Viral activation of the coagulation cascade: molecular interactions at the surface of infected endothelial cells

Viral coagulation: pushing the envelope

Many virus types affect the blood clotting system with correlations to pathology that range widely from thrombosis to hemorrhage linking to inflammation. Here we overview the intricate crosstalk induced by infection between proteins on the virus encoded by either the host or virus genomes, coagulation proteins, platelets, leukocytes, and endothelial cells. For blood-borne viruses with an outer covering acquired from the host cell, the envelope, a key player may be the cell-derived trigger of coagulation on the virus surface, tissue factor (TF). TF is a multifunctional transmembrane cofactor that accelerates factor (F)VIIa-dependent activation of FX to FXa, leading to clot formation. However, the nascent TF/FVIIa/FXa complex also facilitates G protein-coupled modulation of cells via protease-activated receptor 2. As a viral envelope constituent, TF can bypass the physiological modes of regulation, thereby initiating the activation of neighboring platelets, leukocytes, and endothelial cells. A thromboinflammatory environment is predicted due to feedback amplification in response to cellular release of cytokines, procoagulant proteins, neutrophil extracellular traps, and stimulus-induced accessibility of adhesive receptors, resulting in cellular aggregates. The pathobiological effects of thromboinflammation ultimately contribute to innate and adaptive immunity for viral clearance. In contrast, the preceding stages of viral infection may be enhanced via the TF-protease axis.

TRIM28 regulates the coagulation cascade inhibited by p72 of African swine fever virus

In 2018, African swine fever virus (ASFV) emerged in China, causing extremely serious economic losses to the domestic pig industry. Infection with ASFV can cause disseminated coagulation, leading to the consumption of platelets and coagulation factors and severe bleeding. However, the mechanism of virus-induced coagulation has yet to be established. In our study, ASFV downregulated the coagulation process, as detected by D-dimer (D2D) and Factor X (F10) expression in pigs challenged with ASFV HLJ/18. In vitro, ASFV infection increased Factor IX (F9) and Factor XII (F12) expression while downregulating F10 expression in porcine alveolar macrophages (PAMs). African swine fever virus induced both intrinsic and extrinsic coagulation cascades. In addition, several encoded proteins affect the expression of the crucial coagulation protein F10, and among the encoded proteins, p72 inhibits the activity and expression of F10. Proteomic analysis also revealed that p72 is involved in the coagulation cascade. p72 can interact with F10, and its inhibitory functional domains include amino acids 423-432 and amino acids 443-452. Finally, we found that F10 and p72 interact with tripartite motif-containing protein 28 (TRIM28). TRIM28 knockdown resulted in a decrease in F10 expression. Importantly, TRIM28 contributes to the reduction in F10 protein expression regulated by p72. Our findings revealed an inhibitory effect of the viral protein p72 on the ASFV infection-induced coagulation cascade and revealed a role of TRIM28 in reducing F10 expression, revealing a molecular mechanism of ASFV-associated coagulation.

Cytomegalovirus Immunoglobulin G (IgG) Titer and Coronary Artery Disease in People With Human Immunodeficiency Virus (HIV)

BACKGROUND

Cytomegalovirus (CMV) infection is thought to result in increased immune activation in people with human immunodeficiency virus (HIV, PWH). Although some data have linked asymptomatic CMV infection to cardiovascular disease among PWH, it remains unknown whether CMV is associated with increased or high-risk coronary plaque.

METHODS

The Randomized Trial to Prevent Vascular Events in HIV (REPRIEVE) enrolled PWH aged 40-75 years on stable antiretroviral therapy (ART) with low-to-moderate atherosclerotic cardiovascular disease (ASCVD) risk. Among a subset of US REPRIEVE participants, coronary plaque was assessed by coronary computed tomography angiography. Here, we assessed the relationship between CMV immunoglobulin G (IgG) titer and (1) levels of immune activation, (2) inflammatory biomarkers, and (3) coronary plaque phenotypes at study entry.

RESULTS

Of 672 participants, mean age was 51 years, 83% were men, median ASCVD risk score was 4.5%, and 66% had current CD4+ T-cell count ≥500 cells/mm3. Higher CMV IgG quartile group was associated with older age and lower current and nadir CD4+ T-cell counts. CMV IgG titer was associated with specific inflammatory biomarkers (sCD163, MCP-1, interleukin [IL]-6, hsCRP) in univariate analysis, but not after controlling for HIV-specific factors. In contrast, CMV IgG titer was not associated with coronary artery disease indexes, including presence of plaque, coronary artery calcium (CAC) score >0, vulnerable plaque presence, or Leaman score >5.

CONCLUSIONS

No meaningful association was seen between CMV IgG titer and coronary artery disease indexes among ART-treated PWH at study enrollment. Longitudinal assessments in REPRIEVE will determine the relationship of CMV IgG titer to plaque progression and cardiovascular events.

CLINICAL TRIALS REGISTRATION

NCT02344290.

Multicenter study on recent portal venous system thrombosis associated with cytomegalovirus disease

BACKGROUND & AIMS

Recent non-malignant non-cirrhotic portal venous system thrombosis (PVT) is a rare condition. Among risk factors for PVT, cytomegalovirus (CMV) disease is usually listed based on a small number of reported cases. The aim of this study was to determine the characteristics and outcomes of PVT associated with CMV disease.

METHODS

We conducted a French multicenter retrospective study comparing patients with recent PVT and CMV disease ("CMV positive"; n = 23) to patients with recent PVT for whom CMV testing was negative ("CMV negative"; n = 53) or unavailable ("CMV unknown"; n = 297).

RESULTS

Compared to patients from the "CMV negative" and "CMV unknown" groups, patients from the "CMV positive" group were younger, more frequently had fever, and had higher heart rate, lymphocyte count and serum ALT levels (p ≤0.01 for all). The prevalence of immunosuppression did not differ between the 3 groups (4%, 4% and 6%, respectively). Extension of PVT was similar between the 3 groups. Thirteen out of 23 "CMV positive" patients had another risk factor for thrombosis. Besides CMV disease, the number of risk factors for thrombosis was similar between the 3 groups. Heterozygosity for the prothrombin G20210A gene variant was more frequent in "CMV positive" patients (22%) than in the "CMV negative" (4%, p = 0.01) and "CMV unknown" (8%, p = 0.03) groups. Recanalization rate was not influenced by CMV status.

CONCLUSIONS

In patients with recent PVT, features of mononucleosis syndrome should raise suspicion of CMV disease. CMV disease does not influence thrombosis extension nor recanalization. More than half of "CMV positive" patients have another risk factor for thrombosis, with a particular link to the prothrombin G20210A gene variant.

LAY SUMMARY

Patients with cytomegalovirus (CMV)-associated portal venous system thrombosis have similar thrombosis extension and evolution as patients without CMV disease. However, patients with CMV-associated portal venous system thrombosis more frequently have the prothrombin G20210A gene variant, suggesting that these entities act synergistically to promote thrombosis.

Clinical consequences of asymptomatic cytomegalovirus in treated human immunodeficency virus infection

PURPOSE OF REVIEW

Despite antiretroviral therapy (ART)-mediated viral suppression, people with human immunodeficiency virus (HIV) (PWH) have increased morbidity and mortality. Immune activation and inflammation persist on ART and predict these complications. Over 90% of PWH have cytomegalovirus (CMV) co-infection, and CMV is considered a plausible contributor to this persistent immune activation.

RECENT FINDINGS

A detailed understanding of the link between CMV and multimorbidity is needed, particularly as research moves toward identifying potential targeted therapeutics to attenuate inflammation-mediated morbidity and mortality in treated HIV. We review the literature on the association between CMV and immune activation as well as multiple end-organ complications including cardiovascular disease, venous thromboembolic disease, metabolic complications, gastrointestinal dysfunction, central nervous system involvement, birth sex-related differences, and the relation to the HIV reservoir. We conclude with a discussion of ongoing therapeutic efforts to target CMV.

SUMMARY

As CMV is a plausible driver of multiple comorbidities through persistent immune activation in treated HIV, future research is needed and planned to address its causal role as well as to test novel therapeutics in this setting.

Antiviral anticoagulation

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel envelope virus that causes coronavirus disease 2019 (COVID-19). Hallmarks of COVID-19 are a puzzling form of thrombophilia that has elevated D-dimer but only modest effects on other parameters of coagulopathy. This is combined with severe inflammation, often leading to acute respiratory distress and possible lethality. Coagulopathy and inflammation are interconnected by the transmembrane receptor, tissue factor (TF), which initiates blood clotting as a cofactor for factor VIIa (FVIIa)-mediated factor Xa (FXa) generation. TF also functions from within the nascent TF/FVIIa/FXa complex to trigger profound changes via protease-activated receptors (PARs) in many cell types, including SARS-CoV-2-trophic cells. Therefore, aberrant expression of TF may be the underlying basis of COVID-19 symptoms. Evidence suggests a correlation between infection with many virus types and development of clotting-related symptoms, ranging from heart disease to bleeding, depending on the virus. Since numerous cell types express TF and can act as sites for virus replication, a model envelope virus, herpes simplex virus type 1 (HSV1), has been used to investigate the uptake of TF into the envelope. Indeed, HSV1 and other viruses harbor surface TF antigen, which retains clotting and PAR signaling function. Strikingly, envelope TF is essential for HSV1 infection in mice, and the FXa-directed oral anticoagulant apixaban had remarkable antiviral efficacy. SARS-CoV-2 replicates in TF-bearing epithelial and endothelial cells and may stimulate and integrate host cell TF, like HSV1 and other known coagulopathic viruses. Combined with this possibility, the features of COVID-19 suggest that it is a TFopathy, and the TF/FVIIa/FXa complex is a feasible therapeutic target.

Coagulation factor VIIa binds to herpes simplex virus 1-encoded glycoprotein C forming a factor X-enhanced tenase complex oriented on membranes

BACKGROUND

The cell membrane-derived initiators of coagulation, tissue factor (TF) and anionic phospholipid (aPL), are constitutive on the herpes simplex virus type 1 (HSV1) surface, bypassing physiological regulation. TF and aPL accelerate proteolytic activation of factor (F) X to FXa by FVIIa to induce clot formation and cell signaling. Thus, infection in vivo is enhanced by virus surface TF. HSV1-encoded glycoprotein C (gC) is implicated in this tenase activity by providing viral FX binding sites and increasing FVIIa function in solution.

OBJECTIVE

To examine the biochemical influences of gC on FVIIa-dependent FX activation.

METHODS

Immunogold electron microscopy (IEM), kinetic chromogenic assays and microscale thermophoresis were used to dissect tenase biochemistry. Recombinant TF and gC were solubilized (s) by substituting the transmembrane domain with poly-histidine, which could be orientated on synthetic unilamellar vesicles containing Ni-chelating lipid (Ni-aPL). These constructs were compared to purified HSV1 TF±/gC ± variants.

RESULTS

IEM confirmed that gC, TF, and aPL are simultaneously expressed on a single HSV1 particle where the contribution of gC to tenase activity required the availability of viral TF. Unlike viral tenase activity, the cofactor effects of sTF and sgC on FVIIa was additive when bound to Ni-aPL. FVIIa was found to bind to sgC and this was enhanced by FX. Orientation of sgC on a lipid membrane was critical for FVIIa-dependent FX activation.

CONCLUSIONS

The assembly of gC with FVIIa/FX parallels that of TF and may involve other constituents on the HSV1 envelope with implications in virus infection and pathology.

Interactions of viruses and the humoral innate immune response

The innate immune response is crucial for defense against virus infections where the complement system, coagulation cascade and natural antibodies play key roles. These immune components are interconnected in an intricate network and are tightly regulated to maintain homeostasis and avoid uncontrolled immune responses. Many viruses in turn have evolved to modulate these interactions through various strategies to evade innate immune activation. This review summarizes the current understanding on viral strategies to inhibit the activation of complement and coagulation cascades, evade natural antibody-mediated clearance and utilize complement regulatory mechanisms to their advantage.

Cytomegalovirus Infection and Relative Risk of Cardiovascular Disease (Ischemic Heart Disease, Stroke, and Cardiovascular Death): A Meta-Analysis of Prospective Studies Up to 2016

BACKGROUND

Several studies have suggested that cytomegalovirus infection is likely associated with an increased relative risk of cardiovascular disease (CVD); however, the results are inconsistent. We aimed to provide a systematic review and meta-analysis of community-based prospective studies assessing the association between cytomegalovirus infection and relative risk of CVD.

METHODS AND RESULTS

We searched Medline and EMBASE to retrieve prospective studies that reported risk estimates of the association between cytomegalovirus infection and relative risk of CVD. The search yielded 10 articles including a total of 34 564 participants and 4789 CVD patients. Overall, exposure to cytomegalovirus infection was associated with a 22% (relative risk: 1.22, 95% CI: 1.07-1.38, P=0.002) increased relative risk of future CVD. We estimated that 13.4% of CVD incidence could be attributable to cytomegalovirus infection.

CONCLUSIONS

In conclusion, cytomegalovirus infection is associated with a significantly increased relative risk of CVD.

From focal sepsis to periodontal medicine: a century of exploring the role of the oral microbiome in systemic disease

The oral microbiome is established within a few minutes after birth and consists of stable multi-species communities that engage in a dynamic equilibrium with the host immune system. Dental caries, endodontic infections and periodontal diseases are bacterially driven diseases that are caused by dysbiotic microbiomes. Over a century ago, the focal infection theory implicated these infections in the aetiology of several systemic diseases, ranging from arthritis to neurodegenerative diseases. However, a lack of concrete evidence, combined with the urgency with which clinicians embraced this approach without regard for appropriate case selection, led to its demise within 30 years. In the last decade of the 20th century, the concept of periodontal medicine was introduced to explain the correlations that were being observed between periodontitis and cardiovascular disease, rheumatoid arthritis, Alzheimer's disease, pulmonary disease, pre-term delivery of low birth weight infants and metabolic disease. It was proposed that periodontal pathobionts played a causal role in the initiating or exacerbating certain diseases either by direct invasion or by stimulating a florid immune-inflammatory response that extended into the systemic circulation. This review will examine the strength of current evidence in establishing a causal link between oral pathobionts and systemic disease.

The Cell Biology of Cytomegalovirus: Implications for Transplantation

Interpretation of clinical data regarding the impact of cytomegalovirus (CMV) infection on allograft function is complicated by the diversity of viral strains and substantial variability of cellular receptors and viral gene expression in different tissues. Variation also exists in nonspecific (monocytes and dendritic cells) and specific (NK cells, antibodies) responses that augment T cell antiviral activities. Innate immune signaling pathways and expanded pools of memory NK cells and γδ T cells also serve to amplify host responses to infection. The clinical impact of specific memory T cell anti-CMV responses that cross-react with graft antigens and alloantigens is uncertain but appears to contribute to graft injury and to the abrogation of allograft tolerance. These responses are modified by diverse immunosuppressive regimens and by underlying host immune deficits. The impact of CMV infection on the transplant recipient reflects cellular changes and corresponding host responses, the convergence of which has been termed the "indirect effects" of CMV infection. Future studies will clarify interactions between CMV infection and allograft injury and will guide interventions that may enhance clinical outcomes in transplantation.

The role of endothelial cell adhesion molecules in the development of atherosclerosis

The vascular endothelium serves as a dynamic interface between circulating blood elements and the interstitial tissues. As such, it communicates to cells within the vessel wall as well as to the surrounding tissue, sensing its environment and responding accordingly. The vasculature must maintain a delicate balance when initiating a functional response by producing both proinflammatory and antiinflammatory mediators, vasoconstrictors and vasodilators, growth stimulators and inhibitors, and prothrombogenic and antithrombogenic factors. Any response to injurious agents could lead to pathology. Confounding this complex interplay is the fact that the very response to injury that may have developed to undo the damage may itself be even more deleterious. One response to injury by the endothelium is the new or increased expression of surface receptors for immune elements. In atherosclerosis, the adhesion of monocytes (and T cells) to the endothelium is a key event triggered by some form of insult. Subsequent events include monocytic infiltration of the vessel wall, alterations in lipid metabolism, and the activation of these cells into foam cells. The presence of large numbers of foam cells in the intima may produce a high concentration of cytokines and growth factors within a localized area, extracellular matrix perturbations, smooth muscle cell proliferation, and ultimately platelet aggregation at the site of stenosis. Endothelial cells themselves will not only elaborate factors after the initial injury to the vessel wall but also in response to the factors produced by foam cells within the plaque. These endothelial cell factors include MCP-1, a chemoattractant for monocytes (179,180), IL-1 (63,64), IL-6 (interleukin-6) (65-67), IL-8 (interleukin 8) (181), and PDGF, a potent smooth muscle mitogen (4,72) (Fig. 3). Endothelial cells will propagate an inflammatory response long after the initial insult to the arterial vessel. A chronic cycle of endothelial cell activation and leukocyte infiltration is constitutively activated. Thus, all of the cellular elements of the vessel wall, as well as the atherosclerotic plaque itself, elaborate cytokines and growth factors that amplify and propagate the pathological process.

The procoagulant envelope virus surface: contribution to enhanced infection

Many virus types are covered by a lipid bilayer. This structure called an envelope, is derived from the host cell and includes host- and virus-encoded proteins. Because envelope components first interact with the host, it is the trigger for infection, immunity and pathology. The roles of especially host-derived constituents are poorly understood. Focusing on herpes simplex type 1 (HSV1) as a model, we have shown that the envelope acquires the physiological initiators of coagulation from the host cell; tissue factor (TF) and procoagulant phospholipid (proPL). Unlike resting cells, where TF and proPL accessibility is carefully restricted, their expression is constitutive on the purified virus enabling factor VIIa (FVIIa)-dependant factor Xa (FXa) and thrombin generation. Interestingly, HSV1-encoded glycoprotein C (gC) on the virus enhances FXa production. In addition to coagulation proteases, HSV1 also facilitates fibrinolytic plasmin generation. HSV1 TF and gC combine to optimally enhance cultured cell infection when both FVIIa and FXa are available through protease activated receptor (PAR) 2. Plasmin also increases infection through PAR2, whereas thrombin provides an additive effect via PAR1. Thus, depending on the host cell, TF and proPL may be a general feature of enveloped viruses, enabling coagulation protease activation and PAR-mediated effects on infection.

Helicobacter pylori infection and eye diseases: a systematic review

The connection between Helicobacter pylori (Hp) infection and eye diseases has been increasingly reported in the literature and in active research. The implication of this bacterium in chronic eye diseases, such as blepharitis, glaucoma, central serous chorioretinopathy and others, has been hypothesized. Although the mechanisms by which this association occurs are currently unknown, this review describes shared pathogenetic mechanisms in an attempt to identify a lowest common denominator between eye diseases and Hp infection. The aim of this review is to assess whether different studies could be compared and to establish whether or not Hp infection and Eye diseases share common pathogenetic aspects. In particular, it has been focused on oxidative damage as a possible link between these pathologies. Text word search in Medline from 1998 to July 2014. 152 studies were included in our review. Were taken into considerations only studies that related eye diseases more frequent and/or known. Likely oxidative stress plays a key role. All of the diseases studied seem to follow a common pattern that implicates a cellular response correlated with a sublethal dose of oxidative stress. These alterations seem to be shared by both Hp infections and ocular diseases and include the following: decline in mitochondrial function, increases in the rate of reactive oxygen species production, accumulation of mitochondrial DNA mutations, increases in the levels of oxidative damage to DNA, proteins and lipids, and decreases in the capacity to degrade oxidatively damaged proteins and other macromolecules. This cascade of events appears to repeat itself in different diseases, regardless of the identity of the affected tissue. The trabecular meshwork, conjunctiva, and retina can each show how oxidative stress may acts as a common disease effector as the Helicobacter infection spreads, supported by the increased oxidative damage and other inflammation.

Multiple roles of the coagulation protease cascade during virus infection

The coagulation cascade is activated during viral infections. This response may be part of the host defense system to limit spread of the pathogen. However, excessive activation of the coagulation cascade can be deleterious. In fact, inhibition of the tissue factor/factor VIIa complex reduced mortality in a monkey model of Ebola hemorrhagic fever. Other studies showed that incorporation of tissue factor into the envelope of herpes simplex virus increases infection of endothelial cells and mice. Furthermore, binding of factor X to adenovirus serotype 5 enhances infection of hepatocytes but also increases the activation of the innate immune response to the virus. Coagulation proteases activate protease-activated receptors (PARs). Interestingly, we and others found that PAR1 and PAR2 modulate the immune response to viral infection. For instance, PAR1 positively regulates TLR3-dependent expression of the antiviral protein interferon β, whereas PAR2 negatively regulates expression during coxsackievirus group B infection. These studies indicate that the coagulation cascade plays multiple roles during viral infections.

Cytomegalovirus-associated splenic infarcts in an adult immune-competent man: a case report and review of the literature

INTRODUCTION

Cytomegalovirus-associated thrombosis has been extensively reported in the medical literature, mainly in immune-compromised patients. However, the association with splenic infarcts has been rarely mentioned.

CASE PRESENTATION

We report the case of a 38-year-old Caucasian man of Hellenic origin with acute cytomegalovirus infection presenting with spontaneous splenic infarcts. Echocardiography did not show any vegetations or mural thrombi. Anticoagulation treatment was not considered due to implication of minor vessels and since cytomegalovirus was the probable trigger for thrombosis in this patient.

CONCLUSIONS

This case report serves as additional evidence for the role of cytomegalovirus in thrombosis.

Oral microbiota and systemic disease

It is well known that bacteria are the primary cause of infectious diseases, however, evidence is emerging that these organisms are also indirectly responsible for several diseases including cancer and rheumatoid arthritis. The oral cavity is home to several million bacteria that can cause two major diseases-periodontitis and caries. The relationship between periodontopathic bacteria and systemic diseases has been explored for several years. The concept of the oral cavity as a source of distant infection has been debated for at least a century. This review will discuss the historic aspects of the development of the focal infection theory, the reasons for its demise, its re-emergence and current status.

Atherosclerosis and infection: is the jury still not in?

Atherosclerosis is a chronic inflammatory process accounting for increased cardiovascular and cerebrovascular morbidity and mortality. A wealth of recent data has implicated several infectious agents, mainly Chlamydophila pneumoniae, Helicobacter pylori, CMV and periodontal pathogens, in atherosclerosis. Thus, we sought to comprehensively review the available data on the topic, exploring in particular the pathogenetic mechanisms, and discuss anticipated future directions.

Humoral innate immune response and disease

The humoral innate immune response consists of multiple components, including the naturally occurring antibodies (NAb), pentraxins and the complement and contact cascades. As soluble, plasma components, these innate proteins provide key elements in the prevention and control of disease. However, pathogens and cells with altered self proteins utilize multiple humoral components to evade destruction and promote pathogy. Many studies have examined the relationship between humoral immunity and autoimmune disorders. This review focuses on the interactions between the humoral components and their role in promoting the pathogenesis of bacterial and viral infections and chronic diseases such as atherosclerosis and cancer. Understanding the beneficial and detrimental aspects of the individual components and the interactions between proteins which regulate the innate and adaptive response will provide therapeutic targets for subsequent studies.

Herpesviruses enhance fibrin clot lysis

The incorporation of virus- and host-derived procoagulant factors initiates clotting directly on the surface of herpesviruses, which is an explanation for their correlation to vascular disease. The virus exploits the resulting thrombin to enhance infection by modulating the host cell through protease activated receptor (PAR) 1 signalling. Prior reports demonstrated that at least one herpesvirus expresses surface annexin A2 (A2), a cofactor for tissue plasminogen activator (tPA)-dependent activation of plasminogen to plasmin. Since plasmin is both a fibrinolytic protease and PAR agonist, we investigated whether herpesviruses enhance fibrinolysis and the effect of plasmin on cell infection. Herpes simplex virus types 1 (HSV1) and 2, and cytomegalovirus (CMV) purified from various cell lines each accelerated the proteolytic activation of plasminogen to plasmin by tPA. Ligand blots identified A2 as one of several plasminogen binding partners associated with the virus when compared to an A2-deficient virus. This was confirmed with inhibitory A2-antibodies. However, A2 was not required for virus-enhanced plasmin generation. HSV1, HSV2 and CMV accelerated tPA-dependent fibrin clot lysis by up to 2.8-fold. Modest plasmin generation and fibrinolysis was detected independent of exogenous tPA, which was inhibited by plasminogen activator inhibitor type-1 and ε-aminocaproic acid; however, the molecular basis remains speculative. Up to a ~6-fold enhancement of infection was provided by plasmin-mediated cell infection. Inhibitory antibodies revealed that plasmin increased HSV1 infection through a mechanism involving PAR2. Thus, virus-enhanced fibrinolysis may help explain the paradox of the highly procoagulant in vitro herpesvirus surface eliciting only relatively weak independent vascular disease risk.

Detection of human cytomegalovirus and epstein-barr virus in coronary atherosclerotic tissue

Previous studies indicated that patients with atherosclerosis are predominantly infected by human cytomegalovirus (HCMV), but rarely infected by type 1 Epstein-Barr virus (EBV-1). In this study, atheromas of 30 patients who underwent aortocoronary bypass surgery with coronary endartherectomy were tested for the presence of these two viruses. HCMV occurred in 93.3% of the samples and EBV-1 was present in 50% of them. Concurrent presence of both pathogens was detected in 43.3% of the samples.

A key role for Toll-like receptor-3 in disrupting the hemostasis balance on endothelial cells

Various virus infections cause dysfunctional hemostasis and in some instances lead to the development of viral hemorrhagic fever syndrome. How do diverse viruses induce the expression of tissue factor on vascular cells? We hypothesize that a direct stimulation of pattern recognition receptors (PRR) by viral nucleic acids may be the key. Double-stranded RNA (dsRNA) is produced by many viruses and is recognized by various PRR, including Toll-like receptor-3 (TLR3). We have investigated whether poly I:C, a model for viral dsRNA, can influence cellular hemostasis. Poly I:C could up-regulate tissue factor and down-regulate thrombomodulin expression on endothelial cells but not on monocytes. The response to poly I:C was diminished upon small interfering RNA (siRNA)-mediated inhibition of TLR3, but not other PRR. In vivo, application of poly I:C induced similar changes in the aortic endothelium of mice as determined by enface microscopy. D-dimer, a circulating marker for enhanced coagulation and fibrinolysis, and tissue fibrin deposition was elevated. All the hemostasis-related responses to poly I:C, but not cytokine secretion, were blunted in TLR3(-/-) mice. Hence, the activation of TLR3 can induce the procoagulant state in the endothelium, and this could be relevant for understanding the mechanisms of viral stimulation of hemostasis.

Acute respiratory tract infections: a potential trigger for the acute coronary syndrome

Clinical studies suggest that acute respiratory tract infection (ARTI) may be a risk factor for the acute coronary syndrome (ACS). ARTI is associated with an increased risk for ACS up to 2 weeks prior to a cardiac event. The mechanism that may underlie this association is unclear. Infections are thought to play a role in the progression and instability of atherosclerotic plaques, resulting in plaque rupture, sudden constriction, and/or blockage of coronary arteries. Inflammation, endothelial dysfunction and thrombotic activation seem to play an important role in this. Influenza vaccination may reduce the risk of ACS in patients with coronary artery disease. Future studies will provide more information about the underlying mechanisms of infection-related ACS.

Thrombin enhances herpes simplex virus infection of cells involving protease-activated receptor 1

BACKGROUND

We have previously shown that the surface of purified herpes family viruses can initiate thrombin production by expressing host-encoded and virus-encoded procoagulant factors. These enable the virus to bypass the normal cell-regulated mechanisms for initiating coagulation, and provide a link between infection and vascular disease.

OBJECTIVE

In the current study we investigated why these viruses may have evolved to generate thrombin.

METHODS

Using cytolytic viral plaque assays, the current study examines the effect of thrombin on human umbilical vein endothelial cell (HUVEC) or human foreskin fibroblast (HFF) infection by purified herpes simplex virus type 1 (HSV1) and type 2 (HSV2).

RESULTS

Demonstrating that the availability of thrombin is an advantage to the virus, purified thrombin added to serum-free inoculation media resulted in up to a 3-fold enhancement of infection depending on the virus strain and cell type. The effect of thrombin on HUVEC infection was generally greater than its effect on HFF. To illustrate the involvement of thrombin produced during inoculation, hirudin was shown to inhibit the infection of each HSV strain, but only when serum containing clotting factors for thrombin production was present in media. The involvement of protease-activated receptor 1 (PAR1) was supported using PAR1-activating peptides in place of thrombin and PAR1-specific antibodies to inhibit the effects of thrombin.

CONCLUSION

These data show that HSV1 and HSV2 initiate thrombin production to increase the susceptibility of cells to infection through a mechanism involving PAR1-mediated cell modulation.

Herpes simplex virus type 1-encoded glycoprotein C contributes to direct coagulation factor X-virus binding

The HSV1 (herpes simplex virus type 1) surface has been shown recently to initiate blood coagulation by FVIIa (activated Factor VII)-dependent proteolytic activation of FX (Factor X). At least two types of direct FX-HSV1 interactions were suggested by observing that host cell-encoded tissue factor and virus-encoded gC (glycoprotein C) independently enhance FVIIa function on the virus. Using differential sedimentation to separate bound from free 125I-ligand, we report in the present study that, in the presence of Ca2+, FX binds directly to purified wild-type HSV1 with an apparent dissociation constant (K(d)) of 1.5+/-0.4 muM and 206+/-24 sites per virus at saturation. The number of FX-binding sites on gC-deficient virus was reduced to 43+/-5, and the remaining binding had a lower K(d) (0.7+/-0.2 microM), demonstrating an involvement of gC. Engineering gC back into the deficient strain or addition of a truncated soluble recombinant form of gC (sgC), increased the K(d) and the number of binding sites. Consistent with a gC/FX stoichiometry of approximately 1:1, 121+/-6 125I-sgC molecules were found to bind per wild-type HSV1. In the absence of Ca2+, the number of FX-binding sites on the wild-type virus was similar to the gC-deficient strain in the presence of Ca2+. Furthermore, in the absence of Ca2+, direct sgC binding to HSV1 was insignificant, although sgC was observed to inhibit the FX-virus association, suggesting a Ca2+-independent solution-phase FX-sgC interaction. Cumulatively, these data demonstrate that gC constitutes one type of direct FX-HSV1 interaction, possibly providing a molecular basis for clinical correlations between recurrent infection and vascular pathology.

The role of viruses in cardiac allograft vasculopathy

Considerable evidence suggests a role for viruses in transplant arteriosclerosis (TA), including observational data, experimental models and therapeutic trials implicating human cytomegalovirus (HCMV) in the progression to TA. In pediatric heart transplant patients, adenoviral genome in endomyocardial biopsies (EMB) is an important predictor of TA and graft loss. During CMV viremia, EMBs from adult patients demonstrate endothelialitis and vascular smooth muscle cell proliferation. These changes are predictors of subsequent diffuse TA. HCMV immediate early proteins (IE-1 and IE-2) increase the constitutive expression of intercellular adhesion molecule-1 (ICAM-1) independent of other intracellular cytokines. Likewise, viral chemokines such as US28 have been implicated in vascular disease because of their ability to induce smooth muscle cell migration. Recent data suggests that CMV might accelerate TA through its ability to abrogate the vascular protective effects of the endothelium-derived nitric oxide system (eNOS). Confirmation of causality requires clinical trials demonstrating that antiviral agents such as ganciclovir inhibit TA. Such studies in patients though limited to retrospective analyses, suggest that ganciclovir prophylaxis early after heart transplantation reduces the risk of TA. These observations emphasize the need for randomized controlled clinical trials to confirm a causal role for CMV (and other viruses) in TA.

Coagulation dysfunction in sepsis and multiple organ system failure

In patients diagnosed with sepsis, severe sepsis or septic shock, cytokine-mediated endothelial injury, and TF activation initiate a cascade of events that culminate in the development of coagulation dysfunction characterized as procoagulant and antifibrinolytic. This abnormal state predisposes the patient to develop microvascular thrombosis, tissue ischemia, and organ hypoperfusion. Multiple organ dysfunction syndrome may be a product of this pertubation in coagulation regulation. Treatments aimed at correcting this coagulation dysfunction have met with mixed success. Current data suggest that AT III replacement therapy has limited efficacy in adults with severe sepsis. In contrast, adult patients diagnosed with severe sepsis and organ failure and treated with aPC (drotrecogin alfa activate) have a significantly reduced risk of death when compared with placebo-treated patients. A phase III trial examining the efficacy of protein C replacement therapy in pediatric patients with severe sepsis and organ failure is underway.

Genetic Polymorphisms in Cytokine and Adhesion Molecule Genes in Coronary Artery Disease

Both inflammation and genetics play an important role in the pathogenesis of atherosclerosis and coronary artery disease. Epidemiological studies have investigated the association between coronary artery disease (CAD) and gene polymorphisms of the inflammatory molecules tumor necrosis factors (TNF) alpha and beta, transforming growth factors (TGF) beta-1 and beta-2, interleukin (IL)-1 and its receptor antagonist (IL-1ra), CD14 (the receptor for lipopolysaccharide), P- and E-selectins, and platelet endothelial cell adhesion molecule (PECAM)-1. Current evidence suggests that the TNF polymorphisms explored so far are not linked to CAD. The majority of studies conducted showed no significant association between TGFbeta-1 and coronary atherosclerosis, but the data currently available are somewhat controversial. Some polymorphisms may increase the risk of myocardial infarction (MI) within specific ethnic groups or in certain populations. The association between the IL-1 system and atherosclerosis is complex and may vary as a result of a number of factors, such as stage of disease, clinical phenotype, and possibly population characteristics. The E-selectin gene (SELE) Arg128, 98T, and Phe554 alleles may increase the risk of atherosclerosis, but not necessarily the risk of MI. This association seems to be more pronounced in younger patients. The PECAM1 Leu125Val and Ser563Asn polymorphisms may increase the risk of atherosclerosis but not necessarily of MI. This association may be especially important in patients with a low risk for developing atherosclerosis. Current data indicate that screening for CD14-260C/T genotypes is unlikely to be a useful tool for risk assessment and it remains unclear whether CD14 polymorphisms significantly increase the risk of MI. The associations between candidate gene polymorphisms and CAD are complex as a consequence of pleiotropy, variations with age, selection due to the high lethality of the disease, and interactions with other genes and environmental factors. Nonetheless, although the current data is preliminary and partly conflicting, it does provide some evidence that alterations in the genetics of the inflammatory system may modify the risk of CAD.

Influenza A and B IgG seropositivity and coronary atherosclerosis assessed by angiography

Infectious agents, in particular intracellular pathogens that can establish long-term, persistent seropositivity, may play an important role in atherogenesis. The possible association between influenza type A and B infection and angiographically proven coronary artery disease (CAD) and the effect of the aggregate pathogen burden on CAD was studied by testing blood from 218 patients undergoing coronary angiography for serum IgG antibodies to influenza A and B, and for antibodies to four other pathogens (hepatitis A, Chlamydia pneumoniae, Helicobacter pylori, and cytomegalovirus). This analysis demonstrates that although influenza (A and B) seropositivity represents no predictor of risk for CAD, infectious burden is independently associated with coronary atherosclerosis.

Chronic infections and atherosclerosis

The inability of traditional risk factors such as hypercholesterolemia, hypertension, and smoking to explain the incidence of atherosclerosis (AT) in about 50% of the cases prompted a search for additional putative risk factors involved in the development of the disease. Infectious agents have long been suspected to initiate/contribute to the process of AT. It has also been suggested that inflammation, either related to infectious agents or independent from infection, may mediate the atherogenic process [1, 2].

Predisposition to atherosclerosis by infections: role of endothelial dysfunction

BACKGROUND

Several microorganisms have been implicated in the pathogenesis of atherosclerosis. We hypothesized that infections may predispose to atherosclerosis by inflicting endothelial injury.

METHODS AND RESULTS

Of 375 patients undergoing coronary angiography, 218 had assessment of endothelial function using intracoronary acetylcholine (ACH) and of endothelium-independent function with sodium nitroprusside and adenosine. Immunoglobulin-G antibody titers to cytomegalovirus, Chlamydia pneumoniae, Helicobacter pylori, hepatitis A virus, and herpes simplex virus-1 were measured. Pathogen burden was defined as the number of positive antibodies. Although positive serology to individual pathogens tended to be associated with increased incidence of coronary arteriosclerosis (CAD), the pathogen burden correlated with the presence of CAD, even after adjustment for risk factors (OR 1.3; 95% CI, 1.05 to 1.6, P=0.018). Moreover, the severity of CAD was independently associated with the pathogen burden (P=0.001). Pathogen burden was an independent predictor of endothelial dysfunction, determined as the percent change in coronary vascular resistance in response to ACH (P=0.009) but not the responses to sodium nitroprusside or adenosine. Pathogen burden was also an independent determinant of endothelial function in the subgroup with angiographically normal coronary arteries.

CONCLUSIONS

The immunoglobulin-G antibody response to multiple pathogens (pathogen burden) is an independent risk factor for endothelial dysfunction and the presence and severity of CAD. Endothelial dysfunction provides the crucial link by which pathogens may contribute to atherogenesis.

Infections and their role in atherosclerotic vascular disease

BACKGROUND

Complications of atherosclerosis are the leading cause of mortality in developed countries, and infections may play a role in the pathogenesis. Numerous studies have addressed this issue in the past decade.

TYPES OF STUDIES REVIEWED

The author examined peer-reviewed studies and reviews on the role of microbes or infections in atherosclerosis, cardiovascular disease and cerebrovascular disease. He included selected articles on epidemiology, pathology, in vitro experiments, animal models and clinical studies.

RESULTS

Cross-sectional and retrospective studies have shown an association between Chlamydia pneumoniae antibodies and cardiovascular disease, but prospective studies have not been as convincing. Studies on the association between cardiovascular disease and periodontal disease or loss of teeth have produced conflicting results. Cytomegalovirus infection is associated mainly with accelerated arteriosclerosis after cardiac transplantation. Infectious agents can induce biological mechanisms important for atherogenesis. Mice and rabbit studies have indicated that C. pneumoniae is capable of initiating or accelerating the progression of atherosclerosis. Limited studies on cytomegalovirus also suggest the ability to induce early changes of atherosclerosis in a rodent model. Preliminary clinical trials of treatment for C. pneumoniae infection suggest a possible short-term benefit, but larger randomized trials for longer periods are in progress.

CONCLUSION AND CLINICAL IMPLICATIONS

Infectious agents may play an important role in atherogenesis, but currently the jury is not in. Further management of cardiovascular disease could change radically if this concept were proven.

Endothelium: interface between coagulation and inflammation

OBJECTIVE

To review the involvement of endothelial cells in the pathogenesis of coagulation abnormalities during severe infection, the differential role of proinflammatory cytokines in these mechanisms, and the cross talk between coagulation and inflammation.

DATA SOURCES

Published articles on experimental studies of coagulation activation during inflammation and clinical studies of patients with sepsis and associated hemostatic abnormalities.

DATA SYNTHESIS AND CONCLUSION

The endothelium plays a central role in all major pathways involved in the pathogenesis of the hemostatic derangement observed during severe inflammation (i.e., initiation and regulation of thrombin generation and inhibition of fibrinolysis). Rather than being a unidirectional relationship, the interaction between inflammation and coagulation involves significant cross talk in which the endothelium seems to play a pivotal role.

Pseudorabies virus (PRV) is protected from complement attack by cellular factors and glycoprotein C (gC)

Swine kidney derived CPK cells were resistant to swine complement attack in vitro while rabbit kidney derived RK13 cells were destroyed by swine complement. To rabbit complement, RK13 cells were resistant but CPK cells were sensitive. This phenomenon was known as homologous restriction (Proc. Natl. Acad. Sci. USA 78 (1981) 5118). The gC deletion mutant of pseudorabies virus (PRVdlgC) grown in CPK cells was resistant to swine complement while the same virus grown in RK13 cells was neutralized by swine complement. PRVdlgC grown in RK13 cells was more resistant to rabbit complement than the virus grown in CPK cells. Hence, the sensitivity of PRVdlgC to swine or rabbit complement was similar to that of the cells in which the virus was grown. It would appear that cell derived factors were present on the virion and they were protective against homologous complement but not against heterologous complement. The expression of gC rendered PRV more resistant to swine or rabbit complement, but the protective effect of gC was much less than that of cell derived factors. The best protection against complement was obtained when gC and cell derived factors were coexistent on the virion.

Herpesvirus (HSV-1, EBV and CMV) infections in atherosclerotic compared with non-atherosclerotic aortic tissue

The viral nucleic acid of herpes simplex virus type 1 (HSV-1), Epstein-Barr virus (EBV) and cytomegalovirus (CMV) was studied by polymerase chain reaction (PCR), Southern blotting and in situ hybridization (ISH) in aortic tissues from 33 autopsies. In 23 cases involving persons who ranged from 23 weeks to 75 years of age at the time of death, the tissue was histologically non-atherosclerotic. Of these 23, aortic tissues tested positive for HSV-1 in 13%, for EBV in 13% and for CMV in 4%. In the other 10 cases involving persons who were 53-75 years old at death, atherosclerotic aortic tissue tested positive for HSV-1 in 80%, for EBV in 80% and for CMV in 40%. Neither double nor triple infections occurred in the non-atherosclerotic group, whereas six of 10 were positive for two viruses, and two of 10 were positive for three viruses in the atherosclerotic group. By in situ hybridization, the viruses were localized in cells morphologically consistent with endothelial cells and smooth muscle cells. We detected HSV-1, EBV and CMV DNA in cells in the upper portion of the non-atherosclerotic aortic wall, whereas viral DNA was detected more extensively in atherosclerotic lesions than in non-atherosclerotic tissue. We also are the first to show the existence of EBV DNA in the human aortic wall. In conclusion, we suggest that the high incidence and kinds of herpesviruses are related to the high incidence of atherosclerosis.

Infection of Endothelium With E1 − E4 + , but Not E1 − E4 − , Adenovirus Gene Transfer Vectors Enhances Leukocyte Adhesion and Migration by Modulation of ICAM-1, VCAM-1, CD34, and Chemokine Expression

Abstract —Intravascular introduction of replication-deficient adenoviral vectors (Advectors) provides an ideal model of delivery of transgenes for the treatment of various vascular abnormalities. On the basis of the knowledge that Advectors can induce inflammatory responses after intravascular administration, we speculated that cellular activation by Advector infection could directly modulate the endothelial cell (EC) adhesion molecule/chemokine expression repertoire. Infection of human umbilical vein ECs or bone marrow microvascular ECs with an E1 − E4 + Advector resulted in the upregulation of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and CD34, but not E-selectin, P-selectin, CD36, CD13, CD44, HLA-DR or PECAM. Upregulation of ICAM-1, VCAM-1, and CD34 was apparent 12 hours after infection and persisted for weeks after infection. Selective induction of adhesion molecules was mediated by the presence of the E4 gene in the Advector, because infection of ECs with an E1 − E4 − Advector had no effect on adhesion molecule expression. ECs infected with E1 − E4 + Advector, but not those infected with E1 − E4 − Advector, supported the adhesion of leukocytes. Monoclonal antibodies to ICAM-1 and VCAM-1 inhibited adhesion of leukocytes to E1 − E4 + -infected ECs. Infection of the ECs with E1 − E4 + Advector, but not E1 − E4 − Advector, resulted in downregulation of expression of chemocytokines, including interleukin-8, MCP-1, RANTES, and GM-CSF. Nonetheless, a large number of leukocytes migrated through ECs infected with E1 − E4 + , but not those infected with E1 − E4 l− , in response to exogenous chemokines. These results demonstrate that infection of ECs with E1 − E4 + Advectors, but not E1 − E4 − Advectors, may directly augment inflammatory responses by upregulating expression of adhesion molecules and enhancing migration through Advector-infected ECs and suggest that E1 − E4 − Advectors may be a better choice for gene-transfer strategies directed to the ECs.

Acute cytomegalovirus infection complicated by vascular thrombosis: a case report

We present a case report of a previously healthy adult with cytomegalovirus infection that was complicated by extensive mesenteric arterial and venous thrombosis. To our knowledge, this is the first reported case of this syndrome in an immunocompetent individual who had no predisposing risk factors for thrombosis, and it demonstrates the propensity for cytomegalovirus to be involved in vascular disease.

Association of influenza vaccination and reduced risk of recurrent myocardial infarction

BACKGROUND

Numerous studies have suggested that microbial agents may promote atherosclerosis. A smaller body of research has suggested that acute respiratory infection may be a risk factor for myocardial infarction (MI). We hypothesized that influenza vaccine might reduce the risk of recurrent MI in patients with documented coronary heart disease (CHD).

METHODS AND RESULTS

A case-control study was performed on 218 CHD patients seen at Memorial Hermann Hospital during the influenza season of October 1997 through March 1998. Patients who experienced new MI were included in the case group, and those who did not experience new MI or unstable angina were assigned to the control group. Data were collected by structured review of patients' charts and through a subsequent telephone survey. Adjusted for history of influenza vaccination in previous years, multivariate logistic regression revealed risk of MI to be associated with current hypertension (OR 4.96, 95% CI 2.06 to 11.96, P<0.0001), hypercholesterolemia (OR 4.08, 95% CI 1.67 to 9.99, P=0.002), smoking (OR 3.75, 95% CI 1.76 to 7.98, P=0.001), and influenza vaccination (OR 0.33, 95% CI 0.13 to 0.82, P=0.017). Despite significant association in univariate analysis, multivitamin therapy and physical exercise were not associated with risk of reinfarction in multivariate analysis.

CONCLUSIONS

In this study in patients with chronic CHD, vaccination against influenza was negatively associated with the development of new MI during the same influenza season. However, to address causal inference, examination of prospective data sets will be needed.

Infection and atherosclerosis: potential roles of pathogen burden and molecular mimicry

Infection has been implicated as a cause of atherosclerosis since the first half of the 19th century. Over the years, sporadic publications have appeared in the literature reflecting a persistent but relatively low level of research activity in this area. In the last decade, however, publications relating to this topic have increased markedly. And very recently, new epidemiological and mechanistic data relating infection to several different diseases, including atherosclerosis, have appeared, stimulating the emergence of important paradigm shifts in how we think about the causes of chronic disease. The following article reviews some of these newer concepts as they relate to a possible role of infection in atherosclerosis.

Vascular protease receptors: integrating haemostasis and endothelial cell functions

The endothelium plays a crucial dynamic role as a protective interface between blood and the underlying tissues during the haemostatic process, which maintains blood flow in the circulation and prevents life-threatening blood loss. Following vessel wall injury with initial platelet adhesion and aggregation to exposed subendothelial extracellular matrix, the initiation, amplification, and control of haemostasis depend on structurally unrelated membrane-associated receptors for blood coagulation proteases including tissue factor, G-protein-coupled protease-activatable receptors, thrombomodulin, and protein C receptor, respectively. In addition to their regulatory role in haemostasis, the respective (pro-)enzyme ligands such as Factors VIIa and Xa, thrombin or protein C mediate specific signalling pathways in vascular cells related to migration, proliferation or adhesion. The functional importance of these receptors beyond haemostasis has been manifested by various lethal and pathological phenotypes in knock-out mice. These protease receptors thereby provide important molecular links in the vascular system and serve to integrate haemostasis with endothelial cell functions which are relevant for the (patho-)physiological responses to injury or inflammatory challenges.

Cytomegalovirus infection of rats increases the neointimal response to vascular injury without consistent evidence of direct infection of the vascular wall

BACKGROUND

Previous studies suggest that infection may play a role in restenosis and atherogenesis; cytomegalovirus (CMV) is one of the implicated pathogens. To determine a potential causal role of CMV in these disease processes, we assessed whether CMV infection increases the neointimal response to injury of the rat carotid artery.

METHODS AND RESULTS

Carotid injury was performed on 60 rats; immediately thereafter, 30 rats were infected with rat CMV, and the other 30 were mock-infected. Six weeks later, rats were euthanized, and the salivary glands, spleen, and carotid arteries were harvested. CMV infection was associated with significant exacerbation of the neointimal response to injury (neointimal to medial ratio 0.81+/-0. 59 versus 0.31+/-0.38 in CMV-infected versus control rats; P<0.0001). This occurred despite absence of infectious virus from vascular tissues and detection of CMV DNA by polymerase chain reaction in the injured artery only at day 3 after infection. Persistent distant infection, associated with systemic cytokine response, was evidenced by isolation of infectious virus from homogenates of both salivary glands and spleen and by higher serum levels of interleukin (IL)-2 and IL-4 (but not interferon-gamma and tumor necrosis factor-alpha) in infected versus noninfected rats.

CONCLUSIONS

CMV infection of immunocompetent adult rats increases the neointimal response to vascular injury, suggesting that CMV may play a causal role in atherosclerosis/restenosis. Importantly, this CMV-induced response occurs even without the presence of virus in the vascular wall, suggesting that inflammatory and immune responses to infection of nonvascular tissues may contribute to the vascular response to injury.

Endothelial cell function and thrombosis

The endothelium is pivotal in the control of haemostasis and thrombosis because it is the primary source of many of the major haemostatic regulatory molecules. Healthy endothelial cells, unlike extravascular cells, are anticoagulant and antithrombotic. This is due to the regulated secretion of antiplatelet agents, including prostacyclin and nitric oxide. Following vessel injury, platelet adhesion to exposed matrix requires von Willebrand Factor, another endothelial cell product. Local generation of thrombin causes a series of receptor-mediated endothelial cell functional responses, while the surface of the endothelium is additionally the site for inactivation of thrombin by antithrombin, and its conversion to a coagulation inhibitor by interaction with thrombomodulin. Endothelial cells are also the source of circulating tissue-type plasminogen activator and its inhibitor, and Tissue Factor pathway inhibitor. In disease states, many of these endothelial cell properties are perturbed towards a more procoagulant and prothrombotic phenotype.

Herpesviruses and thrombosis: activation of coagulation on the endothelium

Vascular injury is an initiating event in the development of atherosclerosis and herpesviruses have been proposed as potential mediators of vascular injury. The demonstration that an avian herpesvirus could induce atherosclerosis in chickens [Fabricant CG, Fabricant J, Litrenta MM, Minick CR. Virus induced atherosclerosis. J Exp Med 1978;148:335-340; Fabricant CG, Fabricant J, Minick CR, Litrenta MM. Herpes virus induced atherosclerosis in chickens. Fed Proc 1983;42:2476-2479; Minick CR, Fabricant CG, Fabricant J, Litrenta MM. Atheroarteriosclerosis induced by infection by herpesvirus. Am J Pathol 1978;96:673-706] suggested the potential of these viral agents to cause similar lesions in humans. In addition, epidemiological evidence linking herpesvirus infection and atherosclerosis [Cunningham MJ, Pasternak RC. The potential role of viruses in the pathogenesis of atherosclerosis. Circulation 1988;77:964-996; Melnick JL, Adam E, DeBakey ME. Cytomegalovirus and atherosclerosis. BioEssays 1995;17:899-903; Adam E, Melnick JL, Probesfield JL et al. High levels of cytomegalovirus antibody in patients requiring vascular surgery for atherosclerosis. Lancet 1987;2:291-293] adds further credence to their role as possible etiologic agents. However, the link between herpesviruses and vascular thrombosis is more tenuous. In this review, we highlight some recent advances in this field, from our laboratory and others, to support the hypothesis that herpesviruses act as prothrombotic agents by activating the coagulation cascade.

Infection and atherosclerosis: emerging mechanistic paradigms

Although definitive proof of a causal role of infection contributing to atherogenesis is lacking, multiple investigations have demonstrated that infectious agents evoke cellular and molecular changes supportive of such a role. Moreover, both Chlamydia pneumoniae and cytomegalovirus exacerbate lesion development in animal models of atherosclerosis and restenosis. The fact that multiple pathogens have been associated with atherosclerosis implies that many "atherogenic" pathogens exist, and recent data suggest that the risk of atherosclerosis conveyed by infection relates to the number of atherogenic pathogens with which an individual is infected. It also is evident that variability in host susceptibility to the atherogenic effects of pathogens exists; this variability appears to be related at least in part to whether the host can generate an immune response that successfully controls pathogen inflammatory activity and in part to the specific pattern of immune response--humoral or cellular. The latter may relate to host capacity to control pathogen activity and to a pathogen-induced autoimmune component of the atherogenic process. Additional animal and human studies are necessary to further test the validity of the infection/atherosclerosis link and to provide more insight into the mechanisms by which infection may contribute to atherosclerosis, information critical for devising strategies to reduce or eliminate any contribution to atherosclerosis caused by infection.

Impact of neuroendocrine activation on coronary artery disease

Several independent predictors of the risk of atherosclerosis are known including plasma cholesterol concentration, cigarette smoking, elevated blood pressure, as well as genetic factors such as non-insulin-dependent diabetes and plasma fibrinogen. Also known are the 3 major elements of the pathogenesis of atherosclerosis, involving modification of endothelial function, changes in vascular tone, and clinical sequelae of hyperplasia of smooth muscle cells in the intima of the affected blood vessels. This article further examines vasoconstrictor/vasodilator balance, the role of angiotensin II, and the significant role played by the endothelium in the complex events and interactions that occur both with smooth muscle cells and platelets. Clinical evidence of endothelial dysfunction in coronary artery disease is presented. The importance of the association of the progression of coronary artery disease with signs of neuroendocrine activation, the relation of endothelin-1 to mechanisms of neuroendocrine activation, and how the counteraction of this activation may have beneficial effects on disease progression are discussed.