content. Analysis of a homogeneous population of coronary artery bypass graft patients yielded similar observations. Therefore, evidence from this study suggests that increased atrial mast cell populations are associated with decreased clinical cardiac fibrotic remodelling and improved outcomes, in cardiac surgery patients.

Chagas disease in Italy: the study's contribution of Italian researchers

Chagas disease (CD) is an emerging infection in Italy as the consequence of the huge immigration from Latin American countries observed during the last ten-fifteen years. However, the interest of Italian researchers on CD dates back to the '80-90s of the last century with studies conducted in collaboration with Brazilian and Argentinian colleagues by Italian cardiologists and pathologists. Moreover, the first demonstration of the existence in the pre-Columbian America of Chagas disease in a Peruvian mummy was made by a group of Italian paleopathologists. Seroprevalence studies performed between 2010-2014 in Negrar (Verona), Bergamo, Milan, Florence and Rome shows Trypanosoma cruzi infection ranging from 3.9% to 17.1% with people coming from Bolivia as the most affected. As observed in Latin America about 30% of screened subjects in Italy are affected by cardiac or digestive forms of CD. More than 20% of subjects treated with benznidazole discontinued it permanently due to adverse events.

Mast Cells in Cardiac Fibrosis: New Insights Suggest Opportunities for Intervention

Mast cells (MC) are innate immune cells present in virtually all body tissues with key roles in allergic disease and host defense. MCs recognize damage-associated molecular patterns (DAMPs) through expression of multiple receptors including Toll-like receptors and the IL-33 receptor ST2. MCs can be activated to degranulate and release pre-formed mediators, to synthesize and secrete cytokines and chemokines without degranulation, and/or to produce lipid mediators. MC numbers are generally increased at sites of fibrosis. They are potent, resident, effector cells producing mediators that regulate the fibrotic process. The nature of the secretory products produced by MCs depend on micro-environmental signals and can be both pro- and anti-fibrotic. MCs have been repeatedly implicated in the pathogenesis of cardiac fibrosis and in angiogenic responses in hypoxic tissues, but these findings are controversial. Several rodent studies have indicated a protective role for MCs. MC-deficient mice have been reported to have poorer outcomes after coronary artery ligation and increased cardiac function upon MC reconstitution. In contrast, MCs have also been implicated as key drivers of fibrosis. MC stabilization during a hypertensive rat model and an atrial fibrillation mouse model rescued associated fibrosis. Discrepancies in the literature could be related to problems with mouse models of MC deficiency. To further complicate the issue, mice generally have a much lower density of MCs in their cardiac tissue than humans, and as such comparing MC deficient and MC containing mouse models is not necessarily reflective of the role of MCs in human disease. In this review, we will evaluate the literature regarding the role of MCs in cardiac fibrosis with an emphasis on what is known about MC biology, in this context. MCs have been well-studied in allergic disease and multiple pharmacological tools are available to regulate their function. We will identify potential opportunities to manipulate human MC function and the impact of their mediators with a view to preventing or reducing harmful fibrosis. Important therapeutic opportunities could arise from increased understanding of the impact of such potent, resident immune cells, with the ability to profoundly alter long term fibrotic processes.

Trypanosoma cruzi Neurotrophic Factor Facilitates Cardiac Repair in a Mouse Model of Chronic Chagas Disease

Most patients acutely infected with Trypanosoma cruzi undergo short-term structural and functional cardiac alterations that heal without sequelae. By contrast, in patients whose disease progresses to chronic infection, irreversible degenerative chronic Chagas cardiomyopathy (CCC) may develop. To account for the contrast between cardiac regeneration in high-parasitism acute infection and progressive cardiomyopathy in low-parasitism CCC, we hypothesized that T. cruzi expresses repair factors that directly facilitate cardiac regeneration. We investigated, as one such repair factor, the T. cruzi parasite-derived neurotrophic factor (PDNF), known to trigger survival of cardiac myocytes and fibroblasts and upregulate chemokine chemokine C-C motif ligand 2, which promotes migration of regenerative cardiac progenitor cells (CPCs). Using in vivo and in vitro models of Chagas disease, we tested whether T. cruzi PDNF promotes cardiac repair. Quantitative PCR and flow cytometry of heart tissue revealed that stem-cell antigen-1 (Sca-1⁺) CPCs expand in acute infection in parallel to parasitism. Recombinant PDNF induced survival and expansion of ex vivo CPCs, and intravenous administration of PDNF into naïve mice upregulated mRNA of cardiac stem-cell marker Sca-1. Furthermore, in CCC mice, a 3-week intravenous administration of PDNF protocol induced CPC expansion and reversed left ventricular T-cell accumulation and cardiac remodeling including fibrosis. Compared with CCC vehicle-treated mice, which developed severe atrioventricular block, PDNF-treated mice exhibited reduced frequency and severity of conduction abnormalities. Our findings are in support of the novel concept that T. cruzi uses PDNF to promote mutually beneficial cardiac repair in Chagas disease. This could indicate a possible path to prevention or treatment of CCC.

Recognizing and meeting the challenge of Chagas disease in the USA

It is estimated that over 300,000 people with Chagas disease are living in the USA, with more than 30,000 cases of Chagas cardiomyopathy expected per year. The epidemiology of Chagas disease in Central and South America differs from that of the USA, where particular attention must focus on blood bank screening, organ donation and vertical transmission. It is essential that healthcare practitioners have heightened awareness of Chagas disease in the differential diagnosis of certain patients and are aware of recommendations for the management of these patients in the USA. Ongoing attention must focus on trials that determine whether all patients will benefit from treatment as well as studies of new agents for therapy.

Prognostic impact of Chagas disease in the United States

A prior publication from our group reported the fact that Chagas disease is underdiagnosed. This review will summarize several aspects of Chagas disease in the United States including modes of transmission, which will demonstrate that clinicians should be more aware of the disease and its consequences. Trypanosoma cruzi is present in many animal species spread throughout most of the United States. Chagas disease also reaches the North American continent through immigration, making it more frequent than expected. Apart from immigration, non-endemic countries should be aware of transmissions through blood transfusions, organ transplantations, or mother-to-child infections. In conclusion, it is possible that many chagasic cardiomyopathies are being misdiagnosed as "primary dilated idiopathic cardiomyopathies." Recognizing that there is an evident threat of Chagas disease present in the United States will allow an increase of clinician's awareness and hence will permit to correctly diagnose and treat this cardiomyopathy. Health authorities should guarantee a generalized screening of T cruzi of blood donors, before organ donations, and of pregnant women who were born or have lived in endemic areas.

Cardiac involvement in acquired immunodeficiency syndrome--a review to push action. The Committee for the Study of Cardiac Involvement in AIDS

As more effective therapies have produced longer survival times for human immunodeficiency virus (HIV)-infected patients, new complications of late-stage HIV infection including HIV-related heart disease have emerged. Almost any agent that can cause disseminated infection in patients with acquired immunodeficiency syndrome (AIDS) may involve myocardium, but clinical evidence of cardiac disease is usually overshadowed by manifestations in other organs, primarily the brain and lungs. Cardiac abnormalities are found at autopsy in two-thirds of patients with AIDS, and more than 150 reports of cardiac complications have been published. Cardiac involvement in HIV disease includes pericardial effusion, myocarditis, dilated cardiomyopathy, and/or endocardial involvement at any stage of the disease. This review deals with all the cardiac manifestations of AIDS and serves to highlight two problems and one indication. First of all, there are very few clinical studies. Current knowledge is based almost exclusively on echocardiography and autopsy studies. Observational or clinical trials would be useful. Second, there exists very poor information on the impact of treatment; and epidemiologic and clinicopathologic studies are mandatory for obtaining detailed data concerning the mechanisms of myocardial damage in AIDS. Finally, because cardiac complications are often clinically inapparent or subtle in the initial stages, periodic screening of HIV-positive patients by electrocardiogram and echocardiogram is probably indicated. In addition, AIDS may also provide the opportunity to gain insights into the pathogenesis of little understood cardiac diseases such as lymphocytic myocarditis and dilated cardiomyopathy.

Chronic chagasic cardiopathy: the product of a turbulent host-parasite relationship

The pathogenesis of chronic chagasic cardiopathy is still a debated matter. In this review, the main theories raised about it since the first description of the disease in 1909 by Carlos Chagas, are considered. The scarcity of T.cruzi parasites into the myocardium and the apparent lack of correlation between their presence and the occurrence of myocardial inflammatory infiltrate, have originated many theories indicating that chronic Chagas' cardiopathy is an autoimmune disease. Recently however, papers using immunohistochemical technique or PCR have demonstrated a strong association between moderate or severe myocarditis and presence of T.cruzi Ags, indicating a direct participation of the parasite in the genesis of chronic chagasic myocarditis. Different patterns of cytokine production seem to have important role in the outcome of the disease. Participation of the microcirculatory alterations and fibrosis as well as the relationship with the parasite are also emphasized. Finally, the author suggests that the indeterminate form of the disease occurs when the host immunological response against the parasite is more efficient while the chronic cardiopathy occurs in patients with hyperergic and inefficient immune response.