Antigen presentation plays positive roles in the regenerative response to cardiac injury in zebrafish

In contrast to adult mammals, adult zebrafish can fully regenerate injured cardiac tissue, and this regeneration process requires an adequate and tightly controlled immune response. However, which components of the immune response are required during regeneration is unclear. Here, we report positive roles for the antigen presentation-adaptive immunity axis during zebrafish cardiac regeneration. We find that following the initial innate immune response, activated endocardial cells (EdCs), as well as immune cells, start expressing antigen presentation genes. We also observe that T helper cells, a.k.a. Cd4+ T cells, lie in close physical proximity to these antigen-presenting EdCs. We targeted Major Histocompatibility Complex (MHC) class II antigen presentation by generating cd74a; cd74b mutants, which display a defective immune response. In these mutants, Cd4+ T cells and activated EdCs fail to efficiently populate the injured tissue and EdC proliferation is significantly decreased. cd74a; cd74b mutants exhibit additional defects in cardiac regeneration including reduced cardiomyocyte dedifferentiation and proliferation. Notably, Cd74 also becomes activated in neonatal mouse EdCs following cardiac injury. Altogether, these findings point to positive roles for antigen presentation during cardiac regeneration, potentially involving interactions between activated EdCs, classical antigen-presenting cells, and Cd4+ T cells.

A double-edged sword of immuno-microenvironment in cardiac homeostasis and injury repair

The response of immune cells in cardiac injury is divided into three continuous phases: inflammation, proliferation and maturation. The kinetics of the inflammatory and proliferation phases directly influence the tissue repair. In cardiac homeostasis, cardiac tissue resident macrophages (cTMs) phagocytose bacteria and apoptotic cells. Meanwhile, NK cells prevent the maturation and transport of inflammatory cells. After cardiac injury, cTMs phagocytose the dead cardiomyocytes (CMs), regulate the proliferation and angiogenesis of cardiac progenitor cells. NK cells prevent the cardiac fibrosis, and promote vascularization and angiogenesis. Type 1 macrophages trigger the cardioprotective responses and promote tissue fibrosis in the early stage. Reversely, type 2 macrophages promote cardiac remodeling and angiogenesis in the late stage. Circulating macrophages and neutrophils firstly lead to chronic inflammation by secreting proinflammatory cytokines, and then release anti-inflammatory cytokines and growth factors, which regulate cardiac remodeling. In this process, dendritic cells (DCs) mediate the regulation of monocyte and macrophage recruitment. Recruited eosinophils and Mast cells (MCs) release some mediators which contribute to coronary vasoconstriction, leukocyte recruitment, formation of new blood vessels, scar formation. In adaptive immunity, effector T cells, especially Th17 cells, lead to the pathogenesis of cardiac fibrosis, including the distal fibrosis and scar formation. CMs protectors, Treg cells, inhibit reduce the inflammatory response, then directly trigger the regeneration of local progenitor cell via IL-10. B cells reduce myocardial injury by preserving cardiac function during the resolution of inflammation.

Role of Cardiac Macrophages on Cardiac Inflammation, Fibrosis and Tissue Repair

The immune system plays a pivotal role in the initiation, development and resolution of inflammation following insult or damage to organs. The heart is a vital organ which supplies nutrients and oxygen to all parts of the body. Heart failure (HF) has been conventionally described as a disease associated with cardiac tissue damage caused by systemic inflammation, arrhythmia and conduction defects. Cardiac inflammation and subsequent tissue damage is orchestrated by the infiltration and activation of various immune cells including neutrophils, monocytes, macrophages, eosinophils, mast cells, natural killer cells, and T and B cells into the myocardium. After tissue injury, monocytes and tissue-resident macrophages undergo marked phenotypic and functional changes, and function as key regulators of tissue repair, regeneration and fibrosis. Disturbance in resident macrophage functions such as uncontrolled production of inflammatory cytokines, growth factors and inefficient generation of an anti-inflammatory response or unsuccessful communication between macrophages and epithelial and endothelial cells and fibroblasts can lead to aberrant repair, persistent injury, and HF. Therefore, in this review, we discuss the role of cardiac macrophages on cardiac inflammation, tissue repair, regeneration and fibrosis.

[CME: Post-Cardiac Injury Syndrome – a Special Form of Acute Pericarditis.]

Zusammenfassung. Angesichts der zunehmenden Anzahl kardialer Interventionen steigt auch die Inzidenz eines «Post-Cardiac Injury Syndrome» (PCIS). Dies stellt eine Form einer akuten Perikarditis dar und schliesst verschiedene pleuroperikardiale Syndrome ein, welche durch eine initiale Verletzung des Perikards/Myokards auftreten können. Klinisch präsentieren diese sich in einer Bandbreite von einer unkomplizierten Perikarditis bis hin zu komplexen Pleuroperikarditiden, Perikardtamponaden oder massiven Pleuraergüssen. Es wird eine immunvermittelte Pathogenese bei prädisponierten Patienten angenommen. Die Therapie basiert auf einer empirischen antiinflammatorischen Behandlung, inklusive Colchizin zur Prävention von Rezidiven.

A novel intracellular isoform of matrix metalloproteinase-2 induced by oxidative stress activates innate immunity

BACKGROUND

Experimental and clinical evidence has pinpointed a critical role for matrix metalloproteinase-2 (MMP-2) in ischemic ventricular remodeling and systolic heart failure. Prior studies have demonstrated that transgenic expression of the full-length, 68 kDa, secreted form of MMP-2 induces severe systolic failure. These mice also had unexpected and severe mitochondrial structural abnormalities and dysfunction. We hypothesized that an additional intracellular isoform of MMP-2, which affects mitochondrial function is induced under conditions of systolic failure-associated oxidative stress.

METHODOLOGY AND PRINCIPAL FINDINGS

Western blots of cardiac mitochondria from the full length MMP-2 transgenics, ageing mice and a model of accelerated atherogenesis revealed a smaller 65 kDa MMP-2 isoform. Cultured cardiomyoblasts subjected to transient oxidative stress generated the 65 kDa MMP-2 isoform. The 65 kDa MMP-2 isoform was also induced by hypoxic culture of cardiomyoblasts. Genomic database analysis of the MMP-2 gene mapped transcriptional start sites and RNA transcripts induced by hypoxia or epigenetic modifiers within the first intron of the MMP-2 gene. Translation of these transcripts yields a 65 kDa N-terminal truncated isoform beginning at M(77), thereby deleting the signal sequence and inhibitory prodomain. Cellular trafficking studies demonstrated that the 65 kDa MMP-2 isoform is not secreted and is present in cytosolic and mitochondrial fractions, while the full length 68 kDa isoform was found only in the extracellular space. Expression of the 65 kDa MMP-2 isoform induced mitochondrial-nuclear stress signaling with activation of the pro-inflammatory NF-κB, NFAT and IRF transcriptional pathways. By microarray, the 65 kDa MMP-2 induces an innate immunity transcriptome, including viral stress response genes, innate immunity transcription factor IRF7, chemokines and pro-apoptosis genes.

CONCLUSION

A novel N-terminal truncated intracellular isoform of MMP-2 is induced by oxidative stress. This isoform initiates a primary innate immune response that may contribute to progressive cardiac dysfunction in the setting of ischemia and systolic failure.

Macrophage depletion impairs wound healing and increases left ventricular remodeling after myocardial injury in mice

Macrophages have been suggested to be beneficial for myocardial wound healing. We investigated the role of macrophages in myocardial wound healing by inhibition of macrophage infiltration after myocardial injury. We used a murine cryoinjury model to induce left ventricular damage. Infiltrating macrophages were depleted during the 1st week after cryoinjury by serial intravenous injections of clodronate-containing liposomes. After injury, the presence of macrophages, which secreted high levels of transforming growth factor-beta and vascular endothelial growth factor-A, led to rapid removal of cell debris and replacement by granulation tissue containing inflammatory cells and blood vessels, followed by myofibroblast infiltration and collagen deposition. In macrophage-depleted hearts, nonresorbed cell debris was still observed 4 weeks after injury. Secretion of transforming growth factor-beta and vascular endothelial growth factor-A as well as neovascularization, myofibroblast infiltration, and collagen deposition decreased. Moreover, macrophage depletion resulted in a high mortality rate accompanied by increased left ventricular dilatation and wall thinning. In conclusion, infiltrating macrophage depletion markedly impairs wound healing and increases remodeling and mortality after myocardial injury, identifying the macrophage as a key player in myocardial wound healing. Based on these findings, we propose that increasing macrophage numbers early after myocardial infarction could be a clinically relevant option to promote myocardial wound healing and subsequently to reduce remodeling and heart failure.

Molecular mechanisms of cardiomyocyte regeneration and therapeutic outlook

Differently from some lower vertebrates, which can completely regenerate their heart, in higher vertebrates cardiac injury generally leads to progressive failure. Induction of cycle re-entry in terminally differentiated cardiomyocytes and stem-cell transplantation are strategies to increase the regenerative potential of the heart. As experimental and clinical studies progress, demonstrating that adult stem-cell administration has a favorable impact on myocardial function, the identification of cardiac stem cells suggests that some endogenous repair mechanisms actually exist in the mammalian heart. However, a deeper understanding of the mechanism that drives cardiomyocyte proliferation and stem-cell-mediated cardiac repair is required to translate such strategies into effective therapies.

SEX DIFFERENCES IN THE MYOCARDIAL INFLAMMATORY RESPONSE TO ACUTE INJURY

Hemorrhage, trauma, ischemia/reperfusion, burn, and sepsis each lead to cardiac dysfunction. These insults lead to an inflammatory cascade, which plays an important role in this process. Gender has been shown to influence the inflammatory response, as well as outcomes after acute injury. The mechanisms by which gender affects the inflammatory response to and the outcome of acute injury are being actively investigated. We searched PubMed for articles in the English language by using the search words sex, gender, estrogen, testosterone, inflammation, acute injury, ischemia reperfusion, sepsis, trauma, and burns. These were used in various combinations. We read the abstracts of the relevant titles to confirm their relevance, and the full articles were then extracted. References from extracted articles were checked for any additional relevant articles. This review will examine evidence for gender differences in the outcome to acute injury, explain the myocardial inflammatory response to acute injury, and elucidate the various mechanisms by which gender affects the myocardial response to acute injury.

Percutaneous coronary intervention in the context of systemic inflammation: more injury and worse outcome

Minor myocardial injury (MMI), identified by elevated serum levels of cardiac markers, is not uncommon after successful, uncomplicated elective percutaneous coronary intervention (PCI) in patients with stable angina. Serum cardiac troponin, especially cardiac troponin I (cTnI), are more sensitive than serum creatine kinase - MB in detecting MMI. Occlusion of small side-branch vessels, visualized by angiography, may explain the mechanism of the MMI in some, but not all patients. Occlusion of small intramyocardial vessels, not visualized by angiography, might be the mechanism of MMI in these patients. Recent reports have shown that cardiac troponin I elevation after successful, uncomplicated elective PCI in patients with stable angina may be a marker of adverse long-term outcome. Also, it has recently been reported that increased serum C-Reactive protein (CRP) is common in patients with stable angina and is a significant and independent determinant of MMI after uncomplicated elective PCI, indicating involvement of the systemic inflammatory state in the etiology of this periprocedural myocardial injury. An intense inflammatory response is expected following PCI in patients with increased baseline CRP levels, which can cause small vessel occlusion and/or microembolization that will lead to troponin elevation. With these findings in mind, and with the observation that increased risk associated with systemic inflammation can be reduced with certain preventive therapies, CRP may help to identify those who would benefit most from these pharmacological therapies before coronary interventions.

Amyloid myopathy: evidence for mechanical injury to the sarcolemma

Myopathy is a rare clinical manifestation in primary systemic amyloidosis. The clinical phenotype and muscle histology are well described but the pathophysiological mechanisms remain poorly understood. We report a 40-year-old man who presented with hypertrophic cardiomyopathy and a limb girdle syndrome associated with deposition of amyloid and free lambda light chains in skeletal muscle. Electron microscopy showed amyloid fibrils, physically disrupting the plasma membrane and basal lamina, while laminin immunocytochemistry revealed a reduction of laminin beta1 and upregulation of laminin alpha1. We believe that one of the possible pathophysiological mechanisms in amyloid myopathy is mechanical disruption of the sarcolemma by the abutting amyloid fibrils.

Immunological analysis of pleural fluid in post-cardiac injury syndrome

Post-cardiac injury syndrome (PCIS) is an inflammatory process involving pleura and pericardium secondary to cardiac injury. Even though this clinical entity has been recognised for decades, diagnosis is difficult because of lack of a diagnostic test. Antimyocardial antibody titre in pleural fluid and serum has been proposed to have diagnostic value. However there are inherent difficulties in measuring and interpreting the role of antimyocardial antibody. A case of PCIS with low pleural fluid complement level is reported, which it is believed can be useful to support the diagnosis of PCIS.

In vivo responses of macrophages and myofibroblasts in the healing following isoproterenol-induced myocardial injury in rats

To clarify the relation between macrophage and myofibroblast involvement in various myocardial diseases, the authors investigated the kinetics of these cells in the healing (scar tissue formation) following isoproterenol-induced myocardial injury in rats. Alpha-smooth muscle actin (alpha-SMA) expressing myofibroblasts were seen at the border of the affected area and appeared in the greatest numbers on days 3-7 post-injection, followed by a gradual decrease by day 35. The peak on day 3 was consistent with the timing of the highest proliferative activity of myofibroblasts. The number of ED1-positive macrophages began to increase as early as day 1, reaching a peak on day 3 within the injured myocardium. The expansion of ED1-positive macrophages preceded an increased number of alpha-SMA-positive myofibroblasts suggesting that myofibroblast proliferation and activation may be mediated by factors released by ED1-positive macrophages in response to myocardial injury. The number of ED2-positive tissue-fixed, resident macrophages gradually, increased from day 3 post-injection, and peaked on day 14, but the number of ED2-positive macrophages was consistently fewer than that of ED1-positive macrophages during the 35 day-observation period after the injection. The labelling index of the ED2-positive cells was maximal on day 14, indicative of local proliferation of resident macrophages. In the healing process after myocardial injury, ED1-positive macrophages increase markedly in the early stages: ED2-positive macrophages appear later.

Differential effects of IFN-gamma on kidney cell expression of MHC class II molecules, kidney cell associated molecules and their stimulatory capacity in mixed lymphocyte kidney cell culture

Mixed cell co-cultures of lymphocytes responding to kidney cells (MLKC), islets of Langerhans (MLIC) and mixed lymphocyte culture (MLC), were used to clarify mechanisms in allogeneic and autoimmune (tissue-associated) antigen presentation. Fresh kidney cortical tubular cells (KC), Madin-Darby canine kidney (MDCK), and dog kidney (6247) (DK) cell lines were used in MLKC reactions, and islets of Langerhans were used in the MLIC as putative antigen presenting cells (APC). The stimulating cells were treated with purified or recombinant dog interferon-gamma (IFN-gamma), and the detection of class II MHC molecule expression was assessed by a moneclonal antibody (mAb) (B1F6). Transcription of MHC class II mRNA and IFN-gamma mRNA was measured by semiquantitative polymerase chain reaction, and detection of a kidney cell (tissue-associated) antigen molecule was assessed by the mAb I1F6 that recognizes 72 and 150 kDa tubular cell protein(s) (KT1). The MDCK cell line constitutively expressed low levels of MHC class II molecules and KT1. The steady-state level of the MHC class II mRNA transcription was virtually unaltered by treatment with IFN-gamma (400 units) for 48 hours; however, the MHC cell surface protein expression was enhanced. The KC and DK cell lines constitutively expressed KT1, but not MHC class II molecules; these cells required a minimum of 4000 units, and a 62-hour incubation with IFN-gamma was needed to upregulate both surface MHC class II molecules and the transcription of corresponding specific mRNA. In the MLKC reaction both the MDCK and DK cell lines, as well as fresh KC cells, could serve as lymphocyte activators. This could be amplified by exogenous IFN-gamma. The removal of APC from the responding T cell population did not reduce the IFN-gamma effect. This indicates that IFN-gamma treatment allows for the expression of all of the co-stimulating factors and/or adhesion molecules necessary for these cells to serve as (surrogate) APC (direct as opposed to indirect antigen presentation). The requirements for purified IFN-gamma to increase this amplification was greater in the MLKC reactions with kidney cells than in the MLC reactions. The mAbs anti-IFN-gamma and I1F6 differed in their ability to inhibit lymphocyte proliferation depending on the different cell types involved. The I1F6 inhibited the MDCK and DK cell-driven MLKC (in the absence of exogenous IFN-gamma).(ABSTRACT TRUNCATED AT 400 WORDS)

Anti-myosin humoral immune response following cardiac injury

A sensitive and highly specific ELISA assay was developed to determine the anti-myosin humoral immune response (AMA) in various heart diseases: acute viral myocarditis, infective endocarditis, acute myocardial infarction, and valve and coronary bypass surgery. The mean study entry AMA titer of each patient group was already significantly increased compared with age matched controls. During further follow-up (90 d) all the groups except for endocarditis showed a significant increase of AMA titer compared with their entry titer. Anti-myosin antibody titer were higher after cardiac surgery than after myocardial infarction or inflammatory heart disease. These results suggest that anti-myosin immune response is not limited to infectious processes in which the pathogen induces antibodies which cross-react with heart constituents but is merely caused by direct cardiac injury. Myosin as a major compound of heart cellular proteins turned out to be a good candidate to trigger immune response after cardiac injury.

Postoperative immunological response against contractile proteins after coronary bypass surgery

The pathogenesis of post-cardiac injury syndrome was studied prospectively in 62 patients who underwent coronary bypass grafting. Preoperative and serial postoperative titres of actin and myosin antibodies were measured by an enzyme linked immunosorbent assay. Perioperative cumulative release of serum aspartate and alanine aminotransferases, lactate dehydrogenase, and creatine kinase was calculated by approximation formulas that are used to estimate infarct size. Complete post-cardiac injury syndrome developed in eight (13%) patients and an incomplete syndrome developed in 16 (26%). There was a significant correlation between frequency and intensity of the syndrome and the ratio of postoperative to preoperative titres of actin and myosin antibodies. Furthermore, there was a significant correlation between the cumulative release of lactate dehydrogenase, serum aspartate aminotransferase, and creatine kinase and the number of coronary vessels that were grafted, but no correlation was found between the incidence of post-cardiac injury syndrome and the number of coronary bypasses grafted or between the cumulative enzyme release and the postoperative immunological response against the major contractile proteins, actin and myosin. The amount of enzymes released during coronary bypass surgery seems to be a good indicator of the extent of myocardial damage during operation but it does not determine either the incidence of post-cardiac injury syndrome or the postoperative immunological response against the main contractile proteins actin and myosin.

Immunologic aspects of heart disease

All forms of heart disease, whether caused by streptococcus group A, aseptic heart injury, virus, hypersensitivity, autoimmune conditions, or graft-versus-host reactions, have in common allogenic transformation of the myocardial cell membrane and production of multifunctional autoantibodies, in addition to cause-specific antibodies, some of which cross-react with heart tissue. The outcome of this immunologic insult depends on the ability of the host's immunoregulatory mechanisms to dispose swiftly of the offending antigen and antibody or their complexes. Heart disease often results when these mechanisms, exemplified here, are not intact or when they function inappropriately in genetic or acquired settings and in varying haplotype frames.

Tamponade in Dressler's syndrome with immunological studies

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