Vessel Wall–Embedded Dendritic Cells Induce T-Cell Autoreactivity and Initiate Vascular Inflammation

Signal Regulatory Protein α Expression in Systemic Vasculitis

OBJECTIVE

Signal regulatory protein α (SIRPα) is found primarily on myeloid cells, including macrophages and neutrophils; binds to CD47; and regulates phagocytosis, antigen presentation, cellular fusion, cell proliferation, and migration. Therefore, SIRPα may be involved in the pathogenesis of autoimmune diseases, including systemic vasculitis. This study aimed to assess SIRPα expression in tissue samples from patients with vasculitis.

METHODS

Immunohistochemical staining for SIRPα was performed on temporal artery (TA), kidney, and lung biopsy samples from patients with giant cell arteritis (GCA), patients with microscopic polyangiitis (MPA), patients with granulomatosis with polyangiitis (GPA), and patients without vasculitis. A score of SIRPα+ expression was calculated, derived from the percentages of monocytes, macrophages, and dendritic cells and neutrophils with different staining intensities in affected tissues.

RESULTS

A total of 46 samples from patients with different vasculitides (GCA, MPA, and GPA) were included in the study. Tissue samples included TA samples from 15 patients with GCA; kidney samples from 11 and 9 patients with GPA and MPA, respectively; and lung samples from 11 patients with GPA. Most tissue samples from patients with active vasculitis (15 of 15 TA samples, 17 of 20 kidney samples, and 9 of 11 lung samples) showed SIRPα staining. SIRPα staining intensity was less in kidney samples compared to TA and lung samples.

CONCLUSION

This study demonstrates high-level expression of SIRPα in macrophages and monocytes in affected tissue in systemic vasculitis. These findings provide a foundation for further studies exploring the role of the SIRPα-CD47 pathway in the pathogenesis of systemic vasculitis and the potential for the blockade of SIRPα and/or the depletion of SIRPα+ cells as treatment of systemic vasculitis.

Current Insights into Tissue Injury of Giant Cell Arteritis: From Acute Inflammatory Responses towards Inappropriate Tissue Remodeling

Giant cell arteritis (GCA) is an autoimmune disease affecting large vessels in patients over 50 years old. It is an exemplary model of a classic inflammatory disorder with IL-6 playing the leading role. The main comorbidities that may appear acutely or chronically are vascular occlusion leading to blindness and thoracic aorta aneurysm formation, respectively. The tissue inflammatory bulk is expressed as acute or chronic delayed-type hypersensitivity reactions, the latter being apparent by giant cell formation. The activated monocytes/macrophages are associated with pronounced Th1 and Th17 responses. B-cells and neutrophils also participate in the inflammatory lesion. However, the exact order of appearance and mechanistic interactions between cells are hindered by the lack of cellular and molecular information from early disease stages and accurate experimental models. Recently, senescent cells and neutrophil extracellular traps have been described in tissue lesions. These structures can remain in tissues for a prolonged period, potentially favoring inflammatory responses and tissue remodeling. In this review, current advances in GCA pathogenesis are discussed in different inflammatory phases. Through the description of these-often overlapping-phases, cells, molecules, and small lipid mediators with pathogenetic potential are described.

Giant Cell Arteritis: Advances in Understanding Pathogenesis and Implications for Clinical Practice

Giant cell arteritis (GCA) is a noninfectious granulomatous vasculitis of unknown etiology affecting individuals older than 50 years. Two forms of GCA have been identified: a cranial form involving the medium-caliber temporal artery causing temporal arteritis (TA) and an extracranial form involving the large vessels, mainly the thoracic aorta and its branches. GCA generally affects individuals with a genetic predisposition, but several epigenetic (micro)environmental factors are often critical for the onset of this vasculitis. A key role in the pathogenesis of GCA is played by cells of both the innate and adaptive immune systems, which contribute to the formation of granulomas that may include giant cells, a hallmark of the disease, and arterial tertiary follicular organs. Cells of the vessel wall cells, including vascular smooth muscle cells (VSMCs) and endothelial cells, actively contribute to vascular remodeling responsible for vascular stenosis and ischemic complications. This review will discuss new insights into the molecular and cellular pathogenetic mechanisms of GCA, as well as the implications of these findings for the development of new diagnostic biomarkers and targeted drugs that could hopefully replace glucocorticoids (GCs), still the backbone of therapy for this vasculitis.

Molecular mechanisms and therapeutic perspectives of peroxisome proliferator-activated receptor α agonists in cardiovascular health and disease

The prevalence of cardiovascular disease (CVD) has been rising due to sedentary lifestyles and unhealthy dietary patterns. Peroxisome proliferator-activated receptor α (PPARα) is a nuclear receptor regulating multiple biological processes, such as lipid metabolism and inflammatory response critical to cardiovascular homeostasis. Healthy endothelial cells (ECs) lining the lumen of blood vessels maintains vascular homeostasis, where endothelial dysfunction associated with increased oxidative stress and inflammation triggers the pathogenesis of CVD. PPARα activation decreases endothelial inflammation and senescence, contributing to improved vascular function and reduced risk of atherosclerosis. Phenotypic switch and inflammation of vascular smooth muscle cells (VSMCs) exacerbate vascular dysfunction and atherogenesis, in which PPARα activation improves VSMC homeostasis. Different immune cells participate in the progression of vascular inflammation and atherosclerosis. PPARα in immune cells plays a critical role in immunological events, such as monocyte/macrophage adhesion and infiltration, macrophage polarization, dendritic cell (DC) embedment, T cell activation, and B cell differentiation. Cardiomyocyte dysfunction, a major risk factor for heart failure, can also be alleviated by PPARα activation through maintaining cardiac mitochondrial stability and inhibiting cardiac lipid accumulation, oxidative stress, inflammation, and fibrosis. This review discusses the current understanding and future perspectives on the role of PPARα in the regulation of the cardiovascular system as well as the clinical application of PPARα ligands.

The innate face of Giant Cell Arteritis: Insight into cellular and molecular innate immunity pathways to unravel new possible biomarkers of disease

Giant cell arteritis (GCA) is an inflammatory chronic disease mainly occurring in elderly individuals. The pathogenesis of GCA is still far from being completely elucidated. However, in susceptible arteries, an aberrant immune system activation drives the occurrence of vascular remodeling which is mainly characterized by intimal hyperplasia and luminal obstruction. Vascular damage leads to ischemic manifestations involving extra-cranial branches of carotid arteries, mostly temporal arteries, and aorta. Classically, GCA was considered a pathological process resulting from the interaction between an unknown environmental trigger, such as an infectious agent, with local dendritic cells (DCs), activated CD4 T cells and effector macrophages. In the last years, the complexity of GCA has been underlined by robust evidence suggesting that several cell subsets belonging to the innate immunity can contribute to disease development and progression. Specifically, a role in driving tissue damage and adaptive immunity activation was described for dendritic cells (DCs), monocytes and macrophages, mast cells, neutrophils and wall components, such as endothelial cells (ECs) and vascular smooth muscle cells (VSMCs). In this regard, molecular pathways related to cytokines, chemokines, growth factors, vasoactive molecules and reactive oxygen species may contribute to the inflammatory process underlying GCA. Altogether, innate cellular and molecular pathways may clarify many pathogenetic aspects of the disease, paving the way for the identification of new biomarkers and for the development of new treatment targets for GCA. This review aims to deeply dissect past and new evidence on the innate immunological disruption behind GCA providing a comprehensive description of disease development from the innate perspective.

Self-Tolerance of Vascular Tissues Is Broken Down by Vascular Dendritic Cells in Response to Systemic Inflammation to Initiate Regional Autoinflammation

The correlation of infections with vascular autoinflammatory diseases such as vasculitis and atherosclerosis has been long recognized, and progressive inflammation with the formation of tertiary lymphoid organs in arterial adventitia intensively studied, the immunological basis of the nondiseased vasculatures that predispose to subsequent vascular autoimmunity during inflammation, however, is not well characterized. Here, we investigated the vascular immunity in situ of steady-state C57BL/6 mice and found that healthy vascular tissues contained a comprehensive set of immune cells with relatively higher proportion of innate components than lymphoid organs. Notably, a complete set of dendritic cell (DC) subsets was observed with monocyte-derived DCs (moDCs) constituting a major proportion; this is in contrast to moDCs being considered rare in the steady state. Interestingly, these vascular DCs constitutively expressed more suppressive factors with cDC1 for PD-L1 and moDCs for IL-10; this is concordant with the inhibitive phenotype of T cells in normal vascular tissues. The immunotolerant state of the vascular tissues, however, was readily eroded by systemic inflammation, demonstrated by the upregulation of proinflammatory cytokines and enhanced antigen presentation by vascular DCs to activate both cellular and humoral immunity in situ, which ultimately led to vascular destruction. Different vascular DC subsets elicited selective effects: moDCs were potent cytokine producers and B-cell activators, whereas cDCs, particularly, cDC1, were efficient at presenting antigens to stimulate T cells. Together, we unveil regional immunological features of vascular tissues to explain their dual facets under physiological versus pathological conditions for the better understanding and treatment of cardiovascular autoinflammation.

Glucocorticoid Effects on Tissue Residing Immune Cells in Giant Cell Arteritis: Importance of GM-CSF

Giant cell arteritis (GCA) is a systemic granulomatous vasculitis clinically characterized by a prompt response to glucocorticoid therapy. Dendritic cells (DCs) play a central role in the pathogenesis of the disease and are increased in temporal arteries from GCA patients. The aim of this study was to determine the effects of glucocorticoid therapy on granulomatous infiltrates and on peripheral DCs of GCA patients. Immunohistochemical staining of temporal artery specimens from 41 GCA patients revealed a rapid reduction of the number of DCs after initiation of glucocorticoid treatment. TUNEL staining was performed to quantify apoptotic S100+ DC, CD3+ T cells, and CD68+ macrophages in the granulomatous infiltrates. An increase of apoptotic cells up to 9 ± 2% after 4–5 days of glucocorticoid therapy and up to 27 ± 5% (p < 0.001, compared to earlier timepoints) after 6–10 days was detected. A decrease of CCL19 and CCL21 expression was observed after starting glucocorticoid therapy. Granulocyte-macrophage colony-stimulating factor (GM-CSF) expression also significantly decreased under glucocorticoid therapy. No GM-CSF expression was detected in the control specimens. Glucocorticoid therapy leads to a rapid, time-dependent reduction of DCs in temporal arteries from GCA patients and reduction of mediators for cell migration. Our data suggest GM-CSF as a novel therapeutic target of GCA.

Nickel Hypersensitivity to Atrial Septal Occluders: Smoke Without Fire?

Nickel is one of the most common contact allergens worldwide; it is used as the main component of the devices used for atrial septal defects (ASDs) and patent foramen ovale (PFO) closure. Developing nickel hypersensitivity after PFO/ASD occlusion is significantly rarer described in medical literature than typical nickel contact sensitization. The exact pathophysiological mechanism of this "device syndrome" remains unknown, and many question the real incidence or even the existence of this clinical entity. Nevertheless, it has been associated with a wide spectrum of symptoms, including chest pain, migraines, palpitation, and dyspnea. Skin patch tests are the first-line approach to diagnose nickel hypersensitivity. However, diagnostic criteria for the device syndrome have not been developed, and diagnosis in reported cases is established by a process of elimination. Management-drug therapy (corticosteroids, clopidogrel, etc.) or even surgical explantation in severe cases-of patients developing such clinical manifestations after percutaneous PFO/ASD occlusion is empirical. Undoubtedly, endocardiac device-related nickel hypersensitivity requires more focused research to discover the underlying mechanism as well as to develop reliable prognostic tests for detecting high-risk patients and preventing severe nickel hypersensitivity reactions.

Innate and Adaptive Immunity in Giant Cell Arteritis

Autoimmune diseases can afflict every organ system, including blood vessels that are critically important for host survival. The most frequent autoimmune vasculitis is giant cell arteritis (GCA), which causes aggressive wall inflammation in medium and large arteries and results in vaso-occlusive wall remodeling. GCA shares with other autoimmune diseases that it occurs in genetically predisposed individuals, that females are at higher risk, and that environmental triggers are suspected to beget the loss of immunological tolerance. GCA has features that distinguish it from other autoimmune diseases and predict the need for tailored diagnostic and therapeutic approaches. At the core of GCA pathology are CD4⁺ T cells that gain access to the protected tissue niche of the vessel wall, differentiate into cytokine producers, attain tissue residency, and enforce macrophages differentiation into tissue-destructive effector cells. Several signaling pathways have been implicated in initiating and sustaining pathogenic CD4⁺ T cell function, including the NOTCH1-Jagged1 pathway, the CD28 co-stimulatory pathway, the PD-1/PD-L1 co-inhibitory pathway, and the JAK/STAT signaling pathway. Inadequacy of mechanisms that normally dampen immune responses, such as defective expression of the PD-L1 ligand and malfunction of immunosuppressive CD8⁺ T regulatory cells are a common theme in GCA immunopathology. Recent studies are providing a string of novel mechanisms that will permit more precise pathogenic modeling and therapeutic targeting in GCA and will fundamentally inform how abnormal immune responses in blood vessels lead to disease.

Characterization of circulating immune cells in acute Kawasaki disease suggests exposure to different antigens

Kawasaki disease (KD) is an acute pediatric vasculitis of unknown etiology that can cause coronary artery aneurysms, and is the leading cause of acquired heart disease in children. We studied aspects of the innate and adaptive immune response in 17 acute KD children prior to treatment with intravenous immunoglobulin. Distinct patterns within the innate immune response correlated with specific clinical features. Proinflammatory myeloid dendritic cells (mDC) were abundant in four of 17 (23·5%) subjects who were older and manifested severe inflammation with clinical myocarditis and elevated hepatobiliary enzyme levels. Of the nine subjects with low levels of anti‐inflammatory, tolerogenic mDC, six had enlarged cervical lymph nodes at diagnosis. In contrast, the adaptive immune repertoire varied greatly with no discernible patterns or associations with clinical features. Two subjects with aneurysms had numerous circulating CD8⁺ T cells. Ten subjects showed low CD4⁺ T cell numbers and seven subjects had CD4⁺ T cells in the normal range. CD4⁺ T cells expressed interleukin‐7 receptor (IL‐7R), suggesting repeated antigenic stimulation. Thymic‐derived regulatory T cells (nT_reg) and peripherally induced regulatory T cells (iT_reg) were also enumerated, with the majority having the nT_reg phenotype. Natural killer (NK) and NK T cell numbers were similar across all subjects. Taken together, the results of the immune monitoring suggest that KD may have multiple triggers that stimulate different arms of the innate and adaptive compartment in KD patients. Thus, it is possible that diverse antigens may participate in the pathogenesis of KD.

Functional crosstalk between T cells and monocytes in cancer and atherosclerosis

Monocytes and monocyte-derived cells, including Mϕs and dendritic cells, exhibit a diverse array of phenotypic states that are dictated by their surrounding microenvironment. These cells direct T cell activation and function via cues that range from being immunosuppressive to immunostimulatory. Solid tumors and atherosclerotic plaques represent two pathological niches with distinct immune microenvironments. While monocytes and their progeny possess a phenotypic spectrum found within both disease contexts, most within tumors are pro-tumoral and support evasion of host immune responses by tumor cells. In contrast, monocyte-derived cells within atherosclerotic plaques are usually pro-atherogenic, pro-inflammatory, and predominantly directed against self-antigens. Consequently, cancer immunotherapies strive to enhance the immune response against tumor antigens, whereas atherosclerosis treatments seek to dampen the immune response against lipid antigens. Insights into monocyte-T cell interactions within these niches could thus inform therapeutic strategies for two immunologically distinct diseases. Here, we review monocyte diversity, interactions between monocytes and T cells within tumor and plaque microenvironments, how certain therapies have leveraged these interactions, and novel strategies to assay such associations.

Reviewing the Pathophysiology Behind the Advances in the Management of Giant Cell Arteritis

Improving understanding of the underlying pathophysiology of giant cell arteritis (GCA) is transforming clinical management by identifying novel avenues for targeted therapies. One key area of concern for both clinicians and patients with GCA is glucocorticoid (GC) morbidity. The first randomised controlled trials of targeted treatment to reduce cumulative GC use in GCA have been published, with tocilizumab, an interleukin (IL)-6 receptor inhibitor, now the first ever licensed treatment for GCA. Further potential therapies are emerging owing to our enhanced understanding of the pathophysiology of the disease. Other improvements in the care of our patients are rapid access pathways and imaging techniques, such as ultrasound, which are becoming part of modern rheumatology practice in the UK, Europe and beyond. These have been highlighted in the literature to reduce delay in diagnosis and improve long-term outcomes for those investigated for GCA.

Does low risk of infections as a marker of effective immunity predict increased risk of subsequent giant cell arteritis or polymyalgia rheumatica? A Danish population-based case-control study

Objective

It has been suggested that a hyper-effective immune system (“hyper-immunity”) is central to the pathogenesis of giant cell arteritis and polymyalgia rheumatica (GCA/PMR). We examined if a low risk of infections, as a marker of hyper-immunity, can predict increased subsequent risk of GCA/PMR.

Patients and methods

We conducted a population-based case–control study including all patients aged ≥50 years with incident GCA/PMR diagnosed between 1997 and 2012 in Northern Denmark. For each case, we selected 10 population controls matched on gender, age, place of residence, and time spent in the region. Complete history of hospital-treated infections and community-based anti-infective prescriptions was assessed in population-based registries. We used conditional logistic regression to compute OR of GCA/PMR associated with infections while adjusting for comorbidities, immunosuppressive treatment, and other potential confounders.

Results

We included 7,225 GCA/PMR cases and 72,250 controls. When excluding all infections occurring within the last year before GCA/PMR diagnosis, there was no decreased risk for GCA/PMR in people with a history of hospital-treated infection (adjusted OR=1.04, 95% CI: 0.98–1.10) or community anti-infective treatment (adjusted OR=1.07, 95% CI: 0.99–1.16). Within the last year preceding the GCA/PMR index date, patients with hospital-treated infections (adjusted OR=1.59, 95% CI: 1.44–1.75) or community anti-infective treatment (adjusted OR=1.63, 95% CI: 1.48–1.79) had a greatly increased risk of a GCA/PMR diagnosis.

Conclusion

These results do not support the hypothesis of “hyper-immunity” leading to GCA/PMR. Instead, incident GCA/PMR is preceded by a slightly increased risk of infection, which may be related to protopathic bias or support theories that infections may be directly involved in the pathogenesis of GCA/PMR.

The microvascular niche instructs T cells in large vessel vasculitis via the VEGF-Jagged1-Notch pathway

Microvascular networks in the adventitia of large arteries control access of inflammatory cells to the inner wall layers (media and intima) and thus protect the immune privilege of the aorta and its major branches. In autoimmune vasculitis giant cell arteritis (GCA), CD4 T helper 1 (T_H1) and T_H17 cells invade into the wall of the aorta and large elastic arteries to form tissue-destructive granulomas. Whether the disease microenvironment provides instructive cues for vasculitogenic T cells is unknown. We report that adventitial microvascular endothelial cells (mvECs) perform immunoregulatory functions by up-regulating the expression of the Notch ligand Jagged1. Vascular endothelial growth factor (VEGF), abundantly present in GCA patients' blood, induced Jagged1 expression, allowing mvECs to regulate effector T cell induction via the Notch-mTORC1 (mammalian target of rapamycin complex 1) pathway. We found that circulating CD4 T cells in GCA patients have left the quiescent state, actively signal through the Notch pathway, and differentiate into T_H1 and T_H17 effector cells. In an in vivo model of large vessel vasculitis, exogenous VEGF functioned as an effective amplifier to recruit and activate vasculitogenic T cells. Thus, systemic VEGF co-opts endothelial Jagged1 to trigger aberrant Notch signaling, biases responsiveness of CD4 T cells, and induces pathogenic effector functions. Adventitial microvascular networks function as an instructive tissue niche, which can be exploited to target vasculitogenic immunity in large vessel vasculitis.

Dendritic cells in atherosclerosis: Functions in immune regulation and beyond

Chronic inflammation drives the development of atherosclerosis. Dendritic cells (DCs) are known as central mediators of adaptive immune responses and the development of immunological memory and tolerance. DCs are present in non-diseased arteries, and accumulate within atherosclerotic lesions where they can be localised in close vicinity to T cells. Recent work has revealed important functions of DCs in regulating immune mechanisms in atherogenesis, and vaccination strategies using DCs have been explored for treatment of disease. However, in line with a phenotypical and functional overlap with plaque macrophages vascular DCs were also identified to engulf lipids, thus contributing to lipid burden in the vessel wall and initiation of lesion growth. Furthermore, a function of DCs in regulating cholesterol homeostasis has been revealed. Finally, phenotypically distinct plasmacytoid dendritic cells (pDCs) have been identified within atherosclerotic lesions. This review will dissect the multifaceted contribution of DCs and pDCs to the initiation and progression of atherosclerosis and the experimental approaches utilising DCs in therapeutic vaccination strategies.

Pro-inflammatory and anti-inflammatory T cells in giant cell arteritis

Giant cell arteritis is an autoimmune disease defined by explicit tissue tropism to the walls of medium and large arteries. Pathognomic inflammatory lesions are granulomatous in nature, emphasizing the functional role of CD4T cells and macrophages. Evidence for a pathogenic role of antibodies and immune complexes is missing. Analysis of T cell populations in giant cell arteritis, both in the tissue lesions and in the circulation, has supported a model of broad, polyclonal T cell activation, involving an array of functional T cell lineages. The signature of T cell cytokines produced by vasculitic lesions is typically multifunctional, including IL-2, IFN-γ, IL-17, IL-21, and GM-CSF, supportive for a general defect in T cell regulation. Recent data describing the lack of a lymph node-based population of anti-inflammatory T cells in giant cell arteritis patients offers a fresh look at the immunopathology of this vasculitis. Due to defective CD8+NOX2+ regulatory T cells, giant cell arteritis patients appear unable to curtail clonal expansion within the CD4T cell compartment, resulting in widespread CD4T cell hyperimmunity. Why unopposed expansion of committed CD4 effector T cells would lead to invasion of the walls of medium and large arteries needs to be explored in further investigations.

Immune checkpoint dysfunction in large and medium vessel vasculitis

Giant cell arteritis (GCA) is a granulomatous vasculitis of the aorta and its medium-sized branch vessels. CD4 T cells, macrophages, and dendritic cells (DCs) build granulomatous infiltrates that injure the vessel wall and elicit a maladaptive response to injury. Pathological consequences include fragmentation of elastic membranes, destruction of the medial layer, microvascular neoangiogenesis, massive outgrowth of myofibroblasts, and lumen-occlusive intimal hyperplasia. Antigens have been suspected to drive the local activation of vasculitogenic CD4 T cells, but recent data have suggested a more generalized defect in the threshold setting of such T cells, rendering them hyperreactive. Under physiological conditions, immune checkpoints provide negative signals to curb T cell activation and prevent inflammation-associated tissue destruction. This protective mechanism is disrupted in GCA. Vessel wall DCs fail to express the immunoinhibitory ligand programmed cell death ligand-1, leaving lesional T cells unchecked. Consequently, programmed cell death protein-1-positive CD4 T cells can enter the immunoprivileged vessel wall, where they produce a broad spectrum of inflammatory cytokines (interferon-γ, IL-17, and IL-21) and have a direct role in driving intimal hyperplasia and intramural neoangiogenesis. The deficiency of the programmed cell death protein-1 immune checkpoint in GCA, promoting unopposed T cell immunity, contrasts with checkpoint hyperactivity in cancer patients in whom excessive programmed cell death ligand-1 expression paralyzes the function of antitumor T cells. Excessive checkpoint activity is the principle underlying cancer-immune evasion and is therapeutically targeted by immunotherapy with checkpoint inhibitors. Such checkpoint inhibitors, which unleash anticancer T cells and induce immune-related toxicity, may lead to drug-induced vasculitis.

The role of toll like receptors in giant cell arteritis

GCA is a common primary systemic vasculitis that results in granulomatous inflammation of medium to large arteries. Both innate and adaptive immune mechanisms combine to drive intimal hyperplasia, luminal stenosis and ultimately occlusion. While the pathogenesis of GCA is incompletely understood, the activation of resident adventitial dendritic cells via toll like receptors (TLRs) appears to be a crucial inciting event. Here we explore the role of TLRs in the pathogenesis of GCA, including their effects on dendritic cell and T cell activation and recruitment, putative infectious triggers for GCA and the potential of TLR inhibition as a novel therapeutic strategy in GCA.

Toll-like receptors mediating vascular malfunction: Lessons from receptor subtypes

Toll-like receptors (TLR) are a subfamily of pattern recognition receptors (PRR) implicated in a variety of vascular abnormalities. However, the pathophysiological role and the interplay between different TLR-mediated innate and adaptive immune responses during the development of vascular diseases remain largely unspecified. TLR are widely distributed in both immune and nonimmune cells in the blood vessel wall. The expressions and locations of TLR are dynamically regulated in response to distinct molecular patterns derived from pathogens or damaged host cells. As a result, the outcome of TLR signaling is agonist- and cell type-dependent. A better understanding of discrete TLR signaling pathways in the vasculature will provide unprecedented opportunities for the discovery of novel therapies in many inflammatory vascular diseases. The present brief review discusses the role of individual TLR in controlling cellular functions of the vascular system, by focusing on the inflammatory responses within the blood vessel wall which contribute to the development of hypertension and atherosclerosis.

Innate immune cells in the pathogenesis of primary systemic vasculitis

Innate immune system forms the first line of defense against foreign substances. Neutrophils, eosinophils, erythrocytes, platelets, monocytes, macrophages, dendritic cells, γδ T cells, natural killer and natural killer T cells comprise the innate immune system. Genetic polymorphisms influencing the activation of innate immune cells predispose to development of vasculitis and influence its severity. Abnormally activated innate immune cells cross-talk with other cells of the innate immune system, present antigens more efficiently and activate T and B lymphocytes and cause tissue destruction via cell-mediated cytotoxicity and release of pro-inflammatory cytokines. These secreted cytokines further recruit other cells to the sites of vascular injury. They are involved in both the initiation as well as the perpetuation of vasculitis. Evidences suggest reversal of aberrant activation of immune cells in response to therapy. Understanding the role of innate immune cells in vasculitis helps understand the potential of therapeutic modulation of their activation to treat vasculitis.

Decreased regulatory T cells in vulnerable atherosclerotic lesions: imbalance between pro- and anti-inflammatory cells in atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the arterial wall in which presentation of autoantigens by dendritic cells (DCs) leads to the activation of T cells. Anti-inflammatory cells like Tregs counterbalance inflammation in atherogenesis. In our study, human carotid plaque specimens were classified as stable (14) and unstable (15) according to established morphological criteria. Vessel specimens (n = 12) without any signs of atherosclerosis were used as controls. Immunohistochemical staining was performed to detect different types of DCs (S100, fascin, CD83, CD209, CD304, and CD123), proinflammatory T cells (CD3, CD4, CD8, and CD161), and anti-inflammatory Tregs (FoxP3). The following results were observed: in unstable lesions, significantly higher numbers of proinflammatory cells like DCs, T helper cells, cytotoxic T cells, and natural killer cells were detected compared to stable plaques. Additionally, there was a significantly higher expression of HLA-DR and more T cell activation (CD25, CD69) in unstable lesions. On the contrary, unstable lesions contained significantly lower numbers of Tregs. Furthermore, a significant inverse correlation between myeloid DCs and Tregs was shown. These data suggest an increased inflammatory state in vulnerable plaques resulting from an imbalance of the frequency of local pro- and anti-inflammatory immune cells.

National Institutes of Health State of the Science Symposium in Therapeutic Apheresis: scientific opportunities in extracorporeal photopheresis

The clinical use of extracorporeal photopheresis (ECP) for accepted indications such as graft-versus-host disease, transplant rejection, and cutaneous T-cell lymphoma continues to increase. Expanded applications for ECP, such as the treatment of select autoimmune diseases, are being explored. Extracorporeal photopheresis's capacity to both immunotolerize in the autoreactive setting, while immunizing against a lymphoma is unusual and suggestive of a unique mechanism. It is likely that ECP's induction of dendritic cells is key to its efficacy in both of these settings, but exactly how ECP impacts other immune components and their interactions is not fully understood. Further basic science research is necessary to elucidate how these dissimilar cellular activities are functionally integrated. On the clinical side, collaborative multicenter trials designed to recognize the principal variables controlling therapeutic responses and improve prognostic indicators may enable tailoring devices, treatment schedules, and doses to the needs of the individual patients or diseases. This review describes our current understanding of how ECP influences the immune system, reviews the existing clinical applications of ECP, and explores areas for future basic science and clinical research as presented at the National Institutes of Health State of the Science Symposium in Therapeutic Apheresis in November 2012.

Adipose tissue dendritic cells enhances inflammation by prompting the generation of Th17 cells

BACKGROUND

Obesity has become a global challenge for public health. It has been reported that obesity is associated with chronic inflammation. However, the mechanism for the chronic inflammation contributes to obesity remains elusive.

METHODOLOGY/PRINCIPAL FINDINGS

In our study, we found a novel CD11c+ dendritic cell subset existed in murine adipose tissues which was immature phenotype. Moreover, as compared to the lean controls, the number of CD11c+ DCs and CD4+IL-17+T cells were higher in adipose tissue of high fat diet (HFD) mice. Adipose tissues derived dendritic cells (ATDCs) displayed lower levels of CD40, CD80, CD86, MHCI and MHCII expression than splenic DCs (SPDCs). However, ATDCs showed higher levels of IL-6, TGF-β and IL-23 secretion. Moreover, our in vitro experiments demonstrated that ATDCs were capable of promoting Th17 cell generation.

CONCLUSIONS/SIGNIFICANCE

Our results indicate the existence of CD11c+ DCs in adipose tissues, which displays an immature phenotype but possessing pro-inflammatory function.

Immune mechanisms in medium and large-vessel vasculitis

Vasculitis of the medium and large arteries, most often presenting as giant cell arteritis (GCA), is an infrequent, but potentially fatal, type of immune-mediated vascular disease. The site of the aberrant immune reaction, the mural layers of the artery, is strictly defined by vascular dendritic cells, endothelial cells, vascular smooth muscle cells and fibroblasts, which engage in an interaction with T cells and macrophages to, ultimately, cause luminal stenosis or aneurysmal wall damage of the vessel. A multitude of effector cytokines, all known as critical mediators in host-protective immunity, have been identified in vasculitic lesions. Two dominant cytokine clusters--the IL-6-IL-17 axis and the IL-12-IFN-γ axis--have been linked to disease activity. These two clusters seem to serve different roles in the vasculitic process. The IL-6-IL-17 cluster is highly responsive to standard corticosteroid therapy, whereas the IL-12-IFN-γ cluster is resistant to steroid-mediated immunosuppression. The information exchange between vascular and immune cells and stabilization of the vasculitic process involves members of the Notch receptor and ligand family. Focusing on elements in the tissue context of GCA, instead of broadly suppressing host immunity, might enable a more tailored therapeutic approach that avoids unwanted adverse effects of aggressive immunosuppression.

The adventitia: Essential role in pulmonary vascular remodeling

A rapidly emerging concept is that the vascular adventitia acts as a biological processing center for the retrieval, integration, storage, and release of key regulators of vessel wall function. It is the most complex compartment of the vessel wall and comprises a variety of cells including fibroblasts, immunomodulatory cells, resident progenitor cells, vasa vasorum endothelial cells, and adrenergic nerves. In response to vascular stress or injury, resident adventitial cells are often the first to be activated and reprogrammed to then influence tone and structure of the vessel wall. Experimental data indicate that the adventitial fibroblast, the most abundant cellular constituent of adventitia, is a critical regulator of vascular wall function. In response to vascular stresses such as overdistension, hypoxia, or infection, the adventitial fibroblast is activated and undergoes phenotypic changes that include proliferation, differentiation, and production of extracellular matrix proteins and adhesion molecules, release of reactive oxygen species, chemokines, cytokines, growth factors, and metalloproteinases that, collectively, affect medial smooth muscle cell tone and growth directly and that stimulate recruitment and retention of circulating inflammatory and progenitor cells to the vessel wall. Resident dendritic cells also participate in "sensing" vascular stress and actively communicate with fibroblasts and progenitor cells to simulate repair processes that involve expansion of the vasa vasorum, which acts as a conduit for further delivery of inflammatory/progenitor cells. This review presents the current evidence demonstrating that the adventitia acts as a key regulator of pulmonary vascular wall function and structure from the "outside in."

Dynamic T cell-APC interactions sustain chronic inflammation in atherosclerosis

Atherosclerosis is a chronic inflammatory disease of large and medium-sized arteries characterized by leukocyte accumulation in the vessel wall. Both innate and adaptive immune responses contribute to atherogenesis, but the identity of atherosclerosis-relevant antigens and the role of antigen presentation in this disease remain poorly characterized. We developed live-cell imaging of explanted aortas to compare the behavior and role of APCs in normal and atherosclerotic mice. We found that CD4+ T cells were capable of interacting with fluorescently labeled (CD11c-YFP+) APCs in the aortic wall in the presence, but not the absence, of cognate antigen. In atherosclerosis-prone Apoe-/-CD11c-YFP+ mice, APCs extensively interacted with CD4+ T cells in the aorta, leading to cell activation and proliferation as well as secretion of IFN-γ and TNF-α. These cytokines enhanced uptake of oxidized and minimally modified LDL by macrophages. We conclude that antigen presentation by APCs to CD4+ T cells in the arterial wall causes local T cell activation and production of proinflammatory cytokines, which promote atherosclerosis by maintaining chronic inflammation and inducing foam cell formation.

Clinical features of polymyalgia rheumatica and giant cell arteritis

Polymyalgia rheumatica (PMR) and giant cell arteritis (GCA) are inflammatory diseases that typically affect white individuals >50 years. Women are affected ∼2-3 times more often than men. PMR and GCA occur together more frequently than expected by chance. The main symptoms of PMR are pain and stiffness in the shoulders, and often in the neck and pelvic girdle. Imaging studies reveal inflammation of joints and bursae of the affected areas. GCA is a large-vessel and medium-vessel arteritis predominantly involving the branches of the aortic arch. The typical clinical manifestations of GCA are new headache, jaw claudication and visual loss. PMR and GCA usually remit within 6 months to 2 years from disease onset. Some patients, however, have a relapsing course and might require long-standing treatment. Diagnosis of PMR and GCA is based on clinical features and elevated levels of inflammatory markers. Temporal artery biopsy remains the gold standard to support the diagnosis of GCA; imaging studies are useful to delineate large-vessel involvement in GCA. Glucocorticoids remain the cornerstone of treatment of both PMR and GCA, but patients with GCA require higher doses. Synthetic immunosuppressive drugs also have a role in disease management, whereas the role of biologic agents is currently unclear.

Recruitment of circulating dendritic cell precursors into the infarcted myocardium and pro-inflammatory response in acute myocardial infarction

DC (dendritic cells) play an important role in the immune system. They invade peripheral tissues to detect harmful antigens, inducing a local immune response. Studies suggest that DCPs (dendritic cell precursors) might be reduced in AMI (acute myocardial infarction); however, the reason for their reduction is unknown yet. In the present study, circulating mDCPs (myeloid DCPs), pDCPs (plasmacytoid DCPs), tDCPs (total DCPs) and serum levels of TNFα (tumour necrosis factor α), IL (interleukin)-2, -4, -5, -6, -10 and -12 were analysed by flow cytometry in blood of patients with NSTEMI [non-STEMI (ST-segment elevation myocardial infarction)] (n=44) and STEMI (n=34) compared with controls with excluded CAD (coronary artery disease) (n=45). Post-mortem myocardial specimens of patients with AMI (n=12) and healthy myocardium of accident victims (n=10) were immunostained for mDCs (myeloid dendritic cells) T-cells and macrophages. Compared with controls, in patients with AMI a significant decrease in circulating mDCPs, pDCPs and tDCPs was observed (each P<0.0001). The extent of the decrease was higher in STEMI than NSTEMI patients. Serum levels were significantly higher in patients with AMI compared with controls for IL-6, -10, -12 and TNFα (each P<0.03). Immunostaining revealed significantly higher number of DCs, T-cells and macrophages (each P<0.002) in infarcted than control myocardium. We show that circulating DCPs are significantly reduced in AMI, with a pronounced reduction in STEMI patients. This was accompanied by a significant increase of inflammatory serum cytokines in patients with AMI. Immunohistochemical analysis unravelled that the reduction of circulating DCPs might be due to recruitment into the infarcted myocardium.

[Giant cell arteritis: etiological knowledge and diagnostic challenge for pathologists]

Giant cell arteritis is a potentially systemic disease of medium-sized and large caliber arteries, showing a preferential manifestation in the extracranial branches of the carotid artery. The diagnosis is oriented to clinical and histomorphological criteria which will be critically reviewed. Particular emphasis is placed on the differentiation from normal aging processes and from healing stages under steroid therapy. In addition, the advances in our understanding of the disease pathomechanism during the last 10 years will be briefly presented as the basis for the hitherto empiric steroid treatment.

FDG PET Imaging of Large-Vessel Vasculitis

Diagnosis of vasculitis is challenging given the nonspecific manifestations of the diseases. [(18)F]Fluorodeoxyglucose (FDG) positron emission tomography (PET) has been increasingly used for vasculitis in clinic and has been shown to have a potential role in diagnosing large-vessel vasculitis such as giant cell vasculitis and Takayasu vasculitis, in monitoring treatment response, and in predicting disease progression. However, the exact clinical role of FDG PET for vasculitis has not been determined. Diagnosis of vasculitis should not be made solely based on PET. It is also worth noting that FDG PET has limited role in small-size vasculitis, although case reports have shown some success.

Phenotypic and functional heterogeneity of macrophages and dendritic cell subsets in the healthy and atherosclerosis-prone aorta

Atherosclerosis continues to be the leading cause of cardiovascular disease. Development of atherosclerosis depends on chronic inflammation in the aorta and multiple immune cells are involved in this process. Importantly, resident macrophages and dendritic cells (DCs) are present within the healthy aorta, but the functions of these cells remain poorly characterized. Local inflammation within the aortic wall promotes the recruitment of monocytes and DC precursors to the aorta and micro-environmental factors direct the differentiation of these emigrated cells into multiple subsets of macrophages and DCs. Recent data suggest that several populations of macrophages and DCs can co-exist within the aorta. Although the functions of M1, M2, Mox, and M4 macrophages are well characterized in vitro, there is a limited set of data on the role of these populations in atherogenesis in vivo. Recent studies on the origin and the potential role of aortic DCs provide novel insights into the biology of aortic DC subsets and prospective mechanisms of the immune response in atherosclerosis. This review integrates the results of experiments analyzing heterogeneity of DCs and macrophage subsets in healthy and diseased vessels and briefly discusses the known and potential functions of these cells in atherogenesis.

Atherosclerosis: current pathogenesis and therapeutic options

Coronary artery disease (CAD) arising from atherosclerosis is a leading cause of death and morbidity worldwide. The underlying pathogenesis involves an imbalanced lipid metabolism and a maladaptive immune response entailing a chronic inflammation of the arterial wall. The disturbed equilibrium of lipid accumulation, immune responses and their clearance is shaped by leukocyte trafficking and homeostasis governed by chemokines and their receptors. New pro- and anti-inflammatory pathways linking lipid and inflammation biology have been discovered, and genetic profiling studies have unveiled variations involved in human CAD. The growing understanding of the inflammatory processes and mediators has uncovered an intriguing diversity of targetable mechanisms that can be exploited to complement lipid-lowering therapies. Here we aim to systematically survey recently identified molecular mechanisms, translational developments and clinical strategies for targeting lipid-related inflammation in atherosclerosis and CAD.

Giant cell arteritis: immune and vascular aging as disease risk factors

Susceptibility for giant cell arteritis increases with chronological age, in parallel with age-related restructuring of the immune system and age-induced remodeling of the vascular wall. Immunosenescence results in shrinkage of the naïve T-cell pool, contraction of T-cell diversity, and impairment of innate immunity. Aging of immunocompetent cells forces the host to take alternative routes for protective immunity and confers risk for pathogenic immunity that causes chronic inflammatory tissue damage. Dwindling immunocompetence is particularly relevant as the aging host is forced to cope with an ever growing infectious load. Immunosenescence coincides with vascular aging during which the arterial wall undergoes dramatic structural changes and medium and large arteries lose their pliability and elasticity. On the molecular level, elastic fibers deteriorate and matrix proteins accumulate biochemical modifications. Thus, the aging process impacts the two major biologic systems that liaise to promote giant cell arteritis; the immune system and the vessel wall niche.

Transcriptional profiling and network analysis of the murine angiotensin II-induced abdominal aortic aneurysm

We sought to characterize temporal gene expression changes in the murine angiotensin II (ANG II)-ApoE-/- model of abdominal aortic aneurysm (AAA). Aortic ultrasound measurements were obtained over the 28-day time-course. Harvested suprarenal aortic segments were evaluated with whole genome expression profiling at 7, 14, and 28 days using the Agilent Whole Mouse Genome microarray platform and Statistical Analysis of Microarrays at a false discovery rate of <1%. A group of angiotensin-treated mice experienced contained rupture (CR) within 7 days and were analyzed separately. Progressive aortic dilatation occurred throughout the treatment period. However, the numerous early expression differences between ANG II-treated and control were not sustained over time. Ontologic analysis revealed widespread upregulation of inflammatory, immune, and matrix remodeling genes with ANG II treatment, among other pathways such as apoptosis, cell cycling, angiogenesis, and p53 signaling. CR aneurysms displayed significant decreases in TGF-β/BMP-pathway signaling, MAPK signaling, and ErbB signaling genes vs. non-CR/ANG II-treated samples. We also performed literature-based network analysis, extracting numerous highly interconnected genes associated with aneurysm development such as Spp1, Myd88, Adam17 and Lox. 1) ANG II treatment induces extensive early differential expression changes involving abundant signaling pathways in the suprarenal abdominal aorta, particularly wide-ranging increases in inflammatory genes with aneurysm development. 2) These gene expression changes appear to dissipate with time despite continued growth, suggesting that early changes in gene expression influence disease progression in this AAA model, and that the aortic tissue adapts to prolonged ANG II infusion. 3) Network analysis identified nexus genes that may constitute aneurysm biomarkers or therapeutic targets.

IFN-γ and IL-17: the two faces of T-cell pathology in giant cell arteritis

PURPOSE OF REVIEW

Granuloma formation in giant cell arteritis (GCA) emphasizes the role of adaptive immunity and highlights the role of antigen-specific T cells. Recent data demonstrate that at least two separate lineages of CD4 T cells participate in vascular inflammation, providing an important clue that multiple disease instigators may initiate pathogenic immunity.

RECENT FINDING

IFN-γ-producing Th1 cells and IL-17-producing Th17 cells have been implicated in GCA. Patients with biopsy-positive GCA underwent two consecutive temporal artery biopsies, one prior to therapy and one while on corticosteroids. In untreated patients, Th1 and Th17 cells co-existed in the vascular lesions. Following therapy, Th17 cells were essentially lost, whereas Th1 cells persisted almost unaffected. In the peripheral blood of untreated patients Th17 frequencies were increased eight-fold, but normalized with therapy. Blood Th1 cells were doubled in frequency, independent of therapy. Corticosteroids functioned by selectively suppressing IL-1β, IL-6 and IL-23-releasing antigen-presenting cells (APCs), disrupting induction of Th17 cells.

SUMMARY

At least two distinct CD4 T-cell subsets promote vascular inflammation in GCA. In early disease, APCs promote differentiation of Th17 as well as Th1 cells. Chronic disease is characterized by persistent Th1-inducing signals, independent of IL-17-mediated inflammation. More than one disease instigator may trigger APCs to induce multiple T-cell lineages. Cocktails of therapies will be needed for appropriate disease control.

Homozygous mutation in SAMHD1 gene causes cerebral vasculopathy and early onset stroke

We describe an autosomal recessive condition characterized with cerebral vasculopathy and early onset of stroke in 14 individuals in Old Order Amish. The phenotype of the condition was highly heterogeneous, ranging from severe developmental disability to normal schooling. Cerebral vasculopathy was a major hallmark of the condition with a common theme of multifocal stenoses and aneurysms in large arteries, accompanied by chronic ischemic changes, moyamoya morphology, and evidence of prior acute infarction and hemorrhage. Early signs of the disease included mild intrauterine growth restriction, infantile hypotonia, and irritability, followed by failure to thrive and short stature. Acrocyanosis, Raynaud's phenomenon, chilblain lesions, low-pitch hoarse voice, glaucoma, migraine headache, and arthritis were frequently observed. The early onset or recurrence of strokes secondary to cerebral vasculopathy seems to always be associated with poor outcomes. The elevated erythrocyte sedimentation rate (ESR), IgG, neopterin, and TNF-α found in these patients suggested an immune disorder. Through genomewide homozygosity mapping, we localized the disease gene to chromosome (Chr) 20q11.22-q12. Candidate gene sequencing identified a homozygous mutation, c.1411-2A > G, in the SAMHD1 gene, being associated with this condition. The mutation appeared at the splice-acceptor site of intron 12, resulted in the skipping of exon 13, and gave rise to an aberrant protein with in-frame deletion of 31 amino acids. Immunoblotting analysis showed lack of mutant SAMHD1 protein expression in affected cell lines. The function of SAMHD1 remains unclear, but the inflammatory vasculopathies of the brain found in the patients with SAMHD1 mutation indicate its important roles in immunoregulation and cerebral vascular hemeostasis.

Blocking the NOTCH pathway inhibits vascular inflammation in large-vessel vasculitis

BACKGROUND

Giant cell arteritis is a granulomatous vasculitis of the aorta and its branches that causes blindness, stroke, and aortic aneurysm. CD4 T cells are key pathogenic regulators, instructed by vessel wall dendritic cells to differentiate into vasculitic T cells. The unique pathways driving this dendritic cell-T-cell interaction are incompletely understood, but may provide novel therapeutic targets for a disease in which the only established therapy is long-term treatment with high doses of corticosteroids.

METHODS AND RESULTS

Immunohistochemical and gene expression analyses of giant cell arteritis-affected temporal arteries revealed abundant expression of the NOTCH receptor and its ligands, Jagged1 and Delta1. Cleavage of the NOTCH intracellular domain in wall-infiltrating T cells indicated ongoing NOTCH pathway activation in large-vessel vasculitis. NOTCH activation did not occur in small-vessel vasculitis affecting branches of the vasa vasorum tree. We devised 2 strategies to block NOTCH pathway activation: γ-secretase inhibitor treatment, preventing nuclear translocation of the NOTCH intracellular domain, and competing for receptor-ligand interactions through excess soluble ligand, Jagged1-Fc. In a humanized mouse model, NOTCH pathway disruption had strong immunosuppressive effects, inhibiting T-cell activation in the early and established phases of vascular inflammation. NOTCH inhibition was particularly effective in downregulating Th17 responses, but also markedly suppressed Th1 responses.

CONCLUSIONS

Blocking NOTCH signaling depleted T cells from the vascular infiltrates, implicating NOTCH- NOTCH ligand interactions in regulating T-cell retention and survival in vessel wall inflammation. Modulating the NOTCH signaling cascade emerges as a promising new strategy for immunosuppressive therapy of large-vessel vasculitis.

iNOS expression in vascular resident macrophages contributes to circulatory dysfunction of splanchnic vascular smooth muscle contractions in portal hypertensive rats

Portal hypertension, a major complication of cirrhosis, is caused by both increased portal blood flow due to arterial vasodilation and augmented intrahepatic vascular resistance due to sinusoidal constriction. In this study, we examined the possible involvement of resident macrophages in the tone regulation of splanchnic blood vessels using bile duct ligated (BDL) portal hypertensive rats and an in vitro organ culture method. In BDL cirrhosis, the number of ED2-positive resident macrophages increased by two- to fourfold in the vascular walls of the mesenteric artery and extrahepatic portal vein compared with those in sham-operated rats. Many ED1-positive monocytes were also recruited into this area. The expression of inducible nitric oxide (NO) synthase (iNOS) mRNA was increased in the vascular tissues isolated from BDL rats, and accordingly, nitrate/nitrite production was increased. Immunohistochemistry revealed that iNOS was largely expressed in ED1-positive and ED2-positive cells. We further analyzed the effect of iNOS expression on vascular smooth muscle contraction using an in vitro organ culture system. iNOS mRNA expression and nitrate production significantly increased in vascular tissues (without endothelium) incubated with 1 μg/ml lipopolysaccharide (LPS) for 6 h. Immunohistochemistry indicated that iNOS was largely expressed in ED2-positive resident macrophages. α-Adrenergic-stimulated contractility of the mesenteric artery was greatly suppressed by LPS treatment and was restored by N(G)-nitro-L-arginine methyl ester (NO synthase inhibitor); in contrast, portal vein contractility was largely unaffected by LPS. Sodium nitroprusside (NO donor) and 8-bromo-cGMP showed greater contractile inhibition in the mesenteric artery than in the portal vein with decreasing myosin light chain phosphorylation. In the presence of an α-adrenergic agonist, the mesenteric artery cytosolic Ca(2+) level was greatly reduced by sodium nitroprusside; however, the portal vein Ca(2+) level was largely unaffected. These results suggest that the induction of iNOS in monocytes/macrophages contributes to a hypercirculatory state in the cirrhosis model rat in which the imbalance of the responsiveness of visceral vascular walls to NO (mesenteric artery >> portal vein) may account for the increased portal venous flow in portal hypertension.

Histiocytic and Dendritic Cell Neoplasms

This article reviews the features of dendritic cells (DCs) of myeloid-derived, plasmacytoid, and follicle-associated types and tumors of these cells, as well as myeloid sarcoma. The morphologic and immunophenotypic features in this group of neoplasms is featured, including mature neoplasms such as Langerhans cell histiocytosis, its malignant counterpart Langerhans cell sarcoma, and S100-negative histiocytic proliferations. More immature or precursor malignancies in this group include myeloid and monocytic leukemias presenting in extramedullary tissues as well as the newly codified blastic plasmacytoid dendritic cell neoplasm. Although likely not related histogenetically to myeloid-derived DCs, mesenchymal-type lymph node tumors including follicular dendritic cell and fibroblastic reticulum sarcomas are also discussed. All of these neoplasms can exhibit a range of immunophenotypic and morphologic features that underscore the plasticity of the non-neoplastic precursors from which they are derived.

CD4+ T cells sensitized by vascular smooth muscle induce vasculitis, and interferon gamma is critical for the initiation of vascular pathology

Primary vasculitis is the result of idiopathic inflammation in blood vessel walls. T cells are believed to play a critical role, but the nature of the pathological T-cell response remains obscure. In this study, we provide evidence that CD4(+) T lymphocytes, activated in the presence of syngeneic vascular smooth muscle cells, were sufficient to induce vasculitic lesions after adoptive transfer to recipient mice. Additionally, the disease is triggered in the absence of antibodies in experiments in which both the donors of stimulated lymphocytes and the transfer recipients were mice that were deficient in B cells. Tracking and proliferation of the transferred cells and their cytokine profiles were assessed by fluorescence tagging and flow cytometry. Proliferating CD4(+) T cells were evident 3 days after transfer, corresponding to the occurrence of vasculitic lesions in mouse lungs. The transferred T lymphocytes exhibited Th1 and Th17 cytokine profiles and minimal Th2. However, 1 week after vasculitis induction, effector functions could be successfully recalled in Th1 cells, but not in Th17 cells. Additionally, in the absence of constitutive interferon-γ expression, T cells sensitized by vascular smooth muscle cells failed to induce vasculitis. In conclusion, our results show that Th1 cells play a key role in eliciting vasculitis in this murine model and that induction of the disease is possible in the absence of pathogenic antibodies.

Immune responses regulating the response to vascular injury

PURPOSE OF REVIEW

Immune modulation of neointimal formation after vascular injury has been investigated for several decades but the complexities involved continue to obscure a clearer understanding of the process. The rapidly changing field of immunology makes this knowledge imperative.

RECENT FINDINGS

The review discusses immune factors involved in the response to vascular injury. Although innate immune responses play a predominantly detrimental role, the adaptive immune response is more complex. Mechanisms of T-cell activation, recruitment, as well as possible regulation are highlighted.

SUMMARY

Progress in understanding the role of the immune system in the response to arterial injury has been impressive. However, recent findings underscore the need to unravel the intricacies involved such as the kinetics and specific pathways of activation, specificity of immune cell involvement, and identification of targets for therapy. This is relevant in light of the increasing reports of immune factors involved in vascular disease and intervention in the clinical setting.

The detrimental effects of IFN-α on vasculogenesis in lupus are mediated by repression of IL-1 pathways: potential role in atherogenesis and renal vascular rarefaction

Systemic lupus erythematosus (SLE) is characterized by increased vascular risk due to premature atherosclerosis independent of traditional risk factors. We previously proposed that IFN-α plays a crucial role in premature vascular damage in SLE. IFN-α alters the balance between endothelial cell apoptosis and vascular repair mediated by endothelial progenitor cells (EPCs) and myeloid circulating angiogenic cells (CACs). In this study, we demonstrate that IFN-α promotes an antiangiogenic signature in SLE and control EPCs/CACs, characterized by transcriptional repression of IL-1α and β, IL-1R1, and vascular endothelial growth factor A, and upregulation of IL-1R antagonist and the decoy receptor IL-1R2. IL-1β promotes significant improvement in the functional capacity of lupus EPCs/CACs, therefore abrogating the deleterious effects of IFN-α. The beneficial effects from IL-1 are mediated, at least in part, by increases in EPC/CAC proliferation, by decreases in EPC/CAC apoptosis, and by preventing the skewing of CACs toward nonangiogenic pathways. IFN-α induces STAT2 and 6 phosphorylation in EPCs/CACs, and JAK inhibition abrogates the transcriptional antiangiogenic changes induced by IFN-α in these cells. Immunohistochemistry of renal biopsies from patients with lupus nephritis, but not anti-neutrophil cytoplasmic Ab-positive vasculitis, showed this pathway to be operational in vivo, with increased IL-1R antagonist, downregulation of vascular endothelial growth factor A, and glomerular and blood vessel decreased capillary density, compared with controls. Our study introduces a novel putative pathway by which type I IFNs may interfere with vascular repair in SLE through repression of IL-1-dependent pathways. This could promote atherosclerosis and loss of renal function in this disease.

Dendritic cells and their role in atherogenesis

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