Evidence of perforin-mediated cardiac myocyte injury in acute murine myocarditis caused by Coxsackie virus B3

Small Molecule Inhibitors of Lymphocyte Perforin as Focused Immunosuppressants for Infection and Autoimmunity

New drugs that precisely target the immune mechanisms critical for cytotoxic T lymphocyte (CTL) and natural killer (NK) cell driven pathologies are desperately needed. In this perspective, we explore the cytolytic protein perforin as a target for therapeutic intervention. Perforin plays an indispensable role in CTL/NK killing and controls a range of immune pathologies, while being encoded by a single copy gene with no redundancy of function. An immunosuppressant targeting this protein would provide the first-ever therapy focused specifically on one of the principal cell death pathways contributing to allotransplant rejection and underpinning multiple autoimmune and postinfectious diseases. No drugs that selectively block perforin-dependent cell death are currently in clinical use, so this perspective will review published novel small molecule inhibitors, concluding with in vivo proof-of-concept experiments performed in mouse models of perforin-mediated immune pathologies that provide a potential pathway toward a clinically useful therapeutic agent.

Successful treatment of fulminant myocarditis with intra-aortic balloon pump counterpulsation combined with immunoglobulin and glucocorticoid in a young male adult

Background

Fulminant myocarditis (FM) is a serious non-specific inflammatory disease of the myocardium. FM tends to occur in adolescents and the course of the disease progresses rapidly. It is prone to cardiogenic shock (CGS) and multiple organ failure (MOF) with high mortality. We report a case of FM with CGS and MOF in a young male who was successfully treated with intra-aortic balloon pump counterpulsation (IABP) combined with intravenous immunoglobulin (IVIG) and glucocorticoid (GC).

Case summary

A 21-year-old previously healthy man presented with fever, headache, and chest tightness. He came to the hospital for emergency treatment. The laboratory data showed that the levels of serum cardiac troponin I (cTnI), N-terminal B-type natriuretic peptide (NT-proBNP), myocardial zymogram, and neutrophils increased. Echocardiography showed pericardial effusion and decreased left ventricular systolic function. ECG showed diffuse ST-segment elevation. He was clinically diagnosed with FM and admitted to the intensive care unit for treatment. Within 48 h of admission, the clinical course of the patient deteriorated rapidly, with CGS accompanied by MOF, high atrioventricular block (AVB), and ventricular tachycardia (VT). After using mechanical circulatory support (MCS) therapy with IABP, IVIG, GC, continuous renal replacement therapy (CRRT), and mechanical ventilation complicated with a temporary cardiac pacemaker, he recovered normal cardiac function. He made a full recovery and was discharged home on day 21.

Discussion

For patients with FM, early diagnosis, close monitoring, timely use of MCS devices, and active comprehensive treatment are very important. MCS devices such as IABP can become lifesaving tools for the treatment of FM.

CD8+ T cell cytotoxicity mediates pathology in the skin by inflammasome activation and IL-1β production

Deregulated CD8+ T cell cytotoxicity plays a central role in enhancing disease severity in several conditions. However, we have little understanding of the mechanisms by which immunopathology develops as a consequence of cytotoxicity. Using murine models of inflammation induced by the protozoan parasite leishmania, and data obtained from patients with cutaneous leishmaniasis, we uncovered a previously unrecognized role for NLRP3 inflammasome activation and IL-1β release as a detrimental consequence of CD8+ T cell-mediated cytotoxicity, ultimately resulting in chronic inflammation. Critically, pharmacological blockade of NLRP3 or IL-1β significantly ameliorated the CD8+ T cell-driven immunopathology in leishmania-infected mice. Confirming the relevance of these findings to human leishmaniasis, blockade of the NLRP3 inflammasome in skin biopsies from leishmania-infected patients prevented IL-1β release. Thus, these studies link CD8+ T cell cytotoxicity with inflammasome activation and reveal novel avenues of treatment for cutaneous leishmaniasis, as well as other of diseases where CD8+ T cell-mediated cytotoxicity induces pathology.

Leishmaniasis is a neglected tropical disease endemic in 98 countries and approximately 1 million new cases occur each year. Disease caused by Leishmania braziliensis, the main causative agent of leishmaniasis in South America, leads to skin ulcers that are difficult to heal with drugs that target the parasites. This is because disease severity seen in patients infected with L. braziliensis is largely due to the immune response that develops, rather than the number of parasites in the skin. CD8+ T cells induce cell death in the lesions of L. braziliensis-infected mice, as well as in the lesions from L. braziliensis-infected patients, which promotes disease. However, the mechanism mediating CD8+ T cell dependent pathology is unknown. Here, using studies in mice and experiments with L. braziliensis patients’ samples we show that increased disease severity is due to inflammasome activation, and furthermore that therapies that block either inflammasome activation or IL-1β ameliorate disease in mouse models of severe leishmaniasis. Based on these studies we propose a novel strategy of therapy for L. braziliensis infection and other diseases in which cytotoxicity plays a central role in promoting disease severity.

Presence of perforin in endomyocardial biopsies of patients with inflammatory cardiomyopathy predicts poor outcome

AIMS

Intramyocardial inflammation is considered an adverse prognostic factor in inflammatory cardiomyopathy (CMi). However, the precise nature of immune system factors relevant for the prediction of long-term course remains elusive. The aim of this study was to analyse the prognostic relevance of perforin in a large cohort of patients with CMi.

METHODS AND RESULTS

We investigated 495 consecutive patients with suspected CMi, undergoing endomyocardial biopsies (EMBs), and examined haemodynamic measurements after a long follow-up period (interquartile range 10.2-37.1 months). In EMBs, myocardial inflammation was assessed by histology and immunohistology. At follow-up, 388 patients (Group I) showed stable mild dysfunction or significant improvement, with LVEF rising from 46.2 ± 14.8% to 64.3 ± 12.3% (P < 0.0001). Lack of improvement of LV function or significant deterioration of LVEF from 42.1 ± 14.2% to 32.3 ± 11.6% (P < 0.0001) was observed in 107 patients (Group II). Multivariable statistical analysis of LVEF and immunohistochemical parameters in all patients revealed that the single most important predictor of LVEF development was detection of perforin in EMBs, with an odds ratio (OR) of 7.922 [95% confidence interval (CI) 4.380-14.326; P < 0.001] for deteriorating LVEF. Importantly, baseline LVEF (OR 0.962), LV end-diastolic diameter (OR 1.847), and other immmunohistochemical parameters (CD3, Mac-1, CD45R0, LFA-1, HLA-1, and ICAM-1) made minor or insignificant contributions to LVEF course in these 495 patients.

CONCLUSIONS

In this EMB-based analysis of the long-term course of CMi we identified, for the first time, that detection of perforin in the myocardium is a key predictor of LVEF course.

The adapter protein c-Cbl-associated protein (CAP) protects from acute CVB3-mediated myocarditis through stabilization of type I interferon production and reduced cytotoxicity

c-Cbl-associated protein (CAP), also called Sorbs1 or ponsin, has been described as an essential adapter protein in the insulin-signalling pathway. Here, we describe for the first time a unique protective role for CAP in viral myocarditis. Mortality and heart failure development were increased in CAP(-/-) mice compared to CAP(+/+) littermates after Coxsackievirus (CVB3) infection. Mechanistically, CAP protected from tissue apoptosis because of reduced CD8(+) T and natural killer cell cytotoxicity. Despite reduced cytotoxic elimination of CVB3-infected cells in CAP(+/+) hearts, however, CAP enhanced interferon regulatory factor 3 (IRF3)-dependent antiviral type I interferon production and decreased viral proliferation in vitro by binding to the cytoplasmic RIG-I-like receptor melanoma differentiation-associated protein 5 (MDA5). Taken together, these findings reveal a novel modulatory role for CAP in the heart as a key protein stabilizing antiviral type I interferon production, while protecting from excessive cytotoxic responses. Our study will help to define future strategies to develop treatments to limit detrimental responses during viral heart inflammation.

Mechanisms of NK cell-macrophage Bacillus anthracis crosstalk: a balance between stimulation by spores and differential disruption by toxins

NK cells are important immune effectors for preventing microbial invasion and dissemination, through natural cytotoxicity and cytokine secretion. Bacillus anthracis spores can efficiently drive IFN-γ production by NK cells. The present study provides insights into the mechanisms of cytokine and cellular signaling that underlie the process of NK-cell activation by B. anthracis and the bacterial strategies to subvert and evade this response. Infection with non-toxigenic encapsulated B. anthracis induced recruitment of NK cells and macrophages into the mouse draining lymph node. Production of edema (ET) or lethal (LT) toxin during infection impaired this cellular recruitment. NK cell depletion led to accelerated systemic bacterial dissemination. IFN-γ production by NK cells in response to B. anthracis spores was: i) contact-dependent through RAE-1-NKG2D interaction with macrophages; ii) IL-12, IL-18, and IL-15-dependent, where IL-12 played a key role and regulated both NK cell and macrophage activation; and iii) required IL-18 for only an initial short time window. B. anthracis toxins subverted both NK cell essential functions. ET and LT disrupted IFN-γ production through different mechanisms. LT acted both on macrophages and NK cells, whereas ET mainly affected macrophages and did not alter NK cell capacity of IFN-γ secretion. In contrast, ET and LT inhibited the natural cytotoxicity function of NK cells, both in vitro and in vivo. The subverting action of ET thus led to dissociation in NK cell function and blocked natural cytotoxicity without affecting IFN-γ secretion. The high efficiency of this process stresses the impact that this toxin may exert in anthrax pathogenesis, and highlights a potential usefulness for controlling excessive cytotoxic responses in immunopathological diseases. Our findings therefore exemplify the delicate balance between bacterial stimulation and evasion strategies. This highlights the potential implication of the crosstalk between host innate defences and B. anthracis in initial anthrax control mechanisms.

NK cells are important immune effectors that perform a surveillance task and react to transformed, stressed, and virally infected cells. They represent a first-line defence against cancer and pathogen invasion. Different pathogens trigger distinct NK-cell activation pathways. The Bacillus anthracis spore is the highly resistant form that enters the host and provokes anthrax. This microbe kills through a combination of acute bacterial infection and devastating toxemia. In the present study, we characterise the crosstalk between NK cells and spores, as well as the strategies used by B. anthracis to evade initial control mechanisms and impact anthrax pathogenesis. Our findings exemplify the spores' property to efficiently drive a high production of IFN-γ by NK cells, as well as the complex pathways used for activation which require both cytokine and cellular signaling. B. anthracis subverts this response through its toxins by paralysing essential NK cell functions. Furthermore, edema toxin from B. anthracis blocks natural cytotoxicity without affecting IFN-γ secretion. The CyaA toxin of Bordetella pertussis possesses the same enzymatic activity and has a similar effect. The high efficiency of these toxins in blocking cytotoxicity in vivo implies possible exploitation of their subverting activity to modulate excessive cytotoxic responses in immunopathological diseases.

Granzyme B as a novel factor involved in cardiovascular diseases

Apoptosis plays an important role in cardiovascular diseases such as atherosclerosis, ischemic heart disease, and congestive heart failure. Previous studies have demonstrated that oxidative stress, physiological stress, and inflammatory cytokines such as tumor necrosis factor and Fas ligand are involved in apoptosis of cardiovascular system. We demonstrate that another apoptosis-related pathway, i.e. granzyme B/perforin system is involved in cardiovascular diseases. Expression of granzyme B, a member of serine protease family is increased in acute coronary syndrome, coronary artery disease with end-stage renal disease, and subacute stage of acute myocardial infarction. Although granzyme B is extensively researched in immunological disorders, the role of granzyme B/perforin system was not clear in the cardiovascular field. In addition, little is known regarding the inhibition of granzyme B system in the clinical situation. In this review we demonstrate recent findings of granzyme B in cardiovascular diseases and possible therapeutic applications of inhibiting the granzyme B/perforin system.

Anti-perforin neutralizing antibody reduces myocardial injury in viral myocarditis

AIM

To investigate the role of anti-perforin neutralizing antibody in viral myocarditis.

METHODS

We divided 45 Balb/c mice randomly into 3 groups, a normal control group, a control group inoculated with coxsackie virus B3, and a group inoculated with anti-perforin neutralizing antibody. The second group was inoculated with 0.15 milliliters coxsackie virus B3, and the third group additionally with 0.1 milligrams/kilogram anti-perforin neutralizing antibody at time points of 6 hours and 3 days after infection. Histopathology was performed using haematoxylin and eosin, with apoptosis examined by the terminal transferase-mediated 2'-deoxyuridine 5'-triphosphate-biotin nick, end-labeling method, or Tunel. The expression of caspase-3 in myocardium was investigated by immunohistochemistry and reverse-transcription polymerase chain reaction.

RESULTS

The pathologic score, myocardial viral titers, average percentages of apoptotic cardiomyocytes, expression of active caspase-3 protein and messenger ribonucleic acid in the myocardium of the mice receiving anti-PFP neutralizing antibody therapy were all significantly reduced when compared to values from the group inoculated with coxsackie virus B3. The rates of expression of Caspase-3 and myocardial apoptosis were positively correlated with the scores for myocardial pathology.

CONCLUSION

Our results suggest that anti- perforin neutralizing antibody can reduce the myocardial damage by blocking the perforin/granzyme pathway, and downregulating the expression of messenger ribonucleic acid and protein of Caspase-3. These approaches may offer promising novel therapeutic strategies for the clinical treatment of viral myocarditis.

Anti-viral treatment in patients with virus-induced cardiomyopathy

Ongoing viral persistence in the myocardium is associated with an adverse prognosis of cardiomyopathy eventually resulting in a reduced capacity for work and thus it is associated with enormous social costs. Experimental and clinical data highlight that an imbalance of the cytokine network and a defect in the cytokine-induced immune response may constitute major causes leading to the development of virus persistence and progression of myocardial dysfunction. Reversibility of cardiac impairment during the early stages of the disease and the arising chance of specific treatment options demand early diagnosis and treatment of the disease. Our pilot data on anti-viral treatment using INF-beta showed beneficial clinical effects and suggest that some of the ventricular dysfunction and wall motion abnormalities resolved after elimination of the responsible agents. The data also suggest that elimination of cardiotropic viruses and associated clinical effects may occur even in DCM patients presenting with a long history.

Arrhythmogenic right ventricular cardiomyopathy/dysplasia: is there a role for viruses?

Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) is a primary heart muscle disease characterized structurally by progressive fibrofatty replacement of the right ventricle and clinically by life-threatening ventricular arrhythmias with left bundle branch block morphology. Recently, there has been a great deal of interest on ARVC/D as a cause of sudden death in young people, and it has been reported as the most common cause of exercise-related sudden death among competitive athletes in Italy. An autosomic dominant familial occurrence has been recognized, and four disease-causing genes have been recently identified in the dominant forms: ryanodinic cardiac receptor 2, desmoplakin, plakophilin 2, and transforming growth factor (TGF)-beta3. Furthermore, plakoglobin has been identified as the first gene responsible for the recessive variant of ARVC/D associated with palmoplantar keratosis and woolly hair (Naxos disease). However, although much progress has been made in molecular genetics, up to today, the pathogenesis of the disease is still unclear. The occurrence of myocyte apoptosis has been documented, suggesting that recurrent bouts of apoptosis may account for progressive atrophy of the myocardium, which is then replaced by fibrofatty tissue. Considering the frequent finding of myocarditis at histology, an inflammatory theory has been advanced, and infective mechanisms have been postulated to contribute to the onset and the progression of the disease. Cardiotropic viruses have been detected in some ARVC/D cases, and they have been proposed as possible etiologic agents. Several etiopathogenetic theories are herein presented in detail with particular attention to the inflammatory/infective one and its possible links between this and the genetic/dystrophic theories are discussed.

Cytotoxic perforin+ and TIA-1+ infiltrates are associated with cell adhesion molecule expression in dilated cardiomyopathy

OBJECTIVE

To phenotypically characterize cytotoxic T-lymphocytes (CTLs: Perforin+ and TIA-1+ phenotypes) and to study the interactions with cell adhesion molecules (CAMs) in dilated cardiomyopathy (DCM).

BACKGROUND

DCM is linked to intramyocardial inflammation, being characterized by T-lymphocytic infiltration and CAMs abundance. However, the pathogenic significance of increased CD3+ lymphocytes remains obscure as these do not correlate with CTLs (perforin+ and TIA1+ phenotypes). CAMs participate in the phenotypic repertoire and effector pathways of CTLs.

METHODS

CAMs-expression (ICAM-1, VCAM-1, LFA-3, CD29, CD62E and CD62P and beta(2)-integrins), CD3+ (T-lymphocytes), CD57+ (NK-cells) and adhesion related (CD18+, CD11a+, CD11b+, CDw49d+) phenotyped infiltrates were investigated in endomyocardial biopsies (EMBs) from 89 DCM patients (33 female; LVEF<40%) using immunohistochemisty. The enteroviral genome was identified by nested RT-PCR.

RESULTS

CAMs abundance was confirmed in 55 DCM patients (62%) and 29 EMBs (33%) were graded CTLs+ (>1.5 TIA-1+ and/or >2.0 perforin+ infiltrates/hpf). CTLs correlated with all endothelial CAMs-markers studied (P<0.01), the adhesion related phenotypes of infiltrates (LFA-1, VLA-4, CD18) and CD57+ NK-cells (P<0.02). There was no correlation of CTLs with CD3+ T-lymphocytes, CD11b+ macrophages, enteroviral infection (present in n=16/18%), clinical history and LVEF (P>0.05). Phenomena suggestive of CTLs mediated myocytolysis were observed in 10 patients (11%).

CONCLUSIONS

CTLs-infiltrates are associated with endothelial CAMs-abundance and co-express adhesion related (beta2-integrins, VLA-4) and NK-cellular antigens (CD57) in DCM. Endothelial CAMs expression also reflects cytotoxic activation of intramyocardial infiltrates, which is not reflected by immunologically nai;ve CD3 T-lymphocytes.

Interferon-beta treatment eliminates cardiotropic viruses and improves left ventricular function in patients with myocardial persistence of viral genomes and left ventricular dysfunction

BACKGROUND

Viral infections are important causes of myocarditis and may induce cardiac dysfunction and finally lead to dilated cardiomyopathy. We investigated whether interferon (IFN)-beta therapy is safe and may achieve virus clearance and prevent deterioration of left ventricular (LV) function in patients with myocardial virus persistence.

METHODS AND RESULTS

In this phase II study, 22 consecutive patients with persistence of LV dysfunction (history of symptoms, 44+/-27 months) and polymerase chain reaction-proven enteroviral or adenoviral genomes were treated with 18x10(6) IU/week IFN-beta (Beneferon) subcutaneously for 24 weeks. Histological and immunohistological analysis of endomyocardial biopsies was used to characterize myocardial inflammation. LV diameters and ejection fraction were assessed by echocardiography and angiography, respectively. During the treatment period, IFN-beta was well tolerated by all patients. No patient deteriorated. Clearance of viral genomes was observed in 22 of 22 of patients after antiviral therapy. Virus clearance was paralleled by a significant decrease of LV end diastolic and end systolic diameters, decreasing from 59.7+/-11.1 to 56.5+/-10.0 mm (P<0.001) and 43.2+/-13.6 to 39.4+/-12.1 mm (P<0.001), respectively. LV ejection fraction increased from 44.6+/-15.5% to 53.1+/-16.8% (P<0.001).

CONCLUSIONS

A 6 months, IFN-beta treatment was safe in patients with myocardial enteroviral or adenoviral persistence and LV dysfunction and resulted in elimination of viral genomes (22 of 22 patients) and improved LV function (15 of 22 patients).

Cytotoxic lymphocytes and cardiac electrophysiology

It is widely recognized that immune effector mechanisms contribute to cardiac dysfunction in major cardiac pathologies, such as myocarditis and the consequent dilated cardiomyopathy, Chagas' disease and heart transplant rejection. Of the wealth of immune mechanisms known to affect cardiac function, this review will deal with the adverse effects caused by cytotoxic T lymphocytes (CTL, CD4(+) and CD8(+) T lymphocytes), which participate in a broad range of heart pathologies. The interaction between cytotoxic lymphocytes and their target cells can set off two different effector mechanisms: (1) The perforin/granzymes, and (2) The Fas/FasL. In this review, I will discuss these mechanisms, and present experimental evidence showing that both can adversely affect cardiac myocytes in vitro, in a way that can contribute to a decline in the overall cardiac function.

Role of Fas/FasL pathway in the activation of infiltrating cells in murine acute myocarditis caused by Coxsackievirus B3

OBJECTIVES

This study was designed to investigate the roles of Fas/FasL pathway in myocardial damage in murine acute myocarditis caused by Coxsackie virus B3 (CVB3).

BACKGROUND

Cardiac myocyte apoptosis rarely occurs in murine acute myocarditis caused by CVB3. Fas/FasL belong to the tumor necrosis factor receptor/ligand superfamily of costimulatory molecules and are known to play a critical role in the induction of apoptosis, as well as in the cytotoxicty mediated by T-cells and natural killer cells.

METHODS

We first analyzed the expression of Fas on cardiac myocytes in vivo and in vitro. Second, we examined the development of myocardial damage, in C3H/He mice treated with an anti-FasL monoclonal antibody (mAb), and in C3H/He-lpr/lpr mice and C3H/He-gld/gld mice infected with CVB3. Third, to investigate the effects of anti-FasL mAb treatment on the activation of the infiltrating cells, we examined the expression of interferon (IFN)-gamma and interleukin (IL)-2 as activation markers in the heart of mice by semiquantitative polymerase chain reaction.

RESULTS

Fas was markedly induced on cardiac myocytes with acute myocarditis. Myocardial inflammation was decreased in mice treated with anti-Fas L mAb, C3H/He-lpr/lpr mice and C3H/He-gld/gld mice. Anti-FasL mAb-treatment also decreased the expression of IFN-gamma, IL-2, inducible nitric oxide synthase and CVB3 genomes in myocardial tissue.

CONCLUSIONS

Our findings strongly suggested that the Fas/FasL pathway played a critical role in the development of massive myocardial necrosis through activation of infiltrating cells, and raise the possibility of immunotherapy by blocking the Fas/FasL pathway to prevent myocardial damage and improve the prognosis of patients with viral myocarditis.

Enhanced expression and production of monocyte chemoattractant protein-1 in myocarditis

Monocyte chemoattractant protein-1 (MCP-1) is a member of the C-C chemokine family that has been shown to play a major role in the migration of monocytes and T cells to an inflammatory focus. To clarify the role of MCP-1 in the pathogenesis of myocarditis, we have examined the expression of MCP-1 in rat hearts with experimental autoimmune myocarditis (EAM), and have also measured serum levels of MCP-1 in patients with histology-proven acute myocarditis. Lewis rats were immunized with cardiac myosin and were killed 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 42 and 56 days after immunization. Large mononuclear cells in the myocardial interstitium were stained with an anti-MCP-1 antibody. mRNA of MCP-1 increased in the hearts of EAM rats from days 15--27 as shown by quantitative reverse transcription-polymerase chain reaction. Serum MCP-1 levels of the rats with EAM were significantly elevated from days 15--24. In the clinical study, serum levels of MCP-1 in 24 patients with acute myocarditis at the time of admission (165.2 +/- 55.8 pg/ml) were significantly (P = 0.0301) elevated compared with those of 20 healthy volunteers (61.8 +/- 10.7 pg/ml). Serum MCP-1 levels of 8 fatal cases (371.8 +/- 145.2 pg/ml) were significantly (P = 0.0058) higher than those of 16 cases who survived (65.5 +/- 12.8 pg/ml). In conclusions, MCP-1 may play an important role in the pathogenesis of human acute myocarditis as well as in the progression of rat EAM.

Nitric oxide inhibition improved myocardial metabolism independent of tissue perfusion during ischemia but not during reperfusion

Nitric oxide (NO) is one of the important regulators of cardiac metabolism and function as well as of tissue perfusion. Myocardial NO formation is increased during ischemia and reperfusion. We investigated the roles of endogenous NO in myocardial metabolism during ischemia and reperfusion independent of tissue perfusion changes. In an open-chest pig model, a bolus infusion of 20 mg/kg of N(G)-nitro l -arginine methyl ester (l -NAME), a NO synthase inhibitor, did not alter the regional myocardial perfusion compared with a control saline injection, as measured by colored microsphares. Using(31)P-nuclear magnetic resonance spectroscopy, we showed that the tissue levels of pH and adenosine triphosphate (ATP) but not those of creatine phosphate were significantly preserved in the l -NAME group compared with the placebo group during the subsequent 15-min regional ischemia. Thus, l -NAME reduced myocardial ATP utilization during ischemia, and the mechanism underlying these effects is independent of tissue perfusion changes. However, l -NAME did not accelerate the recovery of ATP levels following reperfusion, suggesting distinct roles of endogenous NO during reperfusion.

Takayasu arteritis: insights into immunopathology

Takayasu arteritis is an acute and sometimes chronic form of vasculitis involving the aorta, its main branches and pulmonary arteries. Although its etiology is still unknown, immunopathologic analyses revealed that the infiltrating cells mainly consisted of gammadelta T-cells as well as alphabeta T-cells and NK cells. The infiltrating gammadelta T-cells, cytotoxic T-lymphocytes (CTLs), and natural killer (NK) cells directly injured the vascular cells by releasing a cytolytic factor, perforin. Expression of heat-shock protein (HSP)-65 as well as human leukocyte antigen (HLA) class I and II was enhanced in Takayasu arteritis lesions, supporting the pathogenic role of gammadelta T-cells and alphabeta T-cells. T-cell receptor (TCR) alphabeta gene usage by the infiltrating cells was restricted, strongly suggesting that a specific antigen was targeted. TCR gammadelta gene usage by the infiltrating cells was also restricted. Furthermore, it has been reported that a strong association with a specific haplotype of major histocompatibility complex (MHC) class I chain-related (MIC), MICA gene with Takayasu arteritis, suggesting that the HLA-linked gene susceptible to the disease is mapped near the MICA gene. This also supports a pathogenic role of gammadelta T-cells in Takayasu arteritis because gammadelta T-cells were shown to recognize MICA molecule, which can be stress-induced. These findings suggest that unknown stress, such as infection, may trigger the autoimmune process of inflammation involved in Takayasu arteritis.

From myocarditis to cardiomyopathy: mechanisms of inflammation and cell death: learning from the past for the future

A progression from viral myocarditis to dilated cardiomyopathy has long been hypothesized, but the actual extent of this progression has been uncertain. However, a causal link between viral myocarditis and dilated cardiomyopathy has become more evident than before with the tremendous developments in the molecular analyses of autopsy and endomyocardial biopsy specimens, new techniques of viral gene amplification, and modern immunology. The persistence of viral RNA in the myocardium beyond 90 days after inoculation, confirmed by the method of polymerase chain reaction, has given us new insights into the pathogenesis of dilated cardiomyopathy. Moreover, new knowledge of T-cell-mediated immune responses in murine viral myocarditis has contributed a great deal to the understanding of the mechanisms of ongoing disease processes. Apoptotic cell death may provide the third concept to explain the pathogenesis of dilated cardiomyopathy, in addition to persistent viral RNA in the heart tissue and an immune system-mediated mechanism. Beneficial effects of alpha1-adrenergic blocking agents, carteolol, verapamil, and ACE inhibitors have been shown clinically and experimentally in the treatment of viral myocarditis and dilated cardiomyopathy. Antiviral agents should be more extensively investigated for clinical use. The rather discouraging results obtained to date with immunosuppressive agents in the treatment of viral myocarditis indicated the importance of sparing neutralizing antibody production, which may be controlled by B cells, and raised the possibility of promising developments in immunomodulating therapy.

Coxsackievirus B3-induced myocarditis: perforin exacerbates disease, but plays no detectable role in virus clearance

Viral myocarditis is remarkably common, being detected in approximately 1% of unselected asymptomatic individuals. Many cases are attributable to enteroviral infection, and in particular to coxsackievirus B3. The underlying pathogenesis is controversial, but most studies admit the important immunopathological role of infiltrating CD8+ (cytotoxic) T lymphocytes (CTLs). We have previously shown that CTLs play conflicting roles in coxsackievirus B (CVB) myocarditis; they assist in controlling virus replication, but also are instrumental in causing the extensive inflammatory disease, which often results in severe myocardial scarring. A role for perforin, the major CTL cytolytic protein, in CVB myocarditis has been suggested, but never proven. In the present study we use perforin knockout (PKO) mice to show that perforin plays a major role in CVB infection; in broad terms, perforin is important in immunopathology, but not in CVB clearance. For example, PKO mice are better able to withstand a normally lethal dose of CVB (100% survival of PKO mice compared with 90% death in +/+ littermates). In addition, PKO mice given a nonlethal dose of CVB develop only a mild myocarditis, whereas their perforin+ littermates have extensive myocardial lesions. The myocarditis in PKO mice resolves more quickly, and these mice show minimal histological sequelae; in contrast, late in disease the perforin+ mice develop severe myocardial fibrosis. PKO mice, despite lacking this major CTL effector function, can control the infection and eradicate the virus; growth kinetics and peak CVB titers are indistinguishable in PKO and perforin+ mice. Therefore, the immunopathological and antiviral effects of CTLs can be uncoupled by ablation of perforin; this offers a promising target for therapy of myocarditis. Furthermore, we evaluate the possible roles of apoptosis, and of chemokine expression, in CVB infection. In perforin+ mice, apoptotic cells are detected within the inflammatory infiltrate, whereas in their PKO counterparts, apoptotic myocyte nuclei are seen. Chemokine expression in both PKO and perforin+ mice precedes and parallels the course of myocarditis. Several chemokines are detectable earlier in PKO mice than in perforin+ mice, but PKO mice show reduced peak levels, and chemokine expression decays sooner. In particular, MIP-1alpha expression is barely detectable at any time point in PKO mice, but it is readily identified in perforin+ animals, peaking just before the time of maximal myocarditis; this is particularly interesting, given that MIP-1alpha knockout mice are resistant to CVB myocarditis, but remain able to control viral infection. Thus, the chemokine pathway offers a second route of intervention to diminish myocarditis and its sequelae, while permitting the host to eradicate the virus.

Perforin-secreting killer cell infiltration in the aortic tissue of patients with atherosclerotic aortic aneurysm

Cell-mediated immunity has been implicated in the pathogenesis of vascular cell injury in patients with atherosclerotic aortic aneurysms. To clarify the immunologic mechanisms involved, we examined the expression of a cytolytic factor, perforin, in infiltrating cells from aortic tissue samples taken from 6 patients with atherosclerotic aortic aneurysms. Immunohistochemical studies showed that the infiltrating cells consisted mainly of macrophages, natural killer (NK) cells, cytotoxic T lymphocytes (CTLs), and T helper cells, and that perforin was expressed in NK cells and CTLs. Immunoelectron microscopic studies demonstrated that the infiltrating cells released massive amounts of perforin directly on to the surface of arterial vascular cells. These findings provide the first direct evidence that some of the infiltrating cells in the aortic tissue consist of killer cells, and strongly suggest that these killer cells, especially NK cells and CTLs, may play a critical role in the vascular cell injury caused by atherosclerotic aortic aneurysm by releasing perforin.

Low-dose N omega-nitro-L-arginine methyl ester treatment improves survival rate and decreases myocardial injury in a murine model of viral myocarditis induced by coxsackievirus B3

Recent reports demonstrated the expression of inducible-type NO synthase in the heart of viral myocarditis. Since NO has multiple biological actions, a substantial amount of NO produced in the diseased heart may act either as a cytotoxic or as a cytoprotective molecule in the process of myocarditis. In the present study, we examined the effect of inhibition of NO synthesis on the mortality and the extent of myocardial injury in a murine model of coxsackievirus B3-induced myocarditis. We fed the infected mice drinking water containing a relatively low concentration (0.37 mmol/L) of N omega-nitro-L-arginine methyl ester (L-NAME) for 14 days after virus inoculation. This dose of L-NAME did not change virus titers in the heart. However, L-NAME-fed mice showed a significant reduction in mortality compared with those fed normal drinking water (nontreated mice). On the contrary, mice given a higher concentration of L-NAME (3.7 mmol/L) exhibited increased mortality. In addition, mice fed a low concentration of L-NAME showed reductions in the severity of heart failure and in the area of myocardial necrosis. Although systemic blood pressure was reduced in nontreated mice, in mice fed a low concentration of L-NAME, it was maintained at a level similar to that in uninfected control mice, L-NAME-treated mice also exhibited a reduction in the degree of inflammatory cell infiltration associated with decreased production of tissue prostaglandin E2 levels in the heart compared with nontreated mice. Therefore, NO is likely to be involved in the pathogenic mechanisms of myocardial injury and resultant cardiac dysfunction in a murine model of coxsackievirus B3-induced viral myocarditis.

Cell-mediated cytotoxicity in hearts with dilated cardiomyopathy: correlation with interstitial fibrosis and foci of activated T lymphocytes

OBJECTIVES

The purpose of this study was to investigate the expression of perforin and T-cell intracellular antigen-1, two crucial components of lymphocyte-mediated cytotoxicity, in endomyocardial biopsies from patients with idiopathic dilated cardiomyopathy.

BACKGROUND

Previous reports have demonstrated the presence of myocardial interstitial fibrosis and increased infiltrating lymphocytes in patients with dilated cardiomyopathy. However, the pathogenic significance of these lymphocytic infiltrates remains unclear.

METHODS

Endomyocardial biopsies from 134 patients with idiopathic dilated cardiomyopathy were histologically and immunohistologically analyzed. Monoclonal antibodies against diverse T-lymphocyte antigens, perforin and T-cell intracellular antigen-1 were used with the highly sensitive avidin-biotin complex technique. Positive cells were counted in at least 10 high power field.

RESULTS

Perforin and T-cell intracellular antigen-1 were immunohistologically detected in all biopsies. Immunoreactivity was restricted to the cytoplasm and was granular in nature, indicating specific staining of cytoplasmic granules. Correlations were established between the expression of perforin and T-cell intracellular antigen-1 and the abundance of foci of various T-lymphocyte subpopulations and, most importantly, the degree of interstitial fibrosis on routine histologic examination (p = 0.015).

CONCLUSIONS

Cytotoxic activity is clearly present in endomyocardial biopsies from patients with idiopathic dilated cardiomyopathy. Local activation-that is, focal accumulation of T lymphocytes-seems to be important for the generation of lymphocyte-mediated cytotoxicity. The interstitial fibrosis commonly seen in dilated cardiomyopathy may be caused by cytotoxic T-lymphocyte damage to the myocardium.

Expression of vascular cell adhesion molecule-1 in murine hearts with acute myocarditis caused by coxsackievirus B3

Cell-mediated autoimmunity has been strongly implicated in the pathogenesis of the myocardial cell damage involved in viral myocarditis. Using a murine model of acute myocarditis caused by Coxsackievirus B3 (CVB3), perforin-expressing killer cells have been shown to infiltrate the heart, and intercellular adhesion molecular-1 (ICAM-1) together with major histocompatibility complex (MHC) antigen was induced on myocardial cells in acute viral myocarditis. To clarify the immunological mechanisms in more detail, the expression of vascular cell adhesion molecular-1 (VCAM-1) has been examined in the heart of acute myocarditis and on cultured cardiac myocytes treated with interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha). The effects of in vivo antibody treatment to VCAM-1 on myocardial damage involved in acute myocarditis were also analysed. CVB3-induced myocarditis resulted in enhanced expression of VCAM-1 on myocardial cells. VCAM-1 expression was also induced on cultured cardiac myocytes by treatment with IFN-gamma and TNF-alpha. The in vivo antibody treatment to VCAM-1 decreased the myocardial damage to some extent, but the effects were not statistically significant. These data suggest that the expression of VCAM-1 on myocardial cells may play at least a partial role in the myocardial damage involved in acute viral myocarditis.

Ultrastructural aspect of myocarditis: its relevance for the diagnosis

The Dallas consensus was used to reveal active or borderline inflammatory loci by light microscopy (LM). When lymphocyte-cardiocyte interaction was observed by electron microscopy (EM), the deleterious or dormant pattern of inflammatory process was recognized. The first was determined by lymphocytes that adhered to cardiocytes, next to necrotic cardiocytes or admixed with debris. The second was marked by scattered lymphocytes between preserved cardiocytes and the absence of lymphocytes adhered to cardiocytes and necrotic cardiocytes. The deleterious pattern of the inflammatory process (EM) commonly supplemented the active appearance of inflammatory loci (LM). In contrast, the borderline outlook of the LM completed either the deleterious or dormant pattern of the EM. This discrepancy was related to the restricted resolution of LM, which might hide the actual stage of the disease. The diagnosis of myocarditis was founded on mutual LM and EM observations. The active or borderline appearance of LM of the deleterious pattern (EM) was considered indicative for the active stage of myocarditis. The borderline outlook of the LM of the dormant pattern of the EM was admitted to indicate either the healing phase of the disease with lymphocytes still lagging behind, or a latent phase of the ongoing myocarditis, according to the patient's hemodynamic status.

Perforin and lymphocyte-mediated cytolysis

We have discussed in the previous sections the recent progress made toward elucidating the regulatory mechanism of perforin gene transcription and the domain structure of the perforin molecule. It appears that the expression of perforin is, at least partially, controlled at the transcription level through the interaction between killer cell-specific cis- and trans- acting factors. One of such cognate pairs, NF-P motif (an EBS-homologous motif) and NF-P2 (a killer cell-specific DNA-binding protein), has been described. The regulatory mechanism of gene transcription, however, is likely to involve multiple factors which act in a coordinated fashion to bring about the most efficient expression of perforin limited strictly to activated killer lymphocytes. Through studies using synthetic peptides and recombinant perforins, it has been suggested that the N-terminal region of the perforin molecule is an important, though not the only, domain responsible for the lytic activity. Further studies are warranted to elucidate the role(s) of other potential amphiphilic structures located in the central portion of the perforin molecule in the overall pore-forming activity. The molecular basis underlying the resistance of killer lymphocytes to perforin-mediated lysis still remains an open question. Preliminary results, however, suggest that the surface protein(s) restricted to killer cells may account for their self-protection against perforin. Based on recent studies using perforin-deficient mice, the involvement of perforin in lymphocyte-mediated cytolysis both in vivo and in vitro has been confirmed. Two functional roles, a direct (lytic) and an indirect (endocytosis enhancer; conduit), both of which may contribute critically to the cell-killing event can be attributed to perforin. The fact that lymphocytes may also employ perforin-independent killing mechanism(s), e.g. Fas-dependent pathway, is beyond the scope of this review. There is, nevertheless, no doubt that these alternative cytolytic mechanisms may also play important roles in immune effector and/or regulatory responses associated with killer lymphocytes. Obviously, we are still a long way from concluding on the functional relevance of each individual cytolytic mechanism seen in different physiopathological situations. Suffice it to say, however, that a wealth of information on lymphocyte-mediated killing has already emerged through the multidisciplinary efforts conducted in our and other laboratories that promise to further dissect this complicated event in the years to come.

Perforin-secreting killer cell infiltration and expression of a 65-kD heat-shock protein in aortic tissue of patients with Takayasu's arteritis

Cell-mediated autoimmunity has been strongly implicated in the pathogenesis of vascular cell injury in Takayasu's arteritis. To clarify the immunological mechanisms involved, we examined the expression of a cytolytic factor, perforin in infiltrating cells of aortic tissue samples from seven patients with Takayasu's arteritis. We also examined the expression of a 65-kD heat-shock protein (HSP-65), human leukocyte antigen classes I and II, and intercellular adhesion molecule-1 in the aortic tissue. Immunohistochemical studies showed that the infiltrating cells mainly consisted of gamma delta T lymphocytes, natural killer cells, macrophages, cytotoxic T lymphocytes and T helper cells, and that perforin was expressed in gamma delta T lymphocytes, natural killer cells, and cytotoxic T lymphocytes. In situ hybridization analysis also revealed expression of perforin mRNA in the infiltrating cells. Immunoelectron microscopic studies demonstrated that the infiltrating cells released massive amounts of perforin directly onto the surface of arterial vascular cells. We also found that expression of HSP-65, human leukocyte antigen classes I and II, and intercellular adhesion molecule-1 was strongly induced in the aortic tissue and might facilitate the recognition, adhesion and cytotoxicity of the infiltrating killer lymphocytes. These findings provide the first direct evidence that the infiltrating cells in the aortic tissue mainly consist of killer cells, and strongly suggest that these killer cells, especially gamma delta T lymphocytes, may recognize HSP-65 and play a critical role in the vascular cell injury of Takayasu's arteritis by releasing perforin.