Dendritic cells in atherosclerosis: current status of the problem and clinical relevance

High-density lipoprotein affects antigen presentation by interfering with lipid raft: a promising anti-atherogenic strategy

Atherosclerosis is a chronic inflammatory disease. Immunomodulation of atherosclerosis emerges as a promising approach to prevention and treatment of this widely prevalent disease. The function of high-density lipoprotein (HDL) to promote reverse cholesterol transport may explain the ability of its protection against atherosclerosis. Findings that HDL and apolipoprotein A-I (apoA-I) inhibited the ability of antigen presenting cells (APCs) to stimulate T cells might be attributed to lipid raft, a cholesterol-rich microdomain exhibiting functional properties depending largely upon its lipid composition. Thus, modulating cholesterol in lipid raft may provide a promising anti-atherogenic strategy.

Functional alterations of myeloid cell subsets in hyperlipidaemia: relevance for atherosclerosis

Atherosclerosis is a chronic inflammatory disease wherein the infiltration of myeloid cells of the vessel wall is a hallmark event. Lymphocytes, platelets and endothelial cells stand out as prominent suspects being involved in atherosclerosis. However, recent advances suggest a crucial role for myeloid leucocytes, specifically monocyte subsets, neutrophils, dendritic cells and endothelial progenitor cells. These cell types are not just rapidly recruited or already reside in the vascular wall, but also initiate and perpetuate core mechanisms in plaque formation and destabilization. Hyperlipidaemia is an independent risk factor for atherosclerosis. Herein, hyperlipidaemia skews myeloid cell haemostasis, phenotype and transcriptional regulation of pro-inflammatory factors ultimately promoting myeloid cell extravasation and atherosclerosis. We here review the role of myeloid cells in atherosclerosis as well as the effects of hyperlipidaemia on these cells.

Vaccination using oxidized low-density lipoprotein-pulsed dendritic cells reduces atherosclerosis in LDL receptor-deficient mice

AIMS

Modification of lipoproteins plays an important role in the development of atherosclerosis. Oxidatively modified low-density lipoprotein (oxLDL) has a number of pro-inflammatory effects, whereas immunization with various forms of oxLDL is able to reduce atherosclerosis. The uptake of modified LDL by dendritic cells (DCs) and the presentation of epitopes thereof may form an important step in the immunomodulatory effects of LDL. In this study, we transferred oxLDL-pulsed mature DCs (mDCs) to LDL receptor-null (LDLr(-/-)) mice and examined the effects on atherosclerosis.

METHODS AND RESULTS

Bone marrow-derived DCs were cultured for 10 days in the presence of granulocyte-macrophage colony-stimulating factor. Immature DCs were matured by lipopolysaccharide and pulsed with copper-oxidized LDL. These mDCs were transferred three times to LDLr(-/-) mice before the induction of atherosclerosis by Western-type diet feeding. The transfer of oxLDL-pulsed mDCs resulted in an 87% reduction in carotid artery lesion size (P < 0.001) with a concurrent increase in plaque stability, whereas treatment using mDCs pulsed with the atherosclerosis-irrelevant antigen, ovalbumin, did not influence lesion size or stability. Furthermore, the vaccination procedure resulted in the induction of oxLDL-specific T cells with a reduced Th1 profile and an increase in oxLDL-specific IgG levels, which contributed to a reduction in foam cell formation.

CONCLUSION

These data indicate that vaccination with oxLDL-pulsed mDCs provides a novel and powerful strategy for the immunomodulation of atherosclerosis.

Short-term 20-mg atorvastatin therapy reduces key inflammatory factors including c-Jun N-terminal kinase and dendritic cells and matrix metalloproteinase expression in human abdominal aortic aneurysmal wall

BACKGROUND

Abdominal aortic aneurysm (AAA) accumulates features of a chronic inflammatory disorder and irreversible destruction of connective tissue. A recent experimental study identified c-Jun N terminal kinase (JNK) as a proximal signaling molecule in the pathogenesis of AAA and vascular dendritic cells as key players in the inflammatory reaction and degradation of the extracellular matrix. Statins can inhibit cell proliferation and vascular inflammation, which might help prevent AAA progression. However, supporting clinical data from human studies are lacking. We hypothesized that atorvastatin might inhibit JNK and dendritic cells, resulting in suppression of inflammatory cells and matrix metalloproteinases (MMPs) in human tissue of AAA.

METHODS

Patients with AAA were randomized to atorvastatin (20mg/day, n=10) and non-treated (n=10) groups. After treatment for 4 weeks, patients underwent abdominal aorta replacement, tissue specimens were obtained, and tissue composition was assessed using immunohistochemistry with quantitative image analysis.

RESULTS

Atorvastatin significantly reduced expression of JNK (1.1% vs. 8.1%, P=0.0002) and dendritic cells (3.2 vs. 7.2, P=0.003) compared to controls. T cells (142 vs. 315, P=0.008), macrophages (13 vs. 24, P=0.048) and immunoreactivity to MMP-2 (7.8% vs. 21%, P=0.049) and MMP-9 (13% vs. 24%, P=0.028) were also suppressed in the atorvastatin group. Serum low-density lipoprotein cholesterol level was decreased by 40% in the atorvastatin group.

CONCLUSIONS

Atorvastatin treatment acutely reduces JNK expression and dendritic cells, resulting in reduced inflammatory cell content and expression of MMPs in the AAA wall.

High ratio of myeloid dendritic cells to plasmacytoid dendritic cells in blood of patients with acute coronary syndrome

BACKGROUND

Dendritic cells (DCs) stimulate T-cells to participate in the inflammatory processes that promote the destruction of vulnerable plaques. The relationship between circulating levels of myeloid DCs (mDCs) and plasmacytoid DCs (pDCs) in patients with acute coronary syndrome (ACS) was evaluated.

METHODS AND RESULTS

Blood samples were obtained from 39 patients with ACS, 41 patients with stable angina pectoris (SAP) and 43 controls. The proportion of mDCs tended to be lower in the ACS group than in the SAP group and controls. Interleukin-12 levels associated with mDCs were significantly higher in the ACS group than in control group. The proportion of pDCs was significantly lower in the ACS groups than in the other two groups. Interferon-alpha levels secreted by pDCs, however, were not significantly different among the 3 groups. The ratio of mDCs to pDCs >or=4 is an important value for distinguishing ACS from SAP patients and control patients through receiver operating characteristic analysis (sensitivity; 85.0%, specificity; 83.4%).

CONCLUSIONS

The ratio of mDCs to pDCs may be a useful marker for detecting ACS and the existence of vulnerable plaques.

Adaptive immunity and atherosclerosis

Atherosclerosis involves the formation of inflammatory arterial lesions and is one of the most common causes of death globally. It has been evident for more than 20 years that adaptive immunity and T cells in particular regulate the magnitude of the atherogenic pro-inflammatory response. T cells also influence the stability of the atherosclerotic lesion and thus the propensity for thrombus formation and the clinical outcome of disease. This review summarizes our current understanding of T cells in atherogenesis, including which antigens they recognize, the role of T cell costimulation/coinhibition, and their secretion of pro- and anti-inflammatory mediators. Furthermore, we outline future areas of research and potential clinical intervention strategies.

Inflammatory cytokines decrease the expression of nicotinic acetylcholine receptor during the cell maturation

It is known that the nervous system significantly attenuates systemic inflammatory responses through the parasympathetic nervous system. Furthermore, it has been reported that the alpha 7 subunit of a nicotinic acetylcholine receptor is required for a cholinergic inhibition against cytokine synthesis in a macrophage. As antigen-presenting cells (APCs) play a central role in the generation of primary T cell responses and the maintenance of immunity, in this study, we investigated the expression level of nicotinic receptors of a p53-deficient APC cell line (JawsII) derived from a mouse bone marrow. We showed that stimulation of the JawsII cells with lipopolysaccharide (LPS) and tumor necrosis factor alpha (TNF-alpha) led increase of CD80 and CD86 expression while diminishment of the surface nicotinic receptor. On the other hand, stimulation of nicotinic receptor had no effect on these phenomena. Furthermore, we examined the ability of the cells to release cytokine when stimulated with both nicotine and LPS and showed that the stimulation with LPS augmented the secretion of IL-1a, IL-1b, IL-6, and TNF-alpha. These results suggested that nicotinic stimulation had no effect on the diminishment of alpha 7 nicotinic acetylcholine receptor on JawsII cells by LPS stimulation.

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.

Innate and adaptive immunity in atherosclerosis

Atherosclerosis, a chronic inflammatory disorder, involves both the innate and adaptive arms of the immune response that mediate the initiation, progression, and ultimate thrombotic complications of atherosclerosis. Most fatal thromboses, which may manifest as acute myocardial infarction or ischemic stroke, result from frank rupture or superficial erosion of the fibrous cap overlying the atheroma, processes that occur in inflammatorily active, rupture-prone plaques. Appreciation of the inflammatory character of atherosclerosis has led to the application of C-reactive protein as a biomarker of cardiovascular risk and the characterization of the anti-inflammatory and immunomodulatory actions of the statin class of drugs. An improved understanding of the pathobiology of atherosclerosis and further studies of its immune mechanisms provide avenues for the development of future strategies directed toward better risk stratification of patients as well as the identification of novel anti-inflammatory therapies. This review retraces leukocyte subsets involved in innate and adaptive immunity and their contributions to atherogenesis.

Quantum dot mediated imaging of atherosclerosis

The progression of atherosclerosis is associated with leukocyte infiltration within lesions. We describe a technique for the ex vivo imaging of cellular recruitment in atherogenesis which utilizes quantum dots (QD) to color-code different cell types within lesion areas. Spectrally distinct QD were coated with the cell-penetrating peptide maurocalcine to fluorescently-label immunomagnetically isolated monocyte/macrophages and T lymphocytes. QD-maurocalcine bioconjugates labeled both cell types with a high efficiency, preserved cell viability, and did not perturb native leukocyte function in cytokine release and endothelial adhesion assays. QD-labeled monocyte/macrophages and T lymphocytes were reinfused in an ApoE(-/-) mouse model of atherosclerosis and age-matched controls and tracked for up to four weeks to investigate the incorporation of cells within aortic lesion areas, as determined by oil red O (ORO) and immunofluorescence ex vivo staining. QD-labeled cells were visible in atherosclerotic plaques within two days of injection, and the two cell types colocalized within areas of subsequent ORO staining. Our method for tracking leukocytes in lesions enables high signal-to-noise ratio imaging of multiple cell types and biomarkers simultaneously within the same specimen. It also has great utility in studies aimed at investigating the role of distinct circulating leukocyte subsets in plaque development and progression.

A novel paradigm for dendritic cells as effectors of cartilage destruction

OBJECTIVE

Dendritic cells (DCs) are enriched in RA synovium and have been implicated in the pathogenesis of RA primarily through their ability to present autoantigen and activate T cells. However, whether DCs play an effector role in cartilage destruction is unknown. The aim of this study was to investigate whether DCs can induce collagen release from cartilage and the mechanism involved.

METHODS

Human monocyte-derived DCs (mDCs) were activated with CD40 ligand (CD40L) to mimic DC-T-cell interaction, and supernatants were incubated with cartilage explants. Hydroxyproline was assessed as a measure of collagen release and collagenolytic activity was measured by a bioassay using tritiated collagen. TNF-alpha in DC supernatants was measured by specific ELISA.

RESULTS

Supernatants from CD40L-activated mDCs, but not unstimulated mDCs, strongly induced the destruction of cartilage collagen. mDC supernatants did not contain collagenases but did induce collagenolytic activity in cartilage explants. Neutralization of TNF-alpha in mDC supernatants completely abolished collagenolysis.

CONCLUSIONS

This study shows that mDCs, upon CD40-ligation, induce cartilage collagen degradation through an indirect mechanism via the production of TNF-alpha. Our data suggest a potential important role for mDC-derived TNF-alpha in RA, which is in line with the previously reported observations that DCs are a major source of TNF-alpha in early autoimmune lesions and that anti-TNF-alpha therapeutics effectively suppress joint damage in RA patients. We propose that DCs can act as effectors in cartilage destruction, adding a new aspect to the functional role of DCs in RA pathogenesis.

Dendritic cell-associated immune inflammation of cardiac mucosa: a possible factor in the formation of Barrett's esophagus

BACKGROUND

The development of Barrett's esophagus is poorly understood, but it has been suggested that cardiac mucosa is a precursor of intestinal type metaplasia and that inflammation of cardiac mucosa may play a role in the formation of Barrett's esophagus. The present study was undertaken to examine the presence and distribution of immune-inflammatory cells in cardiac mucosa, specifically focusing on dendritic cells because of their importance as regulators of immune reactions.

MATERIAL AND METHODS

Endoscopic biopsy specimens were obtained from 12 patients with cardiac mucosa without Barrett's esophagus or adenocarcinoma and from 21 patients with Barrett's esophagus without dysplasia (intestinal metaplasia). According to histology, in nine of the 21 specimens with Barrett's esophagus, areas of mucosa composed of cardiac type epithelium-lined glands were present as well. Immunohistochemical staining and electron microscopy were used to examine immune-inflammatory cells in paraffin-embedded sections.

RESULTS

Immune-inflammatory cells, including T cells, B cells, dendritic cells, macrophages, and mast cells, were present in the connective tissue matrix that surrounded cardiac type epithelium-lined glands in all patients with cardiac mucosa. Clustering of dendritic cells with each other and with lymphocytes and the intrusion of dendritic cells between glandular mucus cells were observed. In the Barrett's esophagus specimens that contained cardiac type glands, computerized CD83 expression quantitation revealed that there were more dendritic cells in cardiac mucosa than in intestinal metaplasia.

CONCLUSION

Immune-inflammatory infiltrates containing dendritic cells are consistently present in cardiac mucosa. The finding of a larger number of dendritic cells in areas of cardiac mucosa in Barrett's esophagus biopsies suggests that the immune inflammation of cardiac mucosa might play a role in modifying the local tissue environment to promote the development of specialized intestinal type metaplasia.

Myeloid cells in atherosclerosis: initiators and decision shapers

Chronic inflammation is the underlying pathophysiological mechanism of atherosclerosis. Prominent suspects being involved in atherosclerosis are lymphocytes, platelets, and endothelial cells. However, recent advances suggest a potent role for myeloid leukocytes, specifically monocyte subsets, polymorphonuclear leukocytes, and mast cells. These three cell types are not just rapidly recruited or already reside in the vascular wall but also initiate and perpetuate core mechanisms in plaque formation and destabilization. Dendritic cell subsets as well as endothelial and smooth muscle progenitor cells may further emerge as important regulators of atheroprogression. To stimulate further investigations about the contribution of these myeloid cells, we highlight the current mechanistic understanding by which these cells tune atherosclerosis.

Identification of antigen-presenting dendritic cells in mouse aorta and cardiac valves

Presumptive dendritic cells (DCs) bearing the CD11c integrin and other markers have previously been identified in normal mouse and human aorta. We used CD11c promoter–enhanced yellow fluorescent protein (EYFP) transgenic mice to visualize aortic DCs and study their antigen-presenting capacity. Stellate EYFP⁺ cells were readily identified in the aorta and could be double labeled with antibodies to CD11c and antigen-presenting major histocompatability complex (MHC) II products. The DCs proved to be particularly abundant in the cardiac valves and aortic sinus. In all aortic locations, the CD11c⁺ cells localized to the subintimal space with occasional processes probing the vascular lumen. Aortic DCs expressed little CD40 but expressed low levels of CD1d, CD80, and CD86. In studies of antigen presentation, DCs selected on the basis of EYFP expression or binding of anti-CD11c antibody were as effective as DCs similarly selected from the spleen. In particular, the aortic DCs could cross-present two different protein antigens on MHC class I to CD8⁺ TCR transgenic T cells. In addition, after intravenous injection, aortic DCs could capture anti-CD11c antibody and cross-present ovalbumin to T cells. These results indicate that bona fide DCs are a constituent of the normal aorta and cardiac valves.

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.

oxLDL uptake by dendritic cells induces upregulation of scavenger-receptors, maturation and differentiation

BACKGROUND

Several studies have proposed a pathogenic role for oxidized LDL (oxLDL) in atherosclerosis. We tested the hypothesis whether oxLDL modulates dendritic cells (DCs), since these important antigen-presenting cells have been implicated in atherogenesis. We investigated the uptake of oxLDL by DCs, the scavenger-receptors involved and the resulting changes in phenotype and cytokine-spectra. In addition, we analyzed the impact of oxLDL on the nuclear transcription factor-kappa B (NF-kappaB)-pathway.

METHODS AND RESULTS

oxLDL (10microg/ml) increased the expression of the scavenger-receptors CD205 and CD36 and decreased the mannose-receptor expression. The lectin-like oxLDL-receptor (LOX-1)-expression was not affected. The endocytotic capacity of dextran and lucifer-yellow was moderately decreased by oxLDL. Blockage of the scavenger-receptors CD36, LOX-1 and CD205 reduced oxLDL uptake. Furthermore, oxLDL induced DC-maturation and triggered differentiation of DCs in myeloid and plasmacytoid DCs. oxLDL decreased IL-10 secretion and increased IL-6 release. Finally, oxLDL induced an activation of the NF-kappaB-pathway. Inhibition of IkappaBalpha-phosphorylation diminished the oxLDL-induced DC-maturation and -differentiation.

CONCLUSION

oxLDL uptake by DCs is mediated by the scavenger-receptors LOX-1, CD36, and CD205. oxLDL induces a proinflammatory cytokine profile in human DCs leading to DC-maturation and -differentiation which can, in part, be explained by an activation of the NF-kappaB-pathway. These results support the hypothesis that vascular inflammation may be aggravated by oxLDL induced DC-activation.

Toll-like receptor modulation: a novel therapeutic strategy in cardiovascular disease?

BACKGROUND

Toll-like receptors (TLRs) have been recently recognised as primary receptors in the innate immune system. Apart from initiating a prompt immune response against invading pathogens, TLRs are also considered to be an important link between innate immunity, inflammation and a variety of clinical disorders, including cardiovascular diseases. TLR signalling manipulation with novel drugs could offer important opportunities for cardiovascular disease modification.

OBJECTIVE

To present the latest knowledge supporting the involvement of TLRs in the pathogenesis and progress of cardiovascular diseases and explore the role of TLRs as potential targets for therapeutic intervention in cardiovascular territory.

METHODS

A review of the literature documenting implication of TLR signalling in cardiovascular disorders. Current progress in TLR-targeting drug development and the potential role of such a treatment strategy in cardiovascular disorders are discussed.

CONCLUSIONS

A growing body of evidence supports a role for TLRs in cardiovascular disease initiation and progression. Altering TLR signalling with novel drugs could be a beneficial therapeutic strategy for patients with cardiovascular disorders.

Different functions of monocyte subsets in familial hypercholesterolemia: potential function of CD14+ CD16+ monocytes in detoxification of oxidized LDL

The study was undertaken to investigate whether the two major monocyte subsets defined by the surface markers CD14(+)CD16(+) and CD14(++)CD16(-) show differences in their responses to hypercholesterolemia. Monocytes were rapidly isolated from the blood of hypercholesterolemic, low-density lipoprotein (LDL) receptor-defective familial hypercholesterolemia (FH) patients and from control persons. Using flow cytometry and uptake, adhesion, and phagocytosis assays as well as laser scanning microscopy, we found significant differences between the monocyte subsets. FH-CD14(+)CD16(+) monocytes exhibit an increased uptake of oxidized LDL (oxLDL) via CD36, whereas FH-CD14(++)CD16(-) monocytes preferentially take up native LDL (nLDL). FH-CD14(+)CD16(+) monocytes have an increased expression of surface proteins CD68, stabilin-1, and CD11c and a higher adherence to activated endothelial cells in response to oxLDL and nLDL stimulation. In addition, all CD14(+)CD16(+) monocytes have an increased ability for phagocytosis and a higher resistance to phagocytosis impairment by oxLDL compared with CD14(++)CD16(-) monocytes. We conclude that FH-CD14(+)CD16(+) monocytes have specialized functions in the uptake of oxLDL at activated endothelial cell surfaces, and we hypothesize that these functions are critical for the clearance of oxLDL deposits and apoptotic cells from the vessel wall under hyperlipidemic conditions.

The multifaceted contributions of leukocyte subsets to atherosclerosis: lessons from mouse models

Chronic inflammation drives the development of atherosclerosis, and details regarding the involvement of different leukocyte subpopulations in the pathology of this disease have recently emerged. This Review highlights the surprising contribution of granulocyte subsets and mast cells to early atherogenesis and subsequent plaque instability, and describes the complex, double-edged role of monocyte, macrophage and dendritic-cell subsets through crosstalk with T cells and vascular progenitor cells. Improved understanding of the selective contributions of specific cell types to atherogenesis will pave the way for new targeted approaches to therapy.

CD11c(+) dendritic cells maintain antigen processing, presentation capabilities, and CD4(+) T-cell priming efficacy under hypercholesterolemic conditions associated with atherosclerosis

Recent reports suggest dyslipidemia impairs dendritic cell (DC) function and adaptive immunity. This study aimed to characterize the effect of hypercholesterolemia on antigen-presenting cell function of DCs and DC-dependent CD4(+) T-cell responses. DCs incubated in vitro with acetylated low-density lipoprotein cholesterol with or without an acyl-coenzyme A:cholesterol acyl-transferase inhibitor maintained their ability to prime CD4(+) T cells. Analysis of T-cell proliferation and interferon-gamma and tumor necrosis factor-alpha production after ex vivo coculture of naïve CD4(+) T cells with splenic, inguinal, or iliac DCs from low-density lipoprotein receptor-deficient (LDLR(-/-)) or apolipoprotein E-deficient (ApoE(-/-)) mice fed an atherogenic diet highlighted DC efficacy in effector T-cell generation under hypercholesterolemic conditions. Adoptive transfer of carboxyfluorescein diacetate, succinimidyl ester (CFSE)-labeled naïve CD4(+) T cells in LDLR(-/-) recipients and subsequent immunization demonstrated effective priming of naïve T cells in hypercholesterolemic mice. CFSE dilution analyses revealed that hypercholesterolemic DCs were equipotent in naïve CD4(+) T-cell priming efficacy with normocholesterolemic DCs. Quantitative real-time PCR and flow cytometric analyses demonstrated that DC expression of multiple molecules involved in antigen processing, presentation, and T-cell stimulation remained unaltered by dyslipidemia. Finally, endogenous antigen-primed CD4(+) T cells responded equivalently to a secondary ex vivo antigenic challenge, regardless of whether they were primed in vivo under hypercholesterolemic or control conditions, demonstrating that all essential steps in CD4(+) T-cell responses remain intact under atherogenic conditions. This study affirms that the adaptive immune response prevails under the hypercholesterolemic conditions present in atherosclerosis. In particular, DCs remain functional antigen-presenting cells and maintain their ability to prime CD4(+) T cells even when cholesterol-loaded.

CD4+ CD28 null T cells in coronary artery disease: when helpers become killers

The crucial role of T cells in atherosclerosis and coronary artery disease (CAD) has been highlighted by recent observations. Helper CD4(+) T cells can both aggravate or attenuate the atherogenic process and the development of CAD. CD4(+)CD28(null) T cells are an unusual subset of helper cells which expand and have deleterious effects in CAD. In this review, we discuss the current issues on the generation of CD4(+)CD28(null) T cells and focus on their phenotypic and functional characteristics relevant to the development of cardiovascular events. The possible effects of the present day therapies for CAD on the CD4(+)CD28(null) T cells are also explored. Targeting the CD4(+)CD28(null) T cell subset in CAD could provide novel therapeutic strategies to prevent acute life-threatening coronary events.

Vascular oxidative stress increases dendritic cell adhesion and transmigration induced by homocysteine

Atherosclerosis is a long-term chronic inflammatory and immunological disease. Endothelial dysfunction and the dendritic cell (DC) immune response are pivotal early events in atherogenesis. This study investigated the effects and possible mechanisms of action of homocysteine (Hcy) on DC adhesion to and transmigration between endothelial cells (ECs), and indicated a novel immunoregulatory mechanism by which Hcy induces atherogenesis. When ECs were stimulated with increasing concentrations of Hcy, immunofluorescence showed that endothelial reactive oxygen species (ROS) generation strikingly increased, while nitrite assay showed that nitric oxide (NO) release markedly decreased. Furthermore, DC adhesion and transmigration were significantly increased when ECs were activated by Hcy. However, pretreatment of ECs with antioxidant before Hcy markedly attenuated the induction of DC adhesion and transmigration, dependent on the intracellular ROS decrease and endothelial NO increase. In conclusion, DC adhesion and transmigration are significantly increased by vascular oxidative stress under conditions of elevated Hcy levels. These findings provide insight into the inflammatory processes and immune responses occurring in atherosclerosis induced by Hcy.

Mature dendritic cells express functional thrombin receptors triggering chemotaxis and CCL18/pulmonary and activation-regulated chemokine induction

Protease-activated receptors (PARs) are a family of G protein-coupled receptors that are activated by serine protease-mediated proteolytic cleavage of their extracellular domain. We have previously characterized the expression and function of PARs in human monocytes and macrophages, yet information about PARs in dendritic cells (DC) is scarce. Monocyte-derived immature DC do not express PARs. Upon maturation with LPS, but not with TNF-alpha or CD40 ligand, DC express PAR1 and PAR3, but not PAR2 or PAR4. Stimulation of DC with the serine protease thrombin or PAR1-activating peptide elicits actin polymerization and concentration-dependent chemotactic responses in LPS-, but not in TNF-alpha-matured DC. The thrombin-induced migration is a true chemotaxis with only negligible chemokinesis. Stimulation of PARs with thrombin or the respective receptor-activating peptides activates ERK1/2 and Rho kinase as well as subsequent phosphorylation of the regulatory myosin L chain 2. The ERK1/2- and Rho kinase 1-mediated phosphorylation of myosin L chain 2 was indispensable for the PAR-mediated chemotaxis as shown by pharmacological inhibitors. Additionally, thrombin stimulated the Rho-dependent release of the CC chemokine CCL18/pulmonary and activation-regulated chemokine, which induces chemotaxis of lymphocytes and immature DC as well as fibroblast proliferation. The colocalization of CD83(+) DC with CCL18 in human atherosclerotic plaques revealed by immunofluorescence microscopy combined with the presence of functionally active thrombin receptors on mature DC point to a previously unrecognized functional role of thrombin in DC biology. The thrombin-induced stimulation of mature DC may be of particular relevance in atherosclerotic lesions, which harbor all components of this novel mechanism.

The autoimmune origin of atherosclerosis

Atherosclerosis is a chronic inflammatory disease. Many studies and observations suggest that it could be caused by an immune reaction against autoantigens at the endothelial level, the most relevant of which are oxidized LDL and heat shock proteins (HSP) 60/65. Endothelial dysfunction plays a fundamental role. The first antigen is related to the increased leakage and oxidation of LDL; the second to cellular reaction to stress. Experimental and clinical observations confirm the pathogenetic role of these antigens. Both innate and adaptive immunity and impaired regulatory mechanisms of the autoimmune reaction are involved. Different triggering factors are examined: infectious agents, smoking, air pollution, diabetes and hypercholesterolemia. Analogies and differences between systemic atherosclerosis and transplant-related coronary atherosclerosis help to understand their respective nature. Immune mechanisms might be responsible for the passage from stable plaque to unstable and rupture-prone plaque. Finally, prospects of treatment and prevention are linked to the induction of tolerance to responsible antigens, activation of immune regulatory response and the use of immunomodulatory drugs.

Graft-infiltrating dendritic cells and coronary endothelial dysfunction after human heart transplantation

BACKGROUND

Indirect allorecognition is involved in chronic transplant rejection. We prospectively characterized graft-infiltrating dendritic cells (DCs) in sequential myocardial biopsies (n = 64; 1 to 24 months after transplantation) from 16 patients after heart transplantation (HTx) and analyzed the relation between graft immune activation and structural and functional coronary changes during follow-up.

METHODS

DC invasion (immunostaining) in the human myocardium was detectable early after HTx, increased further during the first year, and decreased constantly thereafter. Also, graft-infiltrating DCs expressed markers of immaturity and maturity and were time-dependently clustered with CD3-positive T cells.

RESULTS

Both epicardial and microvascular endothelial dysfunction were associated with elevated CD209-positive DCs at 12 months. CD209 positivity early after HTx was an independent marker for coronary endothelial dysfunction during follow-up. Intimal hyperplasia or angiographic disease during follow-up was not associated with myocardial DC infiltration.

CONCLUSIONS

DCs frequently infiltrate the cardiac allograft with a peak during the first post-operative year and time-dependently cluster with T cells. Migratory active graft-infiltrating DCs may serve as a predictor for allograft coronary endothelial dysfunction.

Human C-Reactive Protein Activates Monocyte-Derived Dendritic Cells and Induces Dendritic Cell-Mediated T-Cell Activation

Objective— Recent studies proposed a pathogenic role for C-reactive protein (CRP), an independent predictor of cardiovascular disease (CVD), in atherosclerosis. Therefore, we tested whether CRP may modulate dendritic cell (DC) function, because these professional antigen-presenting cells have been implicated in atherogenesis.

Methods and Results— Human monocyte-derived immature DCs were cultured with human CRP (0 to 60 μg/mL) for 24 hours. Thereafter, activation markers were measured by flow-cytometry and DCs were cocultured with CFSE-labeled lymphocytes to measure T-cell proliferation and interferon (IFN)-γ secretion after 8 days. Exposure to 60 μg/mL CRP (n=5) induced an activated cell morphology and significant (CD40 increase MFI 5.23±0.28, P <0.01 paired t test; CD80 6.18±0.51, P <0.01) to modest (CD83 1.38±0.17, P <0.05, CCR7 1.60±0.29, P =0.05) upregulation of DC activation markers. The expression of CD86 and HLA-DR was high, but not affected. T-lymphocytes incubated with CRP-pulsed DCs displayed increased IFN-γ secretion and proliferation ( P <0.001). DC activation was concentration-dependent and detected from 2 μg/mL CRP; the maximum effect was equivalent to that seen with 0.1 μg/mL lipopolysaccharide (LPS). Polymyxin B abolished the LPS response, without influencing CRP effects. Finally, immunohistochemistry could demonstrate DC/CRP colocalization in human atherosclerotic lesions.

Conclusions— These findings suggest that CRP in plaques or found circulating in CVD patients can influence DC function during atherogenesis.

The effect of three-dimensional matrix-embedding of endothelial cells on the humoral and cellular immune response

The endothelium is a unique immunologic target. The first host-donor reaction in any cell, tissue or organ transplant occurs at the blood-tissue interface, the endothelium. When endothelial cells are themselves the primary component of the implant a second set of immunologic reactions arises. Injections of free endothelial cell implants elicit a profound major histocompatibility complex (MHC) II dominated immune response with significant sensitivity, cascade enhancement and immune memory. Endothelial cells embedded within three-dimensional matrices retain all the biosecretory capacity of quiescent endothelial cells. Perivascular implants of such cells are the most potent inhibitor of intimal hyperplasia and thrombosis following controlled vascular injury, but without any immune reactivity. Allo- and even xenogeneic endothelial cells evoke no significant humoral or cellular immune response in immunocompetent hosts when embedded within matrices. Moreover, endothelial implants are immunomodulatory, reducing the extent of the memory response to previous free cell implants. Attenuated immunogenicity results in muted activation of adaptive and innate immune cells. These findings point toward a pivotal role of matrix-cell-interconnectivity for the cellular immune phenotype and might therefore assist in the design of extracellular matrix components for successful tissue engineering.

Platelets modulate atherogenesis and progression of atherosclerotic plaques via interaction with progenitor and dendritic cells

Platelets not only play a role in the late complications of atherosclerosis, but are also essential in its initiation, interacting with endothelial cells and leukocytes. Platelet adhesion to injured or atherosclerotic vessels is critical for the initiation of atherosclerotic lesion formation in vivo. Increasing evidence has recently highlighted the role of progenitor cells in inflammation, atherogenesis, and atheroprogression. Recruitment of progenitor and dendritic cells to sites of vascular injury is poorly understood so far. Both human progenitor and dendritic cells significantly adhere to platelets, indicating that platelets adherent to collagen or to endothelial cells can serve as a bridging mechanism directing circulating progenitor and dendritic cells to sites of impaired vasculature. Moreover, platelets regulate differentiation of progenitor cells to endothelial cells or macrophages and foam cells and modulate essential functions of dendritic cells, including their activation, differentiation and apoptosis in vitro. This review describes recent findings on platelet interaction with progenitor cells or dendritic cells and discusses potential consequences of this interaction in atherosclerosis.

Proatherogenic immune responses are regulated by the PD-1/PD-L pathway in mice

T lymphocyte responses promote proatherogenic inflammatory events, which are influenced by costimulatory molecules of the B7 family. Effects of negative regulatory members of the B7 family on atherosclerosis have not been described. Programmed death-ligand 1 (PD-L1) and PD-L2 are B7 family members expressed on several cell types, which inhibit T cell activation via binding to programmed death-1 (PD-1) on T cells. In order to test whether the PD-1/PD-L pathway regulates proatherogenic T cell responses, we compared atherosclerotic lesion burden and phenotype in hypercholesterolemic PD-L1/2(-/-)LDLR(-/-) mice and LDLR(-/-) controls. PD-L1/2 deficiency led to significantly increased atherosclerotic burden throughout the aorta and increased numbers of lesional CD4(+) and CD8(+) T cells. Compared with controls, PD-L1/2(-/-)LDLR(-/-) mice had iliac lymphadenopathy and increased numbers of activated CD4(+) T cells. Serum levels of TNF-alpha were higher in PD-L1/2(-/-)LDLR(-/-) mice than in controls. PD-L1/2-deficient APCs were more effective than control APCs in activating CD4(+) T cells in vitro, with or without cholesterol loading. Freshly isolated APCs from hypercholesterolemic PD-L1/2(-/-)LDLR(-/-) mice stimulated greater T cell responses than did APCs from hypercholesterolemic controls. Our findings indicate that the PD-1/PD-L pathway has an important role in downregulating proatherogenic T cell response and atherosclerosis by limiting APC-dependent T cell activation.

Endothelial cell-matrix interactions determine maturation of dendritic cells

The fate of allo- and xenogeneic endothelial cell (EC) implants is regulated by EC-matrix interactions. While free EC are destroyed by a vigorous immune reaction, EC embedded within 3D collagen cells are well tolerated. Given the critical role DC serve in immune reactivity, we hypothesized that EC-driven DC maturation depends on EC-matrix contact. In marked contrast to DC co-cultured with a cytokine cocktail or with allo- and xenogeneic EC grown to confluence on 2D tissue culture plates, DC exposed to 3D matrix-embedded allo- and xenogeneic EC failed to mature, retaining their endocytic activity and exhibiting significantly reduced expression of maturation markers (costimulatory molecules, HLA-DR, CD83; p <0.01). Matrix-embedded EC also limited cytokine-induced maturation and activity of DC. Incubation with matrix-embedded EC inhibited DC induction of allogeneic lymphocyte proliferation (p <0.002) and EC cross-activation (ICAM-1, VCAM-1, HLA-DR, TLR2 and 4; p <0.01). The endothelium in its quiescent state is confluent and substrate adherent. The former ensures secretion of growth inhibitors rather than promoters, and the latter may ensure immune acceptance. We now demonstrate for the first time that interactions of EC with an underlying 3D matrix affect the ability of EC to drive DC maturation.

Peripheral-blood dendritic cells in men with coronary heart disease

Accumulating evidence suggests that an imbalance in T-helper type 1 (Th1)/Th2 response with enhanced Th1 immune response has an important role in the process of coronary artery disease (CAD). Dendritic cell (DC) subsets, myeloid DCs (mDCs) and plasmacytoid DCs (pDCs), could regulate immune reactions by polarizing naive T-helper cells into Th1 or Th2 effector cells. In this study, total peripheral-blood DCs and mDC and pDC subsets were examined in patients with coronary heart disease. Thirty-two men who underwent coronary angiography for chest pain were divided into the CAD group (n = 21) and control group (normal coronary angiographic results, n = 11). Peripheral-blood DCs and DC subsets were detected using a 3-color flow cytometry technique. DCs were defined as Lin1(-)HLA-DR(+); mDCs, as Lin1(-)HLA-DR(+)CD11c(+); and pDCs, as Lin1(-)HLA-DR(+)CD123(+). The absolute number of peripheral-blood DCs was significantly higher in the CAD group compared with the control group (p = 0.04). The mDC fraction in terms of both percentage and absolute number was also significantly increased in the CAD group compared with the control group (all p <0.05), whereas the pDC fraction was similar between the 2 groups (p >0.05). The mDC/pDC ratio was significantly increased in the CAD group than in the control group (p = 0.01). In conclusion, total peripheral-blood DCs are significantly higher in patients with CAD because of an increase in mDC subset, which might contribute to enhanced Th1 response in patients with CAD.

Homocysteine at pathophysiological concentrations enhances binding of dendritic cells to endothelial cells mediated by DC-SIGN

Elevated plasma homocysteine (Hcy) is an independent risk factor for atherosclerosis, which is recognized as inflammatory and immune responses. The purpose of this study was to investigate the effect of Hcy on the interaction between dendritic cells (DCs) and endothelial cells (ECs) by upregulating the expression of DC-specific ICAM-3-grabbing nonintegrin (DC-SIGN) in cultured DCs. The immunophenotype of Hcy-treated DCs was monitored by flow cytometry. Then, they were coincubated with cultured human umbilical vein endothelial cells, and adhesion of DCs to ECs, and migration of DCs through an endothelial monolayer growing on the insert of a transwell plate, were assessed using a confocal microscope and a multi-detection microplate reader. The expression of DC-SIGN on Hcy-stimulated DCs was assessed by Western blot and immunofluorescence staining. The presence of Hcy did not change the phenotype of immature and mature DCs. Hcy promoted adhesion of DCs to ECs and migration in a concentration-dependent fashion. This effect was inhibited by an anti-DC-SIGN monoclonal antibody. The expression of DC-SIGN on DCs was significantly upregulated by Hcy in a concentration-dependent manner. Taken together, our results show for the first time that Hcy can potentiate the adhesion of DCs to ECs and migration by upregulating the expression of DC-SIGN on DCs, suggesting a novel role of Hcy in the pathogenesis of human vascular disease.

The expression of vascular dendritic cells in human atherosclerotic carotid plaques

Atherosclerosis is currently considered a chronic inflammatory disease, and evidence is accumulating for a role of the immune system in the progression of atherosclerosis. Dendritic cells are specialized antigen-presenting cells with the unique ability to initiate a primary immune response to certain antigens by the activation of naive T-lymphocytes. Although dendritic cells are well known to be important in the development of different diseases, studies of vascular dendritic cells in atherosclerosis are rare, and their role is not clearly understood. Therefore, we investigated the immunohistochemical expression of vascular dendritic cells in atherosclerotic plaques. Between April 2003 and December 2005, carotid endarterectomy was performed in 26 consecutive patients, and 27 carotid plaque specimens were analyzed. We investigated the immunohistochemical expression of vascular dendritic cells in human carotid plaques by measuring the signal intensity of fascin-positive cells using an image analyzer. In addition, these immunohistochemical results were related to clinical data. The highest signal intensity of dendritic cells was found in plaque shoulders, and the mean signal intensity of dendritic cells was significantly higher in complicated than in uncomplicated plaques (P = .0029). Moreover, the mean signal intensity of dendritic cells in plaques from symptomatic patients was significantly elevated compared with plaques from asymptomatic patients (P = .0004). Although atherosclerotic plaque instability is determined by multiple factors, the immune and inflammatory pathways play a particularly important role. Dendritic cells play a role in atherosclerosis, and the present study suggests that the expression of dendritic cells in human carotid arteries may be strongly associated with the occurrence of ischemic stroke.

Accumulation of immune cells and high expression of chemokines/chemokine receptors in the upstream shoulder of atherosclerotic carotid plaques

The presence of immune cells is important for plaque destabilization. Disturbed flow conditions were shown to enhance the recruitment of circulating immune cells. Thus, we analyzed in 54 atherosclerotic carotid plaques the frequency of different immune cells, HLA-DR, chemokines, and chemokine receptors, comparing the upstream with the downstream plaque shoulder. The presence of neovascularization and intraplaque hemorrhages was investigated by CD34 immunostaining and Mallory's iron stain. Immunohistochemical analyses were performed to detect smooth muscle cells (SMC: actin), macrophages (CD68), T cells (CD3), dendritic cells (DC: fascin), mature DC (CD83), and the expression of HLA-DR, chemokine receptors (CCR-2, CCR-6), and chemokines (MCP-1, MIP-3alpha). Significantly more SMC were detected downstream than upstream (p<0.001). In contrast, significantly more macrophages (p=0.01), DC (p=0.03), mature DC (p=0.007), and a higher expression of HLA-DR (p=0.004), CCR-2 (p=0.002), CCR-6 (p<0.001), MCP-1 (p=0.04), and MIP-3alpha (p=NS) were observed upstream than downstream. Immune cells were strongly associated with neovascularization. The abundance of SMC downstream provides an explanation for distal plaque growth. Enhanced recruitment of immune cells through neovessels into the upstream shoulder might be contributing to plaque destabilization.

Platelets Recruit Human Dendritic Cells Via Mac-1/JAM-C Interaction and Modulate Dendritic Cell Function In Vitro

OBJECTIVE

Thrombotic events and immunoinflammatory processes take place next to each other during vascular remodeling in atherosclerotic lesions. In this study we investigated the interaction of platelets with dendritic cells (DCs).

METHODS AND RESULTS

The rolling of DCs on platelets was mediated by PSGL-1. Firm adhesion of DCs was mediated through integrin alphaMbeta2 (Mac-1). In vivo, adhesion of DCs to injured carotid arteries in mice was mediated by platelets. Pretreatment with soluble GPVI, which inhibits platelet adhesion to collagen, substantially reduced recruitment of DCs to the injured vessel wall. In addition, preincubation of DCs with sJAM-C significantly reduced their adhesion to platelets. Coincubation of DCs with platelets induced maturation of DCs, as shown by enhanced expression of CD83. In the presence of platelets, DC-induced lymphocyte proliferation was significantly enhanced. Moreover, coincubation of DCs with platelets resulted in platelet phagocytosis by DCs, as verified by different cell phagocytosis assays. Finally, platelet/DC interaction resulted in apoptosis of DCs mediated by a JAM-C-dependent mechanism.

CONCLUSIONS

Recruitment of DCs by platelets, which is mediated via CD11b/CD18 (Mac-1) and platelet JAM-C, leads to DC activation and platelet phagocytosis. This process may be of importance for progression of atherosclerotic lesions.

Toll-like receptor signaling and atherosclerosis

PURPOSE OF REVIEW

Chronic inflammation and disordered lipid metabolism represent hallmarks of atherosclerosis. Considerable evidence has accumulated to suggest that innate immune defense mechanisms might interact with proinflammatory pathways and exacerbate or perhaps even initiate development of arterial plaques. Until recently the preponderance of such evidence has been indirectly emerging from clinical and epidemiologic studies, with some support from experimental animal models of atherosclerosis.

RECENT FINDINGS

Recent data now directly implicate signaling by toll-like receptor 4 and the common adaptor molecule MyD88 in the pathogenesis of atherosclerosis, establishing a key link between atherosclerosis and defense against both foreign pathogens and endogenously generated inflammatory ligands.

SUMMARY

Here we briefly review these and closely related studies, highlighting areas that should provide fertile ground for future studies aimed at a more comprehensive understanding of the interplay between innate immune defense mechanisms, atherosclerosis and related vascular disorders.

Granulocyte macrophage colony-stimulating factor regulates dendritic cell content of atherosclerotic lesions

OBJECTIVE

Recent evidence suggests that dendritic cells may play an important role in atherosclerosis. Based primarily on previous in vitro studies, we hypothesized that granulocyte macrophage colony-stimulating factor (GM-CSF)-deficient mice would have decreased dendritic cells in lesions.

METHODS AND RESULTS

To test this, we characterized gene targeted GM-CSF(-/-) mice crossed to hypercholesterolemic low-density lipoprotein receptor null mice. Our results provide conclusive evidence that GM-CSF is a major regulator of dendritic cell formation in vivo. Aortic lesion sections in GM-CSF(-/-) low-density lipoprotein receptor null animals showed a dramatic 60% decrease in the content of dendritic cells as judged by CD11c staining but no change in the overall content of monocyte-derived cells. The GM-CSF-deficient mice exhibited a significant 20% to 50% decrease in the size of aortic lesions, depending on the location of the lesions. Other prominent changes in GM-CSF(-/-) mice were decreased lesional T cell content, decreased autoantibodies to oxidized lipids, and striking disruptions of the elastin fibers adjacent to the lesion.

CONCLUSION

Given that GM-CSF is dramatically induced by oxidized lipids in endothelial cells, our data suggest that GM-CSF serves to regulate dendritic cell formation in lesions and that this, in turn, influences inflammation, plaque growth and possibly plaque stability.

T cells in atherogenesis: for better or for worse?

The idea that atherosclerosis is an inflammatory disease is no longer controversial. Instead, much of the current research is now focused on understanding what drives this inflammation and how it is regulated. Adaptive immunity, in particular T cells, is highly involved in atherogenesis. It is well known that different subsets of T cells can drive or dampen inflammatory processes, but we still have much to learn about the regulation of this balance in the context of atherosclerosis. This review summarizes our knowledge of T cells in atherogenesis, their potential antigens, their contact-dependent activities, and their secretion of inflammatory and antiinflammatory mediators, aiming to illustrate how T cells can aggravate or attenuate this disease through cross-talk with other cells within or outside the atherosclerotic plaque.

Decrease in Circulating Myeloid Dendritic Cell Precursors in Coronary Artery Disease

OBJECTIVES

We analyzed the frequency of myeloid dendritic cell (mDC) and plasmacytoid dendritic cell (pDC) precursors in blood of patients with coronary artery disease (CAD) and in atherosclerotic carotid plaques of patients with cerebrovascular disease (CVD).

BACKGROUND

Circulating DC precursors are reduced in several autoimmune diseases. Atherosclerosis has features of an autoimmune disease, such as the presence of autoantibodies or autoreactive T cells. Tissue-resident DCs were previously described in atheromata, and it is assumed that they are important for the activation of T cells against autoantigens there.

METHODS

Circulating mDC and pDC precursors were flow cytometrically detected in healthy controls (n = 19), CAD patients with stable (n = 20) and unstable angina pectoris (n = 19), and acute myocardial infarction (n = 17). In human carotid plaques (n = 65), mDC and pDC precursors were identified immunohistochemically.

RESULTS

Circulating mDC precursors were significantly reduced in patients with stable angina pectoris (0.19%, p = 0.04), unstable angina pectoris (0.16%, p = 0.004), and acute myocardial infarction (0.08%, p < 0.001) compared with control patients (0.22% of peripheral blood mononuclear cells). In contrast, pDC numbers were not significantly altered. Circulating mDC precursors inversely correlated with high-sensitivity C-reactive protein (r = -0.38, p = 0.001) or interleukin-6 (r = -0.42, p < 0.001). In contrast to pDC, significantly more mDC precursors were observed in vulnerable carotid plaques (24, 0.25 mm2; n = 31; p = 0.003) than in stable ones (6.4, 0.25 mm2; n = 34).

CONCLUSIONS

Similar to autoimmune diseases, circulating mDC precursors were significantly reduced in patients with CAD. The emergence of mDC precursors in vulnerable plaques suggests their recruitment into atheromata as a possible reason for their decrease in blood. In contrast, no significant association of circulating pDC precursors with atherosclerosis was observed.

Atherosclerosis progression and monocyte emigration from plaque

Evaluation of: Llodrá J, Angeli V, Liu J, Trogan E, Fisher AE, Randolph GJ: Emigration of monocyte-derived cells from atherosclerotic lesions characterizes regressive, but not progressive, plaques. Proc. Natl Acad. Sci. 101(32), 11779–11784 (2004). Monocyte/macrophages are the most abundant immune cells in atherosclerotic lesions, in which they have a pivotal role. The present study sought to determine how dyslipidemia affects the fate of monocytes recruited to the plaque. The researchers used an in vitro model of a vessel wall to demonstrate that platelet-activating factor and lysophosphatidic acid, two key mediators of atherosclerosis, impair the ability of monocytes to emigrate from the cultured vessel wall. Furthermore, an in vivo model of aortic arch transplantation demonstrated reduced emigration of monocyte-derived cells into the plaque-draining lymph node under conditions of atherosclerotic lesion progression. Thus, progression of atherosclerosis is characterized by reduced emigration of monocyte-derived cells in addition to new monocyte recruitment into the vessel wall. Interestingly, these sequestered cells bear features reminiscent of dendritic cells, which may locally exacerbate inflammatory reactions.

Decreased number of circulating plasmacytoid dendritic cells in patients with atherosclerotic coronary artery disease

BACKGROUND

Dendritic cells are potent antigen-presenting and immune modulating cells that have been implicated in the development of atherosclerosis. In human blood, two distinct lineages are distinguished: plasmacytoid dendritic cells and myeloid dendritic cells. Although dendritic cells have been described in atherosclerotic plaques, no information exists concerning circulating blood dendritic cells in atherosclerosis. This study aims to evaluate the number of circulating dendritic cells in patients with coronary artery disease. The relation with the extent of coronary artery disease, the clinical syndrome and with a marker of inflammation will be documented.

METHODS

Patients with angiographically proven coronary artery disease (n=18) and age and sex-matched controls (n=18) were included. Myeloid dendritic cells and plasmacytoid dendritic cells were detected with the specific blood dendritic cell antigens, blood dendritic cell antigen-1 and blood dendritic cell antigen-2, respectively.

RESULTS

Absolute and relative numbers of circulating plasmacytoid dendritic cells were significantly lower in patients with coronary artery disease (5722+/-601/ml and 0.08+/-0.01%) than in controls (12,640+/-1289/ml and 0.21+/-0.02%). Plasmacytoid dendritic cells were more decreased in patients with troponin-positive unstable coronary syndromes than in patients with low troponin values, and tended to be lower in more extensive coronary artery disease. Absolute myeloid dendritic cells numbers tended to be reduced in patients, whereas relative numbers were significantly decreased: 11,857+/-1895/ml versus 15,226+/-928/ml and 0.17+/-0.03% versus 0.26+/-0.01% in controls.

CONCLUSIONS

The present study shows a significant decrease of circulating blood dendritic cell antigen-2 positive plasmacytoid dendritic cells in patients with coronary artery disease. The decrease tended to be more pronounced in unstable coronary syndromes and extensive coronary artery disease, suggesting a possible role of dendritic cells in plaque progression and rupture.

Cytokines in Atherosclerosis: Pathogenic and Regulatory Pathways

Atherosclerosis is a chronic disease of the arterial wall where both innate and adaptive immunoinflammatory mechanisms are involved. Inflammation is central at all stages of atherosclerosis. It is implicated in the formation of early fatty streaks, when the endothelium is activated and expresses chemokines and adhesion molecules leading to monocyte/lymphocyte recruitment and infiltration into the subendothelium. It also acts at the onset of adverse clinical vascular events, when activated cells within the plaque secrete matrix proteases that degrade extracellular matrix proteins and weaken the fibrous cap, leading to rupture and thrombus formation. Cells involved in the atherosclerotic process secrete and are activated by soluble factors, known as cytokines. Important recent advances in the comprehension of the mechanisms of atherosclerosis provided evidence that the immunoinflammatory response in atherosclerosis is modulated by regulatory pathways, in which the two anti-inflammatory cytokines interleukin-10 and transforming growth factor-β play a critical role. The purpose of this review is to bring together the current information concerning the role of cytokines in the development, progression, and complications of atherosclerosis. Specific emphasis is placed on the contribution of pro- and anti-inflammatory cytokines to pathogenic (innate and adaptive) and regulatory immunity in the context of atherosclerosis. Based on our current knowledge of the role of cytokines in atherosclerosis, we propose some novel therapeutic strategies to combat this disease. In addition, we discuss the potential of circulating cytokine levels as biomarkers of coronary artery disease.

Monocyte recruitment and foam cell formation in atherosclerosis

Atherosclerosis is a chronic immune-inflammatory disease in which the interactions of monocytes with activated endothelium are crucial events leading to atherosclerotic alteration of the arterial intima. In early atherosclerosis, monocytes migrate into the subendothelial layer of the intima where they differentiate into macrophages or dendritic cells. In the subendothelial space enriched with atherogenic lipoproteins, most macrophages transform into foam cells. Foam cells aggregate to form the atheromatous core and as this process progresses, the atheromatous centres of plaques become necrotic, consisting of lipids, cholesterol crystals and cell debris. This review highlights some aspects of monocyte recruitment and foam cell formation in atherosclerosis.