Identification of a monocyte receptor on herpesvirus-infected endothelial cells

Comprehensive analysis of liquid-liquid phase separation propensities of HSV-1 proteins and their interaction with host factors

In recent years, it has been shown that the liquid-liquid phase separation (LLPS) of virus proteins plays a crucial role in their life cycle. It promotes the formation of viral replication organelles, concentrating viral components for efficient replication and facilitates the assembly of viral particles. LLPS has emerged as a crucial process in the replication and assembly of herpes simplex virus-1 (HSV-1). Recent studies have identified several HSV-1 proteins involved in LLPS, including the myristylated tegument protein UL11 and infected cell protein 4; however, a complete proteome-level understanding of the LLPS-prone HSV-1 proteins is not available. We provide a comprehensive analysis of the HSV-1 proteome and explore the potential of its proteins to undergo LLPS. By integrating sequence analysis, prediction algorithms and an array of tools and servers, we identified 10 HSV-1 proteins that exhibit high LLPS potential. By analysing the amino acid sequences of the LLPS-prone proteins, we identified specific sequence motifs and enriched amino acid residues commonly found in LLPS-prone regions. Our findings reveal a diverse range of LLPS-prone proteins within the HSV-1, which are involved in critical viral processes such as replication, transcriptional regulation and assembly of viral particles. This suggests that LLPS might play a crucial role in facilitating the formation of specialized viral replication compartments and the assembly of HSV-1 virion. The identification of LLPS-prone proteins in HSV-1 opens up new avenues for understanding the molecular mechanisms underlying viral pathogenesis. Our work provides valuable insights into the LLPS landscape of HSV-1, highlighting potential targets for further experimental validation and enhancing our understanding of viral replication and pathogenesis.

Monocyte Recruitment for Vascular Tissue Regeneration

A strategy to recruit monocytes (MCs) from blood to regenerate vascular tissue from unseeded (cell-free) tissue engineered vascular grafts is presented. When immobilized on the surface of vascular grafts, the fusion protein, H2R5 can capture blood-derived MC under static or flow conditions in a shear stress dependent manner. The bound MC turns into macrophages (Mϕ) expressing both M1 and M2 phenotype specific genes. When H2R5 functionalized acellular-tissue engineered vessels (A-TEVs) are implanted into the mouse aorta, they remain patent and form a continuous endothelium expressing both endothelial cell (EC) and MC specific proteins. Underneath the EC layer, multiple cells layers are formed coexpressing both smooth muscle cell (SMC) and MC specific markers. Lineage tracing analysis using a novel CX3CR1-confetti mouse model demonstrates that fluorescently labeled MC populates the graft lumen by two and four weeks postimplantation, providing direct evidence in support of MC/Mϕ recruitment to the graft lumen. Given their abundance in the blood, circulating MCs may be a great source of cells that contribute directly to the endothelialization and vascular wall formation of acellular vascular grafts under the right chemical and biomechanical cues.

COVID-19 and the heart

An outbreak of coronavirus disease 2019 (COVID-19) occurred in December 2019 due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is a strain of SARS-CoV. Patients infected with the virus present a wide spectrum of manifestations ranging from mild flu-like symptoms, cough, fever and fatigue to severe lung injury, appearing as bilateral interstitial pneumonia or acute respiratory failure. Although SARS-CoV-2 infection predominantly offends the respiratory system, it has been associated with several cardiovascular complications as well. For example, patients with COVID-19 may either develop type 2 myocardial infarction due to myocardial oxygen demand and supply imbalance or acute coronary syndrome resulting from excessive inflammatory response to the primary infection. The incidence of COVID-19 related myocarditis is estimated to be accountable for an average of 7% of all COVID-19 related fatal cases, whereas heart failure (HF) may develop due to infiltration of the heart by inflammatory cells, destructive action of pro-inflammatory cytokines, micro-thrombosis and new onset or aggravated endothelial and respiratory failure. Lastly, SARS-CoV-2 can engender arrhythmias through direct myocardial damage causing acute myocarditis or through HF decompensation or secondary, through respiratory failure or severe respiratory distress syndrome. In this comprehensive review we summarize the COVID-19 related cardiovascular complications (acute coronary syndromes, myocarditis, HF, arrhythmias) and discuss the main underlying pathophysiological mechanisms.

Viral infection and atherosclerosis

Several risk factors have been described for the pathogenesis of atherosclerosis. Infectious diseases are suggested to be a causative factor, and some viruses have been studied for their relation with atherosclerotic diseases. Studies report two hypotheses, direct and indirect effects, for the role of viral infections in atherogenesis. Viruses are able to initiate atherosclerosis by two different pathways. They can exert their direct effects on atherogenesis by infecting vascular cells and then inducing inflammation in the endothelium and smooth muscle cells. Alternatively, they can also apply indirect effects by infecting non-vascular cells and inducing systemic inflammation. In this review, we consider the available data about the effects and correlations of DNA and RNA viruses on atherosclerosis.

Herpes Simplex Virus Type 1 and Type 2 Infection Increases Atherosclerosis Risk: Evidence Based on a Meta-Analysis

Objective. The aim of our study was to evaluate the relation of herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) infection with the risk of atherosclerosis (AS). Methods. A systematic literature search was performed through three electronic databases. The pooled odds ratio (OR) and corresponding 95% confidence interval (CI) were used to assess the effect of HSV-1 and HSV-2 infection on AS risk. Results. 17 studies were available for meta-analysis of HSV-1 infection and AS risk and seven studies for meta-analysis of HSV-2 infection and AS risk. Subjects exposed to HSV-1 infection exhibited an increased risk of AS (OR = 1.77; 95% CI: 1.40-2.23; P < 0.001). And consistent elevated AS risks for HSV-1 positive subjects were found in all subgroup analysis of disease type, region, male proportion, and age. HSV-2 positive subjects demonstrated significantly increased AS risk (OR = 1.37; 95% CI: 1.13-1.67; P < 0.005). In subgroup analysis, elevated AS risks were only observed in myocardial ischemia group, male proportion >60% group, and age ≤60-year-old group. Conclusion. Our meta-analysis indicated that HSV-1 and HSV-2 infection could increase the risk of contracting AS.

Increased erythrocyte adhesion to VCAM-1 during pulsatile flow: Application of a microfluidic flow adhesion bioassay

Sickle cell disease (SCD) is characterized by microvascular occlusion mediated by adhesive interactions of sickle erythrocytes (SSRBCs) to the endothelium. Most in vitro flow adhesion assays measure SSRBC adhesion during continuous flow, although in vivo SSRBC adhesive interactions occur during pulsatile flow. Using a well-plate microfluidic flow adhesion system, we demonstrate that isolated SSRBCs adhere to vascular cell adhesion molecule (VCAM-1) at greater levels during pulsatile versus continuous flow. A significant increase in adhesive interactions was observed between all pulse frequencies 1 Hz to 2 Hz (60-120 beats/min) when compared to non-pulsatile flow. Adhesion of isolated SSRBCs and whole blood during pulsatile flow was unaffected by protein kinase A (PKA) inhibition, and exposure of SSRBCs to pulsatile flow did not affect the intrinsic adhesive properties of SSRBCs. The cell type responsible for increased adhesion of whole blood varied from patient to patient. We conclude that low flow periods of the pulse cycle allow more adhesive interactions between sickle erythrocytes and VCAM-1, and sickle erythrocyte adhesion in the context of whole blood may better reflect physiologic cellular interactions. The microfluidic flow adhesion bioassay used in this study may have applications for clinical assessment of sickle erythrocyte adhesion during pulsatile flow.

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 cellular response to herpes simplex virus type 1 (HSV-1) during latency and reactivation

In order to learn more about the cellular response to viral gene activity during latency and reactivation of herpes simplex virus type 1 (HSV-1), the authors have employed microarray analysis. On an array of about 1200 cellular genes, approximately 56 genes were found to be differentially regulated in infected trigeminal ganglia of mice, compared to uninfected mice, during latency and reactivation. Of these genes, 10 were examined more closely using quantitative real-time polymerase chain reaction (PCR) to confirm the microarray results. Genes involved in interferon and other signaling pathways appeared to predominate in response to a latent or reactivating HSV infection. Interestingly, some genes found to be differentially regulated in latently infected ganglia are neuronal-specific genes (pro-opiomelanocortinin; zinc finger proteins of the cerebellum 1 and 2). During reactivation, the involvement of several cell signaling molecules that may be important for the initiation of an HSV infection was observed, including various receptors and molecules involved in cell-cell spread.

The mechanisms by which infectious agents may contribute to atherosclerosis and its clinical manifestations

Three infectious agents have recently gained considerable interest as potential pathogens in atherosclerosis and in its clinical manifestations: herpes simplex virus, cytomegalovirus, and Chlamydia pneumoniae. Chronic and often asymptomatic infections with these agents occur widely in the general population. These pathogens may affect atherosclerosis either directly or indirectly. Direct effects on vascular wall cells might include cell lysis, transformation, lipid accumulation, proinflammatory changes, and augmentation of procoagulant activity. Indirect systemic effects may involve induction of acute-phase proteins, establishment of a prothrombotic state, hemodynamic stress caused by tachycardia, increased cardiac output, or a regional inflammatory activation in response to systemic endotoxemia and cytokinemia. The effects of microbial infection, usually in combination with other risk factors (for example, smoking, hyperlipidemia, family history), might promote atherogenesis and eventually trigger acute coronary events.

Herpes Simplex Virus 1 Induced LOX-1 Expression in an Endothelial Cell Line, ECV 304

Infections, such as by Chlamydophilia pneumoniae, cytomegalovirus, herpes simplex virus, and Helicobacter pylori, have been shown to be involved in atherogenesis. Herpes simplex virus I (HSV-1) could infect vascular endothelial cells, and it has been shown that, when endothelial cells were activated with oxidized LDL (oxLDL), a number of cellular events are occurred, leading to endothelial cell dysfunction. Since LOX-1 is a major receptor for oxLDL on endothelial cells and its expression was increased in atherosclerosis, we investigated whether HSV1 infection can lead to the increase expression of LOX-1 in endothelial cells. LOX-1 mRNA expression determined by RT-PCR and LOX-1 promoter activity measured by luciferase assay were increased in endothelial cells following HSV-1 infection. This suggests that one of the mechanisms by which HSV-1 is involved in atherogenesis maybe the enhanced uptake of oxLDL via the increased expression of LOX-1 in endothelial cells.

Homocysteine increases monocyte and T-cell adhesion to human aortic endothelial cells

Although hyperhomocysteinemia has been recognized as an independent risk factor for atherosclerosis, its mechanism(s) are not well understood. Because chemotaxis and accumulation of leukocytes such as monocytes and T cells have been demonstrated to be critical events in the initiation and development of atherosclerosis, we investigated the effect of homocysteine (HCY) on U937 monocytic cells- and Jurkat T-cell-human aortic endothelial cell (HAEC) interactions under inflammatory cytokine-stimulated conditions. When HAEC were pretreated with HCY followed by stimulation with IL-1 beta, U937 and Jurkat T-cell adhesion to HAEC increased in a dose-dependent manner. The significant increase in U937 cell adhesion to HAEC was also observed when U937 cells were treated with HCY or when both cell types were treated with HCY. We also demonstrated that HCY increases endothelial surface expression and mRNA level of adhesion molecules, VCAM-1 and E-selectin. Attenuation of Jurkat T-cell and U937 cell adhesion to HAEC by monoclonal antibodies directed to specific adhesion molecules demonstrated that both VCAM-1 and E-selectin are involved in Jurkat T-cell adhesion, and VCAM-1 in U937 cell adhesion. Supplementation of HAEC with vitamin E was effective in preventing HCY-stimulated Jurkat T-cell adhesion and VCAM-1 and E-selectin expression in HAEC. These results indicate that HCY-mediated leukocyte-endothelial cell interaction is one potential mechanism by which homocysteinemia may lead to the development of atherosclerosis under inflammatory conditions. Dietary antioxidants such as vitamin E may attenuate HCY-stimulated activation of the endothelium and may help reduce the risk of vascular disease associated with hyperhomocysteinemia.

Effect of plasma metabolites of (+)-catechin and quercetin on monocyte adhesion to human aortic endothelial cells

BACKGROUND

Flavonoids may exert their health benefit in cardiovascular disease by modulating monocyte adhesion in the inflammatory process of atherosclerosis. Most in vitro studies used forms of flavonoids present in food rather than forms that appear in plasma after ingestion.

OBJECTIVES

We tested the effects of plasma metabolites of (+)-catechin and quercetin on the modulation of monocyte adhesion to human aortic endothelial cells (HAEC) and on the production of reactive oxygen species (ROS).

DESIGN

Plasma extracts of flavonoid metabolites were prepared after intragastric administration of pure compounds to rats. The plasma preparations contained sulfate or glucuronide conjugates or both and methylated forms. We measured adhesion of U937 monocytic cells to HAEC and the production of ROS in HAEC when cells were pretreated with either pure compounds or plasma extracts from control or treated rats. Adhesion assays were performed with HAEC stimulated with interleukin (IL)-1 beta or U937 cells activated with phorbol myristyl acetate; ROS were measured after challenging HAEC with IL-1 beta or hydrogen peroxide.

RESULTS

Pretreatment of HAEC with (+)-catechin metabolites inhibited U937 cell adhesion to IL-1 beta-stimulated cells, whereas pretreatment with intact (+)-catechin had no effect. Generation of ROS in hydrogen peroxide-stimulated HAEC was inhibited by (+)-catechin, its metabolites, and control plasma extract, whereas ROS generation in IL-1 beta-stimulated HAEC was inhibited by (+)-catechin metabolites only. In contrast, quercetin inhibited U937 cell adhesion to IL-1 beta-stimulated HAEC, whereas its metabolites were not effective.

CONCLUSIONS

Metabolic conversion of flavonoids such as (+)-catechin and quercetin modifies the flavonoids' biological activity. Metabolites of flavonoids, rather than their intact forms, may contribute to the reported effects of flavonoids on reducing the risk of cardiovascular disease.

Disordered regulation of coagulation and platelet activation in xenotransplantation

Rejection of xenografts is associated with vascular-based inflammation, thrombocytopenia and the consumption of coagulation factors that may evolve into disseminated intravascular coagulation (DIC). Similarly, bone marrow-derived cellular xenotransplantation procedures are associated with endothelial cell activation and thrombotic microangiopathic injury. These complications generally develop despite the best available measures for depletion of xenoreactive natural antibody, inhibition of complement activation and suppression of T- and B-cell mediated immune responses. The mechanisms underlying the DIC and thrombotic microangiopathy associated with xenotransplantation are unclear. A proposed primary biological dysfunction of xenografts with respect to regulation of clotting could amplify vascular injury, promote immunological responses and independently contribute to graft failure. Disordered thromboregulation could have deleterious effects, comparable to unregulated complement activation, in the pathogenesis of xenograft rejection and may therefore represent a substantive barrier to xenotransplantation.

Induction of syncytia by neuropathogenic murine leukemia viruses depends on receptor density, host cell determinants, and the intrinsic fusion potential of envelope protein

Infection by the neuropathogenic murine leukemia virus (MLV) TR1.3 results in hemorrhagic disease that correlates directly to in vivo syncytium formation of brain capillary endothelial cells (BCEC). This phenotype maps to amino acid 102 in the envelope (Env) protein of TR1.3. Substitution of glycine (G) for tryptophan (W) at this position (W102G Env) in the nonpathogenic MLV FB29 induces both syncytium formation and neurologic disease in vivo. Using an in vitro gene reporter cell fusion assay, we showed that fusion either with murine NIH 3T3 cells or with nonmurine target cells that expressed receptors at or below endogenous murine levels mirrored that seen in BCEC in vivo. In these instances only TR1.3 and W102G Env induced cell fusion. In contrast, when receptor levels on nonmurine cells were raised above endogenous murine levels, FB29 Env was as fusogenic as the neuropathogenic TR1.3 and W102G Env. These results indicate that TR1.3 Env and W102G Env are intrinsically more fusogenic than FB29 Env, that the induction of fusion requires a threshold number of receptors that is greater for FB29 Env than for TR1.3 or W102G Env, and that receptor density on murine NIH 3T3 cells and BCEC is below the threshold for FB29-dependent fusion. Surprisingly, receptor density on NIH 3T3 cells could not be increased by stable expression of exogenous receptors, and FB29-dependent fusion was not observed in NIH 3T3 cells that transiently expressed elevated receptor numbers. These results suggest that an additional undefined host cell factor(s) may limit both receptor expression and fusion potential in murine cells.

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.

Disseminated intravascular coagulation in association with the delayed rejection of pig-to-baboon renal xenografts

BACKGROUND

Intravascular fibrin deposition and platelet sequestration occur with porcine xenograft rejection by baboons. Disseminated intravascular coagulopathy may arise either as a direct consequence of the failure to fully deplete xenoreactive natural antibodies and block complement, or because of putative cross-species molecular incompatibilities in this discordant species combination.

METHODS

Three baboons were conditioned with retrovirally transduced autologous bone marrow to induce tolerance to swine antigens. Xenoreactive natural antibodies and complement were depleted by plasmapheresis and the use of Gal alpha1-3Gal column adsorptions; baboons were then splenectomized and underwent renal xenografting from inbred, miniature pigs. Soluble complement receptor type-1 with protocol immunosuppression (mycophenolate mofetil, 15-deoxyspergualin, steroids, and cyclosporine) was administered.

RESULTS

A bleeding diathesis was clinically evident from days 5 to 12 after transplantation in two baboons. Low levels of circulating C3a, C3d, and iC3b were measured despite the absence of functional circulating complement components. Profound thrombocytopenia with abnormalities in keeping with disseminated intravascular coagulopathy were observed. Prolongation of prothrombin and partial thromboplastin times was accompanied by evidence for tissue factor-mediated coagulation pathways, high levels of thrombin generation (prothrombin fragment F(1+2) production and thrombin-antithrombin complex formation), fibrinogen depletion, and production of high levels of the fibrin degradation product D-dimer. Importantly, these disturbances resolved rapidly after the excision of the rejected xenografts in two surviving animals. Histopathological examination of the rejected xenografts confirmed vascular injury, fibrin deposition, platelet deposition, and localized complement activation.

CONCLUSIONS

Systemic coagulation disturbances are associated with delayed xenograft rejection.

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.

An In Vitro Model of T Cell Activation by Autologous Cytomegalovirus (CMV)-Infected Human Adult Endothelial Cells: Contribution of CMV-Enhanced Endothelial ICAM-1

Cellular immunity is strongly implicated in control of CMV disease; however, many mechanistic details remain unresolved. We previously demonstrated T cell activation responses to CMV-infected allogeneic endothelial cells (EC), suggesting EC as a mediator of CMV response in the transplant recipient. We now test the hypothesis that CMV-specific T cell responses can be directly stimulated by infected EC in an environment free of potentially confounding allogeneic factors. By isolating splenic T cells and gonadal vein endothelial cells (GVEC) from individual cadaveric organ donors, we have developed an in vitro model of T cell interaction with autologous CMV-infected EC. Proliferation assays demonstrated significantly enhanced responses by CMV-seropositive donor-derived T cells cocultured with CMV-infected GVEC, as compared with those elicited by uninfected cells. Similarly, as determined by limiting dilution analysis of IL-2-producing cells, T cell response frequencies to infected GVEC were significantly greater than to uninfected EC. In contrast, responses of CMV-seronegative donor-derived T cells were minimal, regardless of CMV status of stimulator GVEC. Intriguingly, CD4 responses were observed in spite of the fact that CMV-infected EC express no HLA class II. Finally, attenuation of CMV-stimulated T cell proliferation observed in the presence of blocking Ab specific for ICAM-1 suggests a contributing role for CMV-enhanced endothelial ICAM-1 expression in the activation response. These studies demonstrate that EC can stimulate autologous T cell responses to CMV in the absence of accessory APC and suggest potentially novel mechanisms of immune activation.

Herpesvirus in atherosclerosis and thrombosis: etiologic agents or ubiquitous bystanders?

The role of herpesvirus infections in the pathogenesis of vascular diseases remains an enigma. Although there is abundant circumstantial evidence of a role for herpesviruses in atherosclerosis and related processes, a cause-and-effect relationship has yet to be definitively established. This article will review the pathological, molecular, and biochemical evidence supporting the hypothesis that herpesviruses are involved in the development of atherosclerosis, restenosis after coronary angioplasty, accelerated atherosclerosis in recipients of heart transplants, and the induction of a prothrombotic phenotype in vascular endothelial cells.

Coagulation initiated on herpesviruses

Herpesviruses have been previously correlated to vascular disease and shown to cause thrombogenic and atherogenic changes to host cells. Herein we show that even in the absence of cells, purified cytomegalovirus (CMV) and herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) can initiate thrombin production. Functional assays demonstrated that purified HSV-1 and HSV-2 provide the necessary phospholipid (proPL) for assembling the coagulation factors Xa and Va into prothrombinase, which is responsible for generating thrombin. These observations are consistent with our earlier studies involving CMV. The presence of proPL on all three herpesviruses was confirmed directly by flow cytometry and electron microscopy by using annexin V and factor Va, respectively, as proPL-specific probes. Of equal importance, we found that CMV, HSV-1, and HSV-2 were also able to facilitate factor Xa generation from the inactive precursor factor X, but only when factor VII/VIIa and Ca2+ were present. Monoclonal antibodies specific for tissue factor (TF), the coagulation initiator, inhibited this factor X activation and, furthermore, enabled identification of TF antigen on each virus type by flow cytometry and electron microscopy. Collectively, these data show that CMV, HSV-1, and HSV-2 can initiate the generation of thrombin by having essential proPL and TF activities on their surface. Unlike the normal cellular source, the viral activity is constitutive and, therefore, not restricted to sites of vascular injury. Thus cell-independent thrombin production may be the earliest event in vascular pathology mediated by herpesviruses.

Selectin-carbohydrate interactions during inflammation and metastasis

L-, E-, and P-selectin are membrane-anchored, C-type lectins that initiate tethering and rolling of flowing leukocytes on endothelial cells, platelets, or other leukocytes during inflammation. The selectins bind to sialylated, fucosylated, or, in some cases, sulfated glycans on glycoproteins, glycolipids, or proteoglycans. However, they bind with relatively high affinity or avidity to only a few, appropriately modified glycoproteins on leukocytes or endothelial cells. One leukocyte mucin, PSGL-1, tethers flowing leukocytes to P-selectin on activated platelets or endothelial cells, and also helps tether leukocytes to L-selectin on other leukocytes. The physiologic expression of the selectins is tightly controlled to limit the inflammatory response. But dysregulated expression of the selectins may contribute to inflammatory and thrombotic disorders, and perhaps to tumor metastases.

Small, freshly arrived histiocytes in cutaneous and mucosal herpetic lesions

We report on the predominance of a special type of small histiocyte in the inflammatory infiltrate accompanying herpetic bullae. These histiocytes, which have previously been taken to be neutrophils, are freshly arrived cells with a hitherto unknown function. Until now, they have been found only in Sweet's syndrome and erythema nodosum where they form Miesscher's radial granulomas. Similar small histiocytes were found in half of those herpetic lesions with intact bullae, and in over two-thirds of ulcerated lesions in which these cells formed a palisade in the fibrinoid material covering the floor of the ulcerated vesicles. Small histiocytes, admixed with neutrophils, were in close proximity to virally infected keratinocytes. Immunohistochemical analysis confirmed their histiocytic nature. With the exception of ecthyma contagiosum (orf), similar small histiocytes were not found in other viral infections or in nonspecific ulcers of the skin. In cases of herpetic folliculitis, small histiocytes showed massive epidermotropism towards hair follicle epithelium. We conclude that cutaneous and oral herpetic infections represent yet another disease in which small, freshly arrived histiocytes occur. They may be involved in antigen presentation, or in killing of infected keratinocytes.

Adenovirus-mediated gene transfer into normal rabbit arteries results in prolonged vascular cell activation, inflammation, and neointimal hyperplasia

Adenovirus vectors are capable of high efficiency in vivo arterial gene transfer, and are currently in use as therapeutic agents in animal models of vascular disease. However, despite substantial data on the ability of viruses to cause vascular inflammation and proliferation, and the presence in current adenovirus vectors of viral open reading frames that are translated in vivo, no study has examined the effect of adenovirus vectors alone on the arterial phenotype. In a rabbit model of gene transfer into a normal artery, we examined potential vascular cell activation, inflammation, and neointimal proliferation resulting from exposure to replication-defective adenovirus. Exposure of normal arteries to adenovirus vectors resulted in: (a) pronounced infiltration of T cells throughout the artery wall; (b) upregulation of intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 in arterial smooth muscle cells; (c) neointimal hyperplasia. These findings were present both 10 and 30 d after gene transfer, with no evidence of a decline in severity over time. Adenovirus vectors have pleiotropic effects on the arterial wall and cause significant pathology. Interpretation of experimental protocols that use adenovirus vectors to address either biological or therapeutic issues should take these observations into account. These observations should also prompt the design of more inert gene transfer vectors.

Cytomegalovirus and atherosclerosis

Finding that an avian herpesvirus can cause atherosclerosis in chickens prompted studies of human herpesviruses in human atherosclerosis. Antigens and nucleic acid sequences of cytomegalovirus (CMV), a widespread member of the herpesvirus family, were found in arterial lesions in human atherosclerosis, but infectious virus has not been observed. In atherosclerosis patients, high levels of CMV antibodies are present, suggesting the presence of virus that had been activated from a latent state. Atherosclerosis also develops in immune-suppressed heart transplant patients infected with CMV. The properties of CMV are consistent with its involvement at several levels of the atherogenic process. If this concept is correct, immunization with a CMV vaccine should prevent CMV infection and atherosclerosis.

Endothelial MHC class II antigen expression and endarteritis associated with Marek's disease virus infection in chickens

Experimental Marek's disease virus (MDV) infection in chickens was used to study the early pathogenesis of virus-induced atherosclerosis. Previous investigations using this model have reported the occurrence of atherosclerotic lesions after approximately 7 months postinfection. In this study, a total of 75 susceptible Cornell P-line chickens were inoculated intraperitoneally with the CU-2 strain of MDV at 3 days of age and subsequently perfused for histologic examination. At 2, 4, 8, 13, and 20 weeks postinoculation, the ascending aorta and the brachiocephalic and coronary arteries were evaluated for early changes. Expression of class II major histocompatibility complex (Ia) antigen by the vascular endothelium was demonstrated by indirect immunodetection as early as 2 weeks after virus inoculation. This change was followed by significant thickening of the intimal layer associated with mononuclear cell infiltration. All the arteries examined from the MDV-infected chickens were affected. Preliminary immunohistochemical staining showed the presence of CD3+ CD4+, and CD8+ cells among the infiltrating cells. The results suggest that an immunopathologic mechanism may be involved in the early pathogenesis of MDV-induced atherosclerosis in chickens.

Increased expression of cell adhesion molecule P-selectin in active inflammatory bowel disease

The pathogenic changes of inflammatory bowel disease (IBD) depend on migration of circulating leucocytes into intestinal tissues. Although leucocyte rolling and tenuous adhesion are probably regulated by inducible selectins on vascular endothelia, little is known about the expression of these molecules in Crohn's disease and ulcerative colitis. Using immunohistochemistry on surgically resected specimens, this study investigated endothelial P-selectin (CD62, granular membrane protein-140) in frozen sections of histologically uninvolved tissues adjacent to inflammation (Crohn's disease = 10; ulcerative colitis = 10), from highly inflamed areas (Crohn's disease = 20; ulcerative colitis = 13), and from normal bowel (n = 20). By light microscopy, two forms of P-selectin immunoreactivity were detected that apparently corresponded ultrastructurally to stored and released distributions. Compared with the normal gut, there was a 3.7-fold increase of P-selectin immunoreactivity on veins (p < 0.0001), venules (p < 0.0001), and capillaries (p < 0.05) in the highly inflamed gut, without differences between Crohn's disease and ulcerative colitis. In the uninvolved gut, P-selectin expression was similar to that seen in normal controls, except for a focal increase of P-selectin in the vicinity of small lymphocyte aggregates. The dramatic upregulation of P-selectin in the inflamed tissue and its potential role in leucocyte trafficking support the concept of P-selectin blocking therapy for the control of active IBD.

Uses of flow cytometry in virology

This article reviews some of the published applications of flow cytometry for in vitro and in vivo detection and enumeration of virus-infected cells. Sample preparation, fixation, and permeabilization techniques for a number of virus-cell systems are evaluated. The use of flow cytometry for multiparameter analysis of virus-cell interactions for simian virus 40, herpes simplex viruses, human cytomegalovirus, and human immunodeficiency virus and its use for determining the effect of antiviral compounds on these virus-infected cells are reviewed. This is followed by a brief description of the use of flow cytometry for the analysis of several virus-infected cell systems, including blue tongue virus, hepatitis C virus, avian reticuloendotheliosis virus, African swine fever virus, woodchuck hepatitis virus, bovine viral diarrhea virus, feline leukemia virus, Epstein-Barr virus, Autographa californica nuclear polyhedrosis virus, and Friend murine leukemia virus. Finally, the use of flow cytometry for the rapid diagnosis of human cytomegalovirus and human immunodeficiency virus in peripheral blood cells of acutely infected patients and the use of this technology to monitor patients on antiviral therapy are reviewed. Future prospects for the rapid diagnosis of in vivo viral and bacterial infections by flow cytometry are discussed.

von Willebrand factor mediates platelet adhesion to virally infected endothelial cells

von Willebrand factor is an adhesive glycoprotein critical to normal hemostasis. It is stored in the Weibel-Palade body of endothelial cells and upon release may mediate platelet adhesion. Herpesvirus-infected endothelium is known to be prothrombotic and to support enhanced platelet adherence. We previously identified P-selectin as a monocyte receptor that is translocated from the Weibel-Palade body to the endothelial cell surface in response to the local generation of thrombin on herpesvirus infected cells. In this study, we show that viral injury to vascular endothelial cells induces secretion of von Willebrand factor which mediates enhanced platelet adhesion to these cells.

Production of a monoclonal antibody against canine GMP-140 (P-selectin) and studies of its vascular distribution in canine tissues

Rapid upregulation of the adhesion molecule GMP-140 (P-selectin) on endothelial cells is believed to play an important role in the initial binding of leukocytes to endothelium, a very early step in the inflammatory response. Activated platelets that are involved in the coagulation system and in inflammatory processes also express GMP-140 on their surfaces. The objectives of the present study were to develop a monoclonal antibody against this adhesion molecule in the dog and to use this antibody to study platelet-neutrophil interactions in whole blood and to characterize the in vivo localization of GMP-140 in canine tissues. Five Balb/c mice were immunized with thrombin-stimulated dog platelets, and clones were screened using an enzyme-linked immunosorbent assay. The clone MD3 (IgG1) showed preferential binding to activated as compared with resting platelets. Flow cytometric analysis using MD3 revealed that 27% of circulating neutrophils in unstimulated blood had platelets bound to their surfaces; stimulation with platelet activating factor increased this percentage to 85%. Immunoblot analysis of solubilized dog platelets resolved by sodium dodecyl sulfate polyacrylamide gel electrophoresis indicated that the antibody MD3 recognized an approximately 140-kd protein. Immunohistochemical study of normal dog tissues with MD3 revealed that the antigen was present in endothelial cells of arteries, capillaries, and veins, depending on the specific tissue examined. Blood vessels staining positively with MD3 were most abundant in the digestive system (liver, stomach, small and large intestines), moderate in the lungs, kidneys, spleen, lymph nodes, and endocrine glands, and minimal in the brain, myocardium, skeletal system, and skin. Based on its presence on stimulated but not resting platelets, its molecular weight, and its vascular distribution, the antigen recognized by MD3 appears to be the selectin GMP-140 of the dog. This study documents that the cellular and tissue distribution of GMP-140 in dogs is very similar to that in human beings.

Selectins

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Mechanisms of monocyte recruitment and accumulation

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Warner-Lambert/Parke-Davis Award Lecture. Viral pathogenesis of atherosclerosis. Impact of molecular mimicry and viral genes

Human atherogenesis is a pleiotropic process with an undefined cause. Several pathologic factors have been linked to the disease process, including arterial injury or activation of the endothelium, which may injury or activation of the endothelium, which may initiate proatherosclerotic events in the vessel wall. Atherosclerotic lesions are characterized, in part, by the presence of activated immune cells, abnormal cell proliferation, and altered cholesterol metabolism. These activated immunocompetent cells in plaques produce vasoactive mediators that can alter homeostasis and may promote the arteriopathy. Both molecular and structural evidence is presented that herpesviruses, by way of induction of altered gene function and cellular cholesterol metabolism, coupled with their ability to activate coagulation and a monocyte receptor on the infected endothelium, are involved in major pathogenic events associated with atherosclerosis and thrombosis. Work from the author's laboratory, as well as from other research groups, have shown that avian and human herpesviruses act specifically to induce alterations to the surface and inner layers of the blood vessel wall that may predispose to atherosclerosis and its attendant clinical complications.