The macrophage scavenger receptor type A directs modified proteins to antigen presentation

MK2206 attenuates atherosclerosis by inhibiting lipid accumulation, cell migration, proliferation, and inflammation

Cardiovascular disease is a common comorbidity in patients with cancer, and the main leading cause of noncancer-related deaths in cancer survivors. Considering that current antitumor drugs usually induce cardiovascular injury, the quest for developing new antitumor drugs, especially those with cardiovascular protection, is crucial for improving cancer prognosis. MK2206 is a phase II clinical anticancer drug and the role of this drug in cardiovascular disease is still unclear. Here, we revealed that MK2206 significantly reduced vascular inflammation, atherosclerotic lesions, and inhibited proliferation of vascular smooth muscle cell in ApoE^-/- mice in vivo. We demonstrated that MK2206 reduced lipid accumulation by promoting cholesterol efflux but did not affect lipid uptake and decreased inflammatory response by modulating inflammation-related mRNA stability in macrophages. In addition, we revealed that MK2206 suppressed migration, proliferation, and inflammation in vascular smooth muscle cells. Moreover, MK2206 inhibited proliferation and inflammation of endothelial cells. The present results suggest that MK2206, as a promising drug in clinical antitumor therapy, exhibits anti-inflammatory and antiatherosclerotic potential. This report provides a novel strategy for the prevention of cardiovascular comorbidities in cancer survivors.

Modulating Repolarization of Tumor-Associated Macrophages with Targeted Therapeutic Nanoparticles as a Potential Strategy for Cancer Therapy

There are always some components in the tumor microenvironment (TME), such as tumor-associated macrophages (TAMs), that help tumor cells escape the body's immune surveillance. Therefore, this situation can lead to tumor growth, progression, and metastasis, resulting in low response rates for cancer therapy. Macrophages play an important role with strong plasticity and functional diversity. Facing different microenvironmental stimulations, macrophages undergo a dynamic change in phenotype and function into two major macrophage subpopulations, namely classical activation/inflammation (M1) and alternative activation/regeneration (M2) type. Through various signaling pathways, macrophages polarize into complex groups, which can perform different immune functions. In this review, we emphasize the use of nanopreparations for macrophage related immunotherapy based on the pathological knowledge of TAMs phenotype. These macrophages targeted nanoparticles re-edit and re-educate macrophages by attenuating M2 macrophages and reducing aggregation to the TME, thereby relieving or alleviating immunosuppression. Among them, we describe in detail the cellular mechanisms and regulators of several major signaling pathways involved in the plasticity and polarization functions of macrophages. The advantages and challenges of those nanotherapeutics for these pathways have been elucidated, providing the basis and insights for the diagnosis and treatment strategies of various diseases centered on macrophages.

Surface chemistry-mediated modulation of adsorbed albumin folding state specifies nanocarrier clearance by distinct macrophage subsets

Controlling nanocarrier interactions with the immune system requires a thorough understanding of the surface properties that modulate protein adsorption in biological fluids, since the resulting protein corona redefines cellular interactions with nanocarrier surfaces. Albumin is initially one of the dominant proteins to adsorb to nanocarrier surfaces, a process that is considered benign or beneficial by minimizing opsonization or inflammation. Here, we demonstrate the surface chemistry of a model nanocarrier can be engineered to stabilize or denature the three-dimensional conformation of adsorbed albumin, which respectively promotes evasion or non-specific clearance in vivo. Interestingly, certain common chemistries that have long been considered to convey stealth properties denature albumin to promote nanocarrier recognition by macrophage class A1 scavenger receptors, providing a means for their eventual removal from systemic circulation. We establish that the surface chemistry of nanocarriers can be specified to modulate adsorbed albumin structure and thereby tune clearance by macrophage scavenger receptors.

Scavenger Receptor A Mediates the Clearance and Immunological Screening of MDA-Modified Antigen by M2-Type Macrophages

In this study, we investigated the uptake of malondialdehyde (MDA)-modified myelin oligodendrocyte glycoprotein (MOG) in the context of lipid peroxidation and its implications in CNS autoimmunity. The use of custom-produced fluorescently labeled versions of MOG or MDA-modified MOG enabled us to study and quantify the uptake by different macrophage populations and to identify the responsible receptor, namely SRA. The SRA-mediated uptake of MDA-modified MOG is roughly tenfold more efficient compared to that of the native form. Notably, this uptake is most strongly associated with anti-inflammatory M2-type macrophages. MDA-modified MOG was demonstrated to be resistant to degradation by lysine-dependent proteases in vitro, but the overall digestion fragments appeared to be similar in cell lysates, although their relative abundance appeared to be altered as a result of faster uptake. Accordingly, MDA-modified MOG is processed for presentation by APCs, allowing maximized recall proliferation of MOG_35-55-specific 2D2 T cells in vitro due to higher uptake. However, MDA modification of MOG did not enhance immune priming or disease course in the in vivo MOG-EAE model, but did induce antibody responses to both MOG and MDA adducts. Taken together our results indicate that MDA adducts primarily constitute clearance signals for phagocytes and promote rapid removal of antigen, which is subjected to immunological screening by previously licensed T cells.

Maillard reaction in food allergy: Pros and cons

Food allergens have a notable potential to induce various health concerns in susceptible individuals. The majority of allergenic foods are usually subjected to thermal processing prior to their consumption. However, during thermal processing and long storage of foods, Maillard reaction (MR) often takes place. The MR is a non-enzymatic glycation reaction between the carbonyl group of reducing sugars and compounds having free amino groups. MR may sometimes be beneficial by damaging epitope of allergens and reducing allergenic potential, while exacerbation in allergic reactions may also occur due to changes in the motifs of epitopes or neoallergen generation. Apart from these modulations, non-enzymatic glycation can also modify the food protein(s) with various type of advance glycation end products (AGEs) such as Nϵ-(carboxymethyl-)lysine (CML), pentosidine, pyrraline, and methylglyoxal-H1 derived from MR. These Maillard products may act as immunogen by inducing the activation and proliferation of various immune cells. Literature is available to understand pathogenesis of glycation in the context of various diseases but there is hardly any review that can provide a thorough insight on the impact of glycation in food allergy. Therefore, present review explores the pathogenesis with special reference to food allergy caused by non-enzymatic glycation as well as AGEs.

Inflammation in coronary artery disease

Coronary artery disease (CAD) is the leading cause of death in the United States. Although CAD was formerly considered a lipid accumulation-mediated disease, it has now been clearly shown to involve an ongoing inflammatory response. Advances in basic science research have established the crucial role of inflammation in mediating all stages of CAD. Today, there is convincing evidence that multiple interrelated immune mechanisms interact with metabolic risk factors to initiate, promote, and ultimately activate lesions in the coronary arteries. This review aims to provide current evidence pertaining to the role of inflammation in the pathogenesis of CAD and discusses the impact of inflammatory markers and their modification on clinical outcomes.

Identification of SCARA3, SCARA5 and MARCO of class A scavenger receptor-like family in Pseudosciaena crocea

The class A scavenger receptors are important pattern recognition receptors of the innate immune system in living organisms. According to the whole-genome data of large yellow croaker (Pseudosciaena crocea), three kinds of scavenger receptors, SCARA3, SCARA5 and MARCO were cloned from the spleen, designated severally as TycSA3, TycSA5 and TycMAC. The complete cDNAs open reading frames (ORF) of TycSA3, TycSA5 and TycMAC were 1938 bp, 1677 bp and 1218 bp (GenBank accession no. KJ467772, KJ467773 and KJ467771), encoding 645, 558 and 405 amino acid (aa) residues respectively. The BLASTp analysis strongly suggested that the sequences shared high similarity with known SCARA3, SCARA5 and MARCO. The phylogenetic relationship analysis illustrated that different subtype of SRs formed their own separate branches, TycSA3 and TycSA5 were placed in SCARA3 and SCARA5 branch of Osteichthyes fish respectively with strong bootstrap support. Curiously, the TycMAC was clustered with Alligator sinensis. ClustalW analysis with amino acid sequences revealed that the proportion of identity with other species was 59-71% for TycSA3 and 55-72% for TycSA5, but the scale of TycMAC was considerable lower than those of other two genes (only approximately 38%). The SR family motifs, such as transmembrane helix region, colied coli region and collagens region in the TycSA3, TycSA5 and TycMAC were conserved. There was an optional cysteine-rich (SRCR) domain (from 457 to 557 residues) containing 6 conserved cysteines (C-482, C-495, C-526, C-536, C-546 and C-556) in TycSA5. Likewise, the SRCR domains of TycMAC (from 310 to 405 residues) also contained C-333, C-346, C-374, C-384, C-394 and C-404 cysteines residues. Particularly, there were the major TRAF2-binding consensus motif and two main motifs on internalization of receptor in TycSA3 and TycSA5. The gene structures of different species were analyzed with GeneMaper v2.5, and the number of introns and exons of TycSA3, TycSA5 and TycMAC in DNA sequences were different, for example some corresponding exon regions were divided into several smaller exon portions. Furthermore, quantitative real-time PCR (qRT-PCR) analysis indicated the highest mRNA expression of TycSA3, TycSA5 and TycMAC all appeared in spleen among eight detected tissues, and the expression of them were up-regulated in spleen after Vibrio alginolyticus injection. All these results demonstrated that class A SRs played a significant role in the defense against pathogenic bacteria infection in innate immune of sciaenidae fish.

Malondialdehyde-acetaldehyde (MAA) adducted proteins bind to scavenger receptor A in airway epithelial cells

Co-exposure to cigarette smoke and ethanol generates malondialdehyde and acetaldehyde, which can subsequently lead to the formation of aldehyde-adducted proteins. We have previously shown that exposure of bronchial epithelial cells to malondialdehyde-acetaldehyde (MAA) adducted protein increases protein kinase C (PKC) activity and proinflammatory cytokine release. A specific ligand to scavenger receptor A (SRA), fucoidan, blocks this effect. We hypothesized that MAA-adducted protein binds to bronchial epithelial cells via SRA. Human bronchial epithelial cells (BEAS-2B) were exposed to MAA-adducted protein (either bovine serum albumin [BSA-MAA] or surfactant protein D [SPD-MAA]) and SRA examined using confocal microscopy, fluorescent activated cell sorting (FACS), and immunoprecipitation. Differentiated mouse tracheal epithelial cells (MTEC) cultured by air-liquid interface were assayed for MAA-stimulated PKC activity and keratinocyte-derived chemokine (KC) release. Specific cell surface membrane dye co-localized with upregulated SRA after exposure to MAA for 3-7 min and subsided by 20 min. Likewise, MAA-adducted protein co-localized to SRA from 3 to 7 min with a subsequent internalization of MAA by 10 min. These results were confirmed using FACS analysis and revealed a reduced mean fluorescence of SRA after 3 min. Furthermore, increased amounts of MAA-adducted protein could be detected by Western blot in immunoprecipitated SRA samples after 3 min treatment with MAA. MAA stimulated PKCε-mediated KC release in wild type, but not SRA knockout mice. These data demonstrate that aldehyde-adducted proteins in the lungs rapidly bind to SRA and internalize this receptor prior to the MAA-adducted protein stimulation of PKC-dependent inflammatory cytokine release in airway epithelium.

Ovalbumin modified with pyrraline, a Maillard reaction product, shows enhanced T-cell immunogenicity

The Maillard reaction (also referred to as "glycation") takes place between reducing sugars and compounds with free amino groups during thermal processing of foods. In the final stage of the complex reaction cascade, the so-called advanced glycation end products (AGEs) are formed, including proteins with various glycation structures. It has been suggested that some AGEs could have immunostimulatory effects. Here, we aimed to identify specific glycation structure(s) that could influence the T-cell immunogenicity and potential allergenicity of food allergens, using ovalbumin (OVA, an egg white allergen) as a model allergen. OVA was specifically modified with representative glycation structures: N(ε)-carboxymethyl lysine (CM-OVA), N(ε)-carboxyethyl lysine (CE-OVA), pyrraline (Pyr-OVA), or methylglyoxal-derived arginine derivatives (MGO-OVA). As well as AGE-OVA, a crude glycation product in thermal incubation of OVA with glucose, only Pyr-OVA, and not other modified OVAs, was efficiently taken up by bone marrow-derived murine dendritic cells (BMDCs). The uptake of Pyr-OVA was reduced in scavenger receptor class A (SR-A)-deficient BMDCs, but not in cells treated with inhibitors of scavenger receptor class B, galectin-3, or blocking antibodies against CD36, suggesting that pyrraline binds to SR-A. Compared with other modified OVAs, Pyr-OVA induced higher activation of OVA-specific CD4(+) T-cells in co-culture with BMDCs. Furthermore, compared with native OVA, AGE-OVA and Pyr-OVA induced higher IgE production in mice. Pyrraline could induce better allergen uptake by DCs via association with SR-A and subsequently enhance CD4(+) T-cell activation and IgE production. Our findings help us to understand how Maillard reaction enhances the potential allergenicity of food allergens.

The class A scavenger receptor SR-A/CD204 and the class B scavenger receptor CD36 regulate immune functions of macrophages differently

SR-A/CD204 and CD36 are major receptors responsible for oxidized lipoproteins uptake by macrophages in atherosclerotic plaques. Both receptors also share the role as receptors for different pathogens, but studies on their signaling have been hampered by the lack of selective ligands. We report that, upon specific ligation by Ab, SR-A does not induce cytokine production, but mediates inhibition of LPS-stimulated production of IL-6 and IL-12/23p40, enhancement of IL-10 release, and has no effect on TNF-α and RANTES production in murine macrophages. In contrast, anti-CD36 Ab alone stimulated production of all these cytokines, with IL-10 production being exceptionally high. Effects of anti-CD36 Ab, except of IL-10 production, were mediated by CD14 and TLR2, whereas those of SR-A ligation by heterotrimeric Gi/o proteins and by phosphatidylinositol 3-kinases. Surprisingly, we found that LPS uptake by macrophages was mediated in part by CD36 cooperating with CD14, whereas SR-A was not involved in this process. Finely, during in vitro Ag presentation to naïve CD4(+) lymphocytes, pre-incubation of macrophages with anti-CD36 Ab enhanced IFN-γ production in the co-culture, but exerted the opposite effect under conditions enabling IL-10 accumulation. In contrast, anti-SR-A Ab was ineffective alone, but reversed the Th1-polarizing effect of LPS.

Expression of scavenger receptor A on antigen presenting cells is important for CD4+ T-cells proliferation in EAE mouse model

BACKGROUND

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS) characterized by damage to the neuronal myelin sheath. One of the key effectors for inflammatory injury is the antigen-presenting cell (APC). The class A scavenger receptor (SRA), constitutively expressed by APCs, such as macrophages and dendritic cells in peripheral tissues and the CNS, was shown to play a role in the phagocytosis of myelin; however, the role of SRA in the development of experimental autoimmune encephalomyelitis (EAE) and autoimmune reaction in the periphery has not yet been studied.

METHODS

We investigated EAE progression in wild-type (WT) vs. SRA-/- mice using clinical score measurements and characterized CNS pathology using staining. Furthermore, we assessed SRA role in mediating anti myelin pro-inflammatory response in cell cultures.

RESULTS

We discovered that EAE progression and CNS demyelination were significantly reduced in SRA-/- mice compared to WT mice. In addition, there was a reduction of infiltrating peripheral immune cells, such as T cells and macrophages, in the CNS lesion of SRA-/- mice, which was associated with reduced astrogliosis. Immunological assessment showed that SRA deficiency resulted in significant reduction of pro-inflammatory cytokines that play a major role in EAE progression, such as IL-2, IFN-gamma, IL-17 and IL-6. Furthermore, we discovered that SRA-/- APCs showed impairments in activation and in their ability to induce pro-inflammatory CD4+ T cell proliferation.

CONCLUSION

Expression of SRA on APCs is important for CD4+ T-cells proliferation in EAE mouse model. Further studies of SRA-mediated cellular pathways in APCs may offer useful insights into the development of MS and other autoimmune diseases, providing future avenues for therapeutic intervention.

The conserved scavenger receptor cysteine-rich superfamily in therapy and diagnosis

The scavenger receptor cysteine-rich (SRCR) superfamily of soluble or membrane-bound protein receptors is characterized by the presence of one or several repeats of an ancient and highly conserved protein module, the SRCR domain. This superfamily (SRCR-SF) has been in constant and progressive expansion, now up to more than 30 members. The study of these members is attracting growing interest, which parallels that in innate immunity. No unifying function has been described to date for the SRCR domains, this being the result of the limited knowledge still available on the physiology of most members of the SRCR-SF, but also of the sequence versatility of the SRCR domains. Indeed, involvement of SRCR-SF members in quite different functions, such as pathogen recognition, modulation of the immune response, epithelial homeostasis, stem cell biology, and tumor development, have all been described. This has brought to us new information, unveiling the possibility that targeting or supplementing SRCR-SF proteins could result in diagnostic and/or therapeutic benefit for a number of physiologic and pathologic states. Recent research has provided structural and functional insight into these proteins, facilitating the development of means to modulate the activity of SRCR-SF members. Indeed, some of these approaches are already in use, paving the way for a more comprehensive use of SRCR-SF members in the clinic. The present review will illustrate some available evidence on the potential of well known and new members of the SRCR-SF in this regard.

The immune system in atherosclerosis

Cardiovascular disease, a leading cause of mortality worldwide, is caused mainly by atherosclerosis, a chronic inflammatory disease of blood vessels. Lesions of atherosclerosis contain macrophages, T cells and other cells of the immune response, together with cholesterol that infiltrates from the blood. Targeted deletion of genes encoding costimulatory factors and proinflammatory cytokines results in less disease in mouse models, whereas interference with regulatory immunity accelerates it. Innate as well as adaptive immune responses have been identified in atherosclerosis, with components of cholesterol-carrying low-density lipoprotein triggering inflammation, T cell activation and antibody production during the course of disease. Studies are now under way to develop new therapies based on these concepts of the involvement of the immune system in atherosclerosis.

Immunotherapy with tolerogenic apolipoprotein B-100-loaded dendritic cells attenuates atherosclerosis in hypercholesterolemic mice

BACKGROUND

Atherosclerosis is a chronic inflammatory disease characterized by a massive intimal accumulation of low-density lipoprotein that triggers chronic vascular inflammation with an autoimmune response to low-density lipoprotein components.

METHODS AND RESULTS

To dampen the inflammatory component of atherosclerosis, we injected hypercholesterolemic huB100(tg) × Ldlr(-/-) mice (mice transgenic for human apolipoprotein B100 [ApoB100] and deficient for the low-density lipoprotein receptor) intravenously with dendritic cells (DCs) that had been pulsed with the low-density lipoprotein protein ApoB100 in combination with the immunosuppressive cytokine interleukin-10. DCs treated with ApoB100 and interleukin-10 reduced proliferation of effector T cells, inhibited production of interferon-γ, and increased de novo generation of regulatory T cells in vitro. Spleen cells from mice treated with DCs plus ApoB100 plus interleukin-10 showed diminished proliferative responses to ApoB100 and significantly dampened T-helper 1 and 2 immunity to ApoB100. Spleen CD4(+) T cells from these mice suppressed activation of ApoB100-reactive T cells in a manner characteristic of regulatory T cells, and mRNA analysis of lymphoid organs showed induction of transcripts characteristic of these cells. Treatment of huB100(tg) × Ldlr(-/-) mice with ApoB100-pulsed tolerogenic DCs led to a significant (70%) reduction of atherosclerotic lesions in the aorta, with decreased CD4(+) T-cell infiltration and signs of reduced systemic inflammation.

CONCLUSIONS

Tolerogenic DCs pulsed with ApoB100 reduced the autoimmune response against low-density lipoprotein and may represent a novel possibility for treatment or prevention of atherosclerosis.

SR-A/MARCO–mediated ligand delivery enhances intracellular TLR and NLR function, but ligand scavenging from cell surface limits TLR4 response to pathogens

Phagocytic and pathogen sensing receptors are responsible for particle uptake and inflammation. It is unclear how these receptors' systems influence each other's function to shape an innate response. The class-A scavenger receptors SR-A (scavenger receptor A) and MARCO (macrophage receptor with collagenous structure) are 2 well-characterized phagocytic receptors that are unable to initiate inflammatory responses by themselves, yet are implicated in the pathogenesis of various inflammatory disorders. However, the mechanism for such an apparent discrepancy is still unclear. We utilized SR-A−/−, MARCO−/−, and SR-A−/−-MARCO−/− mice, along with microbe-derived, environmental, and synthetic polyanions to assess the inflammatory responses following combinatorial ligation of SR-A/MARCO and selected Toll-like receptors (TLRs) and nucleotide-binding oligomerization domain (NOD)–like receptors (NLRs) by their shared ligands. In addition to ligating SR-A and MARCO, these agonists also selectively activated the cell-surface sensor TLR4, endosomal TLR3, and the cytosolic NOD2 and NALP3 (NACHT domain–, leucine-rich repeat–, and pyrin domain–containing protein 3). We show that, following recognition of common ligands, SR-A and MARCO attenuate TLR4-mediated responses while enhancing responses by the intracellular TLR3, NOD2, and NALP3. We conclude that SR-A/MARCO-mediated rapid ligand internalization prevented sensing by surface TLRs while increasing ligand availability in intracellular compartments, thus allowing sensing and robust responses by intracellular sensors.

Scavenger receptors and their potential as therapeutic targets in the treatment of cardiovascular disease

Scavenger receptors act as membrane-bound and soluble proteins that bind to macromolecular complexes and pathogens. This diverse supergroup of proteins mediates binding to modified lipoprotein particles which regulate the initiation and progression of atherosclerotic plaques. In vascular tissues, scavenger receptors are implicated in regulating intracellular signaling, lipid accumulation, foam cell development, and cellular apoptosis or necrosis linked to the pathophysiology of atherosclerosis. One approach is using gene therapy to modulate scavenger receptor function in atherosclerosis. Ectopic expression of membrane-bound scavenger receptors using viral vectors can modify lipid profiles and reduce the incidence of atherosclerosis. Alternatively, expression of soluble scavenger receptors can also block plaque initiation and progression. Inhibition of scavenger receptor expression using a combined gene therapy and RNA interference strategy also holds promise for long-term therapy. Here we review our current understanding of the gene delivery by viral vectors to cells and tissues in gene therapy strategies and its application to the modulation of scavenger receptor function in atherosclerosis.

Inhibition of T cell response to native low-density lipoprotein reduces atherosclerosis

Immune responses to oxidized low-density lipoprotein (oxLDL) are proposed to be important in atherosclerosis. To identify the mechanisms of recognition that govern T cell responses to LDL particles, we generated T cell hybridomas from human ApoB100 transgenic (huB100(tg)) mice that were immunized with human oxLDL. Surprisingly, none of the hybridomas responded to oxidized LDL, only to native LDL and the purified LDL apolipoprotein ApoB100. However, sera from immunized mice contained IgG antibodies to oxLDL, suggesting that T cell responses to native ApoB100 help B cells making antibodies to oxLDL. ApoB100 responding CD4(+) T cell hybridomas were MHC class II-restricted and expressed a single T cell receptor (TCR) variable (V) beta chain, TRBV31, with different Valpha chains. Immunization of huB100(tg)xLdlr(-/-) mice with a TRBV31-derived peptide induced anti-TRBV31 antibodies that blocked T cell recognition of ApoB100. This treatment significantly reduced atherosclerosis by 65%, with a concomitant reduction of macrophage infiltration and MHC class II expression in lesions. In conclusion, CD4(+) T cells recognize epitopes on native ApoB100 protein, this response is associated with a limited set of clonotypic TCRs, and blocking TCR-dependent antigen recognition by these T cells protects against atherosclerosis.

Inflammatory and autoimmune reactions in atherosclerosis and vaccine design informatics

Atherosclerosis is the leading pathological contributor to cardiovascular morbidity and mortality worldwide. As its complex pathogenesis has been gradually unwoven, the regime of treatments and therapies has increased with still much ground to cover. Active research in the past decade has attempted to develop antiatherosclerosis vaccines with some positive results. Nevertheless, it remains to develop a vaccine against atherosclerosis with high affinity, specificity, efficiency, and minimal undesirable pathology. In this review, we explore vaccine development against atherosclerosis by interpolating a number of novel findings in the fields of vascular biology, immunology, and bioinformatics. With recent technological breakthroughs, vaccine development affords precision in specifying the nature of the desired immune response—useful when addressing a disease as complex as atherosclerosis with a manifold of inflammatory and autoimmune components. Moreover, our exploration of available bioinformatic tools for epitope-based vaccine design provides a method to avoid expenditure of excess time or resources.

An accessory to the 'Trinity': SR-As are essential pathogen sensors of extracellular dsRNA, mediating entry and leading to subsequent type I IFN responses

Extracellular RNA is becoming increasingly recognized as a signaling molecule. Virally derived double stranded (ds)RNA released into the extracellular space during virus induced cell lysis acts as a powerful inducer of classical type I interferon (IFN) responses; however, the receptor that mediates this response has not been identified. Class A scavenger receptors (SR-As) are likely candidates due to their cell surface expression and ability to bind nucleic acids. In this study, we investigated a possible role for SR-As in mediating type I IFN responses induced by extracellular dsRNA in fibroblasts, a predominant producer of IFNbeta. Fibroblasts were found to express functional SR-As, even SR-A species thought to be macrophage specific. SR-A specific competitive ligands significantly blocked extracellular dsRNA binding, entry and subsequent interferon stimulated gene (ISG) induction. Candidate SR-As were systematically investigated using RNAi and the most dramatic inhibition in responses was observed when all candidate SR-As were knocked down in unison. Partial inhibition of dsRNA induced antiviral responses was observed in vivo in SR-AI/II(-/-) mice compared with WT controls. The role of SR-As in mediating extracellular dsRNA entry and subsequent induced antiviral responses was observed in both murine and human fibroblasts. SR-As appear to function as 'carriers', facilitating dsRNA entry and delivery to the established dsRNA sensing receptors, specifically TLR3, RIGI and MDA-5. Identifying SR-As as gatekeepers of the cell, mediating innate antiviral responses, represents a novel function for this receptor family and provides insight into how cells recognize danger signals associated with lytic virus infections. Furthermore, the implications of a cell surface receptor capable of recognizing extracellular RNA may exceed beyond viral immunity to mediating other important innate immune functions.

Oxidative risk for atherothrombotic cardiovascular disease

In the vasculature, reactive oxidant species, including reactive oxygen, nitrogen, or halogenating species, and thiyl, tyrosyl, or protein radicals may oxidatively modify lipids and proteins with deleterious consequences for vascular function. These biologically active free radical and nonradical species may be produced by increased activation of oxidant-generating sources and/or decreased cellular antioxidant capacity. Once formed, these species may engage in reactions to yield more potent oxidants that promote transition of the homeostatic vascular phenotype to a pathobiological state that is permissive for atherothrombogenesis. This dysfunctional vasculature is characterized by lipid peroxidation and aberrant lipid deposition, inflammation, immune cell activation, platelet activation, thrombus formation, and disturbed hemodynamic flow. Each of these pathobiological states is associated with an increase in the vascular burden of free radical species-derived oxidation products and, thereby, implicates increased oxidant stress in the pathogenesis of atherothrombotic vascular disease.

Glycation of a food allergen by the Maillard reaction enhances its T-cell immunogenicity: role of macrophage scavenger receptor class A type I and II

BACKGROUND

The Maillard reaction occurs between reducing sugars and proteins during thermal processing of foods. It produces chemically glycated proteins termed advanced glycation end products (AGEs). The glycation structures of AGEs are suggested to function as pathogenesis-related immune epitopes in food allergy.

OBJECTIVE

This study aimed at defining the T-cell immunogenicity of food AGEs by using ovalbumin (OVA) as a model allergen.

METHODS

AGE-OVA was prepared by means of thermal processing of OVA in the presence of glucose. Activation of OVA-specific CD4(+) T cells by AGE-OVA was evaluated in cocultures with bone marrow-derived murine myeloid dendritic cells (mDCs) as antigen-presenting cells. The uptake mechanisms of mDCs for AGE-OVA were investigated by using inhibitors of putative cell-surface receptors for AGEs, as well as mDCs deficient for these receptors.

RESULTS

Compared with the controls (native OVA and OVA thermally processed without glucose), AGE-OVA enhanced the activation of OVA-specific CD4(+) T cells on coculture with mDCs, indicating that the glycation of OVA enhanced the T-cell immunogenicity of the allergen. The mDC uptake of AGE-OVA was significantly higher than that of the controls. We identified scavenger receptor class A type I and II (SR-AI/II) as a mediator of the AGE-OVA uptake, whereas the receptor for AGEs and galectin-3 were not responsible. Importantly, the activation of OVA-specific CD4(+) T cells by AGE-OVA was attenuated on coculture with SR-AI/II-deficient mDCs.

CONCLUSION

SR-AI/II targets AGE-OVA to the MHC class II loading pathway in mDCs, leading to an enhanced CD4(+) T-cell activation. The Maillard reaction might thus play an important role in the T-cell immunogenicity of food allergens.

Interferon gamma: a master regulator of atherosclerosis

Atherosclerosis is a chronic inflammatory disease that is characterized by the development of fibrotic plaques in the arterial wall. The disease exhibits a complex aetiology and its progression is influenced by a number of environmental and genetic risk factors. The cytokine interferon-gamma (IFN-gamma), a key regulator of immune function, is highly expressed in atherosclerotic lesions and has emerged as a significant factor in atherogenesis. Evidence from both mouse models of atherosclerosis and in vitro cell culture has suggested that the role of IFN-gamma is complex since both pro- and anti-atherogenic actions have been affiliated to it. This review will focus on evaluating the contribution of IFN-gamma to atherosclerosis and, in particular, how it regulates immune responses to the disease.

Macrophage scavenger receptors and host-derived ligands

The scavenger receptors are a large family of molecules that are structurally diverse and have been implicated in a range of functions. They are expressed by myeloid cells, selected endothelial cells and some epithelial cells and recognise many different ligands, including microbial pathogens as well as endogenous and modified host-derived molecules. This review will focus on the eight classes of scavenger receptors (class A-H) in terms of their structure, expression and recognition of host-derived ligands. Scavenger receptors have been implicated in a range of physiological and pathological processes, such as atherosclerosis and Alzheimer's disease, and function in adhesion and tissue maintenance. More recently, some of the scavenger receptors have been shown to mediate binding and endocytosis of chaperone proteins, such as the heat shock proteins, thereby playing an important role in antigen cross-presentation.

CX3CR1 deficiency impairs dendritic cell accumulation in arterial intima and reduces atherosclerotic burden

OBJECTIVE

Dendritic cells (DCs) have recently been found in atherosclerosis-predisposed regions of arteries and have been proposed to be causal in atherosclerosis. The chemokine receptor CX3CR1 is associated with arterial injury and atherosclerosis. We sought to determine whether a link exists between arterial DC accumulation, CX3CR1, and atherosclerosis.

METHODS AND RESULTS

Mouse aortas were isolated and subjected to en face immunofluorescence analysis. We found that DCs were located predominantly in the intimal regions of arterial branch points and curvatures. Consistent with the increased accumulation of intimal DCs in aged and ApoE-/- aortas compared with young WT aortas (P=0.004 and 0.05, respectively), the incidence of atherosclerosis was 88.9% for aged WT and 100% for ApoE-/- mice compared with 0% for young WT mice. CX3CR1 was expressed on intimal DCs and DC numbers were decreased in CX3CR1-deficient aortas of young, aged, and ApoE-/- mice (P=0.0008, 0.013, and 0.0099). The reduced DC accumulation in CX3CR1-deficiency was also correlated with decreased atherosclerosis in these animals.

CONCLUSIONS

The accumulation of intimal DC increases in aged and ApoE-/- aortas and correlates with the generation of atherosclerosis. CX3CR1-deficiency impairs the accumulation of DC in the aortic wall and markedly reduces the atherosclerotic burden.

Individual variation of scavenger receptor expression in human macrophages with oxidized low-density lipoprotein is associated with a differential inflammatory response

Atherosclerosis is an inflammatory disease in which oxidized low-density lipoprotein (oxLDL) plays important roles. Scavenger receptors (SR) CD36, SR-A, and LOX-1 uptake over 90% of the oxLDL leading to foam cell formation and secretion of inflammatory cytokines. To investigate whether the interindividual differences in macrophage SR gene expression could determine the inflammatory variability in response to oxLDL, we quantified the gene and protein expression of SR and inflammatory molecules from macrophages isolated from 18 volunteer subjects and incubated with oxLDL for 1, 3, 6, and 18 h. The individual gene expression profile of the studied SR at 1 h of incubation was highly variable, showing a wide fold-change range: CD36: -3.57-4.22, SR-A: -5.0-4.43, and LOX-1: -1.56-75.32. We identified subjects as high and low responders depending on whether their SR gene expression was above or below the median, showing a different inflammation response pattern. CD36 and LOX-1 gene expression correlated positively with IL-1beta; SR-A correlated negatively with IL-8 and positively with PPARgamma and NF-kappaBIotaA. These results were confirmed in the same subjects 3 mo after the first sampling. Furthermore, a negative correlation existed between CD36 and SR-A at protein level after 18 h of oxLDL incubation (R = -0.926, p = 0.024). These data would suggest that the type of SR could determine the macrophage activation: more proinflammatory when associated to CD36 and LOX-1 than when associated with SR-A.

Malondialdehyde modification of myelin oligodendrocyte glycoprotein leads to increased immunogenicity and encephalitogenicity

Self proteins may become autoantigenic through structural modification. We studied malondialdehydation of recombinant rat (rr) myelin oligodendrocyte glycoprotein (MOG), an autoantigen in multiple sclerosis. Malondialdehyde (MDA) modification changed protein weight and charge, the location of these adducts being mapped by Fourier transform ion cyclotron resonance. Molecular modelling revealed significant differences in the MDA-rrMOG three-dimensional structure. DBA/1 mice immunised with MDA-rrMOG developed greater proliferative responses and more severe experimental autoimmune encephalomyelitis than mice immunised with unmodified rrMOG. MDA-rrMOG was taken up more effectively by antigen-presenting cells (APC), at least partially through scavenger receptors. Exposure to MDA-rrMOG led to increased expression of IL-23, IL-12 and IL-12R, indicating a role not only for increased antigen uptake but also for activation of APC. We thus provide biochemical, structural, immunological and clinical data that suggest that the post-translationally modified form of this myelin autoantigen is a more relevant form of the molecule.

Phosphorylcholine-Targeting Immunization Reduces Atherosclerosis

OBJECTIVES

The present study evaluated the effect of phosphorylcholine (PC) immunization on the extent of experimental atherosclerosis.

BACKGROUND

Immunization against oxidized lipoprotein (oxLDL) or Streptococcus pneumoconiae reduces atherosclerosis. Phosphorylcholine is the main epitope recognized by both antipneumococcus and anti-oxLDL antibodies. Therefore we reasoned that PC-specific antibodies might play an important role in atherogenesis.

METHODS

Apolipoprotein E knockout mice were immunized with PC every second week over 4 months. At the end of the study, serum antibodies directed to either PC or oxLDL were measured. Splenic and peritoneal B cells were analyzed by flow cytometry. Aortic root atherosclerotic lesions were quantified by morphometry and phenotyped by immunohistochemistry. Immune and control sera were also tested for their effect on foam cell formation in macrophage culture in the presence of oxLDL.

RESULTS

The PC-immunized mice showed 3-fold increase in titers of anti-PC and -oxLDL antibodies compared with control mice (p < 0.01). The PC-immunized mice also showed a significant increase in the number of splenic mature B cells. The extent of atherosclerotic aorta root lesions was reduced by >40% in the PC-immunized mice (p < 0.01). Immunohistochemistry showed reduced expression of major histocompatibility complex class II antigens (p < 0.05) and the presence of B-cell clusters in plaques of PC-immunized mice. Finally, PC-immune serum was able to reduce macrophage-derived foam cell formation in the presence of oxLDL in vitro.

CONCLUSIONS

Phosphorylcholine immunization drives a specific humoral immune response that reduces foam cell formation in vitro and is atheroprotective in vivo.

Scavenger Receptors SR-AI/II and MARCO limit pulmonary dendritic cell migration and allergic airway inflammation

The class A scavenger receptors (SR-A) MARCO and SR-AI/II are expressed on lung macrophages (MPhis) and dendritic cells (DCs) and function in innate defenses against inhaled pathogens and particles. Increased expression of SR-As in the lungs of mice in an OVA-asthma model suggested an additional role in modulating responses to an inhaled allergen. After OVA sensitization and aerosol challenge, SR-AI/II and MARCO-deficient mice exhibited greater eosinophilic airway inflammation and airway hyperresponsiveness compared with wild-type mice. A role for simple SR-A-mediated Ag clearance ("scavenging") by lung MPhis was excluded by the observation of a comparable uptake of fluorescent OVA by wild-type and SR-A-deficient lung MPhis and DCs. In contrast, airway instillation of fluorescent Ag revealed a significantly higher traffic of labeled DCs to thoracic lymph nodes in SR-A-deficient mice than in controls. The increased migration of SR-A-deficient DCs was accompanied by the enhanced proliferation in thoracic lymph nodes of adoptively transferred OVA-specific T cells after airway OVA challenge. The data identify a novel role for SR-As expressed on lung DCs in the down-regulation of specific immune responses to aeroallergens by the reduction of DC migration from the site of Ag uptake to the draining lymph nodes.

Temporal gene expression profiles of target-ablated olfactory epithelium in mice with disrupted expression of scavenger receptor A: impact on macrophages

Target ablation [removal of the olfactory bulb (OBX)] induces apoptotic death of olfactory sensory neurons (OSNs) and an immune response in which activation and recruitment of macrophages (ms) into the olfactory epithelium (OE) occupy a central role. Ms phagocytose apoptotic neurons and secrete cytokines/growth factors that regulate subsequent progenitor cell proliferation and neurogenesis. Scavenger receptor A (SR-A) is a pattern recognition receptor that mediates binding of ms to apoptotic cells and other relevant immune response functions. The aim of this study was to determine the impact of the absence of SR-A on the immune response to OBX. The immune response to OBX was evaluated in mice in which functional expression of the m scavenger receptor (MSR) was eliminated by gene disruption (MSR-/-) and wild-type (wt) mice of the same genetic background. OBX induced significant apoptotic death of mature OSNs in the two strains. However, subsequent m infiltration and activation and progenitor cell proliferation were significantly reduced in MSR-/- vs. wt mice. Gene expression profiling at short intervals after OBX demonstrated significant differences in temporal patterns of expression of several gene categories, including immune response genes. Many immune response genes that showed different temporal patterns of expression are related to m function, including cytokine and chemokine secretion, phagocytosis, and m maturation and activation. These studies suggest that impairment of the immune response to OBX in the OE of MSR-/- mice most likely resulted from decreased m adhesion and subsequent reduced infiltration and activation, with a resultant decrease in neurogenesis.

Cellular, molecular and immunological mechanisms in the pathophysiology of vein graft intimal hyperplasia

Coronary artery disease, leading to myocardial infarction and ischaemia, affects millions of persons and is one of the leading causes of morbidity and mortality worldwide. Invasive techniques such as coronary artery bypass grafting are used to alleviate the sequelae of arterial occlusion. Unfortunately, restenosis or occlusion of the grafted conduit occurs over a time frame of months to years with a gradual reduction in patency, especially in vein grafts. The events leading to intimal hyperplasia (IH) formation involve numerous cellular and molecular components. Various cellular elements of the vessel wall are involved as are leucocyte-endothelial interactions that trigger the coagulation cascade leading to localized thrombus formation. Subsequent phenotypic modification of the medial smooth muscle cells and their intimal migration is the basis of the lesion formation that is thought to be propagated by an immune-mediated reaction. Despite intense scrutiny, the pathophysiology of IH remains an enigma. Although several growth factors, cytokines and numerous other biomolecules have been implicated and their relationship to prohyperplasia pathways such as the phosphatidyl-inositol 3-kinase (PI3K)-Akt pathway has been established, many pieces of the puzzle are still missing. An in-depth understanding of early vein graft adaptation and progression is necessary to improve the long-term prognosis and develop more effective therapeutic measures. In this review, we have critically evaluated and summarized the literature to elucidate and interlink the numerous established and emerging factors that play a key role in the development of IH leading to vein graft restenosis.

The immune response in atherosclerosis: a double-edged sword

Immune responses participate in every phase of atherosclerosis. There is increasing evidence that both adaptive and innate immunity tightly regulate atherogenesis. Although improved treatment of hyperlipidaemia reduces the risk for cardiac and cerebral complications of atherosclerosis, these remain among the most prevalent of diseases and will probably become the most common cause of death globally within 15 years. This Review focuses on the role of immune mechanisms in the formation and activation of atherosclerotic plaques, and also includes a discussion of the use of inflammatory markers for predicting cardiovascular events. We also outline possible future targets for prevention, diagnosis and treatment of atherosclerosis.

Adoptive Transfer of CD4 + T Cells Reactive to Modified Low-Density Lipoprotein Aggravates Atherosclerosis

Objective— Atherosclerosis is associated with immune responses to oxidized low-density lipoprotein (oxLDL). The presence of activated macrophages and T cells in lesions suggests that cell-mediated immune reactions are taking place during the disease process. However, the role of specific immune responses has remained unclear. We have previously shown that transfer of CD4 + T cells from apolipoprotein E knockout mice (apoE −/− ) into immunodeficient apoE −/− scid/scid mice accelerates disease.

Methods and Results— To test whether this effect is dependent on specific disease-associated antigens, purified CD4 + T cells from oxLDL-immunized mice were transferred into apoE −/− scid/scid mice. CD4 + T cells from mice immunized with a nonrelevant antigen, keyhole limpet hemocyanin (KLH), and naïve CD4 + T cells were used as controls. After 12 weeks, all mice that received T cells had larger lesions than untouched apoE −/− scid/scid controls. However, mice receiving CD4 + T cells from oxLDL immunized mice had substantially accelerated lesion progression compared with those receiving naive or KLH-primed T cells. Circulating levels of interferon-γ were increased in proportion to the acceleration of atherosclerosis.

Conclusion— These data show that adoptive transfer of purified CD4+ T cells from oxLDL-immunized mice accelerates atherosclerosis. They support the notion that Th1 cellular immunity is proatherogenic and identify oxLDL as a culprit autoantigen.

Cells, cytokines and cellular immunity in the pathogenesis of fibroproliferative vasculopathies

Atherosclerosis and restenosis are the result of vascular injury followed by an inflammatory and fibroproliferative response that involves a large number of growth factors, cytokines, and cellular elements. Platelet activation and leukocyte recruitment into the arterial intima play a crucial role, initiating a whole spectrum of reactions leading to vascular smooth muscle cell hyperplasia and intimal migration. The roles of macrophages and lymphocytes and mast cells as mediators of inflammation and immune response is discussed, as are the roles of growth factors and cytokines. New light on the 'old' problems will help us to devise newer and better therapeutic strategies to combat these clinical entities.

Atheroprotective effect of adjuvants in apolipoprotein E knockout mice

Strategies aimed at treating atherosclerosis by immunization protocols are emerging. Such protocols commonly use adjuvants as non-specific stimulators of immune responses. However, adjuvants are known to modify various disease processes. The aim of this study was to determine whether adjuvants alter the development of atherosclerosis. We performed immunization protocols in apolipoprotein E knockout mice (E degrees ) following chronic administration schedules commonly employed in experimental atherosclerosis. Our results point out a dramatic effect of several adjuvants on the development of atherosclerosis; three of the four adjuvants tested reduced lesion size. The Alum adjuvant, which is the adjuvant currently used in most vaccination protocols in humans, displayed a strong atheroprotective effect. Mechanisms accounting for atheroprotective effect of Freund's adjuvants included their capacity to increase both Th2 responses and anti-MDA-LDL IgM titers, and/or to impose atheroprotective lipoprotein profiles. The present study indicates that adjuvants have potent atheromodulating capabilities, and thus, implies that the choice of adjuvant is crucial in long-term immunization protocols in experimental atherosclerosis.

Leukotriene receptors in atherosclerosis

Leukotriene-forming enzymes are expressed within atherosclerotic lesions and locally produced leukotrienes exert pro-inflammatory actions within the vascular wall by means of cell surface receptors of the BLT and CysLT receptor subtypes. The migration and accumulation of inflammatory cells that follow leukotriene receptor activation have been implicated in atherosclerosis initiation and progression. Leukotriene receptors are in addition expressed on endothelial and vascular smooth muscle cells, associated with intimal hyperplasia in early atherosclerosis and restenotic lesions after angioplasty. Taken together, recent evidence suggests that leukotriene receptors may be a potential target in the treatment of atherosclerosis and in the prevention of restenosis after coronary interventions.

Scavenger receptors on sinusoidal liver endothelial cells are involved in the uptake of aldehyde-modified proteins

Scavenger receptors on sinusoidal liver endothelial cells (SECs) eliminate potentially harmful modified proteins circulating through the liver. It was shown recently that aldehyde-modified proteins bind to scavenger receptors and are associated with the development/progression of alcoholic liver diseases. For these studies, rat livers were perfused in situ with 125I-formaldehyde-bovine serum albumin (f-Alb) or 125I-malondialdehyde-acetaldehyde-bovine serum albumin (MAA-Alb) in the presence of known scavenger receptor ligands as inhibitors. Reverse transcription-polymerase chain reaction (RT-PCR) analysis and scavenger receptor Type A (SRA) knock-out mice were used to assess the role of these receptors in mediating immune responses. The degradation of 125I-f-Alb or 125I-MAA-Alb in whole livers and isolated SECs can be inhibited by known scavenger receptor ligands, including f-Alb, maleylated bovine albumin, and fucoidan. 125I-f-Alb could not be completely inhibited by MAA-Alb. In contrast, 125I-MAA-Alb was only partially inhibited with advanced glycosylated endproduct albumin. RT-PCR data show the presence of a number of scavenger receptors on SECs that may be responsible for the binding of MAA-modified proteins. SRA seems to be one of these receptors involved in the effects mediated by MAA-modified proteins. In a study using SRA knockout mice, it was shown that a decreased antibody response to MAA-Alb resulted. By RT-PCR, CD36, LOX-1, and SR-AI are the scavenger receptors most likely involved in the degradation of MAA-Alb.

Lesion Development and Response to Immunization Reveal a Complex Role for CD4 in Atherosclerosis

Atherosclerosis is a complex disease, bearing many of the characteristics of a chronic inflammatory process. Both cellular and humoral immune responses may be involved in the disease development. Oxidized low-density lipoprotein (oxLDL) is suggested to be an autoantigen in atherosclerosis. A protective effect against atherosclerosis has been demonstrated in animals immunized with oxLDL. Such a protection is associated with elevation of T cell–dependent IgG antibodies against oxLDL. In addition, it has been shown that immunization with Freund adjuvant alone also confers protection against development of atherosclerosis. We therefore hypothesized that CD4+ T cells are critical in the development of atherosclerosis and that they are involved in protective immune reactions after immunization. The development of atherosclerosis was studied in apolipoprotein E knockout (apoE KO) mice and CD4/apoE double knockout (dKO) mice that were immunized with either oxLDL in Freund adjuvant or adjuvant alone, or left untreated. Our results show that (1) the absence of CD4+ cells in apoE KO mice leads to reduced atherosclerosis, indicating that CD4+ cells constitute a major proatherogenic cell population, and (2) the atheroprotective effect of LDL immunization does not depend on CD4+ cells, whereas (3) the atheroprotective effect of adjuvant injection is CD4-dependent. These findings demonstrate complex roles of immune cell-cell interactions in the regulation of the atherosclerotic process and point to several possible targets in the treatment and prevention of atherosclerosis.

Immunomodulation and vaccination for atherosclerosis

During the last few decades, the pathogenesis of atherosclerosis has been related not only to cholesterol deposition and cell proliferation in the lesions, but also to infiltration of immune cells, which are involved in both systemic and local, innate as well as adaptive, immune responses. A number of antigen candidates, such as oxidised low-density lipoprotein and heat-shock proteins, have been associated with the disease process. As some inflammatory and autoimmune diseases could be treated by immunologically based therapy, it is of particular interest whether such principles can also be applied to prevent or treat atherosclerosis. Indeed, modification of immune reactions in animal models can greatly affect the development and progression of atherosclerosis. This review provides an overview of our current understanding of how immunomodulation changes the course of atherosclerosis and how vaccination may be used for preventing the disease.

Atherosclerosis and the immune system

The immune system is involved at all stages of the atherosclerotic disease process. Innate immunity, represented by macrophages and other cells, is directly activated by microbial components and possibly also by autologous lipids and proteins. It elicits inflammatory activity, which is a key component of the atherosclerotic lesion. Adaptive immunity is initiated by recognition of disease-related antigens, which include oxidatively modified lipoproteins, heat shock proteins and microbial macromolecules. In the artery wall, adaptive immune recognition mainly leads to Thl effector responses, which are characterized by secretion of proinflammatory cytokines and by activation of macrophages and vascular cells. Therefore, both the innate and adaptive arms of the immune system lead to inflammation in the developing atherosclerotic lesion. Interestingly, several effector pathways of cellular as well as humoral immunity tend to counteract proatherogenic, proinflammatory immunity. The notion that immunity plays an important role in the development of atherosclerosis has focused attention on a number of potential novel targets for intervention based on modulation of such immune responses.

Murine cytomegalovirus infection directs macrophage differentiation into a pro-inflammatory immune phenotype: implications for atherogenesis

We have previously demonstrated that mouse cytomegalovirus (MCMV) aggravates atherosclerosis in apolipoprotein E knockout (apoE(-/-)) mice, most likely by enhancing both systemic and local (e.g. in the vascular wall) cytokine production. However, until now it was unclear which cell type is responsible for this enhanced pro-inflammatory cytokine production. In this study we focused on the macrophage (mPhi), which besides being an important source of such cytokines, is known to be an important player in both atherosclerosis and viral clearance. We investigated whether MCMV could induce a pro-inflammatory immune mPhi phenotype, which ultimately may contribute to the development of atherosclerosis. To this end, peritoneal exudate cells (PEC) were elicited in apoE(-/-) mice by either MCMV or thioglycolate injection, and mPhi were phenotyped at 1 week post-intraperitoneal injection. MCMV-induced peritoneal mPhi contained MCMV DNA but had limited MCMV mRNA expression, indicating latent infection. These mPhi showed increased production of interferon-gamma (IFNgamma), exclusive production of interleukin-18 (IL-18) and increased expression of major histocompatibility complex (MHC) class II, CD40, CD80 and CD86, when compared with thioglycolate-induced mPhi. From these results, we conclude that intraperitoneal injection of MCMV induces an immune-responsive exudate in which at 7 days post-infection, MCMV-infected mPhi express a pro-inflammatory immune phenotype. As such, the MCMV-induced mPhi may be an important player in aggravating atherosclerosis through systemic and/or local immune activation.

The role of scavenger receptors in pathogen recognition and innate immunity

Scavenger receptors represent a large family of structurally unrelated distinct gene products, expressed by myeloid and selected endothelial cells and able to recognise modified low-density lipoproteins. They also bind and internalise a variety of microbial pathogens, as well as modified or endogenous molecules derived from the host, and contribute to a range of physiological or pathological processes.

Vaccination and atherosclerosis

Atherosclerosis is an inflammatory disease. Both innate and adaptive immunity are involved in lesion formation and development. A number of antigen candidates, such as oxidized low-density lipoprotein and heat shock protein, have been associated with the inflammation and immune reaction that is part of the atherosclerotic process. Because experimental models of some other inflammatory/autoimmune diseases can be improved by vaccination, it is of interest to investigate if vaccination can also be applied to prevent or retard atherosclerosis. Indeed, the modification of immune responses in animal models can greatly affect the development and progression of atherosclerosis. This review provides an overview of our current understanding of effects and proposed mechanisms of immunization on preventing atherosclerosis.

Rôle de l’immunité dans l’athérosclérose et dans les syndromes coronariens aigus

Cardiovascular diseases represent one of the most important causes of death in the world. The underlying pathogenetic process is atherosclerosis which leads to the progressive reduction of the arterial lumen and therefore to the ischemia of the perfused organs. Atherogenesis results from the interaction between the biology of the arterial wall and the various stress stimuli present in the circulating blood. The first steps of atherogenesis occur very early, already during the fetal life. Those arterial segments that are subjected to the initiating causes (including hemodynamic stress) show altered endothelial permeability and allow the infiltration of macromolecules, like lipoproteins, in the subintimal space. At the same time, the smooth muscle cells that are subjected to the same local factors produce proteoglycans able to bind lipoproteins and to promote their oxidation. Oxidized lipoproteins induce the expression of chemokines and adhesion molecules on the luminal surface of the endothelium, which then allow the local recruitment of monocytes-macrophages and T lymphocytes. This is a local inflammatory process that, in theory, should contribute to reestablish the homeostasis of the vascular wall by promoting the elimination of injured tissue and its repair. Unfortunately, for unknown reasons, the immuno-inflammatory reaction persists and autoamplifies, the various components of the immune response finally contributing to the pathogenesis of atherosclerosis as well as of atherosclerotic complications.

T cell proliferative responses to malondialdehyde-acetaldehyde haptenated protein are scavenger receptor mediated

Malondialdehyde-acetaldehyde (MAA) haptenated proteins have been described in disease processes related to prolonged oxidative stress (via malondialdehyde production), such as alcohol liver disease (ALD), non-alcoholic non-steatohepatitis (NASH) and atherosclerosis. Experimentally, high titer IgG1 antibody responses are seen after immunization without adjuvant; however, T cell proliferative responses and the role of scavenger receptors in this immunogenicity has not previously been described. In this study, T cell proliferative responses to the carrier protein, but not the MAA hapten itself, were identified in vitro. Moreover, these T proliferative responses were inhibited when MAA-hen egg lysozyme (HEL) was co-immunized with excess scavenger receptor ligand polyG (poly-guanylic acid), implicating the role of (a) scavenger receptor(s) in initiating the T helper cell response. Activated B cells were unable to process and present MAA-HEL preferentially to T cells, while thioglycollate-elicited (but not Con A-elicited) macrophages and dendritic cells (DC) did so with approximately 32-fold less MAA-HEL than native antigen necessary to initiate equal proliferative responses. While this preferential processing and presentation may be related to several factors, preferential binding of MAA haptenated proteins mediated by scavenger receptors may be one mechanism. IL-4 was absent from the supernatants of T proliferative assays despite a strong IgG1 response in vivo, although the TH2 cytokines IL-6 and IL-10 were expressed. Since the modification of proteins by the MAA have previously been shown to occur after ethanol consumption in vivo, the ability of MAA haptens to experimentally enhance immune responses, specifically humoral and T cell responses, may represent mechanisms by which autoimmune phenomena found in ALD occur.