Measles virus nucleoprotein induces a regulatory immune response and reduces atherosclerosis in mice

Measles Virus-Induced Host Immunity and Mechanisms of Viral Evasion

The immune system deploys a complex network of cells and signaling pathways to protect host integrity against exogenous threats, including measles virus (MeV). However, throughout its evolutionary path, MeV developed various mechanisms to disrupt and evade immune responses. Despite an available vaccine, MeV remains an important re-emerging pathogen with a continuous increase in prevalence worldwide during the last decade. Considerable knowledge has been accumulated regarding MeV interactions with the innate immune system through two antagonistic aspects: recognition of the virus by cellular sensors and viral ability to inhibit the induction of the interferon cascade. Indeed, while the host could use several innate adaptors to sense MeV infection, the virus is adapted to unsettle defenses by obstructing host cell signaling pathways. Recent works have highlighted a novel aspect of innate immune response directed against MeV unexpectedly involving DNA-related sensing through activation of the cGAS/STING axis, even in the absence of any viral DNA intermediate. In addition, while MeV infection most often causes a mild disease and triggers a lifelong immunity, its tropism for invariant T-cells and memory T and B-cells provokes the elimination of one primary shield and the pre-existing immunity against previously encountered pathogens, known as "immune amnesia".

Regulatory T Cell-Enhancing Therapies to Treat Atherosclerosis

Experimental studies have provided strong evidence that chronic inflammation triggered by the sub-endothelial accumulation of cholesterol-rich lipoproteins in arteries is essential in the initiation and progression of atherosclerosis. Recent clinical trials highlighting the efficacy of anti-inflammatory therapies in coronary patients have confirmed that this is also true in humans Monocytes/macrophages are central cells in the atherosclerotic process, but adaptive immunity, through B and T lymphocytes, as well as dendritic cells, also modulates the progression of the disease. Analysis of the role of different T cell subpopulations in murine models of atherosclerosis identified effector Th1 cells as proatherogenic, whereas regulatory T cells (Tregs) have been shown to protect against atherosclerosis. For these reasons, better understanding of how Tregs influence the atherosclerotic process is believed to provide novel Treg-targeted therapies to combat atherosclerosis. This review article summarizes current knowledge about the role of Tregs in atherosclerosis and discusses ways to enhance their function as novel immunomodulatory therapeutic approaches against cardiovascular disease.

Myeloid-Specific Deletion of Epsins 1 and 2 Reduces Atherosclerosis by Preventing LRP-1 Downregulation

RATIONALE

Atherosclerosis is, in part, caused by immune and inflammatory cell infiltration into the vascular wall, leading to enhanced inflammation and lipid accumulation in the aortic endothelium. Understanding the molecular mechanisms underlying this disease is critical for the development of new therapies. Our recent studies demonstrate that epsins, a family of ubiquitin-binding endocytic adaptors, are critical regulators of atherogenicity. Given the fundamental contribution lesion macrophages make to fuel atherosclerosis, whether and how myeloid-specific epsins promote atherogenesis is an open and significant question.

OBJECTIVE

We will determine the role of myeloid-specific epsins in regulating lesion macrophage function during atherosclerosis.

METHODS AND RESULTS

We engineered myeloid cell-specific epsins double knockout mice (LysM-DKO) on an ApoE^-/- background. On Western diet, these mice exhibited marked decrease in atherosclerotic lesion formation, diminished immune and inflammatory cell content in aortas, and reduced necrotic core content but increased smooth muscle cell content in aortic root sections. Epsins deficiency hindered foam cell formation and suppressed proinflammatory macrophage phenotype but increased efferocytosis and anti-inflammatory macrophage phenotype in primary macrophages. Mechanistically, we show that epsin loss specifically increased total and surface levels of LRP-1 (LDLR [low-density lipoprotein receptor]-related protein 1), an efferocytosis receptor with antiatherosclerotic properties. We further show that epsin and LRP-1 interact via epsin's ubiquitin-interacting motif domain. ox-LDL (oxidized LDL) treatment increased LRP-1 ubiquitination, subsequent binding to epsin, and its internalization from the cell surface, suggesting that epsins promote the ubiquitin-dependent internalization and downregulation of LRP-1. Crossing ApoE^-/-/LysM-DKO mice onto an LRP-1 heterozygous background restored, in part, atherosclerosis, suggesting that epsin-mediated LRP-1 downregulation in macrophages plays a pivotal role in propelling atherogenesis.

CONCLUSIONS

Myeloid epsins promote atherogenesis by facilitating proinflammatory macrophage recruitment and inhibiting efferocytosis in part by downregulating LRP-1, implicating that targeting epsins in macrophages may serve as a novel therapeutic strategy to treat atherosclerosis.

Eating the Dead to Keep Atherosclerosis at Bay

Atherosclerosis is the primary cause of coronary heart disease (CHD), ischemic stroke, and peripheral arterial disease. Despite effective lipid-lowering therapies and prevention programs, atherosclerosis is still the leading cause of mortality in the United States. Moreover, the prevalence of CHD in developing countries worldwide is rapidly increasing at a rate expected to overtake those of cancer and diabetes. Prominent risk factors include the hardening of arteries and high levels of cholesterol, which lead to the initiation and progression of atherosclerosis. However, cell death and efferocytosis are critical components of both atherosclerotic plaque progression and regression, yet, few currently available therapies focus on these processes. Thus, understanding the causes of cell death within the atherosclerotic plaque, the consequences of cell death, and the mechanisms of apoptotic cell clearance may enable the development of new therapies to treat cardiovascular disease. Here, we review how endoplasmic reticulum stress and cholesterol metabolism lead to cell death and inflammation, how dying cells affect plaque progression, and how autophagy and the clearance of dead cells ameliorates the inflammatory environment of the plaque. In addition, we review current research aimed at alleviating these processes and specifically targeting therapeutics to the site of the plaque.

Immune-mediated mechanisms of atherosclerosis and implications for the clinic

INTRODUCTION

A large body of evidence supports the inflammatory hypothesis of atherosclerosis, and both innate and adaptive immune responses play important roles in all disease stages. Areas covered: Here, we review our understanding of the role of the immune response in atherosclerosis, focusing on the pathways currently amenable to therapeutic modulation. We also discuss the advantages or undesirable effects that may be foreseen from targeting the immune response in patients at high cardiovascular risk, suggesting new avenues for research. Expert commentary: There is an extraordinary opportunity to directly test the inflammatory hypothesis of atherosclerosis in the clinic using currently available therapeutics. However, a more balanced interpretation of the experimental and translational data is needed, which may help address and identify in more detail the appropriate settings where an immune pathway can be targeted with minimal risk.

Association of measles and mumps with cardiovascular disease: The Japan Collaborative Cohort (JACC) study

OBJECTIVE

Although it has been suggested that exposure to infections during childhood could decrease risk of atherosclerotic cardiovascular disease (CVD), the evidence is scarce. We investigated the association of measles and mumps with CVD.

METHODS

43,689 men and 60,147 women aged 40-79 years at baseline (1988-1990) completed a lifestyle questionnaire, including their history of measles and mumps, and were followed until 2009. Histories of infections were categorized as having no infection (reference), measles only, mumps only, or both infections. Hazard ratios (HR) for mortality from CVD across histories of infections were calculated.

RESULTS

Men with measles only had multivariable HR (95% confidence interval) of 0.92 (0.85-0.99) for total CVD, those with mumps only had 0.52 (0.28-0.94) for total stroke and 0.21 (0.05-0.86) for hemorrhagic stroke, and those with both infections had 0.80 (0.71-0.90) for total CVD, 0.71 (0.53-0.93) for myocardial infarction, and 0.83 (0.69-0.98) for total stroke. Women with both infections had 0.83 (0.74-0.92) for total CVD and 0.84 (0.71-0.99) for total stroke. We also compared subjects with measles only or mumps only (reference) and those with both infections. Men with both infections had 0.88 (0.78-0.99) for total CVD. Women with both infections had 0.85 (0.76-0.94) for total CVD, 0.79 (0.67-0.93) for total stroke, 0.78 (0.62-0.98) for ischemic stroke and 0.78 (0.62-0.98) for hemorrhagic stroke.

CONCLUSIONS

Measles and mumps, especially in case of both infections, were associated with lower risks of mortality from atherosclerotic CVD.

Anti-inflammatory therapies for atherosclerosis

The view of atherosclerosis as an inflammatory disease has emerged from observations of immune activation and inflammatory signalling in human atherosclerotic lesions, from the definition of inflammatory biomarkers as independent risk factors for cardiovascular events, and from evidence of low-density lipoprotein-induced immune activation. Studies in animal models of hyperlipidaemia have also supported the beneficial effects of countering inflammation to delay atherosclerosis progression. Specific inflammatory pathways with relevance to human diseases have been identified, and inhibitors of these pathways are either already in use for the treatment of other diseases, or are under development and evaluation. These include 'classic' drugs (such as allopurinol, colchicine, and methotrexate), biologic therapies (for example tumour necrosis factor inhibitors and IL-1 neutralization), as well as targeting of lipid mediators (such as phospholipase inhibitors and antileukotrienes) or intracellular pathways (inhibition of NADPH oxidase, p38 mitogen-activated protein kinase, or phosphodiesterase). The evidence supporting the use of anti-inflammatory therapies for atherosclerosis is mainly based on either observational or small interventional studies evaluating surrogate markers of disease activity. Nevertheless, these data are crucial to understand the role of inflammation in atherosclerosis, and to design randomized controlled studies to evaluate the effect of specific anti-inflammatory strategies on cardiovascular outcomes.

Adaptive (T and B cells) immunity and control by dendritic cells in atherosclerosis

Chronic inflammation in response to lipoprotein accumulation in the arterial wall is central in the development of atherosclerosis. Both innate and adaptive immunity are involved in this process. Adaptive immune responses develop against an array of potential antigens presented to effector T lymphocytes by antigen-presenting cells, especially dendritic cells. Functional analysis of the role of different T-cell subsets identified the Th1 responses as proatherogenic, whereas regulatory T-cell responses exert antiatherogenic activities. The effect of Th2 and Th17 responses is still debated. Atherosclerosis is also associated with B-cell activation. Recent evidence established that conventional B-2 cells promote atherosclerosis. In contrast, innate B-1 B cells offer protection through secretion of natural IgM antibodies. This review discusses the recent development in our understanding of the role of T- and B-cell subsets in atherosclerosis and addresses the role of dendritic cell subpopulations in the control of adaptive immunity.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

Accumulation of splice variants and transcripts in response to PI3K inhibition in T cells

Background

Measles virus (MV) causes T cell suppression by interference with phosphatidylinositol-3-kinase (PI3K) activation. We previously found that this interference affected the activity of splice regulatory proteins and a T cell inhibitory protein isoform was produced from an alternatively spliced pre-mRNA.

Hypothesis

Differentially regulated and alternatively splice variant transcripts accumulating in response to PI3K abrogation in T cells potentially encode proteins involved in T cell silencing.

Methods

To test this hypothesis at the cellular level, we performed a Human Exon 1.0 ST Array on RNAs isolated from T cells stimulated only or stimulated after PI3K inhibition. We developed a simple algorithm based on a splicing index to detect genes that undergo alternative splicing (AS) or are differentially regulated (RG) upon T cell suppression.

Results

Applying our algorithm to the data, 9% of the genes were assigned as AS, while only 3% were attributed to RG. Though there are overlaps, AS and RG genes differed with regard to functional regulation, and were found to be enriched in different functional groups. AS genes targeted extracellular matrix (ECM)-receptor interaction and focal adhesion pathways, while RG genes were mainly enriched in cytokine-receptor interaction and Jak-STAT. When combined, AS/RG dependent alterations targeted pathways essential for T cell receptor signaling, cytoskeletal dynamics and cell cycle entry.

Conclusions

PI3K abrogation interferes with key T cell activation processes through both differential expression and alternative splicing, which together actively contribute to T cell suppression.

Regulatory T cells and Atherosclerosis

Atherosclerosis is a chronic autoimmune inflammatory disease. The involvement of both innate and adaptive immune responses in the pathogenesis of the disease has been well recognized. Tregs are an essential part of the immune system and have indispensable functions in maintaining immune system homeostasis, mediating peripheral tolerance, preventing autoimmune diseases, and suppressing inflammatory and proatherogenic immune response. Tregs carry out their immunosuppressive functions via several mechansims. One of the well-documented suppressive mechanisms of Tregs is the secretion of anti-inflammatory cytokines including IL-10, TGF-β, and IL-35. Studies have found that IL-10 and TGF-β have atheroprotective properties. In addition, Tregs can suppress the activity of proatherogenic effector T cells, suggesting an atheroprotective role. In fact, fewer Tregs are found in atherogenic ApoE-/- mice comparing to wild-type mice, suggesting an uncontrolled balance between weakened Tregs and effector T cells in atherogenesis. Some clinical studies of autoimmune diseases also suggest that decreased Tregs numbers are associated with increased disease activity. The importance of Tregs in many autoimmune diseases and experimental atherosclerosis has been established in in vivo and in vitro studies. However, the roles of Tregs in atherosclerosis in the clinical setting remains to be further characterized.

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.

Stroke and the immune system: from pathophysiology to new therapeutic strategies

Stroke is the second most common cause of death worldwide and a major cause of acquired disability in adults. Despite tremendous progress in understanding the pathophysiology of stroke, translation of this knowledge into effective therapies has largely failed, with the exception of thrombolysis, which only benefits a small proportion of patients. Systemic and local immune responses have important roles in causing stroke and are implicated in the primary and secondary progression of ischaemic lesions, as well as in repair, recovery, and overall outcome after a stroke. However, potential therapeutic targets in the immune system and inflammatory responses have not been well characterised. Development of novel and effective therapeutic strategies for stroke will require further investigation of these pathways in terms of their temporal profile (before, during, and after stroke) and risk-to-benefit therapeutic ratio of modulating them.

Adaptive immunity in atherosclerosis: mechanisms and future therapeutic targets

Chronic inflammation drives the development of atherosclerosis, and adaptive immunity is deeply involved in this process. Initial studies attributed a pathogenic role to T cells in atherosclerosis, mainly owing to the proatherogenic role of the T-helper (T(H))-1 cell subset, whereas the influence of T(H)2 and T(H)17 subsets is still debated. Today we know that T regulatory cells play a critical role in the protection against atherosclerotic lesion development and inflammation. In contrast to T cells, B cells were initially considered to be protective in atherosclerosis, assumingly through the production of protective antibodies against oxidized LDL. This concept has now been refined and proatherogenic roles of certain mature B cell subsets have been identified. We review the current knowledge about the role of various lymphocyte subsets in the development and progression of atherosclerosis and highlight future targets for immunomodulatory therapy.

Immunotherapy of viral infections

Among the microorganisms that cause diseases of medical or veterinary importance, the only group that is entirely dependent on the host, and hence not easily amenable to therapy via pharmaceuticals, is the viruses. Since viruses are obligate intracellular pathogens, and therefore depend a great deal on cellular processes, direct therapy of viral infections is difficult. Thus, modifying or targeting nonspecific or specific immune responses is an important aspect of intervention of ongoing viral infections. However, as a result of the unavailability of effective vaccines and the extended duration of manifestation, chronic viral infections are the most suitable for immunotherapies. We present an overview of various immunological strategies that have been applied for treating viral infections after exposure to the infectious agent.

Therapeutic targeting of chemokine interactions in atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the arterial wall that is characterized by a disturbed equilibrium of immune responses and lipid accumulation, leading to the development of plaques. The atherogenic influx of mononuclear cells is orchestrated by chemokines and their receptors. Studies using gene-deficient mice and antagonists based on peptides and small molecules have generated insight into targeting chemokine-receptor axes for treating atherosclerosis, which might complement lipid-lowering strategies and risk factor modulation. Combined inhibition of multiple chemokine axes could interfere with the contributions of chemokines to disease progression at specific cells, stages or sites. In addition, the recently characterized heterophilic interactions of chemokines might present a novel target for the treatment and prevention of inflammatory diseases such as atherosclerosis.

Innate and adaptive immunity in atherosclerosis

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

Cytokine network and T cell immunity in atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the arterial wall where both innate and adaptive immune responses contribute to disease initiation and progression. Recent studies established that subtypes of T cells, regulatory T cells (Tregs), actively involved in the maintenance of immunological tolerance, inhibit the development and progression of atherosclerosis. Here, we review the current knowledge on the Treg response and the major cytokines involved in its modulation in the context of atherosclerosis.

Interplay between virus-specific effector response and Foxp3 regulatory T cells in measles virus immunopathogenesis

Measles is a highly contagious childhood disease associated with an immunological paradox: although a strong virus-specific immune response results in virus clearance and the establishment of a life-long immunity, measles infection is followed by an acute and profound immunosuppression leading to an increased susceptibility to secondary infections and high infant mortality. In certain cases, measles is followed by fatal neurological complications. To elucidate measles immunopathology, we have analyzed the immune response to measles virus in mice transgenic for the measles virus receptor, human CD150. These animals are highly susceptible to intranasal infection with wild-type measles strains. Similarly to what has been observed in children with measles, infection of suckling transgenic mice leads to a robust activation of both T and B lymphocytes, generation of virus-specific cytotoxic T cells and antibody responses. Interestingly, Foxp3(+)CD25(+)CD4(+) regulatory T cells are highly enriched following infection, both in the periphery and in the brain, where the virus intensively replicates. Although specific anti-viral responses develop in spite of increased frequency of regulatory T cells, the capability of T lymphocytes to respond to virus-unrelated antigens was strongly suppressed. Infected adult CD150 transgenic mice crossed in an interferon receptor type I-deficient background develop generalized immunosuppression with an increased frequency of CD4(+)CD25(+)Foxp3(+) T cells and strong reduction of the hypersensitivity response. These results show that measles virus affects regulatory T-cell homeostasis and suggest that an interplay between virus-specific effector responses and regulatory T cells plays an important role in measles immunopathogenesis. A better understanding of the balance between measles-induced effector and regulatory T cells, both in the periphery and in the brain, may be of critical importance in the design of novel approaches for the prevention and treatment of measles pathology.

The role of adaptive T cell immunity in atherosclerosis

There is now solid evidence that T cell adaptive immunity is involved in atherogenesis. While initial studies have focused on the pathogenic arm of the immune response, more recent work clearly suggests an important role for several subsets of regulatory T cells in the protection against lesion development. Here, we review the current knowledge on the role of both pathogenic and regulatory adaptive T cell immunity in atherosclerosis, generated mainly from the study of mouse models of the disease.

Regulatory T-cell immunity and its relevance to atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the arterial wall where both innate and adaptive immune responses contribute to disease initiation and progression. Recent studies from several groups suggest that subtypes of T cells, called regulatory T cells, previously shown to maintain immunological tolerance, inhibit the development and progression of atherosclerosis. Here, we review the current knowledge on the regulatory T-cell response and the major cytokines involved in its modulation in the context of atherosclerosis.