Distribution of myocardial macrophages in the normal human heart

Spatiotemporal development and the regulatory mechanisms of cardiac resident macrophages: Contribution in cardiac development and steady state

Cardiac resident macrophages (CRMs) are integral components of the heart and play significant roles in cardiac development, steady-state, and injury. Advances in sequencing technology have revealed that CRMs are a highly heterogeneous population, with significant differences in phenotype and function at different developmental stages and locations within the heart. In addition to research focused on diseases, recent years have witnessed a heightened interest in elucidating the involvement of CRMs in heart development and the maintenance of cardiac function. In this review, we primarily concentrated on summarizing the developmental trajectories, both spatial and temporal, of CRMs and their impact on cardiac development and steady-state. Moreover, we discuss the possible factors by which the cardiac microenvironment regulates macrophages from the perspectives of migration, proliferation, and differentiation under physiological conditions. Gaining insight into the spatiotemporal heterogeneity and regulatory mechanisms of CRMs is of paramount importance in comprehending the involvement of macrophages in cardiac development, injury, and repair, and also provides new ideas and therapeutic methods for treating heart diseases.

Clinicopathological classification of immune checkpoint inhibitor-associated myocarditis: possible refinement by measuring macrophage abundance

BACKGROUND

Immune checkpoint inhibitor (ICI) myocarditis is associated with high morbidity and mortality. While endomyocardial biopsy (EMB) is considered a gold standard for diagnosis, the sensitivity of EMB is not well defined. Additionally, the pathological features that correlate with the clinical diagnosis of ICI-associated myocarditis remain incompletely understood.

METHODS

We retrospectively identified and reviewed the clinicopathological features of 26 patients with suspected ICI-associated myocarditis based on institutional major and minor criteria. Seventeen of these patients underwent EMB, and the histopathological features were assessed by routine hematoxylin and eosin (H&E) staining and immunohistochemical (IHC) staining for CD68, a macrophage marker.

RESULTS

Only 2/17 EMBs obtained from patients with suspected ICI myocarditis satisfied the Dallas criteria. Supplemental IHC staining and quantification of CD68⁺ macrophages identified an additional 7 patients with pathological features of myocardial inflammation (> 50 CD68⁺ cells/HPF). Macrophage abundance positively correlated with serum Troponin I (P = 0.010) and NT-proBNP (N-terminal pro-brain natriuretic peptide, P = 0.047) concentration. Inclusion of CD68 IHC could have potentially changed the certainty of the diagnosis of ICI-associated myocarditis to definite in 6/17 cases.

CONCLUSIONS

While the Dallas criteria can identify a subset of ICI-associated myocarditis patients, quantification of macrophage abundance may expand the diagnostic role of EMB. Failure to meet the traditional Dallas Criteria should not exclude the diagnosis of myocarditis.

Macrophages in myocardial infarction

The heart contains a population of resident macrophages that markedly expands following injury through recruitment of monocytes and through proliferation of macrophages. In myocardial infarction, macrophages have been implicated in both injurious and reparative responses. In coronary atherosclerotic lesions, macrophages have been implicated in disease progression and in the pathogenesis of plaque rupture. Following myocardial infarction, resident macrophages contribute to initiation and regulation of the inflammatory response. Phagocytosis and efferocytosis are major functions of macrophages during the inflammatory phase of infarct healing, and mediate phenotypic changes, leading to acquisition of an anti-inflammatory macrophage phenotype. Infarct macrophages respond to changes in the cytokine content and extracellular matrix composition of their environment and secrete fibrogenic and angiogenic mediators, playing a central role in repair of the infarcted heart. Macrophages may also play a role in scar maturation and may contribute to chronic adverse remodeling of noninfarcted segments. Single cell studies have revealed a remarkable heterogeneity of macrophage populations in infarcted hearts; however, the relations between transcriptomic profiles and functional properties remain poorly defined. This review manuscript discusses the fate, mechanisms of expansion and activation, and role of macrophages in the infarcted heart. Considering their critical role in injury, repair, and remodeling, macrophages are important, but challenging, targets for therapeutic interventions in myocardial infarction.

Cardiac Macrophage Density in Covid-19 Infection: Relationship to Myocyte Necrosis and Acute Lung Injury

SARS-Cov-2 infection is not limited to the respiratory tract and can involve other organs including the heart, blood vessels, kidneys, liver, gastrointestinal tract, placenta, and skin. Covid-19 patients with cardiac involvement usually have higher morbidity and mortality compared to those without cardiac involvement. The frequency and the specificity of the myocardial pathological changes in patients who die after documented infection with SARS-Cov-2 is uncertain. Macrophages can be found in the normal heart (interstitium, around the endothelial cells and in the epicardial adipose tissue), and they are considered part of the major immune cell population in the heart. In this case-control autopsy study, we compare the gross and microscopic cardiac findings, and the available clinical characteristics between a group of 10 Covid-19 decedents and a control group of 20 patients who died with non-SARS-Cov-2 severe bronchopneumonia and/or diffuse alveolar damage. The objectives of this semi-quantitative study are to study single myocyte necrosis and its relation to the strain on the heart caused by lung injury as a causative mechanism, and to study the density of myocardial and epicardial macrophages in Covid-19 hearts in comparison to the control group, and in Covid-19 hearts with single myocyte necrosis in comparison to Covid-19 hearts without single myocyte necrosis. Lymphocytic myocarditis was not identified in any of the hearts from the Covid-19 or the control group. Single myocyte necrosis is more frequent in the Covid-19 group compared to the control group, suggesting that it is unrelated to the strain on the heart caused by underlying lung injury. The density of the macrophages in the epicardium and myocardium in the hearts of the Covid-19 group is higher compared to those in the control group. The density of epicardial macrophages is higher in the Covid-19 hearts with single myocyte necrosis than in those without. These observations contribute to our increasing appreciation of the role of macrophages in the pathophysiologic response to infection by SARS-CoV-2.

Macrophages in the heart: Active players or simple bystanders?

Today, more and more studies focus on the processes in which macrophages are involved. These discoveries provide new perspectives on the cellular mechanisms that regulate the physiological functions of the healthy heart. Moreover, they offer a deeper knowledge of the pathologic processes underlying the onset and the evolution of specific cardiac impairment. The heterogeneous population of macrophages within the heart can be divided by origin, expression profile, and function. The pool of cardiac macrophages includes at least two distinct subsets with different ontogeny. The first one has an embryonic origin, deriving from the yolk sac and the fetal liver, while the other macrophage subset results from the postnatal recruitment of monocytes produced in the bone marrow. This review will focus on new phenotypes and functions of cardiac macrophages that have been identified in the last years and that need to be deeply studied to unveil new potential therapies aimed at treating cardiac diseases.

Macrophages, Metabolism and Heterophagy in the Heart

The heart is a never-stopping engine that relies on a formidable pool of mitochondria to generate energy and propel pumping. Because dying cardiomyocytes cannot be replaced, this high metabolic rate creates the challenge of preserving organelle fitness and cell function for life. Here, we provide an immunologist's perspective on how the heart solves this challenge, which is in part by incorporating macrophages as an integral component of the myocardium. Cardiac macrophages surround cardiomyocytes and capture dysfunctional mitochondria that these cells eject to the milieu, effectively establishing a client cell-support cell interaction. We refer to this heterologous partnership as heterophagy. Notably, this process shares analogies with other biological systems, is essential for proteostasis and metabolic fitness of cardiomyocytes, and unveils a remarkable degree of dependence of the healthy heart on immune cells for everyday function.

COVID-19 and Heart Failure: From Epidemiology During the Pandemic to Myocardial Injury, Myocarditis, and Heart Failure Sequelae

A close and intriguing relationship has been suggested between heart failure (HF) and coronavirus disease 2019 (COVID-19). First, COVID-19 pandemic represented a global public health emergency in the last year and had a catastrophic impact on health systems worldwide. Several studies showed a reduction in HF hospitalizations, ranging from 30 to 66% in different countries and leading to a subsequent increase in HF mortality. Second, pre-existing HF is a risk factor for a more severe clinical course of COVID-19 and an independent predictor of in-hospital mortality. Third, patients hospitalized for COVID-19 may develop both an acute decompensation of chronic HF and de-novo HF as a consequence of myocardial injury and cardiovascular (CV) complications. Myocardial injury occurred in at least 10% of unselected COVID-19 cases and up to 41% in critically ill patients or in those with concomitant CV comorbidities. Few cases of COVID-19-related acute myocarditis, presenting with severe reduction in the left ventricular (LV) ejection fraction and peculiar histopathological findings, were described. However, recent data suggested that COVID-19 may be associated with both systolic and diastolic LV dysfunction, with LV diastolic impairment, pulmonary hypertension, and right ventricular dysfunction representing the most frequent findings in echocardiographic studies. An overview of available data and the potential mechanisms behind myocardial injury, possibly leading to HF, will be presented in this review. Beyond the acute phase, HF as a possible long-term consequence of cardiac involvement in COVID-19 patients has been supposed and need to be investigated yet.

A Fatal Case of Cardiac Contusion After Blunt Chest Injury

ABSTRACT

In this article, we report the autopsy findings of a 48-year-old man who sustained blunt trauma to the thorax. A medical record review revealed no history of cardiac disease. He presented to the hospital with a computed tomography-verified fracture of the left fourth and fifth ribs, and pulmonary and cardiac contusion. He was released from the hospital in stable condition at his own request 7 days later. Because of sudden deterioration, he was readmitted to the hospital the next day. Electrocardiogram detected cardiac arrhythmia on the 15th day after chest trauma. Electrocardiography detected pericardial effusion and severe mitral insufficiency resulting in left ventricular failure. Death was attributed to diffuse alveolar damage-complicating pneumonia due to cardiac contusion with mitral insufficiency occurring 25 days after hospital admission. Internal examination revealed diffuse fibrinous pericarditis, left atrial tear right above the anterior mitral valve leaflet with intrapericardial granulation tissue, and no sign of myocardial damage. Immunohistochemistry showed significantly more CD68-positive macrophages within tissue taken from the heart, a finding indicative of previous atrial and ventricular myocardial contusion. This case report demonstrates that routine hematoxylin and eosin staining may not always reveal significant myocardial damage.

Pathological features of COVID-19-associated myocardial injury: a multicentre cardiovascular pathology study

Aims

Coronavirus disease 2019 (COVID-19) due to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has been associated with cardiovascular features of myocardial involvement including elevated serum troponin levels and acute heart failure with reduced ejection fraction. The cardiac pathological changes in these patients with COVID-19 have yet to be well described.

Methods and results

In an international multicentre study, cardiac tissue from the autopsies of 21 consecutive COVID-19 patients was assessed by cardiovascular pathologists. The presence of myocarditis, as defined by the presence of multiple foci of inflammation with associated myocyte injury, was determined, and the inflammatory cell composition analysed by immunohistochemistry. Other forms of acute myocyte injury and inflammation were also described, as well as coronary artery, endocardium, and pericardium involvement. Lymphocytic myocarditis was present in 3 (14%) of the cases. In two of these cases, the T lymphocytes were CD4 predominant and in one case the T lymphocytes were CD8 predominant. Increased interstitial macrophage infiltration was present in 18 (86%) of the cases. A mild pericarditis was present in four cases. Acute myocyte injury in the right ventricle, most probably due to strain/overload, was present in four cases. There was a non-significant trend toward higher serum troponin levels in the patients with myocarditis compared with those without myocarditis. Disrupted coronary artery plaques, coronary artery aneurysms, and large pulmonary emboli were not identified.

Conclusions

In SARS-CoV-2 there are increased interstitial macrophages in a majority of the cases and multifocal lymphocytic myocarditis in a small fraction of the cases. Other forms of myocardial injury are also present in these patients. The macrophage infiltration may reflect underlying diseases rather than COVID-19.

Characterization of heart macrophages in rhesus macaques as a model to study cardiovascular disease in humans

Rhesus macaques are physiologically similar to humans and, thus, have served as useful animal models of human diseases including cardiovascular disease. The purpose of this study was to characterize the distribution, composition, and phenotype of macrophages in heart tissues of very young (fetus: 0.5 years, n = 6), young adult (2-12 years, n = 12), and older adult (13-24 years, n = 9) rhesus macaques using histopathology and immunofluorescence microscopy. Results demonstrated that macrophages were uniformly distributed throughout the heart in animals of all age groups and were more prevalent than CD3-positve T-cells and CD20-positive B-cells. Macrophages comprised approximately 2% of heart tissue cells in the younger animals and increased to a mean of nearly 4% in the older adults. CD163-positive macrophages predominated over HAM56-positive and CD206-positive macrophages, and were detected at significantly higher percentage in the animals between 13 and 24 years of age, as well as in heart tissues exhibiting severe histopathology or inflammation in animals of all age groups. In vivo dextran labeling and retention indicated that approximately half of the macrophages were longer lived in healthy adult heart tissues and may comprise the tissue-resident population of macrophages. These results provide a basis for continued studies to examine the specific functional roles of macrophage subpopulations in heart tissues during homeostasis and in cardiovascular disease for then developing intervention strategies.

The adult murine heart has a sparse, phagocytically active macrophage population that expands through monocyte recruitment and adopts an 'M2' phenotype in response to Th2 immunologic challenge

Tissue resident macrophages have vital homeostatic roles in many tissues but their roles are less well defined in the heart. The present study aimed to identify the density, polarisation status and distribution of macrophages in the healthy murine heart and to investigate their ability to respond to immune challenge. Histological analysis of hearts from CSF-1 receptor (csf1-GFP; MacGreen) and CX3CR1 (Cx3cr1(GFP/+)) reporter mice revealed a sparse population of GFP positive macrophages that were evenly distributed throughout the left and right ventricular free walls and septum. F4/80+CD11b+ cardiac macrophages, sorted from myocardial homogenates, were able to phagocytose fluorescent beads in vitro and expressed markers typical of both 'M1' (IL-1β, TNF and CCR2) and 'M2' activation (Ym1, Arg 1, RELMα and IL-10), suggesting no specific polarisation in healthy myocardium. Exposure to Th2 challenge by infection of mice with helminth parasites Schistosoma mansoni, or Heligmosomoides polygyrus, resulted in an increase in cardiac macrophage density, adoption of a stellate morphology and increased expression of Ym1, RELMα and CD206 (mannose receptor), indicative of 'M2' polarisation. This was dependent on recruitment of Ly6ChighCCR2+ monocytes and was accompanied by an increase in collagen content. In conclusion, in the healthy heart resident macrophages are relatively sparse and have a phagocytic role. Following Th2 challenge this population expands due to monocyte recruitment and adopts an 'M2' phenotype associated with increased tissue fibrosis.

Macrophage Polarization in AIDS: Dynamic Interface between Anti-Viral and Anti-Inflammatory Macrophages during Acute and Chronic Infection

Monocyte and macrophage inflammation in parenchymal tissues during acute and chronic HIV and SIV infection plays a role in early anti-viral immune responses and later in restorative responses. Macrophage polarization is observed in such responses in the central nervous system (CNS) and the heart and cardiac vessels that suggest early responses are M1 type antiviral responses, and later responses favor M2 restorative responses. Macrophage polarization is unique to different tissues and is likely dictated as much by the local microenvironment as well as other inflammatory cells involved in the viral responses. Such polarization is found in HIV infected humans, and the SIV infected animal model of AIDS, and occurs even with effective anti-retroviral therapy. Therapies that directly target macrophage polarization in HIV infection have recently been implemented, as have therapies to directly block traffic and accumulation of macrophages in tissues.

Differential contribution of monocytes to heart macrophages in steady-state and after myocardial infarction

RATIONALE

Macrophages populate the steady-state myocardium. Previously, all macrophages were thought to arise from monocytes; however, it emerged that, in several organs, tissue-resident macrophages may self-maintain through local proliferation.

OBJECTIVE

Our aim was to study the contribution of monocytes to cardiac-resident macrophages in steady state, after macrophage depletion in CD11b(DTR/+) mice and in myocardial infarction.

METHODS AND RESULTS

Using in vivo fate mapping and flow cytometry, we estimated that during steady state the heart macrophage population turns over in ≈1 month. To explore the source of cardiac-resident macrophages, we joined the circulation of mice using parabiosis. After 6 weeks, we observed blood monocyte chimerism of 35.3±3.4%, whereas heart macrophages showed a much lower chimerism of 2.7±0.5% (P<0.01). Macrophages self-renewed locally through proliferation: 2.1±0.3% incorporated bromodeoxyuridine 2 hours after a single injection, and 13.7±1.4% heart macrophages stained positive for the cell cycle marker Ki-67. The cells likely participate in defense against infection, because we found them to ingest fluorescently labeled bacteria. In ischemic myocardium, we observed that tissue-resident macrophages died locally, whereas some also migrated to hematopoietic organs. If the steady state was perturbed by coronary ligation or diphtheria toxin-induced macrophage depletion in CD11b(DTR/+) mice, blood monocytes replenished heart macrophages. However, in the chronic phase after myocardial infarction, macrophages residing in the infarct were again independent from the blood monocyte pool, returning to the steady-state situation.

CONCLUSIONS

In this study, we show differential contribution of monocytes to heart macrophages during steady state, after macrophage depletion or in the acute and chronic phase after myocardial infarction. We found that macrophages participate in the immunosurveillance of myocardial tissue. These data correspond with previous studies on tissue-resident macrophages and raise important questions on the fate and function of macrophages during the development of heart failure.

An immunohistochemical analysis of tissue thrombin expression in the human atria

Objective

Thrombin, the final coagulation product of the coagulation cascade, has been demonstrated to have many physiological effects, including pro-fibrotic actions via protease-activated receptor (PAR)-1. Recent investigations have demonstrated that activation of the cardiac local coagulation system was associated with atrial fibrillation. However, the distribution of thrombin in the heart, especially difference between the atria and the ventricle, remains to be clarified. We herein investigated the expression of thrombin and other related proteins, as well as tissue fibrosis, in the human left atria and left ventricle.

Methods

We examined the expression of thrombin and other related molecules in the autopsied hearts of patients with and without atrial fibrillation. An immunohistochemical analysis was performed in the left atria and the left ventricle.

Results

The thrombin was immunohistologically detected in both the left atria and the left ventricles. Other than in the myocardium, the expression of thrombin was observed in the endocardium and the subendocardium of the left atrium. Thrombin was more highly expressed in the left atrium compared to the left ventricle, which was concomitant with more tissue fibrosis and inflammation, as detected by CD68 expression, in the left atrium. We also confirmed the expression of prothrombin in the left atrium. The expression of PAR-1 was observed in the endocardium, subendocardium and myocardium in the left atrium. In patients with atrial fibrillation, strong thrombin expression was observed in the left atrium.

Conclusions

The strong expression levels of thrombin, prothrombin and PAR-1 were demonstrated in the atrial tissues of human autopsied hearts.

Effects of tyrosine kinase inhibitors on rat isolated heart function and protein biomarkers indicative of toxicity

INTRODUCTION

Cardiac toxicity, manifested as diminished contractility, ischemic heart disease, and heart failure is a major issue in drug safety. Concerns revolve around targeted drugs (TKIs) where contractility effects were not anticipated. The ability to predict cardiac toxicity early would help to de-risk drugs in development and prepare physicians to manage risk in the clinic. Issues with current preclinical studies include insufficient testing with informative, translatable models, and predictive biomarkers. The isolated heart model is amenable to multiple assessments which can be combined with current technologies to assess toxicity on a multi-scale level.

METHODS

Rat isolated heart model was used to assess changes in left ventricular (LV) contractility and protein biomarkers BNP, IL6, TNFα, and cardiac troponins T (TnT) and I (TnI). Responses were assessed during perfusion with modified Henseleit Krebs (MHK), and 20 min concentration escalations of verapamil, carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP), isoproterenol, or 20 min escalations bracketing clinical blood concentrations of sunitinib, sorafenib, and erlotinib. LV parameters and effluent for biomarkers were collected before and during escalating drug concentrations.

RESULTS

Verapamil reduced inotropy with no change in biomarkers, FCCP and isoproterenol reduced and increased heart function respectively and increased TnT and TNFα. Erlotinib had no significant effects on function or biomarkers. Sunitinib diminished function, increased TNFα at 0.1 μM, and increased TnT at higher concentrations. Sorafenib dose dependently increased TNFα beginning at 0.1 μM, reducing contractility and flow rate at 0.6 μM.

DISCUSSION

The ex-vivo assay is a sensitive and predictive model for assessing changes in heart function and biomarkers of toxicity and injury. This assay demonstrates the potential for sunitinib and sorafenib to cause cardiac toxicity in humans. Also, TNFα appears to be a biomarker in the heart prior to injury. Due to its versatility, the isolated heart assay has potential to fill gaps in cardiac safety testing early in drug development.

Mediators of mineralocorticoid receptor-induced profibrotic inflammatory responses in the heart

Coronary, vascular and perivascular inflammation in rats following MR (mineralocorticoid receptor) activation plus salt are well-characterized precursors for the appearance of cardiac fibrosis. Endogenous corticosterone, in the presence of the 11βHSD2 (11β hydroxysteroid dehydrogenase type 2) inhibitor CBX (carbenoxolone) plus salt, produces similar inflammatory responses and tissue remodelling via activation of MR. MR-mediated oxidative stress has previously been suggested to account for these responses. In the present study we thus postulated that when 11βHSD2 is inhibited, endogenous corticosterone bound to unprotected MR in the vessel wall may similarly increase early biomarkers of oxidative stress. Uninephrectomized rats received either DOC (deoxycorticosterone), CBX or CBX plus the MR antagonist EPL (eplerenone) together with 0.9% saline to drink for 4, 8 or 16 days. Uninephrectomized rats maintained on 0.9% saline for 8 days served as controls. After 4 days, both DOC and CBX increased both macrophage infiltration and mRNA expression of the p22phox subunit of NADPH oxidase, whereas CBX, but not DOC, increased expression of the NOX2 (gp91phox) subunit. eNOS [endothelial NOS (NO synthase)] mRNA expression significantly decreased from 4 days for both treatments, and iNOS (inducible NOS) mRNA levels increased after 16 days of DOC or CBX; co-administration of EPL inhibited all responses to CBX. The responses characterized over this time course occurred before measurable increases in cardiac hypertrophy or fibrosis. The findings of the present study support the hypothesis that endogenous corticosterone in the presence of CBX can activate vascular MR to produce both inflammatory and oxidative tissue responses well before the onset of fibrosis, that the two MR ligands induce differential but overlapping patterns of gene expression, and that elevation of NOX2 subunit levels does not appear necessary for full expression of MR-mediated inflammatory and fibrogenic responses.

THE EXTRACELLULAR CARDIAC PURINE METABOLOME IN SEPSIS

The total cardiac purine metabolome includes all of the adenine and guanine nucleoside and nucleosides and related molecules involved throughout the intracellular and extracellular compartments and various cell types in the heart. In considering purines as molecules involved in autocrine and paracrine communication, effective interstitial concentrations of the nucleoside adenosine, or purine metabolites, are of greatest interest. These molecules arise from the complex interactions between cardiac-specific cell types, including fibroblasts and myocytes, and noncardiac cells, such as tissue-resident macrophages and other immune cells that have vascular access. In the interstitial environment, adenosine can regulate vascular resistance, contractile function, and immunochemical interactions. The breakdown of purines can produce reactive oxygen species that also influence autocrine and paracrine interactions. A central enzyme in this paradigm, adenosine deaminase, is a pivotal molecule in regulating the balance between pro-inflammatory and anti-inflammatory signaling cascades. A new role for adenosine deaminase as an allosteric regulator of relevant membrane proteins has yet to be explored in the heart.

The distribution of cardiac macrophages in myocardial ischaemia and cardiomyopathy

AIMS

Recent evidence has implicated the macrophage as an effector cell in the inflammatory processes in transplant rejection, as well as cardiac disease, including coronary atherosclerosis. Although the latter is a vascular disease, the entire myocardium is affected. We have previously demonstrated the presence and distribution of macrophages in the 'normal' human heart. In this paper the distribution of myocardial macrophages, in the various chambers of the failing human heart, from cases of coronary atheroma and cardiomyopathy undergoing heart transplantation is documented.

METHODS AND RESULTS

Tissue blocks were removed at specific sites taken from six cases with ischaemic heart disease (IHD) (four males, two females, age range 54-62 years), and four cases with idiopathic dilated cardiomyopathy (IDCM) (three males, one female, age range 18-49 years). These were compared with hearts from five cases of sudden death, unrelated to heart disease. Sections were stained with a CD68 pan macrophage marker. Positive cells were enumerated in 20 random fields. Results were analysed using a generalized linear modelling method using a Poisson distribution. Macrophages were identified within the interstitium and often close to blood vessels in all hearts. Macrophages from IHD hearts demonstrated the most intense staining and were often larger and more elongated than those found in 'normal' control hearts. Macrophages were also often degranulated and staining was diffuse in the interstitium. Overall, there were significantly more macrophages in most areas from IHD hearts than from IDCM hearts or control hearts (P < 0.001).

CONCLUSIONS

Significantly more macrophages were found in all four chambers in diseased hearts compared with controls. Macrophage numbers were higher in the atria than in ventricles in the diseased myocardium. This study suggests selective recruitment of macrophages into the atria in the disease states studied.

Right ventricular damage due to pulmonary embolism: examination of the number of infiltrating macrophages

To investigate the pathological changes in the heart induced by pulmonary embolism, 20 autopsy cases of pulmonary embolism and 10 control cases of acute death from traumatic injury were examined. Adding to the routine hematoxylin-eosin (HE) staining, immunostaining with CD68 pan-macrophage marker was performed on the specimens obtained from both right and left ventricular walls. The number of macrophages was counted semi-quantitatively in 100 random high-power fields (HPF). Although typical pathological findings of myocardial infarction was not observed in any of the cases, 16 of the 20 pulmonary embolism cases showed an increase in the number of macrophages, mainly in the right ventricular wall. Four cases showed massive macrophage infiltration in the entire right ventricular wall. It is speculated that ischemia due to pulmonary embolism may be connected to its pathogenesis.

Alcoholic cardiomyopathy versus chronic myocarditis--immunohistological investigations with LCA, CD3, CD68 and tenascin

Dilated cardiomyopathy (DCM) is a disorder of unknown aetiology characterized by the left ventricular cavity enlargement and wall thinning associated with reduced left ventricular wall motion. DCM in chronic alcoholics is supposed to be caused by alcohol induced myocardial damage (alcoholic cardiomyopathy). Nevertheless, cardiotropic viruses, such as enteroviruses have long been suspected as causative agents for at least some forms of DCM. In the present study, 13 cases of DCM in chronic alcoholics were investigated with qualification and quantification of infiltrating leucocytes using immunohistological antibodies against leucocyte common antigen (LCA), T-lymphocytes (CD3) and macrophages (CD68). In addition, the expression of tenascin, playing a role in the initiation of fibrotic changes, was examined. All antigens were known to be possibly enhanced in cases of chronic myocarditis. Using these immunohistological techniques, 2 out of 13 cases had evidence for chronic inflammatory myocardial alterations in the sense of lymphocytic infiltrates (>2.0 CD3 T-lymphocytes/visual field at 400 x (HPF); >7 CD3 T-lymphocytes per mm(2)). These cases were diagnosed as having inflammatory cardiomyopathy. The other cases without myocardial inflammation were diagnosed as idiopathic/alcoholic DCM.

Two cases of right ventricular ischemic injury due to massive pulmonary embolism

In general, massive pulmonary embolism induces severe right ventricular overload, but pathological changes in the right ventricle due to pulmonary embolism is rarely seen. In this report, we describe two autopsy cases of massive pulmonary embolism without pre-existing cardiopulmonary disease. Both cases were accompanied by myocarditis-like changes in the right ventricle and infiltration of a number of polymorphonuclear neutrophils and mononuclear cells into the dilated right ventricular wall. Transmural or subendocardial coagulation necrosis was not apparent. Almost all of the mononuclear cells were immunohistochemically revealed to be CD68-positive macrophages. We speculated that these findings resulted from ischemia due to massive pulmonary embolism.

CD11b+ cells and ultraviolet-B-resistant CD1a+ cells in skin of patients with polymorphous light eruption

After ultraviolet exposure Langerhans cells (epidermal CD1a+ cells) disappear from the healthy skin, and CD11b+ macrophage-like cells, which are reported to produce interleukin-10, appear in a matter of days. These phenomena are related to the ultraviolet-induced local suppression of contact hypersensitivity reactions. A defect in this suppression might allow inadvertent immune reactions to develop after ultraviolet (over)exposure; i.e., it could cause ultraviolet-B-induced polymorphous light eruption. In order to test this we first exposed buttock skin of eight healthy volunteers to six minimal erythema doses from Philips TL12 lamps, and indeed observed a dramatic disappearance of CD1a+ cells 48 and 72 h later, at which time the number of CD11b+ cells increased in the dermis, and some occurred in the epidermis. The epidermis thickened and showed large defects, filled by CD11b+ cells, just below the stratum corneum. In 10 patients with polymorphous light eruption (five with a normal minimal erythema dose and five with a low minimal erythema dose) CD1a+ cells were present in the epidermis as well as in the dermis before exposure. Strikingly, these cells were still present in considerable number at 48 and 72 h after exposure to six minimal erythema doses. CD11b+ cells already present in the dermis before ultraviolet exposure, increased after ultraviolet exposure, and subsequently also invaded the epidermis. Despite the six minimal erythema doses, there were no apparent defects in the epidermis of the polymorphous light eruption patients. This deviant early response to ultraviolet radiation is likely to be of direct relevance to the polymorphous light eruption and is perhaps useful as a diagnostic criterion.