The expression of vascular dendritic cells in human atherosclerotic carotid plaques

Immune cells in carotid artery plaques: what can we learn from endarterectomy specimens?

INTRODUCTION

Endarterectomy specimens represent a unique opportunity to study atherosclerosis. This review aims to summarize the recent knowledge of atherogenesis from studies characterizing a cellular composition of carotid endarterectomy specimens.

EVIDENCE ACQUISITION

A non-systematic literature review was carried out to summarize recent knowledge regarding ex vivo analysis of carotid artery plaque composition. Upon evaluation of their relevance, and elaborate forward and backward search, 95 articles were included in the review.

EVIDENCE SYNTHESIS

Despite the significant advancement of in vivo imaging techniques, the stroke prediction based on carotid artery plaque morphology is not reliable. Besides analyses of plaque morphology, present studies focus on precise characterization of the different immune cell types and elucidation of their role in plaque development. Plaque content analyses revealed the presence of various immune cells in carotid artery plaques. Presence of different immune cells subpopulations can be connected to some undesirable changes in plaque stability.

CONCLUSIONS

Since the destabilization of the atherosclerotic plaque is a multifactorial process, a combination of various methods should be used to characterize the unstable plaques more accurately. In this context, studies characterizing plaque content from a cellular point of view could elucidate some processes underlying the plaque progression. Together with morphological evaluation, these analyses could enable more precise assessment of plaque stability.

Decrease in dendritic cells in endomyocardial biopsies of human dilated cardiomyopathy

AIMS

Dendritic cells (DCs) are sentinels of the immune system-their role in myocardial disease is unknown as yet. We investigated their myocardial presence in human dilated cardiomyopathy (DCM).

METHODS AND RESULTS

Endomyocardial biopsies from 72 patients with DCM (EF ∼30%), as well as myocardial specimens from 18 suicide or accident victims were immunohistochemically analysed for myeloid and plasmacytoid DCs, antigen-presenting cells (APCs), and other leucocytes; also tissue fibrosis and apoptosis were histologically quantified. The myocardial viral genome was identified through polymerase chain reaction, and patients underwent clinical follow-up in 3-6 months. We found myocardial DCs of all examined subtypes and maturation stages (fascin, CD11c, CD209, CD83, and CD304), as well as markers for APCs (HLA-DR and CD40) and T-cell activation (CD69) to be significantly decreased in DCM compared with controls. In contrast, regulatory T cells (the GITR epitope), apoptosis (by TUNEL reaction and immunostaining with BCL-2), and a DC chemokine receptor (CCR7) were overexpressed, while no significant differences were observed for macrophages (CD68). Immature myeloid and plasmacytoid DCs strongly correlated with endothelial progenitor cells (CD34), which were similarly reduced in DCM, and inversely correlated with fibrosis. Myeloid DCs were especially reduced in virus-positive biopsies, and their numbers correlated with positive change in EF (ΔEF) at follow-up.

CONCLUSION

Myocardial DCs are reduced in heart biopsies of symptomatic DCM patients. Such a reduction correlates with an unfavourable short-term outcome in terms of EF, and could result from myocardial tissue damage, cellular death, and insufficient vascularization in chronic heart failure.

Macrophages, dendritic cells, and regression of atherosclerosis

Atherosclerosis is the number one cause of death in the Western world. It results from the interaction between modified lipoproteins and cells such as macrophages, dendritic cells (DCs), T cells, and other cellular elements present in the arterial wall. This inflammatory process can ultimately lead to the development of complex lesions, or plaques, that protrude into the arterial lumen. Ultimately, plaque rupture and thrombosis can occur leading to the clinical complications of myocardial infarction or stroke. Although each of the cell types plays roles in the pathogenesis of atherosclerosis, the focus of this review will be primarily on the macrophages and DCs. The role of these two cell types in atherosclerosis is discussed, with a particular emphasis on their involvement in atherosclerosis regression.

Elevated circulating interleukin-27 in patients with coronary artery disease is associated with dendritic cells, oxidized low-density lipoprotein, and severity of coronary artery stenosis

Coronary artery disease (CAD) is an immune-mediated chronic inflammatory disease mainly caused by atherosclerosis. The aims of this study were to investigate the role of interleukin-27 (IL-27) in patients with CAD and the severity of coronary artery lesions, which was evaluated by Gensini score and to investigate the biosynthesis of IL-27 and oxidized low-density lipoprotein (ox-LDL) in vitro using monocyte-derived dendritic cells (DCs). To this aim, plasma levels of IL-27, ox-LDL, and Gensini score were analyzed in patients with CAD (n = 136) and normal subjects (controls, n = 29). IL-27 concentration of the supernatant and the mRNA expression levels of p28 and ebi3, subunits of IL-27, from cultured immature DCs incubated with different concentrations of ox-LDL for 24 h were also analyzed. We found that circulating IL-27 levels were significantly elevated in patients with CAD than in controls (P < 0.01), and positively correlated to ox-LDL and Gensini score. ox-LDL dose-dependently upregulated expression of both IL-27 protein and IL-27 (p28 and EBI3) mRNA in vitro, indicating that ox-LDL can stimulate DCs to produce IL-27. These results demonstrate that IL-27 might regulate the network of immunity and inflammation in the pathogenesis of atherosclerosis.

A decrease in the percentage of circulating mDC precursors in patients with coronary heart disease: a relation to the severity and extent of coronary artery lesions?

Inflammation plays a pivotal role in coronary heart disease. Dendritic cells (DCs) are principal players in inflammation and atherosclerosis. Although the percentage of circulating DC precursors in coronary heart disease have been investigated, circulating myeloid DC (mDC) and plasmacytoid DC (pDC) precursors have not been extensively studied, particularly in relation to the severity of coronary artery lesions in patients with coronary heart disease. In this study, we recruited controls (n = 29), patients with stable angina pectoris (SAP, n = 30), patients with unstable angina pectoris (UAP, n = 56), and patients with acute myocardial infarction (AMI, n = 50). The severity and extent of coronary artery lesions was evaluated by Gensini score, following coronary angiograms. The percentage of circulating mDC and pDC precursors was determined by fluorescence-activated cell sorting (FACS). Plasma levels of MCP-1 and MMP-9, which correlate with atherosclerosis and DC migration, were also measured. The percentage of circulating mDC precursors was reduced in patients with AMI and UAP compared with control and SAP patients, respectively (p < 0.01 for AMI vs. SAP and Control, p < 0.05 for UAP vs. SAP and Control). The percentage of circulating pDC precursors was not significant changed. The levels of plasma MMP-9 and MCP-1 and Genisi score were all increased in patients with AMI and UAP, compared to control and SAP patients, respectively (p < 0.01 for AMI vs. SAP and control, p < 0.05 for UAP vs. SAP and control). Overall, the percentage of circulating mDC precursors was negatively correlated with MCP-1 (p < 0.001), MMP-9 (p < 0.001) and Genisi scores (p < 0.001). Genisi scores were positively correlated with the levels of MCP-1 (p < 0.001) and MMP-9 (p < 0.001). Our study suggested that the percentage of circulating mDC precursors is negatively correlated with the severity and extent of coronary artery lesions in patients with coronary heart disease.

The ubiquitin-proteasome system and cardiovascular disease

Over the past decade, the role of the ubiquitin-proteasome system (UPS) has been the subject of numerous studies to elucidate its role in cardiovascular physiology and pathophysiology. There have been many advances in this field including the use of proteomics to achieve a better understanding of how the cardiac proteasome is regulated. Moreover, improved methods for the assessment of UPS function and the development of genetic models to study the role of the UPS have led to the realization that often the function of this system deviates from the norm in many cardiovascular pathologies. Hence, dysfunction has been described in atherosclerosis, familial cardiac proteinopathies, idiopathic dilated cardiomyopathies, and myocardial ischemia. This has led to numerous studies of the ubiquitin protein (E3) ligases and their roles in cardiac physiology and pathophysiology. This has also led to the controversial proposition of treating atherosclerosis, cardiac hypertrophy, and myocardial ischemia with proteasome inhibitors. Furthering our knowledge of this system may help in the development of new UPS-based therapeutic modalities for mitigation of cardiovascular disease.

Dendritic cells in human atherosclerosis: from circulation to atherosclerotic plaques

Background. Atherosclerosis is a chronic inflammatory disease with atherosclerotic plaques containing inflammatory infiltrates predominantly consisting of monocytes/macrophages and activated T cells. More recent is the implication of dendritic cells (DCs) in the disease. Since DCs were demonstrated in human arteries in 1995, numerous studies in humans suggest a role for these professional antigen-presenting cells in atherosclerosis. Aim. This paper focuses on the observations made in blood and arteries of patients with atherosclerosis. In principal, flow cytometric analyses show that circulating myeloid (m) and plasmacytoid (p) DCs are diminished in coronary artery disease, while immunohistochemical studies describe increased intimal DC counts with evolving plaque stages. Moreover, mDCs and pDCs appear to behave differently in atherosclerosis. Yet, the origin of plaque DCs and their relationship with blood DCs are unknown. Therefore, several explanations for the observed changes are postulated. In addition, the technical challenges and discrepancies in the research field are discussed. Future. Future studies in humans, in combination with experimental animal studies will unravel mechanisms leading to altered blood and plaque DCs in atherosclerosis. As DCs are crucial for inducing but also dampening immune responses, understanding their life cycle, trafficking and function in atherosclerosis will determine potential use of DCs in antiatherogenic therapies.

Immunohistochemical characterisation of dendritic cells in human atherosclerotic lesions: possible pitfalls

BACKGROUND

Previously we demonstrated decreased blood myeloid (m) and plasmacytoid (p) dendritic cell (DC) counts in atherosclerotic patients. Therefore, we examined whether DCs, in particular DC precursors, accumulate in human plaques.

METHODS

Blood DC antigen (BDCA)-1, CD11c (mDCs), BDCA-2, CD123 (pDCs), langerin, fascin, S-100 (immature/mature DCs), and CD1a and CD83 (mature DCs) were investigated by immunohistochemistry of carotid arteries obtained by endarterectomy (EAS, frozen n = 11, fixed n = 11) or autopsy (fixed, n = 87).

RESULTS

Fascin and S-100 required formaldehyde fixation, other markers needed cryo-preservation. BDCA-1, BDCA-2, langerin, and S-100 appeared specific for intimal DCs, unlike CD123 and fascin (staining endothelial cells), CD11c and CD1a (staining monocytes, foam cells) or CD83 (staining lymphocytes). BDCA-1 and BDCA-2 cells were detected in EAS, preferentially near microvessels. S-100 cells increased successively from intimal thickening, via pathological intimal thickening, fibrous cap atheroma and finally complicated plaques. Fascin cells followed the same pattern, but were more abundant. However, in lesions containing microvessels (complicated plaques, plaque shoulders and most EAS) this was partly explained by fascin positive endothelial cells. Even complicated plaques contained relatively few mature CD83 DCs.

CONCLUSIONS

Accumulation of BDCA-1 and BDCA-2 around neovessels showed that mDCs and pDCs are recruited to advanced plaques, which is in line with the previously described decline of circulating blood DCs in patients with coronary artery disease. Unexpectedly, several DC markers yielded false positive signals. Hence, some accounts on numbers, trafficking and activation of DCs in atherosclerotic plaques may require re-evaluation.

Role of dendritic cells in cardiovascular diseases

Dendritic cells (DCs) are potent antigen-presenting cells that bridge innate and adaptive immune responses. Recent work has elucidated the DC life cycle, including several important stages such as maturation, migration and homeostasis, as well as DC classification and subsets/locations, which provided etiological insights on the role of DCs in disease processes. DCs have a close relationship to endothelial cells and they interact with each other to maintain immunity. DCs are deposited in the atherosclerotic plaque and contribute to the pathogenesis of atherosclerosis. In addition, the necrotic cardiac cells induced by ischemia activate DCs by Toll-like receptors, which initiate innate and adaptive immune responses to renal, hepatic and cardiac ischemia reperfusion injury (IRI). Furthermore, DCs are involved in the acute/chronic rejection of solid organ transplantation and mediate transplant tolerance as well. Advancing our knowledge of the biology of DCs will aid development of new approaches to treat many cardiovascular diseases, including atherosclerosis, cardiac IRI and transplantation.

Dendritic cells and their role in atherogenesis

Dendritic cells (DCs) are the most potent professional antigen-presenting cells with the unique ability of primary immune response initiation. DCs originate from bone marrow progenitors, which circulate in the peripheral blood and subsequently penetrate peripheral tissues, where they give rise to immature DCs. In peripheral tissues, DCs continuously monitor the microenvironment and, when the cells encounter 'danger' signals, DCs undergo differentiation and maturation. Maturing DCs usually migrate to lymphatic tissues, where they form contacts with T cells to initiate a primary immune response. DCs were identified in arteries in 1995 and since then, further knowledge has been gained about the peculiarities of vascular-associated DCs and their role in atherosclerosis. Immune reactions toward modified lipoproteins and other factors ignited by resident vascular DCs as well as by newly arrived DCs, which originate from blood monocytes, are believed to destabilize arterial homeostasis from very earlier stages of atherogenesis. There is a remarkable heterogeneity of DCs in atherosclerotic lesions. Some DCs mature and become capable of forming clusters with T cells directly within the arterial wall. The predictive value of the numbers of circulating DC precursors in coronary artery disease and in atherosclerosis has been assessed, and it has been shown that DCs have a role in plaque destabilization. Over recent decades, DCs have proven to be a valuable instrument in immunotherapy approaches against cancer and various autoimmune diseases, and this explains the demand that the accumulated knowledge be applied to the field of atherosclerosis immunotherapy.

Silencing CX3CR1 production modulates the interaction between dendritic and endothelial cells

CX3CR1, an important chemokine receptor in dendritic cells (DCs), is linked to the progression of atherosclerotic plaques. However, the mechanism(s) determining the role of CX3CR1 in atherosclerosis have not been clearly elucidated. In this study, we developed DCs from monocytes of Sprague-Dawley (SD) rats in the presence of recombinant human granulocyte-macrophage colony-stimulating factor (GM-CSF) and recombinant human interleukin-4 (IL-4). The presence of recombinant human TNF-α and LPS forced the cells to mature. When compared to immature DCs, flow cytometry (FACS) analysis revealed that mature DCs display a sustained increase in the levels of CD11c, CD86, and CD80 expression. The expression of Fractalkine (FKN) in endothelial cells (ECs) contributes to the maturation of DCs and expression of CX3CR1. We revealed that mRNA expression levels of CX3CR1 in mature DCs are significantly higher than those of immature DCs (P<0.001). Transfection of DCs with siRNA specific for the CX3CR1 gene resulted in potent suppression of gene expression and inhibition of interactions between DCs and ECs. Based on these data, we hypothesized that CX3CR1 contributes to the DC-EC interaction. CX3CR1 may serve as a new target molecule for increasing therapeutic interactions in atherosclerosis.

On to the road to degradation: atherosclerosis and the proteasome

Protein metabolism is a central element of every living cell. The ubiquitin-proteasome system (UPS) is an integral part of the protein metabolism machinery mediating post-transcriptional processing and degradation of the majority of intracellular proteins. Over the past few years, remarkable progress has been made in our understanding of the role of the UPS in vascular biology and pathobiology, particularly atherosclerosis. This review reflects on the recent developments from the effects on endothelial cells and the initial stage of atherosclerosis to the effects on vascular smooth muscle and the progression stage of atherosclerosis and finally to the effects on cell viability and the complication stage of atherosclerosis. It will conclude with the integration of the available information in a synoptic view of the involvement of the UPS in atherosclerosis.

Dendritic cells in atherosclerotic disease

Atherosclerosis has been considered a syndrome of dysregulated lipid storage until recent evidence has emphasized the critical contribution of the immune system. Dendritic cells (DC) are positioned at the interface of the innate and adaptive immune system. Recognition of danger signals in atheromas leads to DC activation. Activated DC regulate effector T cells which can kill plaque-resident cells and damage the plaque structure. Two types of DC have been identified in atherosclerotic lesions; classical myeloid DC (mDC) which mainly recognize bacterial signatures and plasmacytoid DC (pDC) which specialize in sensing viral fragments and have the unique potential of producing large amounts of type I interferon (IFN). In human atheromas, type I IFN upregulates expression of the cytotoxic molecule TRAIL which leads to apoptosis of plaque-resident cells. This review will elucidate the role of DC in atherogenesis and particularly in plaque rupture, the underlying pathophysiologic cause of myocardial infarction.

Predictive value of the decrease in circulating dendritic cell precursors in stable coronary artery disease

DCs (dendritic cells) are present in atherosclerotic lesions leading to vascular inflammation, and the number of vascular DCs increases during atherosclerosis. Previously, we have shown that the levels of circulating DCPs (DC precursors) are reduced in acute coronary syndromes through vascular recruitment. In the present study, we have investigated whether DCP levels are also reduced in stable CAD (coronary artery disease). The levels of circulating mDCPs (myeloid DCPs), pDCPs (plasmacytoid DCPs) and tDCP (total DCPs) were investigated using flow cytometry in 290 patients with suspected stable CAD. A coronary angiogram was used to evaluate a CAD score for each patient as follows: (i) CAD excluded (n=57); (ii) early CAD (n=63); (iii) moderate CAD (n=85); and (iv) advanced CAD (n=85). Compared with controls, patients with advanced stable CAD had lower HDL (high-density lipoprotein)-cholesterol (P=0.03) and higher creatinine (P=0.003). In advanced CAD, a significant decrease in circulating mDCPs, pDCPs and tDCPs was observed (each P<0.001). A significant inverse correlation was observed between the CAD score and mDCPs, pDCPs or tDCPs (each P<0.001). Patients who required percutaneous coronary intervention or coronary artery bypass grafting had less circulating mDCPs, pDCPs and tDCPs than controls (each P<0.001). Multiple stepwise logistic regression analysis suggested mDCPs, pDCPs and tDCPs as independent predictors of CAD. In conclusion, we have shown that patients with stable CAD have significantly lower levels of circulating DCPs than healthy individuals. Their decrease appears to be an independent predictor of the presence of, and subsequent therapeutic procedure in, stable CAD.

Innate immunity, Toll-like receptors, and atherosclerosis: mouse models and methods

Chronic inflammation and aberrant lipid metabolism represent hallmarks of atherosclerosis. Innate immunity critically depends upon Toll-like receptor (TLR) signalling. Recent data directly implicate signalling by TLR4 and TLR2 in the pathogenesis of atherosclerosis. The role that TLRs play in the pathogenesis of atherosclerosis can be assessed by using several animal models, which provide a double genetic deficiency in TLRs and molecules implicated in the lipid metabolism, such as ApoE or LDL receptor. Furthermore, a more recent technique, such as the bone marrow transplantation (BMT), can be a useful and straightforward method to elucidate the role of stromal versus hematopoietic cells in the acceleration of the atheroma.

Smooth muscle cells, dendritic cells and mast cells are sources of TNFalpha and nitric oxide in human carotid artery atherosclerosis

INTRODUCTION

In atherogenesis, dendritic cells, beside presenting antigens, may be sources of tumour necrosis factor (TNF)alpha and nitric oxide (NO), together with mast cells and smooth muscle cells.

MATERIAL AND METHODS

We have looked at the expression of TNFalpha and inducible NO synthase (iNOs) by these cells by affinity cytochemistry in autoptical specimens from normal carotid arteries and not ruptured, hemorrhagic or calcified atheromata.

RESULTS

Round to dendritic, major histocompatibility complex class II molecules (MHC-II+) cells and avidin-labeled mast cells were rare in normal arteries and significantly more numerous in atheromata. Many MHC-II+ cells expressed S-100 antigen; while a few were positive for phalloidin; appreciable fractions of these cells were immunoreactive for TNFalpha and iNOs, both in control specimens and atheromata. The fraction of mast cells labeled for iNOs was significantly lower in atheromata than in controls. Phalloidin positive cells were the most abundant cell type in the normal intima and atheromata; the fractions of these cells labeled for TNFalpha and iNOs were significantly higher in atheromata than in controls. Very few of these cells were also labeled for MHC-II. Computerized image analysis confirmed that the amounts of iNOs and TNFalpha were higher in atheromata than in controls. The increase in TNFalpha in atheromata was also confirmed by western blot.

CONCLUSIONS

Dendritic cells and mast cells can participate to the generation of TNFalpha and NO in the normal arterial wall and in atheromata, but myointimal cells are candidates as major sources of these molecules.