Dendritic cells and their involvement in atherosclerosis

The regulation of immune cells by Lactobacilli: a potential therapeutic target for anti-atherosclerosis therapy

Atherosclerosis is an inflammatory disease regulated by several immune cells including lymphocytes, macrophages and dendritic cells. Gut probiotic bacteria like Lactobacilli have been shown immunomodificatory effects in the progression of atherogenesis. Some Lactobacillus stains can upregulate the activity of regulatory T-lymphocytes, suppress T-lymphocyte helper (Th) cells Th1, Th17, alter the Th1/Th2 ratio, influence the subsets ratio of M1/M2 macrophages, inhibit foam cell formation by suppressing macrophage phagocytosis of oxidized low-density lipoprotein, block the activation of the immune system with dendritic cells, which are expected to suppress the atherosclerosis-related inflammation. However, various strains can have various effects on inflammation. Some other Lactobacillus strains were found have potential pro-atherogenic effect through promote Th1 cell activity, increase pro-inflammatory cytokines levels as well as decrease anti-inflammatory cytokines levels. Thus, identifying the appropriate strains is essential to the therapeutic potential of Lactobacilli as an anti-atherosclerotic therapy.

Monocyte-Derived Dendritic Cells Upregulate Extracellular Catabolism of Aggregated Low-Density Lipoprotein on Maturation, Leading to Foam Cell Formation

OBJECTIVE

Although dendritic cells are known to play a role in atherosclerosis, few studies have examined the contribution of the wide variety of dendritic cell subsets. Accordingly, their roles in atherogenesis remain largely unknown. We investigated the ability of different dendritic cell subsets to become foam cells after contact with aggregated low-density lipoprotein (LDL; the predominant form of LDL found in atherosclerotic plaques).

APPROACH AND RESULTS

We demonstrate that both murine and human monocyte-derived dendritic cells use exophagy to degrade aggregated LDL, leading to foam cell formation, whereas monocyte-independent dendritic cells are unable to clear LDL aggregates by this mechanism. Exophagy is a catabolic process in which objects that cannot be internalized by phagocytosis (because of their size or association with extracellular structures) are initially digested in an extracellular acidic lytic compartment. Surprisingly, we found that monocyte-derived dendritic cells upregulate exophagy on maturation. This contrasts various forms of endocytic internalization in dendritic cells, which decrease on maturation. Finally, we show that our in vitro results are consistent with dendritic cell lipid accumulation in plaques of an ApoE(-/-) mouse model of atherosclerosis.

CONCLUSIONS

Our results show that monocyte-derived dendritic cells use exophagy to degrade aggregated LDL and become foam cells, whereas monocyte-independent dendritic cells are unable to clear LDL deposits. Furthermore, we find that exophagy is upregulated on dendritic cell maturation. Thus, exophagy-mediated foam cell formation in monocyte-derived dendritic cells could play a significant role in atherogenesis.

Targeting the adaptive immune system: new strategies in the treatment of atherosclerosis

Atherosclerosis is a lipid-driven chronic inflammatory disease of the arterial wall. Current treatment of atherosclerosis is focused on limiting its risk factors, such as hyperlipidemia or hypertension. However, treatments that target the inflammatory nature of atherosclerosis are still under development. Discovery of novel targets involved in the inflammation of the arterial wall creates opportunities to design new therapeutics that successfully modulate atherosclerosis. Here, we review drug targets that have proven to play pivotal roles in the adaptive immune system in atherosclerosis, and we discuss their potential as novel therapeutics.

The complexity of cell composition of the intima of large arteries: focus on pericyte-like cells

Pericytes, which are also known as Rouget cells or perivascular cells, are considered to represent a likely distinct pool of vascular cells that are extremely branched and located mostly in the periphery of the vascular system. The family of pericytes is a heterogeneous cell population that includes pericytes and pericyte-like cells. Accumulated data indicate that networks of pericyte-like cells exist in normal non-atherosclerotic intima, and that pericyte-like cells can be involved in the development of atherosclerotic lesions from the very early stages of disease. The pathogenic role of arterial pericytes and pericyte-like cells also might be important in advanced and complicated atherosclerotic lesions via realizing mechanisms of vascular remodelling, ectopic ossification, intraplaque neovascularization, and probably thrombosis.

Dendritic cells in atherosclerotic inflammation: the complexity of functions and the peculiarities of pathophysiological effects

Atherosclerosis is considered as a chronic disease of arterial wall, with a strong contribution of inflammation. Dendritic cells (DCs) play a crucial role in the initiation of proatherogenic inflammatory response. Mature DCs present self-antigens thereby supporting differentiation of naïve T cells to effector cells that further propagate atherosclerotic inflammation. Regulatory T cells (Tregs) can suppress proinflammatory function of mature DCs. In contrast, immature DCs are able to induce Tregs and prevent differentiation of naïve T cells to proinflammatory effector T cells by initiating apoptosis and anergy in naïve T cells. Indeed, immature DCs showed tolerogenic and anti-inflammatory properties. Thus, DCs play a double role in atherosclerosis: mature DCs are proatherogenic while immature DCs appear to be anti-atherogenic. Tolerogenic and anti-inflammatory capacity of immature DCs can be therefore utilized for the development of new immunotherapeutic strategies against atherosclerosis.

Plasma levels of interleukin 18, interleukin 10, and matrix metalloproteinase-9 and -137G/C polymorphism of interleukin 18 are associated with incidence of in-stent restenosis after percutaneous coronary intervention

This study aims to investigate the relationship between the levels of IL-18, IL-10, and MMP-9 and -137G/C polymorphism of interleukin 18 with the risk of in-stent restenosis (ISR). The study population consisted of 68 patients with ISR, 173 in non-ISR group, treated with drug-eluting stent and evaluated by coronary angiography post-procedure and at follow-up, and also 109 without angiographic evidence of coronary artery disease (CAD) which formed a reference control group (non-CAD group). The sequential plasma IL-18, IL-10, and MMP-9 levels were assessed at admission, 24 h, and 2 weeks after percutaneous coronary intervention. The -137G/C polymorphism of IL-18 was genotyped by the ligase detection reaction-polymerase chain reaction. Plasma IL-18 and MMP-9 increased significantly from admission, peaking after 24 h and fall after 2 weeks. Compared with the non-ISR group, the ISR group had higher levels of IL-18 and MMP-9, but IL-10 level was the opposite. The -137GG genotype of IL-18 was significantly higher than of the CG and CC genotypes. A significant higher frequency of -137G allele or GG genotype of IL-18 was observed in patients with ISR group compared with the non-ISR group. There is correlation between the changes of IL-18, IL-10, MMP-9, and ISR. IL-18 promoter -137G/C polymorphism influences IL-18 levels and the susceptibility to ISR, suggesting that IL-18-mediated pathways are causally involved in the process of ISR.

Dendritic cells: In vitro culture in two- and three-dimensional collagen systems and expression of collagen receptors in tumors and atherosclerotic microenvironments

Dendritic cells (DCs) are immune cells found in the peripheral tissues where they sample the organism for infections or malignancies. There they take up antigens and migrate towards immunological organs to contact and activate T lymphocytes that specifically recognize the antigen presented by these antigen presenting cells. In the steady state there are several types of resident DCs present in various different organs. For example, in the mouse, splenic DC populations characterized by the co-expression of CD11c and CD8 surface markers are specialized in cross-presentation to CD8 T cells, while CD11c/SIRP-1α DCs seem to be dedicated to activating CD4 T cells. On the other hand, DCs have also been associated with the development of various diseases such as cancer, atherosclerosis, or inflammatory conditions. In such disease, DCs can participate by inducing angiogenesis or immunosuppression (tumors), promoting autoimmune responses, or exacerbating inflammation (atherosclerosis). This change in DC biology can be prompted by signals in the microenvironment. We have previously shown that the interaction of DCs with various extracellular matrix components modifies the immune properties and angiogenic potential of these cells. Building on those studies, herewith we analyzed the angiogenic profile of murine myeloid DCs upon interaction with 2D and 3D type-I collagen environments. As determined by PCR array technology and quantitative PCR analysis we observed that interaction with these collagen environments induced the expression of particular angiogenic molecules. In addition, DCs cultured on collagen environments specifically upregulated the expression of CXCL-1 and -2 chemokines. We were also able to establish DC cultures on type-IV collagen environments, a collagen type expressed in pathological conditions such as atherosclerosis. When we examined DC populations in atherosclerotic veins of Apolipoprotein E deficient mice we observed that they expressed adhesion molecules capable of interacting with collagen. Finally, to further investigate the interaction of DCs with collagen in other pathological conditions, we determined that both murine ovarian and breast cancer cells express several collagen molecules that can contribute to shape their particular tumor microenvironment. Consistently, tumor-associated DCs were shown to express adhesion molecules capable of interacting with collagen molecules as determined by flow cytometry analysis. Of particular relevance, tumor-associated DCs expressed high levels of CD305/LAIR-1, an immunosuppressive receptor. This suggests that signaling through this molecule upon interaction with collagen produced by tumor cells might help define the poorly immunogenic status of these cells in the tumor microenvironment. Overall, these studies demonstrate that through interaction with collagen proteins, DCs can be capable of modifying the microenvironments of inflammatory disease such as cancer or atherosclerosis.

Lymphocytes and the adventitial immune response in atherosclerosis

Although much of the research on atherosclerosis has focused on the intimal accumulation of lipids and inflammatory cells, there is an increasing amount of interest in the role of the adventitia in coordinating the immune response in atherosclerosis. In this review of the contributions of the adventitia and adventitial lymphocytes to the development of atherosclerosis, we discuss recent research on the formation and structural nature of adventitial immune aggregates, potential mechanisms of crosstalk between the intima, media, and adventitia, specific contributions of B lymphocytes and T lymphocytes, and the role of the vasa vasorum and surrounding perivascular adipose tissue. Furthermore, we highlight techniques for the imaging of lymphocytes in the vasculature.

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.

Changes of dendritic cells and fractalkine in type 2 diabetic patients with unstable angina pectoris: a preliminary report

BACKGROUND

It has been shown that dendritic cells (DCs) and fractalkine play a role in accelerating progression of the inflamed atherosclerotic lesions and plaque rupture. We evaluated the numbers and functional changes of DCs and its subsets in human type 2 diabetes with or without unstable angina pectoris (UAP).

METHODS

The study population consisted of 39 diabetic patients (DM:18 without CAD; DM + UAP: 21 with UAP), 18 non-diabetic UAP patients (UAP), and 15 healthy control (Normal). Peripheral blood DCs and its subsets were measured by three color flow cytometry. Serum levels of fractalkine, IL-12, and IFN-α were also measured. The functional status of the monocyte-derived DCs was analyzed by flow cytometry and allogeneic mixed T lymphocytes reaction.

RESULTS

The percent and absolute numbers of DCs and mDC within the total leukocyte population was similar for Normal and DM, while significantly lower in DM + UAP. pDC numbers were not significantly altered. Serum fractalkine in DM + UAP was highest among the four groups (p = 0.04 vs. UAP, p = 0.0003 vs. DM, p < 0.0001 vs. Normal). Circulating mDC inversely correlated with serum fractalkine (r = -0.268, p = 0.01) level. Compared with DM and UAP, the costimulatory molecules CD86 and proliferation of T cells stimulated by DCs were significantly increased in DM + UAP group.

CONCLUSIONS

Our study suggested that increases in the fractalkine level and the number and functional changes of blood DCs might contribute to diabetic coronary atherosclerosis and plaque destabilization.

Enhanced Angiotensin II type 1 receptor expression in leukocytes of patients with chronic kidney disease

Previously, we demonstrated increased Angiotensin II type I receptor expression in leukocytes from patients with untreated, but not in treated, essential hypertension (essential hypertension). We hypothesized that the Angiotensin II AT1 receptor is also increased in leukocytes from patients with chronic kidney disease, however and can still be corrected with combined anti-hypertensive treatment with renin-angiotensin system (RAS) blockers and statins. Blood pressure, cholesterol, renal function oxidative stress parameters, inflammation, and leukocyte Angiotensin II AT1 receptor mRNA expression were measured both on and (6 weeks) off treatment. Data were compared to data of 10 healthy control subjects. Untreated chronic kidney disease patients (n=20) had higher blood pressure, cholesterol and leukocyte Angiotensin II AT1 receptor mRNA expression, but no different ox-LDL, thiobarbituric acid reactive substances, paraoxonase activity or hs-CRP. OxLDL and Lipoprotein(a) were increased in untreated chronic kidney disease. Angiotensin II AT1 receptor expression inversely correlated with renal function (R(2)=0.15, P<0.03) and Lipoprotein(a) but not with the other parameters. Treatment with RAS blockers and statins normalized blood pressure and cholesterol, however it did not correct enhanced leukocyte Angiotensin II AT1 receptor expression. Leukocyte Angiotensin II AT1 receptor expression is inappropriately high in chronic kidney disease, correlates inversely with renal function and does not depend on antihypertensive and lipid-lowering treatment. The uremic environment seems to dominate over previously reported actions of high blood pressure and cholesterol to enhance leukocyte Angiotensin II AT1 receptor expression.

[Histochemical and immunohistochemical analysis of ruptured atherosclerotic abdominal aortic aneurysm wall]

BACKGROUND/AIM

The main complication of the atherosclerotic abdominal aortic aneurysm (AAA) is her rupture that begins with lesion in intima and rupture. The purpose of this work was to determine immunocytochemical and morphofunctional characteristics of the cells in aortic wall in ruptured atherosclerotic abdominal aortic aneurysm.

METHOD

During the course of this study, 20 samples of atherosclerotic AAA were analyzed, all of them obtained during authopsy. The samples were fixed in 4% formalin and embedded in paraffin. Sections of 5 microm thickness were stained histochemically (of Heidenhain azan stain and Periodic acid Schiff--PAS stain) and immunocytochemically using a DAKO LSAB+/HRP technique to identify alpha-smooth muscle actin (alpha-SMA), vimentin, myosin heavy chains (MHC), desmin, S-100 protein, CD45 and CD68 (DAKO specification).

RESULTS

The results of our study showed that ruptured atherosclerotic AAA is characterized by a complete absence of endothelial cells, the disruption of basal membrane and internal elastic lamina, as well as a presence of the remains of hypocellular complicated atherosclerotic lesion in intima. On the plaque margins, as well as in the media, smooth muscle cells (SMCs) are present, which express a alpha-SMA and vimentin (but without MHC or desmin expression), as well as leukocyte infiltration, and a large number of foam cells. Some of the foam cells show a CD68- immunoreactivity, while the others show vimentin- and S-100 protein-immunoreactivity. Media is thinned out with a disorganized elastic lamellas, while adventitia is characterized by inflammatory inflitrate (infection).

CONCLUSION

Rupture of aneurysm occurs from the primary intimal disruption, which spreads into thinned out media and adventitia. Rupture is caused by unstable atherom, hypocellularity, loss of contractile characteristics of smooth muscle cells in intima and media, neovascularization of the media, as well as by the activity of the macrophages in the lesion.

Tongxinluo inhibits oxidized low-density lipoprotein-induced maturation of human dendritic cells via activating peroxisome proliferator-activated receptor gamma pathway

TongXinLuo (TXL) is a traditional Chinese herbal medicine with multiple vasoprotective activities. Dendritic cells (DCs) play an active role in the immunological processes related to atherosclerosis. The purpose of this study was to determine the effect and possible mechanisms of TXL on oxidized low-density lipoprotein (OX-LDL)-induced maturation and immune function of DCs. Human monocyte-derived DCs were incubated with TXL or ciglitazone and were subsequently stimulated with OX-LDL to induce maturation. Similar to ciglitazone, a peroxisome proliferator-activated receptor (PPAR) gamma agonist, TXL could significantly reduce the maturation-associated markers induced by OX-LDL, such as CD40, CD86, CD1a, and human leukocyte antigen-DR; improved the endocytotic function; and decreased secretions of cytokine interleukin-12 and tumor necrosis factor alpha. These inhibitory effects of TXL could be partly reversed by silencing the expression of PPAR gamma in DCs. In conclusion, TXL could inhibit OX-LDL-induced maturation of DCs through activating PPAR gamma pathway.

Anti-phosphorylcholine-opsonized low-density lipoprotein promotes rapid production of proinflammatory cytokines by dendritic cells and natural killer cells

BACKGROUND AND OBJECTIVE

Epidemiological and animal studies suggest that periodontal infections increase atherosclerosis risk. Periodontitis patients have elevated levels of anti-phosphorylcholine (anti-PC) reactive not only with numerous periodontal organisms but also with minimally modified low-density lipoprotein (mmLDL). Dendritic cells (DCs) reside in arterial walls and accumulate in atherosclerotic lesions. The ability of anti-PC to bind mmLDL prompted the hypothesis that opsonized mmLDL would stimulate DCs and enhance the production of proinflammatory cytokines that promote atherogenic plaque development.

MATERIAL AND METHODS

Monocyte-derived DCs (mDCs) were generated using granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin (IL)-4, then stimulated with mmLDL or with anti-PC-opsonized mmLDL. The anti-PC effect was determined using flow cytometry, cofocal microscopy and cytokine assays. The production of CD83, IL-12p35 mRNA, IL-12p40 mRNA, IL-12p70 and IL-10 by DCs was monitored.

RESULTS

Dendritic cells stimulated with mmLDL expressed little CD83 and produced little IL-12p70. However, anti-PC-opsonized mmLDL enhanced DC maturation, as indicated by upregulated CD83 and rapid (≤ 48 h) production of IL-12p70 if a source of interferon-γ (IFN-γ) was available. In leukocyte cultures, natural killer (NK) cells rapidly produced IFN-γ (≤ 48 h) when interacting with IL-12-producing DCs activated by anti-PC-opsonized mmLDL. Moreover, IFN-γ promoted DC IL-12 responses that were further augmented when mmLDL was opsonized with anti-PC.

CONCLUSION

Minimally modified LDL-stimulated DCs and NK cells were mutually stimulatory, with DC IL-12p70 needed by NK cells and with NK cell IFN-γ needed by DCs. Moreover, production of these proinflammatory cytokines was markedly enhanced when LDL was opsonized by anti-PC. In short, the data suggest that the elevated anti-PC levels in periodontitis patients could promote a mechanism that facilitates atherosclerosis.

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.

Resident intimal dendritic cells and the initiation of atherosclerosis

PURPOSE OF REVIEW

To highlight the fact that regional differences in the normal arterial intima are critical to atherosclerotic lesion formation driven by systemic risk factors.

RECENT FINDINGS

At arterial curvatures, bifurcations and branches unique hemodynamics influence endothelial cell signaling and gene expression patterns, which create a proinflammatory environment, with low-grade recruitment of monocytes and accumulation of cells with dendritic features in the intima. Upon induction of hypercholesterolemia, these resident intimal dendritic cells initiate atherosclerosis by rapidly engulfing lipid and becoming the first foam cells in nascent lesions. This step precedes endothelial cell activation and increased monocyte recruitment.

SUMMARY

The unique features of the arterial intima at atherosclerosis-susceptible sites do not lead to disease under normal physiological conditions, but this intimal environment promotes the initiation of atherogenesis upon induction of systemic risk factors such as hypercholesterolemia.

Plasmin Triggers Chemotaxis of Monocyte-Derived Dendritic Cells Through an Akt2-Dependent Pathway and Promotes a T-Helper Type-1 Response

Objective— Dendritic cells (DC) accumulate in atherosclerotic arteries where they can modulate atherogenesis. We investigated whether plasmin might alter the function of human DC.

Methods and Results— Stimulation of monocyte-derived DC with plasmin elicited a time-dependent actin polymerization and chemotaxis comparable to that triggered by the standard chemoattractant formyl-methionyl-leucyl-phenylalanine. Plasmin triggered rapid activation of Akt and mitogen-activated protein kinases, followed by phosphorylation of the regulatory myosin light chain and chemotaxis. For the chemotactic DC migration, the activation of Akt and p38 and extracellular signal-regulated kinase 1/2 mitogen-activated protein kinases were indispensable, as shown by pharmacological inhibitors. DC express Akt1 and Akt2, but not Akt3. However, in DC, plasmin activates exclusively Akt2 via a p38 mitogen-activated protein kinase-dependent pathway. Accordingly, knockdown of Akt2 with short-hairpin RNA, but not of Akt1, blocked the plasmin-induced extracellular signal-regulated kinase 1/2 activation and the chemotactic response. Moreover, plasmin-stimulated DC induced polarization of CD4 + T cells toward the interferon-γ–producing, proinflammatory Th1 phenotype. Consistent with a role for DC and adaptive immune response in atherogenesis, we demonstrate DC in human atherosclerotic vessels and show that plasmin is abundant in human atherosclerotic lesions, where it colocalizes with DC.

Conclusion— Plasmin generation in the atherosclerotic vessel wall might contribute to accumulation of DC, activation of the adaptive immune response, and aggravation of atherosclerosis.

Vascular damage in giant cell arteritis

Immune-mediated damage to medium-sized arteries results in wall remodeling with intimal hyperplasia, luminal stenosis and tissue ischemia. In the case of the aorta, vasculitis may result in dissection, aneurysm or rupture. The response-to-injury program of the blood vessel is a concerted action between the immune system and wall-resident cells, involving the release of growth and angiogenic factors from macrophages and giant cells and the migration and hyperproliferation of vascular smooth muscle cells. Innate immune cells, specifically, dendritic cells (DC) positioned in the vessel wall, have been implicated in the earliest steps of vasculitis. Pathogen-derived molecular patterns are capable of activating vascular DC and initiating adaptive immune responses. The pattern of the emerging vessel wall inflammation is ultimately determined by the initial insult. Ligands to toll-like receptor (TLR) 4, such as lipopolysaccharides, facilitate the recruitment of CD4 T cells that invade deep into the wall and distribute in a panarteritic pattern. Conversely, ligands for TLR5 condition vascular DC to support perivasculitic infiltrates. In essence, both innate and adaptive immune reactions collaborate to render the arterial wall susceptible to inflammatory damage. Unique features of the tissue microenvironment, including specialized DC, shape the course of the inflammatory response. Differences in vascular damage pattern encountered in different patients may relate to distinct instigators of vasculitis.

[Pathogenesis of medium- and large-vessel vasculitis]

Giant cell arteritis (GCA), is a systemic vasculitis which preferentially targets large and medium branches of the upper-body aorta. Typical clinical manifestations result from arterial stenosis/occlusion causing blindness, stroke and aortic arch syndrome. Aortic involvement leads to dissection and aneurysm. On the cellular and molecular level, GCA is a sequel of abnormal innate and adaptive immune responses that occur in the specialized tissue niche of the arterial wall. Based on recent pathogenic studies, a novel disease model for GCA is emerging. It is now understood that the series of pathogenic events begins with dendritic cells (DC) indigenous to the artery's outer wall, leading to inflammatory vasculopathy. Placed close to the vasa vasorum, vascular DC are highly sensitive in recognizing pathogen-associated motifs assigning immune monitoring functions to blood vessels. Thus the large vessels are actively involved in immune monitoring. Each vascular territory expresses a unique profile of pathogen-sensing receptors, emphasizing functional diversity amongst structurally similar arteries. Innate immune stimulators can transform vascular DC into efficient antigen-presenting cells, attracting, activating, and instructing T lymphocytes to acquire tissue-invasive features. Macrophages provide critical tissue-damaging effector functions, directly injuring wall-residing cells and promoting a remodeling process that leads to intimal hyperplasia and luminal occlusion. Novel diagnostic and therapeutic approaches to GCA need to focus on the key position of vascular DC and the signals that break the immunoprivileged state of the vessel wall.

Vaccination against atherosclerosis? Induction of atheroprotective immunity

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 regulates the magnitude of the atherogenic proinflammatory response. T cells may also influence the stability of the atherosclerotic lesion and thus the propensity for thrombus formation and the clinical outcome of disease. Immunization of hypercholesterolemic animals with low-density lipoprotein preparations reduces atherosclerosis, suggesting that vaccination may represent a useful strategy for disease prevention or modulation. This review summarizes our current understanding of the role immunity in atherosclerosis and outlines strategies for antigen-specific prevention of this disease.

Autoimmunity in atherosclerosis: a protective response losing control?

Atherosclerosis is a chronic inflammatory disease characterized by accumulation of oxidized lipoproteins, increased cell death and hypertrophic degeneration of the arterial intima. The disease process is associated with local formation of modified self antigens that are targeted by both innate and adaptive immune responses. Although it remains to be firmly established it is likely that these autoimmune responses initially have a beneficial effect facilitating the removal of potentially harmful rest products from oxidized LDL and dying cells. However, studies performed on hypercholesterolaemic mice deficient in different components of the immune system uniformly suggest that the net effect of immune activation is pro-atherogenic and that atherosclerosis, at least to some extent, should be regarded as an autoimmune disease. These observations point to the possibility of developing new treatments for atherosclerosis based on modulation of immune responses against plaque antigens, an approach presently tested clinically for several other chronic inflammatory diseases with autoimmune components. Pilot studies in animals have provided promising results for both parental and oral vaccines based on oxidized LDL antigens. The time when this concept is ready for clinical testing is rapidly approaching but it will be important not to underestimate the difficulties that will be encountered in transferring the promising results from experimental animals into humans.

Monocyte-derived dendritic cells of patients with coronary artery disease show an increased expression of costimulatory molecules CD40, CD80 and CD86 in vitro

BACKGROUND

Atherosclerosis is a disease triggered by diverse exogenous stimuli and sustained by chronic inflammatory processes. Dendritic cells (DCs) are key regulatory antigen-presenting cells and play a crucial role in regulating the adaptive and innate immune system in any chronic inflammatory process. DCs are present in atherosclerotic lesions in the areas of the highest T-cell density. So far, their role in atherosclerosis has not been fully elucidated. We investigated the phenotypic properties of DCs in patients with coronary artery disease (CAD) in comparison to healthy individuals.

METHODS

Peripheral blood monocytes were isolated from 50 patients with CAD and 19 healthy individuals and differentiated over 9 days to immature and mature DCs. Analysis of the distribution of important stimulatory and costimulatory molecules on the surface of immature and mature DCs was performed by flow cytometry.

RESULTS

We observed no changes between the groups concerning cell numbers or expression of CD1a or HLA-DR on DCs. Patients with CAD, however, showed a significant upregulation of the costimulatory molecules CD80, CD86 and CD40 as compared with healthy controls. Expression of CD40, CD80 and CD86 on DCs partly correlated with smoking, family history of CAD, as well as with C-reactive protein levels. High-density lipoprotein cholesterol was inversely associated with the expression of CD40 and CD80 on mature DCs (P<0.05).

CONCLUSION

Upregulation of important costimulatory molecules on monocyte-derived DCs of CAD patients, is influenced multifactorially. Our results show notable differences between CAD patients and healthy individuals, possibly contributing to the pathophysiological processes in atherogenesis.

Role of cell adhesion molecules and immune-cell migration in the initiation, onset and development of atherosclerosis

Atherosclerosis is currently the leading factor of death in developed countries. It is now recognized as a chronic immune-inflammatory disease, whose initial stages involve the interaction of leukocytes with the endothelial monolayer. The initial stage of atherosclerosis requires the interplay of various cell adhesion molecules and immune cells to trigger leukocyte and lymphocyte migration from the circulating blood into the arterial intima. Studies have unveiled the role of inflammatory mediators in the initiation, onset and progression of the disease. During the last few years we have gained a greater understanding of the mechanism that modulates monocyte, macrophage and T cell infiltration, the role these cells play in the atherosclerotic lesion, in the formation of the fibrous plaque formation with the consequent narrowing of the arteries, and the mechanisms that lead to plaque rupture and the formation of thrombi and emboli. This review talks about the leukocyte recruitment in early atherosclerosis, the formation of the plaque, and the mechanisms that lead to thrombosis in advanced atherosclerosis. Finally, we discuss the potential for novel therapies to treat this disease.

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.

Contribution of VCAF-positive cells to neovascularization and calcification in atherosclerotic plaque development

Calcification of the vessel wall is a regulated process with many similarities to osteogenesis. Progenitor cells may play a role in this process. Previously, we identified a novel gene, Vascular Calcification Associated Factor (VCAF), which was shown to be important in pericyte osteogenic differentiation. The aim of this study was to determine the localization and expression pattern of VCAF in human cells and tissues. Immunohistochemical analysis of seven atherosclerotic arteries confirmed VCAF protein expression within calcified lesions. In addition, individual VCAF-positive cells were detected within the intima and adventitia in areas where sporadic 3G5-positive pericytes were localized. Furthermore, VCAF-positive cells were identified in newly formed microvessels in association with CD34-positive/CD146-positive/c-kit-positive cells as well as in intact CD31-positive endothelium in internal mammary arteries. Western blot analysis confirmed the presence of VCAF (18 kD) in protein lysates extracted from human smooth muscle cells, endothelial cells, macrophages, and osteoblasts. In fracture callus samples from three patients, VCAF was detected in osteoblasts and microvessels. This study demonstrates the presence of VCAF in neovessels and raises the possibility that VCAF could be a new marker for vascular progenitor cells involved in a number of differentiation pathways. These data may have implications for the prevention or treatment of vascular disease.

Th1/Th2 Imbalance, Measured by Circulating and Intracytoplasmic Inflammatory Cytokines – Immunological Alterations in Acute Coronary Syndrome and Stable Coronary Artery Disease

To describe how peripheral immune-parameters reflect the inflammatory alterations of the atherosclerotic plaques in coronary atherosclerosis. We measured general inflammatory markers C-reactive protein (CRP) and granulocyte activity, lymphocyte subpopulations and their state of activation, evaluated circulating Th1/Th2-type cytokines, and specific intracytoplasmic cytokines. We investigated the association of immune-parameters with disease outcome and mortality. Thirty-three patients with acute coronary syndrome (ACS), 62 with stable coronary artery disease (CAD) and 58 healthy controls were studied. Peripheral blood lymphocyte subgroups were quantified by flow cytometry, soluble cytokines and autoantibodies were assessed using enzyme-linked immunosorbent assay (ELISA), while intracellular cytokine levels were measured by flow cytometry after intracellular staining. We found elevated levels of CRP and granulocyte activity in ACS versus CAD (P < 0.001, P = 0.017, respectively). Natural killer (NK) cell percentages were elevated, while percentage of T cells to the total lymphocyte count was slightly decreased in ACS compared to controls (P < 0.0001, P = 0.012, respectively). Both forms of coronary atherosclerosis showed significantly higher percentages of activated T cells than controls when stained for the activation markers HLA-DR3 and CD69(+) (ACS: P < 0.0001, P = 0.002, CAD: P < 0.0001, P = 0.018, respectively). IL-1, IL-4 and IL-10 proved significantly higher in ACS versus controls (P = 0.036, P = 0.01, P < 0.0001 respectively). Th1 to Th2 ratio shifted towards a Th1 dominance in both diseases. Both general proinflammatory markers and activated T cells signify CAD. The orchestrated proinflammatory cascade eventually leads to the development of the disease.

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.

High expression of antioxidant proteins in dendritic cells: possible implications in atherosclerosis

Dendritic cells (DCs) display the unique ability to activate naive T cells and to initiate primary T cell responses revealed in DC-T cell alloreactions. DCs frequently operate under stress conditions. Oxidative stress enhances the production of inflammatory cytokines by DCs. We performed a proteomic analysis to see which major changes occur, at the protein expression level, during DC differentiation and maturation. Comparative two-dimensional gel analysis of the monocyte, immature DC, and mature DC stages was performed. Manganese superoxide dismutase (Mn-SOD) reached 0.7% of the gel-displayed proteins at the mature DC stage. This important amount of Mn-SOD is a primary antioxidant defense system against superoxide radicals, but its product, H(2)O(2), is also deleterious for cells. Peroxiredoxin (Prx) enzymes play an important role in eliminating such peroxide. Prx1 expression level continuously increased during DC differentiation and maturation, whereas Prx6 continuously decreased, and Prx2 peaked at the immature DC stage. As a consequence, DCs were more resistant than monocytes to apoptosis induced by high amounts of oxidized low density lipoproteins containing toxic organic peroxides and hydrogen peroxide. Furthermore DC-stimulated T cells produced high levels of receptor activator of nuclear factor kappaB ligand, a chemotactic and survival factor for monocytes and DCs. This study provides insights into the original ability of DCs to express very high levels of antioxidant enzymes such as Mn-SOD and Prx1, to detoxify oxidized low density lipoproteins, and to induce high levels of receptor activator of nuclear factor kappaB ligand by the T cells they activate and further emphasizes the role that DCs might play in atherosclerosis, a pathology recognized as a chronic inflammatory disorder.

Expression of GM3 synthase in human atherosclerotic lesions

We have previously demonstrated that amounts of ganglioside GM3 are markedly higher in human atherosclerotic lesions compared to that in non-diseased arterial tissue. Because the fatty acid composition of GM3 in blood plasma low density lipoproteins (LDL) and the fatty acid composition of GM3 in atherosclerotic lesions differed, we hypothesized that, in addition to GM3 originating from LDL infiltrating the arterial wall from the blood, excessive GM3 may be synthesized locally in atherosclerotic lesions. In the present work, using an anti-GM3 antibody developed by us, we showed that the levels of GM3 synthase in membrane fractions isolated from the atherosclerotic intima were higher compared to those in non-diseased arterial tissue. Using an immunohistochemical approach, we examined the expression of GM3 synthase in sections of atherosclerotic plaques and non-diseased arterial wall. GM3 synthase immunopositivity was found to be low in non-diseased arterial intima but large numbers of GM3 synthase-immunopositive cells were observed in atherosclerotic plaques. GM3 synthase was overexpressed by macrophages and dendritic cells and double immunostaining demonstrated cellular co-localization of GM3 synthase and GM3. Further in vitro experiments showed that both monocyte-derived dendritic cells and macrophages expressed high levels of GM3 synthase. The findings of the present study indicate that, at least partially, excessive amounts of GM3 in atherosclerotic lesions can be synthesized by macrophages and dendritic cells directly within the arterial wall.

Defects in regulation of local immune responses resulting in atherosclerosis

Atherosclerosis is nowadays generally accepted as an inflammatory disease but the mechanism of its origin and development have not yet been fully clarified. The present review focuses on the role of the local immune system as one of the key players in the pathogenesis of the complex process. Its part represented by vascular-associated lymphoid tissue (VALT) within the arterial wall participates directly in the vascular wall's homeostatis. Its inordinate activation during ontogenic development of an individual, this formerly defensive and physiologic mechanism transform into a pathological process resulting in an impairing inflammation. Hsp60, CRP and oxidized or otherwise modified LDL are serious candidates for triggering these pathological changes. The principal role is played by anti-Hsp60 antibodies and by shear stress originating on the surface of endothelium due to blood flow. The experimental and clinical data supporting this immunological hypothesis of atherosclerosis are discussed.

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.

Co-accumulation of dendritic cells and natural killer T cells within rupture-prone regions in human atherosclerotic plaques

We previously reported that CD1d, a molecule responsible for the presentation of lipid antigens, is expressed in atherosclerotic lesions and that its expression is restricted to dendritic cells. Recent studies demonstrating that CD1d-restricted natural killer T (NKT) cells are involved in atherogenesis prompted the present study investigating whether NKT cells are present in human atherosclerotic lesions and, if so, whether there is an association between NKT cells and dendritic cells. We found that NKT cells do accumulate in rupture-prone shoulders of atherosclerotic plaques and observed direct contacts of dendritic cells with NKT cells in rupture-prone regions of plaque.

Subset of cells immunopositive for neurokinin-1 receptor identified as arterial interstitial cells of Cajal in human large arteries

In the adventitia of large arteries, dendritic cells are located between nerve fibers, some of which contain substance P. The aim of the present study was to examine whether neurokinin 1 receptor (NK-1R) was expressed by dendritic cells in the arterial wall. Parallel sections of aortic and carotid artery segments were immunostained with anti-NK-1R and cell-type-specific antibodies. Dendritic cells in the arterial wall expressed NK-1R, albeit at a low level. Other cells, which intensely expressed NK-1R, were located along the border between the media and adventitia. They did not co-express any dendritic cell markers, including fascin, CD1a, S100, or Lag-antigen, and were negative for CD68, CD3, and mast cell tryptase. These NK-1R(+) cells were laser-capture microdissected and studied by means of electron-microscopic analysis. The microdissected cells were in direct contact with nerve endings, and their ultrastructure was typical of the interstitial cells of Cajal present in the gastrointestinal tract. Further systematic electron-microscopic analysis revealed that the cells displaying the features typical of interstitial cells of Cajal were a basic element of the human arterial wall architectonics. Arterial interstitial cells of Cajal were negative for c-kit but they expressed vasoactive intestinal peptide receptor 1 (VIPR1). Destructive alterations of contacts between arterial interstitial cells of Cajal and nerve endings were observed in arterial segments with atherosclerotic lesions. The functional significance of the arterial interstitial cells of Cajal and their possible involvement in atherosclerosis and other vascular diseases need clarification.

Monocyte retention in the pathology of atherosclerosis

Atherosclerosis is a type of chronic inflammatory disease characterized by the presence of monocyte-derived cells in all stages. Monocytes, macrophages, dendritic and foam cells play important roles in the uptake of oxidized lipids, lesion development, and ultimate plaque disruption. Much is known about the mechanisms of monocyte recruitment in the lumen; however, the fate of monocytes after they enter the artery wall is not well understood. In this review, some of the interesting recent results related to monocyte retention after their migration across the endothelium in the pathology of atherosclerosis will be highlighted. The authors have focused on monocyte inside-out equilibrium, apoptosis and proliferation regulation, and the role of vascular smooth muscle cells in monocyte retention in atherosclerosis. They have also proposed potential treatments for atherosclerosis that target inflammation and monocyte/macrophage retention.

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

Dendritic cells (DCs) are the most potent antigen-presenting cells. DCs were identified in arteries in 1995 and, since then, further knowledge has been gained indicating the importance of DCs in atherosclerosis. Vascular DCs have been shown to become activated from a very early stage of atherosclerosis. Some DCs cluster with T cells directly within atherosclerotic lesions, while others migrate to lymphoid organs to activate T cells. Dyslipidaemia systemically alters DC function and recent findings suggest that DCs play a role in plaque destabilization. This review summarizes the current status of the problem.

Thematic review series: the immune system and atherogenesis. The unusual suspects:an overview of the minor leukocyte populations in atherosclerosis

Atherosclerosis is a complex inflammatory disease process involving an array of cell types and interactions. Although macrophage foam cells and vascular smooth muscle cells constitute the bulk of the atherosclerotic lesion, other cell types have been implicated in this disease process as well. These cellular components of both innate and adaptive immunity are involved in modulating the response of macrophage foam cells and vascular smooth muscle cells to the retained and modified lipids in the vessel wall as well as in driving the chronic vascular inflammation that characterizes this disease. In this review, the involvement of a number of less prominent leukocyte populations in the pathogenesis of atherosclerosis is discussed. More specifically, the roles of natural killer cells, mast cells, neutrophils, dendritic cells, gammadelta T-cells, natural killer T-cells, regulatory T-cells, and B-cells are addressed.

Macropinocytosis Is the Endocytic Pathway That Mediates Macrophage Foam Cell Formation with Native Low Density Lipoprotein

Previously, we reported that fluid-phase endocytosis of native LDL by PMA-activated human monocytederived macrophages converted these macrophages into cholesterol-enriched foam cells (Kruth, H. S., Huang, W., Ishii, I., and Zhang, W. Y. (2002) J. Biol. Chem. 277, 34573-34580). Uptake of fluid by cells can occur either by micropinocytosis within vesicles (<0.1 microm diameter) or by macropinocytosis within vacuoles ( approximately 0.5-5.0 microm) named macropinosomes. The current investigation has identified macropinocytosis as the pathway for fluid-phase LDL endocytosis and determined signaling and cytoskeletal components involved in this LDL endocytosis. The phosphatidylinositol 3-kinase inhibitor, LY294002, which inhibits macropinocytosis but does not inhibit micropinocytosis, completely blocked PMA-activated macrophage uptake of fluid and LDL. Also, nystatin and filipin, inhibitors of micropinocytosis from lipid-raft plasma membrane domains, both failed to inhibit PMA-stimulated macrophage cholesterol accumulation. Time-lapse video phase-contrast microscopy and time-lapse digital confocal-fluorescence microscopy with fluorescent DiI-LDL showed that PMA-activated macrophages took up LDL in the fluid phase by macropinocytosis. Macropinocytosis of LDL depended on Rho GTPase signaling, actin, and microtubules. Bafilomycin A1, the vacuolar H+-ATPase inhibitor, inhibited degradation of LDL and caused accumulation of undegraded LDL within macropinosomes and multivesicular body endosomes. LDL in multivesicular body endosomes was concentrated >40-fold over its concentration in the culture medium consistent with macropinosome shrinkage by maturation into multivesicular body endosomes. Macropinocytosis of LDL taken up in the fluid phase without receptor-mediated binding of LDL is a novel endocytic pathway that generates macrophage foam cells. Macropinocytosis in macrophages and possibly other vascular cells is a new pathway to target for modulating foam cell formation in atherosclerosis.

Detection of Chlamydophila pneumoniae in dendritic cells in atherosclerotic lesions

Dendritic cells (DCs) populate atherosclerotic lesions and might be involved in the regulation of immune reactions in atherosclerosis. The present work was undertaken to examine a possible association of DCs with Chlamydophila pneumoniae in human atherosclerotic plaques obtained by endarterectomy. C. pneumoniae was identified in 17 of 60 (28%) atherosclerotic plaques by a combination of immunohistochemistry and polymerase chain reaction (PCR). Double immunohistochemistry identified the presence of C. pneumoniae within S100(+) DCs that were localised predominantly in the deep layer of the intima under the necrotic core. Quantitative analysis showed that there were no differences in the numbers of DCs between C. pneumoniae(+) and C. pneumoniae(-) groups of atherosclerotic specimens. There were also no differences in the expression of Lag-antigen and HLA-DR by DCs between the groups of specimens. Markers of DC activation CD80 and CD86 were absent from both groups of specimens. Flow cytometry analysis of the effects of C. pneumoniae infection on immature monocyte-derived DCs in vitro showed no changes in the expression of CD1a, MHC class II, CD80 and CD86. The results of this study demonstrate that C. pneumoniae might infect DCs within the atherosclerotic intima but whether the presence of C. pneumoniae in DCs affects the intensity of immune reactions in atherosclerosis needs further clarification.

Emigration of monocyte-derived cells from atherosclerotic lesions characterizes regressive, but not progressive, plaques

Some monocytes normally take up residence in tissues as sessile macrophages, but others differentiate into migratory cells resembling dendritic cells that emigrate to lymph nodes. In an in vitro model of a vessel wall, lipid mediators lysophosphatidic acid and platelet-activating factor, whose signals are implicated in promoting atherosclerosis, blocked conversion of monocytes into migratory cells and favored their retention in the subendothelium. In vivo studies revealed trafficking of monocyte-derived cells from atherosclerotic plaques during lesion regression, but little emigration was detected from progressive plaques. Thus, progression of atherosclerotic plaques may result not only from robust monocyte recruitment into arterial walls but also from reduced emigration of these cells from lesions.

Platelets, after Exposure to a High Shear Stress, Induce IL-10-Producing, Mature Dendritic Cells In Vitro

There is evidence for immune system involvement in atherogenesis. In the present study the effect of platelets on dendritic cells (DC), an important immunologic regulator, was examined in vitro. Platelet-rich plasma, after exposure to shear stress, was added to human monocyte-derived immature DC, which were then examined for surface Ag expression, allogeneic T lymphocyte stimulatory activity, and cytokine production. After exposure, the number of anti-CD40 ligand (anti-CD40L) and anti-P-selectin IgG molecules bound per platelet was increased. These activated platelets induced DC maturation, as revealed by significant up-regulation of CD83, CD80, and CD86 Ags. The addition of platelets in the presence of IFN-gamma plus LPS significantly enhanced IL-10 production from immature DC. After platelet addition, mature DC provoked a significant proliferation of allogeneic naive T lymphocytes. These activated T cells showed lower IFN-gamma production than those stimulated by LPS- and IFN-gamma-treated DC. CD40L on the platelet surface was not involved in maturation of DC, as mAb to CD40L failed to block maturation. The effect of platelets was observed even if platelets and DC were separated using large pore-sized membranes or when platelets were depleted from plasma by centrifugation. Furthermore, it was abrogated after the depletion of protein fraction. Thus, soluble protein factors excreted from activated platelets contribute to IL-10-producing DC maturation.