Enhanced atherogenesis is not an obligatory response to systemic herpesvirus infection in the apoE-deficient mouse: comparison of murine gamma-herpesvirus-68 and herpes simplex virus-1

Lipid-related protein NECTIN2 is an important marker in the progression of carotid atherosclerosis: An intersection of clinical and basic studies

Background:

The nectin cell adhesion molecule 2 (NECTIN2) protein is a cell adhesion molecule involved in lipid metabolism. We aimed to explore the potential role of NECTIN2 in carotid atherosclerosis (CA).

Materials and Methods:

Patients who underwent carotid endarterectomy (CEA) at the First Affiliated Hospital of Zhengzhou University were enrolled in this study. APOE-/- rats fed western or normal diet were used to model early pathological changes in CA. The relationship between patients’ lipid indices and plaque severity was assessed using ordinal regression analysis. Mendelian randomisation (MR) analysis was used to determine the causal links between low-density lipoprotein cholesterol (LDL-C) and atherosclerosis. After matching analysis of the single-cell transcriptome and microarray data of carotid plaques, NECTIN2 was identified as a key factor affecting CA. The importance of NECTIN2 was further verified by immunofluorescence staining of CEA and APOE-/- rat specimens.

Results:

A total of 108 patients were included. The traditional lipid indices did not correlate significantly with the plaque severity (P > 0.05). NECTIN2 provided a strong causal link between LDL-C level and CA (MR effect size >0). Deep-sequencing data illustrated that NECTIN2 expression was cell specific. In early-stage CA, NECTIN2 expression was increased in endothelial cells; however, in advanced-stage CA, NECTIN2 was overexpressed in macrophages located in fibrous caps. APOE-/- rat carotid artery and human carotid plaques modelled the entire atherosclerotic process, showing an upregulation of NECTIN2 expression in CA.

Conclusions:

Lipid-related protein NECTIN2 is a potential marker in CA progression and can potentially be a new therapeutic target for clinical prevention.

Murine gammaherpesvirus-68 expands, but does not activate, CD11b+ gr-1+ splenocytes in vivo

Background

Murine gammaherpesvirus 68 (HV-68) is an efficient pathogen, capable of infecting and establishing lifelong latency in rodents. While many studies have demonstrated the ability of this viral infection to modulate immune responses, a unifying mechanism for HV-68-induced subversion of a protective host response remains elusive. We questioned whether infection with HV-68 could expand a population of myeloid derived suppressor cells (MDSC) as one mechanism for altering protective immunity.

Methods

Mice were infected with HV-68, with viral latency being established in these animals. At varying times post-infection, cells were isolated for detection of viral genomes, phenotyping of myeloid cell populations, and ex vivo analysis of suppressor activity of myeloid cells.

Results

CD11b + Gr-1+ myeloid cells accumulated in the spleens, but not the bone marrow, of HV-68 infected mice. These cells were predominantly Gr-1+ Ly-6 G+, and could be found to contain viral genomes. Increased levels of serum S100A8/A9 produced during viral infection were consistent with the expansion of these CD11b + Gr-1+ myeloid cells. Despite their expansion, these cells exhibited no increased arginase 1 or iNOS activity, and did not have the ability to suppress anti-CD3 antibody activated T lymphocyte responses.

Conclusions

We concluded that HV-68 infection was capable of expanding a population of myeloid cells which were phenotypically similar to MDSC. However these cells were not sufficiently activated during the establishment of viral latency to actively suppress T cell responses.

Immune modulation during latent herpesvirus infection

Nearly all human beings, by the time they reach adolescence, are infected with multiple herpesviruses. At any given time, this family of viruses accounts for 35-40 billion human infections worldwide, making herpesviruses among the most prevalent pathogens known to exist. Compared to most other viruses, herpesviruses are also unique in that infection lasts the life of the host. Remarkably, despite their prevalence and persistence, little is known about how these viruses interact with their hosts, especially during the clinically asymptomatic phase of infection referred to as latency. This review explores data in human and animal systems that reveal the ability of latent herpesviruses to modulate the immune response to self and environmental antigens. From the perspective of the host, there are both potentially detrimental and surprisingly beneficial effects of this lifelong interaction. The realization that latent herpesvirus infection modulates immune responses in asymptomatic hosts forces us to reconsider what constitutes a 'normal' immune system in a healthy individual.

Pathogens and atherosclerosis: update on the potential contribution of multiple infectious organisms to the pathogenesis of atherosclerosis

It is currently unclear what causes the chronic inflammation within atherosclerotic plaques. One emerging paradigm suggests that infection with bacteria and/or viruses can contribute to the pathogenesis of atherosclerosis either via direct infection of vascular cells or via the indirect effects of cytokines or acute phase proteins induced by infection at non-vascular sites. This paradigm has been supported by multiple epidemiological studies that have established positive associations between the risk of cardiovascular disease morbidity and mortality and markers of infection. It has also been supported by experimental studies showing an acceleration of the development of atherosclerosis following infection of hyperlipidaemic animal models. There are now a large number of different infectious agents that have been linked with an increased risk of cardiovascular disease. These include: Chlamydia pneumoniae, Porphyromonas gingivalis, Helicobacter pylori , influenza A virus, hepatitis C virus, cytomegalovirus, and human immunodeficiency virus. However, there are significant differences in the strength of the data supporting their association with cardiovascular disease pathogenesis. In some cases, the infectious agents are found within the plaques and viable organisms can be isolated suggesting a direct effect. In other cases, the association is entirely based on biomarkers. In the following review, we evaluate the strength of the data for individual or groups of pathogens with regard to atherosclerosis pathogenesis and their potential contribution by direct or indirect mechanisms and discuss whether the established associations are supportive of the infectious disease paradigm. We also discuss the failure of antibiotic trials and the question of persistent infection.

Pathogenesis and host control of gammaherpesviruses: lessons from the mouse

Gammaherpesviruses are lymphotropic viruses that are associated with the development of lymphoproliferative diseases, lymphomas, as well as other nonlymphoid cancers. Most known gammaherpesviruses establish latency in B lymphocytes. Research on Epstein-Barr virus (EBV) and murine gammaherpesvirus 68 (MHV68/γHV68/MHV4) has revealed a complex relationship between virus latency and the stage of B cell differentiation. Available data support a model in which gammaherpesvirus infection drives B cell proliferation and differentiation. In general, the characterized gammaherpesviruses exhibit a very narrow host tropism, which has severely limited studies on the human gammaherpesviruses EBV and Kaposi's sarcoma-associated herpesvirus. As such, there has been significant interest in developing animal models in which the pathogenesis of gammaherpesviruses can be characterized. MHV68 represents a unique model to define the effects of chronic viral infection on the antiviral immune response.

Chronic Immune Reactivity Against Persisting Microbial Antigen in the Vasculature Exacerbates Atherosclerotic Lesion Formation

Objective— The purpose of this study was to examine the relative contribution of different immunopathological mechanisms during murine cytomegalovirus (MCMV)-mediated acceleration of atheroma formation in apolipoprotein E–deficient (apoE −/− ) mice.

Methods and Results— To distinguish between the effects of systemic activation and cognate immune reactivity against a pathogen-derived persisting antigen in the vasculature, we used hypercholesterolemic transgenic mice constitutively expressing the β-galactosidase (β-gal) transgene in the cardiovascular system (apoE −/− ×SM-LacZ). After infection with β-gal–recombinant MCMV-LacZ, apoE −/− , and apoE −/− ×SM-LacZ mice mounted comparable cellular immune responses against the virus. β-gal–specific CD8 + T cells expanded rapidly and remained detectable for at least 100 days in both mouse strains. However, compared with apoE −/− mice, apoE −/− ×SM-LacZ mice developed drastically accelerated atherosclerosis. Moreover, atherosclerotic lesions in MCMV-LacZ–infected apoE −/− ×SM-LacZ but not apoE −/− mice were associated with pronounced inflammatory infiltrates.

Conclusions— Taken together, our data indicate that chronic immune reactivity against pathogen-derived antigens persisting in the vasculature significantly exacerbates atherogenesis.

Early structural and functional changes of the vasculature in HIV-infected children: impact of disease and antiretroviral therapy

BACKGROUND

Premature cardiovascular disease is increasingly recognized in HIV-infected patients, but the mechanisms involved are unclear. The purpose of this study was to determine the impact of HIV infection and antiretroviral therapy (ART) on markers of early vascular disease in children.

METHODS AND RESULTS

We studied 83 HIV-infected children (56 had taken ART, of whom 31 received a regimen containing protease inhibitors [PIs]; 27 were never treated) and a control group of 59 healthy children. Carotid intima-media thickness (IMT) and brachial artery flow-mediated dilatation (FMD) were measured. IMT was significantly greater in HIV-infected children compared with the control subjects (P<0.001). Among the HIV-infected children, age and treatment were significantly associated with increased IMT. Children exposed to PIs had greater IMT compared with both non-PI-treated children and untreated children (P=0.02). FMD was also significantly reduced in the HIV-infected children compared with control subjects (P=0.02). Pairwise comparisons of different treatment exposure groups revealed that FMD was impaired by a mean of 3.6% (95% CI, 1.8 to 5.3; P<0.001) for children exposed to PIs compared with untreated children and by a mean of 1.8% (95% CI, 0.01 to 3.5; P=0.05) compared with non-PI-treated children. HIV-infected children had lipid abnormalities, but they did not account for the observed differences in either FMD or IMT.

CONCLUSIONS

HIV infection in childhood is associated with adverse structural and functional vascular changes that are most pronounced in children exposed to PI therapy. Longitudinal studies are required to differentiate the relative impact of HIV disease and ART and to assess the potential for prevention.

Endothelial Dysfunction in Childhood Infection

Background— Atherosclerosis begins in early life, and endothelial dysfunction is recognized as a key initiating event in the development of atherosclerosis. Although infection has been implicated in endothelial dysfunction and atherogenesis, the impact of acute common childhood infections on the vascular endothelium is unknown.

Methods and Results— We studied 600 children aged 10 years drawn from the Avon Longitudinal Study of Parents and Children. The children were divided into 3 groups: those with current acute infection (AI; n=135; 73 boys and 62 girls); a convalescent group with infection in the past 2 weeks (n=166; 78 boys and 88 girls), and a healthy control group (n=299; 131 boys and 168 girls). Endothelial function was determined in all subjects by high-resolution ultrasound to measure brachial artery flow-mediated dilation (FMD) and was expressed as the percentage change in diameter from baseline after reactive hyperemia. FMD was repeated in 40 children in the AI group and 50 in the control group after a mean interval of 1 year. FMD was lower in both the AI group (6.3±2.7%, mean±SD) and the convalescent group (8.1±3.1%) than in the control group (9.7±2.5%; P <0.001 for both). The observed differences in FMD remained after adjustment for potential confounding variables. At the repeat visit, FMD was unchanged in controls ( P =0.85) but improved in the AI group ( P <0.001).

Conclusions— Acute infection in childhood is associated with impaired endothelium-dependent vasodilation. These findings support a potential role for previously unsuspected extrinsic inflammatory stimuli in the pathogenesis of early atherosclerosis.

Immunopathogenesis of atherosclerosis

Recent clinical studies indicate that the number of microbial infections (the "pathogen burden") critically determines the development and progression of atherosclerotic disease. Viruses or bacteria with a specific tropism for cells of the vascular wall may contribute to the initial vascular injury via direct cytopathic effects or via the induction of genuine autoimmune responses. Immunopathological processes such as molecular mimicry, epitope spreading, or bystander activation of self-reactive lymphocytes most likely fuel the chronic inflammatory process in the vascular wall. Recognition of atherogenesis as a pathogen-driven, immunopathological process makes this disease amenable to new treatment strategies such as vaccination or immunomodulation.

Human cytomegalovirus seropositivity is associated with impaired vascular function

BACKGROUND

Herpesvirus infection is a possible risk factor for atherogenesis, and diabetics may be at particular risk. Endothelial dysfunction is an early marker for atherosclerosis, and the present study tests the hypotheses that (1) prior infection with cytomegalovirus (CMV) and herpes simplex virus (HSV) is associated with endothelial dysfunction and (2) this may be more marked in diabetics.

METHODS AND RESULTS

Serum samples were tested for anti-IgG antibodies to CMV and HSV from 400 subjects (mean age for diabetics and nondiabetics, 37.8+/-4.3 and 37.9+/-3.7 [SD]). We also assessed Helicobacter pylori and Chlamydia pneumoniae serology. Coronary atheroma was quantified by means of electron beam computed tomography. Subjects (n=157) underwent venous occlusion plethysmography with acetylcholine, bradykinin, glyceryl trinitrate, norepinephrine, and l-NG-monomethyl-l-arginine. Individuals who were seropositive for CMV had reduced responses to bradykinin (P=0.005) and glyceryl trinitrate (P=0.006). The reduced response to bradykinin remained significant (P=0.045) after adjusting for the response to glyceryl trinitrate and was independent of conventional risk factors. Positive serology for the other organisms did not have an independent effect on reactivity. There was a weaker association between CMV and coronary artery calcification (P=0.09). Positive serology for each of the other pathogens did not affect reactivity, but there was a relation between total pathogen burden and impaired vascular reactivity. No significant differences were found between diabetics and nondiabetics.

CONCLUSIONS

This study shows that CMV-seropositive individuals have endothelial dysfunction and impaired responses to NO. This association was independent of conventional risk factors and may be associated with increased atherosclerosis burden.