FasL/Fas pathway is involved in dengue virus induced apoptosis of the vascular endothelial cells

Impact of apoptotic biomarkers for prognosis of dengue disease severity among eastern Indian patients

Dengue virus (DENV) induced severe manifestations is a precursor for fatality among infected patients. Previous autopsy examinations of severe dengue (SD) patients reported presence of apoptotic cells in liver, brain, intestinal and lung tissues. Thus, serum-level of major apoptotic proteins of dengue patients was evaluated in the current study, along with their biochemical parameters. Patients were categorized according to World Health Organization (WHO)-defined classification. DENV-infection was screened among 165 symptomatic patients by quantitative reverse transcription polymerase chain reaction, antidengue IgM, and IgG ELISA. Serum levels of apoptotic (Capase-3,7,8, Bcl-2 and FasL) and hepatic-markers, lipid profile, hematological parameters of 78 dengue-positive patients were determined by sandwich-ELISA/immunoturbidimetry/auto-analyzer. Significantly higher levels of caspase-3,7,8 and FasL was detected among SD patients compared to those without warning (WOW) signs. Amongst biochemical parameters, bilirubin, aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase serum concentrations significantly increased among severe patients. Principal component analysis followed by hierarchical clustering differentiated severe and with warning dengue patient groups from those WOW using caspase-3,7,8 and FasL biomarkers-thus clearly distinguishing severe-dengue group. Correlation analyses also established strong positive correlation between caspase-3,7,8 and FasL. Thus, serum level of caspase-3,7,8 and FasL during early stage of infection could be used as biomarkers for WHO-defined dengue disease severity.

Apoptosis and Phagocytosis as Antiviral Mechanisms

Viruses are infectious entities that make use of the replication machinery of their hosts to produce more progenies, causing disease and sometimes death. To counter viral infection, metazoan hosts are equipped with various defense mechanisms, from the rapid-evoking innate immune responses to the most advanced adaptive immune responses. Previous research demonstrated that cells in fruit flies and mice infected with Drosophila C virus and influenza, respectively, undergo apoptosis, which triggers the engulfment of apoptotic virus-infected cells by phagocytes. This process involves the recognition of eat-me signals on the surface of virus-infected cells by receptors of specialized phagocytes, such as macrophages and neutrophils in mice and hemocytes in fruit flies, to facilitate the phagocytic elimination of virus-infected cells. Inhibition of phagocytosis led to severe pathologies and death in both species, indicating that apoptosis-dependent phagocytosis of virus-infected cells is a conserved antiviral mechanism in multicellular organisms. Indeed, our understanding of the mechanisms underlying apoptosis-dependent phagocytosis of virus-infected cells has shed a new perspective on how hosts defend themselves against viral infection. This chapter explores the mechanisms of this process and its potential for developing new treatments for viral diseases.

Role of apoptosis in Duck Tembusu virus infection of duckling brains in vivo

The Duck Tembusu virus (DTMUV) is a novel flavivirus that occurs mainly in poultry. DTMUV infection can cause common neurological symptoms in ducklings, but the pathogenesis of DTMUV has not been elucidated yet. In this study, a DTMUV-infected duckling model was constructed to investigate the apoptosis in the duckling brains. After DTMUV infection, apoptotic cells were observed by transmission electron microscopy. It was found that the abundances of apoptosis-related genes and proteins were not obviously changed in the early stage of infection but significantly changed in the middle and late stages of the disease. Terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling assay staining results were also consistent with the above phenomena. Interestingly, although apoptosis occurred in the duckling brains infected by DTMUV, some antiapoptotic genes in the brain increased in varying degrees. In conclusion, DTMUV infection could induce apoptosis in ducklings' brains, and the occurrence of apoptosis was accompanied by the virus infection process with certain regularity. This study provides a scientific basis for elucidating the apoptotic mechanism of brain lesions induced by DTMUV infection.

The Dual Regulation of Apoptosis by Flavivirus

Apoptosis is a form of programmed cell death, which maintains cellular homeostasis by eliminating pathogen-infected cells. It contains three signaling pathways: death receptor pathway, mitochondria-mediated pathway, and endoplasmic reticulum pathway. Its importance in host defenses is highlighted by the observation that many viruses evade, hinder or destroy apoptosis, thereby weakening the host’s immune response. Flaviviruses such as Dengue virus, Japanese encephalitis virus, and West Nile virus utilize various strategies to activate or inhibit cell apoptosis. This article reviews the research progress of apoptosis mechanism during flaviviruses infection, including flaviviruses proteins and subgenomic flaviviral RNA to regulate apoptosis by interacting with host proteins, as well as various signaling pathways involved in flaviviruses-induced apoptosis, which provides a scientific basis for understanding the pathogenesis of flaviviruses and helps in developing an effective antiviral therapy.

Characterization of the IL-17 and CD4+ Th17 Cells in the Clinical Course of Dengue Virus Infections

The aims of this study were to determine the involvement of interleukin 17 (IL-17) and IL-17-producing cells in dengue pathogenesis. Blood samples from dengue virus (DENV)-infected patients were collected on different days after the onset of symptoms. Patients were classified according to 1997 World Health Organization guidelines. Our study examined 152 blood samples from dengue fever (DF, n = 109) and dengue hemorrhagic fever (DHF, n = 43) patients and 90 blood samples from healthy controls (HC). High serum concentrations of IL-17A and IL-22 were also associated with DHF (IL-17A [DHF vs. DF, p < 0.01; DHF vs. HC, p < 0.0001]; IL-22 [DHF vs. DF, p < 0.05; DHF vs. HC, p < 0.0001]). Moreover, there was a positive correlation between serum levels of IL-17A and IL-23, a key cytokine that promotes IL-17-based immune responses (r = 0.4089, p < 0.0001). Consistent with the IL-17-biased immune response in DHF patients, we performed ex vivo activation of peripheral blood mononuclear cells (PBMCs) from DHF patients and flow cytometry analysis showed a robust IL-17-biased immune response, characterized by a high frequency of CD4+IL-17+ producing cells. Our results suggests IL-17-producing cells and their related cytokines can play a prominent role in this viral disease.

Cell death signalling in virus infection

Apoptosis, necroptosis and pyroptosis represent three major regulated cell death modalities. Apoptosis features cell shrinkage, nuclear fragmentation and cytoplasm-blebbing. Necroptosis and pyroptosis exhibit osmotic imbalances in the cell accompanied by early membrane ruptures, which morphologically resembles necrosis. Importantly, these two lytic cell death forms facilitate the release of damage associated molecular patterns into the extracellular space leading to inflammatory response. Whereas, during apoptosis, the membrane integrity is preserved and the apoptotic cell is removed by neighbouring cells ensuring the avoidance of immune-stimulation. Viruses comprise a versatile group of intracellular pathogens, which elicit various strategies to infect and to propagate. Viruses are recognized by a myriad of pathogen recognition receptors in the human cells, which consequently lead to activation of the immune system and in certain circumstances cell-autonomous cell death. Importantly, the long-standing view that a cell death inducing capacity of a virus is equal to its pathogenic potential seems to be only partially valid. The altruistic cell death of an infected cell may serve the whole organism by ultimately curbing the way of virus manufacturing. In fact, several viruses express "anti-cell death" proteins to avoid this viral-defence mechanism. Conversely, some viruses hijack cell death pathways to selectively destroy cell populations in order to compromise the immune system of the host. This review discusses the pros and cons of virus induced cell death from the perspective of the host cells and attempts to provide a comprehensive overview of the complex network of cell death signalling in virus infection.

Post-fever retinitis - Newer concepts

Post-fever retinitis (PFR) is an infectious or para-infectious uveitic entity caused by bacterial or viral agents and seen mainly in tropical countries. Systemic symptoms such as joint pain, skin rash are common during the febrile stage. On the basis of only clinical presentation, it is difficult to pin-point the exact etiology for PFR. Serological investigations, polymerase chain reaction, and knowledge of concurrent epidemics in the community may help to identify the etiological organism. Bacterial causes of PFR such as rickettsia and typhoid are treated with systemic antibiotics, with or without systemic steroid therapy, whereas PFR of viral causes such as chikungunya, dengue, West Nile virus, and Zika virus have no specific treatment and are managed with steroids. Nevertheless, many authors have advocated mere observation and the uveitis resolved with its natural course of the disease. In this article, we have discussed the clinical features, pathogenesis, investigations, and management of PFR.

Crocetin Improves Dengue Virus-Induced Liver Injury

Dengue virus (DENV) infection is one of the most widespread mosquito-borne viral infections. Liver injury is commonly observed in severe DENV infection, and the present study aimed to examine the efficacy of crocetin treatment in an immunocompetent mouse model of DENV infection exhibiting liver injury. The efficacy of crocetin treatment in DENV-induced liver injury was assessed via both transaminase levels and histopathology analysis. A real-time polymerase chain reaction array was then used to describe the expression of 84 apoptosis-related genes. Using real-time RT-PCR and Western blot analysis, the gene expressions of host factors were investigated. Additionally, the effect of crocetin in NF-kB signaling during DENV infection was studied. We did not observe any significant reduction in virus production when DENV-infected mice were treated with crocetin. However, DENV-infected mice treated with crocetin showed reduced DENV-induced apoptosis. The real-time polymerase chain reaction array revealed pro-inflammatory cytokine expressions to be significantly reduced in the crocetin-treated DENV-infected mice. We also found that crocetin could effectively modulate antioxidant status in DENV-infected mice. Moreover, crocetin demonstrated the ability to reduce the nuclear translocation of NF-kB in DENV-infected mice. Our results suggest that crocetin treatment does not inhibit DENV replication in the liver of DENV-infected mice; however, we did find that crocetin improves host responses that reduce liver injury.

Apoptosis characterization in mononuclear blood leukocytes of HIV patients during dengue acute disease

Dengue virus (DENV) co-circulation in Brazil represents a challenge for treatment and vaccine development. Despite public health impact, the occurrence of coinfections with other viruses is a common event. Increased T cell activation and altered inflammatory response are found during DENV coinfection with Human Immunodeficiency Virus (HIV) impacting HIV-pathogenesis. Even with Antiretroviral therapy (ART), HIV- treated patients had chronic immune activation and lymphocyte apoptosis. However, apoptotic mechanisms have not been investigated during coinfection with DENV. Our attention was attracted to apoptotic cell markers expressions in PBMCs from DENV and DENV/HIV coinfected patients. We found CD4/CD8 ratio inversion in most coinfected patients. CD4 T and CD8 T-cell subsets from DENV and DENV/HIV groups expressed low levels of anti-apoptotic protein Bcl-2. Furthermore, CD8 CD95 double positive cells frequency expressing low levels of Bcl-2 were significantly higher in these patients. Additionally, the density of Bcl-2 on classical monocytes (CD14⁺⁺CD16⁻) was significantly lower during DENV infection. Upregulation of pro-apoptotic proteins and anti-apoptotic proteins were found in DENV and DENV/HIV, while catalase, an antioxidant protein, was upregulated mainly in DENV/HIV coinfection. These findings provide evidence of apoptosis triggering during DENV/HIV coinfection, which may contribute to knowledge of immunological response during DENV acute infection in HIV-patients treated with ART.

Different cytokine patterns induced by Helicobacter pylori and Lactobacillus acidophilus extracts in PBMCs of patients with abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a degenerative inflammatory disease with unknown etiology. AAA is characterized by abdominal aortic dilatation more than 3 cm and is often asymptomatic, but the rupture of aneurysm can lead to death. Age, smoking and male sex are major predisposing factors of AAA. This study compares the effect of Helicobacter (H.) pylori and Lactobacillus (L.) acidophilus on the cytokine profile of PBMCs of 5 men with abdominal aortic aneurysm (AAA) and 5 men with normal/insignificant angiography, CT-Scan and ultrasonography results in the single-culture and in the co-culture with HUVECs. IL-2, IL-4, IL-5, IL-6, IL-9, IL-10, IL-13, IL-17A, IL-17 F, IL-21, IL-22, IFN-γ and TNF-α were measured in culture supernatants using a commercial fluorescent-labeled-bead assay. In general, CagA+ H. pylori-extract induced higher production of IFN-γ, IL-13 and IL-21 by PBMCs. Treatment of patients' PBMCs with CagA⁺H. pylori-extract induced Th2 cytokines while treatment of controls' PBMCs with CagA⁺H. pylori-extract increased Th1 cytokines. In the co-culture, however, patients' PBMCs produced Th1 cytokines irrespective of extract treatment, while controls' PBMCs produced Th2 cytokines and decreased IL-10. CagA+ H. pylori- as well as L. acidophilus-extract induced higher levels of IL-9 by controls' PBMCs in co-culture with HUVECs than patients (P = 0.05 and P = 0.01). The cytokine pattern of PBMCs induced by CagA+ H. pylori- and L. acidophilus-extracts in the co-culture with HUVECs shows differences in AAA patients and in comparison to controls. Decreased secretion of IL-9, IL-21 and IL-22 by PBMCs of patients treated with CagA+ H. pylori extract in co-culture, as opposed to non-AAA controls may indicate the active role ECs play in AAA. Simultaneous production of IL-10 and Th1 cytokines in patients and pronounced Th2 cytokines in controls in response to both bacteria may point to the inherent differences between patients and controls, which need further investigation.

The involvement of regulated cell death forms in modulating the bacterial and viral pathogenesis

Apoptosis, necroptosis and pyroptosis represent three distinct types of regulated cell death forms, which play significant roles in response to viral and bacterial infections. Whereas apoptosis is characterized by cell shrinkage, nuclear condensation, bleb formation and retained membrane integrity, necroptosis and pyroptosis exhibit osmotic imbalance driven cytoplasmic swelling and early membrane damage. These three cell death forms exert distinct immune stimulatory potential. The caspase driven apoptotic cell demise is considered in many circumstances as anti-inflammatory, whereas the two lytic cell death modalities can efficiently trigger immune response by releasing damage associated molecular patterns to the extracellular space. The relevance of these cell death modalities in infections can be best demonstrated by the presence of viral proteins that directly interfere with cell death pathways. Conversely, some pathogens hijack the cell death signaling routes to initiate a targeted attack against the immune cells of the host, and extracellular bacteria can benefit from the destruction of intact extracellular barriers upon cell death induction. The complexity and the crosstalk between these cell death modalities reflect a continuous evolutionary race between pathogens and host. This chapter discusses the current advances in the research of cell death signaling with regard to viral and bacterial infections and describes the network of the cell death initiating molecular mechanisms that selectively recognize pathogen associated molecular patterns.

Upregulation of intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 in renal tissue in severe dengue in humans: Effects on endothelial activation/dysfunction

INTRODUCTION

Dengue is an important mosquito-borne disease in tropical and subtropical regions. Adhesion molecules have not been systematically characterized in the renal tissue of patients with severe dengue (SD). The objective of this study was to detect viral antigens in samples from patients that evolved with SD, correlating with the expression of ICAM-1, VCAM-1, VE-cadherin, and E-selectin to contribute to a better understanding of the pathophysiology of SD.

METHODS

Kidney specimens from patients with SD were selected according to clinical and laboratorial data and submitted to histological and immunohistochemistry analysis. A semiquantitative evaluation was performed considering positive immunostaining in 20 glomeruli.

RESULTS

Viral antigens were mainly detected in distal tubules. The intense immunostaining of VCAM-1 and ICAM-1 was observed. The expression of E-selectin was discrete, and VE-cadherin expression varied from mild to moderate. VCAM-1 was slightly intense in the glomerular capsule; the expression of ICAM-1 was diffuse. E-selectin was diffuse, and VE-cadherin varied from mild to moderate. The most frequent histological findings were glomerular congestion, mild glomerulitis, acute renal injury, and glomerular atrophy.

CONCLUSIONS

The results appear to demonstrate an imbalance between vascular endothelial permeability regulating events in renal lesions in SD. The increase in the expression of ICAM-1 and VCAM-1 is an in-situ indicator of higher permeability with a consequent influx of cells favoring the inflammation of the endothelium. These molecules are important in the pathophysiology of the disease and provide the possibility of developing new markers for the evaluation, clinical follow-up, and therapeutic response of patients with SD.

Drug repurposing of N-acetyl cysteine as antiviral against dengue virus infection

Liver injury is one of the hallmark features of severe dengue virus (DENV) infection since DENV can replicate in the liver and induce hepatocytes to undergo apoptosis. N-acetyl cysteine (NAC), which is a clinically-used drug for treating acetaminophen toxicity, was found to benefit patients with DENV-induced liver injury; however, its mechanism of action remains unclear. Accordingly, our aim was to repurpose NAC in the preclinical studies to investigate its mechanism of action. Time of addition experiments in HepG2 cells elucidated effectiveness of NAC to reduce infectious virion at pre-, during- and post infection. In DENV-infected mice, NAC improved DENV-associated clinical manifestations, including leucopenia and thrombocytopenia, and reduced liver injury and hepatocyte apoptosis. Interestingly, we discovered that NAC significantly reduced DENV production in HepG2 cells and in liver of DENV-infected mice by induction of antiviral responses via interferon signaling. NAC treatment in DENV-infected mice helped to maintain antioxidant enzymes and redox balance in the liver. Therefore, NAC reduces DENV production and oxidative damage to ameliorate DENV-induced liver injury. Taken together, these findings suggest the novel therapeutic potential of NAC in DENV-induced liver injury and recommend evaluating its efficacy and safety in humans with DENV-induced liver injury.

Dengue virus non-structural protein 1: a pathogenic factor, therapeutic target, and vaccine candidate

Dengue virus (DENV) infection is the most common mosquito-transmitted viral infection. DENV infection can cause mild dengue fever or severe dengue hemorrhagic fever (DHF)/dengue shock syndrome (DSS). Hemorrhage and vascular leakage are two characteristic symptoms of DHF/DSS. However, due to the limited understanding of dengue pathogenesis, no satisfactory therapies to treat nor vaccine to prevent dengue infection are available, and the mortality of DHF/DSS is still high. DENV nonstructural protein 1 (NS1), which can be secreted in patients’ sera, has been used as an early diagnostic marker for dengue infection for many years. However, the roles of NS1 in dengue-induced vascular leakage were described only recently. In this article, the pathogenic roles of DENV NS1 in hemorrhage and vascular leakage are reviewed, and the possibility of using NS1 as a therapeutic target and vaccine candidate is discussed.

Virus Infection and Death Receptor-Mediated Apoptosis

Virus infection can trigger extrinsic apoptosis. Cell-surface death receptors of the tumor necrosis factor family mediate this process. They either assist persistent viral infection or elicit the elimination of infected cells by the host. Death receptor-mediated apoptosis plays an important role in viral pathogenesis and the host antiviral response. Many viruses have acquired the capability to subvert death receptor-mediated apoptosis and evade the host immune response, mainly by virally encoded gene products that suppress death receptor-mediated apoptosis. In this review, we summarize the current information on virus infection and death receptor-mediated apoptosis, particularly focusing on the viral proteins that modulate death receptor-mediated apoptosis.

Infectious Bronchitis Virus Infection Induces Apoptosis during Replication in Chicken Macrophage HD11 Cells

Avian infectious bronchitis has caused huge economic losses in the poultry industry. Previous studies have reported that infectious bronchitis virus (IBV) infection can produce cytopathic effects (CPE) and apoptosis in some mammalian cells and primary cells. However, there is little research on IBV-induced immune cell apoptosis. In this study, chicken macrophage HD11 cells were established as a cellular model that is permissive to IBV infection. Then, IBV-induced apoptosis was observed through a cell viability assay, morphological changes, and flow cytometry. The activity of caspases, the inhibitory efficacy of caspase-inhibitors and the expression of apoptotic genes further suggested the activation of apoptosis through both intrinsic and extrinsic pathways in IBV-infected HD11 cells. Additionally, ammonium chloride (NH₄Cl) pretreated HD11 cells blocked IBV from entering cells and inhibited IBV-induced apoptosis. UV-inactivated IBV also lost the ability of apoptosis induction. IBV replication was increased by blocking caspase activation. This study presents a chicken macrophage cell line that will enable further analysis of IBV infection and offers novel insights into the mechanisms of IBV-induced apoptosis in immune cells.

Regulation of endothelial Fas expression as a mechanism of promotion of vascular integrity by mural cells in tumors

Angiogenesis is a multi‐step process that culminates in vascular maturation whereby nascent vessels stabilize to become functional, and mural cells play an essential role in this process. Recent studies have shown that mural cells in tumors also promote and maintain vascular integrity, with wide‐reaching clinical implications including the regulation of tumor growth, metastases, and drug delivery. Various regulatory signaling pathways have been hitherto implicated, but whether regulation of Fas‐dependent apoptotic mechanisms is involved has not yet been fully investigated. We first compared endothelial FAS staining in human pancreatic ductal adenocarcinomas and colon carcinomas and show that the latter, characterized by lower mural cell coverage of tumor vasculature, demonstrated higher expression of FAS than the former. Next, in an in vitro coculture system of MS‐1 and 10T1/2 cells as endothelial and mural cells respectively, we show that mural cells decreased endothelial Fas expression. Then, in an in vivo model in which C26 colon carcinoma cells were inoculated together with MS‐1 cells alone or with the further addition of 10T1/2 cells, we demonstrate that mural cells prevented hemorrhage. Finally, knockdown of endothelial Fas sufficiently recapitulated the protection against hemorrhage seen with the addition of mural cells. These results together suggest that regulation of endothelial Fas signaling is involved in the promotion of vascular integrity by mural cells in tumors.

Soluble Fas Ligand as a Potential Marker of Severity of Dengue Infection

BACKGROUND

The apoptosis of microvascular endothelial cells causes plasma leakage in dengue haemorrhagic fever patients. The soluble Fas ligand is a protein with molecular weight of 40 kDa that acts as a mediator of apoptosis. This study aimed to prove whether soluble Fas ligand can be used as a potential marker to predict the severity of dengue infection by comparing the soluble Fas ligand levels in dengue fever (DF) and dengue haemorrhagic fever (DHF) patients early in the course of illness.

METHOD

This was a prospective study. It included 42 dengue patients (22 DF patients and 20 DHF patients) and 20 healthy people as a control group. The soluble Fas ligand was measured by the enzyme-linked immunosorbent assay (ELISA).

RESULT

Soluble Fas ligand was increased significantly (P < 0.001) in DHF patients (median = 130.19, IQR = 36.26) compared to DF patients (median = 104.73, IQR = 53.94) and the control group (median = 87.16, IQR = 24.91).

CONCLUSION

Soluble Fas ligand can be used as a potential marker to predict the severity of dengue infection in the early course of the illness. However, a larger sample size and further objective studies are needed to confirm these findings.

JNK1/2 inhibitor reduces dengue virus-induced liver injury

High viral load with liver injury is exhibited in severe dengue virus (DENV) infection. Mitogen activated protein kinases (MAPKs) including ERK1/2 and p38 MAPK were previously found to be involved in the animal models of DENV-induced liver injury. However, the role of JNK1/2 signaling in DENV-induced liver injury has never been investigated. JNK1/2 inhibitor, SP600125, was used to investigate the role of JNK1/2 signaling in the BALB/c mouse model of DENV-induced liver injury. SP600125-treated DENV-infected mice ameliorated leucopenia, thrombocytopenia, hemoconcentration, liver transaminases and liver histopathology. DENV-induced liver injury exhibited induced phosphorylation of JNK1/2, whereas SP600125 reduced this phosphorylation. An apoptotic real-time PCR array profiler was used to screen how SP600125 affects the expression of 84 cell death-associated genes to minimize DENV-induced liver injury. Modulation of caspase-3, caspase-8 and caspase-9 expressions by SP600125 in DENV-infected mice suggests its efficiency in restricting apoptosis via both extrinsic and intrinsic pathways. Reduced expressions of TNF-α and TRAIL are suggestive to modulate the extrinsic apoptotic signals, where reduced p53 phosphorylation and induced anti-apoptotic Bcl-2 expression indicate the involvement of the intrinsic apoptotic pathway. This study thus demonstrates the pivotal role of JNK1/2 signaling in DENV-induced liver injury and how SP600125 modulates this pathogenesis.

Serum neutrophil gelatinase-associated lipocalin and resistin are associated with dengue infection in adults

BACKGROUND

Dengue is a major health problem in tropical areas, including Taiwan. Dengue virus infection affects various types of cells and results in elevation of serum inflammatory molecules. Because these molecules may be associated with dengue virus infection, the aim of this study was to identify novel molecules in febrile patients with dengue infection. In addition, we determined whether these molecules were correlated with the count of leukocytes and platelets.

METHODS

Febrile adults (Age >18 years old) who presented to the emergency department and were confirmed dengue virus infection were enrolled in this study. Serum from dengue patients and healthy controls was collected and serum level of sepsis-associated inflammatory molecules was measured by Luminex assay.

RESULTS

Elevated level of macrophage migration inhibitory factor, soluble vascular cell adhesion molecule-1, sFasL, resistin and interferon-γ were detected in patients' serum. Higher levels of neutrophil gelatinase-associated lipocalin (NGAL) and resistin were detected in dengue patients with normal leukocyte count and all dengue patients, respectively. Furthermore, the serum level of NGAL, but not resistin, was correlated with cell count in dengue patients.

CONCLUSION

Our results revealed that resistin and NGAL are novel dengue-associated molecules. These results may help elucidate the regulatory mechanisms of anti-dengue immune responses.

SB203580 Modulates p38 MAPK Signaling and Dengue Virus-Induced Liver Injury by Reducing MAPKAPK2, HSP27, and ATF2 Phosphorylation

Dengue virus (DENV) infection causes organ injuries, and the liver is one of the most important sites of DENV infection, where viral replication generates a high viral load. The molecular mechanism of DENV-induced liver injury is still under investigation. The mitogen activated protein kinases (MAPKs), including p38 MAPK, have roles in the hepatic cell apoptosis induced by DENV. However, the in vivo role of p38 MAPK in DENV-induced liver injury is not fully understood. In this study, we investigated the role of SB203580, a p38 MAPK inhibitor, in a mouse model of DENV infection. Both the hematological parameters, leucopenia and thrombocytopenia, were improved by SB203580 treatment and liver transaminases and histopathology were also improved. We used a real-time PCR microarray to profile the expression of apoptosis-related genes. Tumor necrosis factor α, caspase 9, caspase 8, and caspase 3 proteins were significantly lower in the SB203580-treated DENV-infected mice than that in the infected control mice. Increased expressions of cytokines including TNF-α, IL-6 and IL-10, and chemokines including RANTES and IP-10 in DENV infection were reduced by SB203580 treatment. DENV infection induced the phosphorylation of p38MAPK, and its downstream signals including MAPKAPK2, HSP27 and ATF-2. SB203580 treatment did not decrease the phosphorylation of p38 MAPK, but it significantly reduced the phosphorylation of MAPKAPK2, HSP27, and ATF2. Therefore, SB203580 modulates the downstream signals to p38 MAPK and reduces DENV-induced liver injury.

IFI6 Inhibits Apoptosis via Mitochondrial-Dependent Pathway in Dengue Virus 2 Infected Vascular Endothelial Cells

Dengue hemorrhagic fever (DHF)/Dengue shock syndrome (DSS) is a fatal infectious disease that demands an effective treatment. Interferon (IFN)-stimulated genes (ISGs) induced by dengue virus (DENV) exert antiviral effects. Among ISGs, IFN-α inducible gene 6 (IFI6) was increased in DENV infected human umbilical vascular endothelial cells (HUVECs) by microarray analysis in our previous study. However, its function is incompletely understood. In this study, we confirmed that IFI6 was markedly induced in DENV infection of both primary HUVECs and EA.hy926 cell lines. Recombinant EA.hy926 cell lines in which IFI6 was either over-expressed (IFI6+/+) or knocked-down (IFI6-/-) were generated. The activation of caspase-3 and intrinsic apoptosis-related protein caspase-9 were down-regulated in IFI6+/+ but up-regulated in IFI6-/- cells at 24–48 hrs post-infection. After incubation with DENV for 48 hrs, the mitochondrial membrane potential (Δψ(m)) was more stable in IFI6+/+ cells but reduced in IFI6-/- cells, as assayed by fluorescence staining with JC-1. We observed that Bcl-2 expression was increased in IFI6+/+ and decreased in IFI6-/- cells. By contrast, Bax expression was decreased in IFI6+/+ and increased in IFI6-/- cells. It is presumed that the anti-apoptotic function of IFI6 is expressed by regulating the rheostatic balance between bcl-2/bax expression and inhibition of Δψ(m) depolarization during DENV infection of vascular endothelial cells(VECs). In addition, the pro-apoptotic protein X-linked Inhibitor of Apoptosis (XIAP)-Associated Factor 1(XAF1) expression had been reported to be up-regulated and led to the induction of apoptosis in DENV2-infected VECs,but the relationship between XAF1 and IFI6 dengue virus-induced apoptosis in VECs warrants further study.

Endothelial dysfunction in dengue virus pathology

Dengue virus (DENV) is a leading cause of illness and death, mainly in the (sub)tropics, where it causes dengue fever and/or the more serious diseases dengue hemorrhagic fever and dengue shock syndrome that are associated with changes in vascular permeability. Despite extensive research, the pathogenesis of DENV is still poorly understood and, although endothelial cells represent the primary fluid barrier of the blood vessels, the extent to which these cells contribute to DENV pathology is still under debate. The primary target cells for DENV are dendritic cells and monocytes/macrophages that release various chemokines and cytokines upon infection, which can activate the endothelium and are thought to play a major role in DENV-induced vascular permeability. However, recent studies indicate that DENV also replicates in endothelial cells and that DENV-infected endothelial cells may directly contribute to viremia, immune activation, vascular permeability and immune targeting of the endothelium. Also, the viral non-structural protein-1 and antibodies directed against this secreted protein have been reported to be involved in endothelial cell dysfunction. This review provides an extensive overview of the effects of DENV infection on endothelial cell physiology and barrier function.

Endothelial cells in dengue hemorrhagic fever

Therapies to prevent or reverse endothelial dysfunction and vascular leak found in dengue hemorrhagic fever (DHF) have not been identified. In this review we summarize dengue viruses and the spectrum of human disease and highlight evidence of endothelial cell dysfunction in DHF based on studies in patients and mouse and tissue culture models. Evidence suggests that both virus antigen and host immune response, can cause endothelial cell dysfunction and weaken endothelial barrier integrity. We suggest possible therapeutic interventions and highlight how therapies targeting altered endothelial function might be evaluated in animal models and in patients with DHF.

Coordinated regulation of autophagy and apoptosis determines endothelial cell fate during Dengue virus type 2 infection

Dengue is the most prevalent mosquito-borne viral disease in tropical regions. Severe cases may progress to Dengue hemorrhagic fever, suggesting vascular endothelial dysfunction in disease pathogenesis. In our previous study, we found that Dengue virus type 2 (DENV2) induced apoptosis of vascular endothelial cells via FasL/Fas- and XIAP-associated factor 1 (XAF1)-dependent pathways. In this paper, we demonstrate that DENV2 can induce autophagy in primary human umbilical vein endothelial cells (HUVECs) and the human umbilical vein endothelial cell line EA.hy926. Inhibition of autophagy with 3-methyl adenine promoted apoptosis, while inhibition of apoptosis with Z-VAD-FMK facilitated autophagy in DENV2-infected HUVECs and EA.hy926 cells. Interferon-alpha-inducible protein 6 (IFI6), a putative apoptosis regulator, inhibited DENV2-induced autophagy in EA.hy926 cells, while XAF1, an inhibitor of anti-apoptotic XIAP, facilitated autophagy. Molecular regulators of apoptosis and autophagy interact at multiple levels to determine cell fate. Our data suggest that XAF1 and IFI6 are involved in regulating the balance between autophagy and apoptosis in DENV2-infected endothelial cells.

Role of ERK1/2 signaling in dengue virus-induced liver injury

The liver is considered to be an important organ of dengue virus (DENV) replication and pathogenesis. However, molecular mechanisms of hepatic injury are still poorly understood. Modulation of Mitogen Activated Protein Kinases (MAPKs) was previously shown to affect DENV-induced apoptosis of hepatocytes in vitro. However, the in vivo role of ERK1/2, a member of the MAPK family, and the question whether its activation can facilitate cell survival or cell death, has not been thoroughly investigated. Therefore, the role of ERK1/2 in a mouse model of DENV infection was examined. Our results show that DENV induces phosphorylation of ERK1/2 and increases apoptosis. Inhibition of phosphorylated ERK1/2 by the selective ERK1/2 inhibitor, FR180204, limits hepatocyte apoptosis and reduces DENV-induced liver injury. Clinical parameters, including leucopenia, thrombocytopenia, transaminases and histology, show improvements after FR180204 treatment. The expression of cell death genes was further identified using real-time PCR array and Western blot analysis. Caspase-3 was significantly decreased in FR180204 treated DENV-infected mice compared to the levels of untreated DENV-infected mice suggesting the role of ERK1/2 signaling in immune-mediated liver injury during DENV infection.

Apoptotic mediators in patients with severe and non-severe dengue from Brazil

Despite being the most significant arboviral disease worldwide, dengue has no antiviral treatment or reliable severity predictors. It has been shown that apoptotic cells from blood and tissues may be involved in the complex pathogenesis of dengue. However, very little is known about the interplay between proapoptotic and antiapoptotic mediators in this disease. Therefore, plasma levels of the three proapoptotic mediators Fas ligand (FasL), tumor necrosis factor‐α (TNF‐α), and TNF‐related apoptosis‐inducing ligand (TRAIL) were measured in dengue patients. Patients were classified according to the World Health Organization classification of dengue revised in 2009. Additionally, inhibitors of apoptosis protein (IAPs) were determined in plasma (Survivin) and peripheral blood mononuclear cells (PBMCs) lysates (cIAP‐1, cIAP‐2, XIAP). Levels of apoptotic proteins in plasma were correlated with counts of blood cells. FasL and TRAIL levels were elevated in dengue patients without warning signs when compared to patients with severe dengue and controls. Dengue patients with warning signs showed decreased levels of Survivin compared to patients with severe dengue and controls. TRAIL was inversely correlated with counts of lymphocyte subsets. In contrast, Survivin was positively correlated with leukocyte counts. There was a trend of elevated IAPs levels in PBMCs of patients with severe dengue. The results suggest a likely antiviral effect of TRAIL in dengue. It appears that TRAIL might be involved with apoptosis induction of lymphocytes, whereas IAPs might participate in protecting leukocytes from apoptosis. Further research is needed to explore the interactions between pro and antiapoptotic molecules and their implications in dengue pathogenesis. J. Med. Virol. 86:1437–1447, 2014. © 2013 Wiley Periodicals, Inc.

Dengue 2 infection of HepG2 liver cells results in endoplasmic reticulum stress and induction of multiple pathways of cell death

BACKGROUND

A number of studies have implicated the direct involvement of the liver in dengue virus (DENV) infection, and it has been widely shown that liver cells subsequently undergo apoptosis. The mechanism by which liver cells undergo apoptosis in response to DENV infection remains unclear. To provide further information on the mechanism of apoptosis in DENV infected liver cells, HepG2 cells were infected with DENV 2 and analyzed for the induction of ER stress, apoptosis and autophagy.

RESULTS

In response to DENV infection, HepG2 cells showed the induction of both the ER resident unfolded protein response as well as the Noxa/PUMA stress response pathways. Proteolytic activation of caspases 4, 7, 8 and 9 was observed as well as changes in mitochondrial transmembrane potential. Increased monodansylcadaverine staining was observed in DENV infected cells, consistent with the previously reported induction of autophagy.

CONCLUSIONS

These results are consistent with a model in which the induction of multiple ER stress pathways is coupled with the induction of multiple cell death pathways as a mechanism to ensure the removal of infected liver cells from the system.

West Nile virus and dengue virus capsid protein negates the antiviral activity of human Sec3 protein through the proteasome pathway

Flavivirus capsid (C) protein is a key structural component of virus particles. The non-structural role of C protein in the pathogenesis of arthropod-borne flaviviruses is not clearly deciphered. This study showed that West Nile virus (WNV) and dengue virus (DENV) utilized C protein to reduce human Sec3p (hSec3p) levels at post-transcriptional level through activation of chymotrypsin-like proteolytic function of 20S proteasome. Mutagenesis studies confirmed amino acids 14, 109-114 of WNV C protein and 13, 102-107 of DENV C protein played an important role in activating the proteolytic function of 20S proteasome. Amino acid residues at 14 (WNV) and 13 (DENV) of C protein were important for C protein-hSec3p binding and physical interaction between C protein and hSec3p was essential to execute hSec3p degradation. Degradation motif required to degrade hSec3p resided between amino acid residues 109-114 of WNV C protein and 102-107 of DENV C protein. Proteasomes, hSec3p binding motif and degradation motif on C protein must be intact for efficient flavivirus production. Clinical isolates of DENV showed more pronounced effect in manipulating the proteasomes and reducing hSec3p levels. This study portrayed the non-structural function of C protein that helped the flavivirus to nullify the antiviral activity of hSec3p by accelerating its degradation and facilitating efficient binding of elongation factor 1α with flaviviral RNA genome.

Inhibition of p38MAPK and CD137 signaling reduce dengue virus-induced TNF-α secretion and apoptosis

BACKGROUND

Hepatic injury in dengue virus (DENV) infection is authenticated by hepatomegaly and an upsurge in transaminase levels. DENV replicates in hepatocytes and causes hepatocyte apoptosis both in vitro and in vivo. Understanding the molecular mechanisms of DENV-induced hepatic injury could facilitate the development of alternate chemotherapeutic agents and improved therapies.

FINDINGS

The p38 mitogen-activated protein kinase (MAPK) participates in both apoptosis-related signaling and pro- inflammatory cytokine production. The role of p38 MAPK in DENV-infected HepG2 cells was examined using RNA interference. The results showed that DENV infection activated p38 MAPK and induced apoptosis. The p38 MAPK activation and TNF-α production were controlled by p38 MAPK and CD137 signaling in DENV-infected HepG2 cells as activated p38 MAPK, TNF-α and apoptosis were significantly decreased in p38 MAPK and CD137 depleted DENV-infected HepG2 cells. Addition of exogenous TNF-α to p38 MAPK depleted DENV-infected HepG2 cells restored DENV-induced apoptosis in HepG2 cells.

CONCLUSION

DENV induces CD137 signaling to enhance apoptosis by increasing TNF-α production via activation of p38 MAPK.

The battle between infection and host immune responses of dengue virus and its implication in dengue disease pathogenesis

Dengue virus (DENV) is a mosquito-transmitted single stranded RNA virus belonging to genus Flavivirus. The virus is endemic in the tropical and subtropical countries of the world, causing diseases classified according to symptoms and severity (from mild to severe) as dengue fever, dengue hemorrhagic fever, and dengue shock syndrome. Among a variety of human cell types targeted by DENV, monocytes, macrophages, and dendritic cells are members of innate immunity, capable of mounting rapid inflammatory responses. These cells are also major antigen presenting cells, responsible for activating the adaptive immunity for long-term memory. This paper is an overview of the current understanding of the following mutually affected aspects: DENV structure, viral infectivity, cellular receptors, innate immune response, and adaptive immunity.

Essential role of RIG-I in the activation of endothelial cells by dengue virus

Dengue virus (DENV) infection is associated to exacerbated inflammatory response and structural and functional alterations in the vascular endothelium. However, the mechanisms underlying DENV-induced endothelial cell activation and their role in the inflammatory response were not investigated so far. We demonstrated that human brain microvascular endothelial cells (HBMECs) are susceptible to DENV infection, which induces the expression of the cytoplasmic pattern recognition receptor (PRR) RIG-I. Infection of HBMECs promoted an increase in the production of type I IFN and proinflammatory cytokines, which were abolished after RIG-I silencing. DENV-infected HBMECs also presented a higher ICAM-1 expression dependent on RIG-I activation as well. On the other hand, ablation of RIG-I did not interfere with virus replication. Our data suggest that RIG-I activation by DENV may participate in the disease pathogenesis through the modulation of cytokine release and expression of adhesion molecules, probably contributing to leukocyte recruitment and amplification of the inflammatory response.

The NS3 protease and helicase domains of Japanese encephalitis virus trigger cell death via caspase‑dependent and ‑independent pathways

Japanese encephalitis virus (JEV), a mosquito‑borne flavivirus, causes acute encephalitis and nervous damage. Previous studies have demonstrated that JEV induces apoptosis in infected cells. However, to date the mechanisms of JEV‑induced apoptosis are unclear. In order to identify the viral proteins associated with JEV‑induced apoptosis, pEGFP‑non‑structural protein 3 (NS3) 1‑619 (expressing the JEV NS3 intact protein, including the protease and helicase domains), pEGFP‑NS3 1‑180 (expressing the protease domain) and pEGFP‑NS3 163‑619 (expressing the helicase domain) were transfected into target cells to study cell death. Results demonstrate that the JEV NS3 intact protein and protease and helicase domains induce cell death. In addition, cell death was identified to be significantly higher in cells transfected with the NS3 protease domain compared with the intact protein and helicase domain. Caspase activation was also analyzed in the current study. NS3 intact protein and NS3 protease and helicase domains activated caspase‑9/‑3‑dependent and ‑independent pathways. However, caspase‑8 activity was not found to be significantly different in NS3‑transfected cells compared with control. In summary, the present study demonstrates that the NS3 helicase and protease domains of JEV activate caspase‑9/‑3‑dependent and ‑independent cascades and trigger cell death.

XAF1 contributes to dengue virus-induced apoptosis in vascular endothelial cells

The mechanism of vascular leakage in severe dengue infection remains unclear. Here, we used primary human umbilical vein endothelial cells (HUVECs) and the EA.hy926 cell line to study the molecular events that occur after dengue virus serotype 2 (DENV2) infection. DENV2-induced apoptosis was confirmed using nuclear staining, TUNEL assay, and electron microscopy. A genome-wide transcriptome analysis was performed using a microarray of DENV2-infected HUVECs. Notably, interferon-inducible genes were differentially expressed after DENV2 infection. Prominent among these genes was the X chromosome-linked inhibitor of apoptosis protein (XIAP)-associated factor 1 (XAF1; up-regulated 1.2-fold in the microarray analysis and ∼8-fold by qRT-PCR after DENV2 infection). XAF1 protein levels were up-regulated after DENV2 infection in both HUVECs and EA.hy926 cells. Evidence indicated interaction between XAF1 and XIAP during DENV2 infection based on their cellular localization, as observed by confocal microscopy and the coimmunoprecipitation of XIAP with an anti-XAF1 antibody. Next, recombinant EA.hy926 cell lines in which XAF1 was either knocked down or overexpressed were constructed. The expression levels of the apoptosis-related genes caspase 3, caspase 8, caspase 9, and poly-(ADP-ribose) polymerase (PARP) were down-regulated in the XAF1 knockdown (24-48 h postinfection) but were up-regulated in XAF1 overexpressing cells (36 h postinfection). This is the first study of the role of XAF1 in promoting apoptosis in vascular endothelial cells after DENV2 infection.

Dengue retinochoroiditis

Dengue is a mosquito-borne infection caused by a flavivirus. I describe the ocular findings observed in two patients infected with dengue virus who presented with acute onset of loss of vision preceded by febrile illness, malaise, generalized fatigue headache, and maculopapular rash. Ophthalmologic evaluation in each patient revealed a normal anterior segment. Vitreous cells were noted in one patient. Ophthalmoscopy revealed multiple foci of retinochoroiditis, vasculitis, cotton-wool spots, and retinal hemorrhages. The healing of the lesion showed discrete atrophic and pigmented retinochoroiditic scars. Fluorescein angiography displayed early hypofluorescence and late hyperfluorescence suggestive of leakage. The healed scars showed late staining. The serologic testing showed elevated IgG antibodies, and one had high IgM antibodies to dengue virus. Ocular findings of dengue fever consist of multifocal areas of retinochoroiditis and may lead to loss of vision. In Saudi Arabia, dengue fever should be considered in the differential diagnosis of multifocal chorioretinal lesions and retinal vasculitis.

Fas/FasL and perforin-granzyme pathways mediated T cell cytotoxic responses in infectious bursal disease virus infected chickens

Infectious bursal disease (IBD) is a highly contagious disease of chickens which leads to immunosuppression. In our previous study it was demonstrated that, possibly, CD4(+) and CD8(+) T cells may employ perforin and granzyme-A pathway for the clearance of IBDV-infected bursal cells. In this study, we evaluated the cytotoxic T cell responses involving two independently functioning but complementary mechanisms: Fas-Fas ligand and perforin-granzyme pathways in IBDV-infected chickens. As demonstrated previously, infection of chickens with IBDV was accompanied by influx of CD8(+) T cells in the bursa and spleen. There was an upregulation in the gene expression of cytolytic molecules: Fas and Fas ligand (FasL), perforin (PFN) and granzyme-A (Gzm-A) in bursal and in the splenic tissues of IBDV inoculated chickens. Additionally, for the first time, we detected Fas, Fas ligand, Caspase-3 and PFN producing CD8(+) T cells in the bursa and spleen of IBDV-infected chickens. The infiltration and activation of CD8(+) T cells was substantiated by the detection of Th1 cytokine, IFN-γ. These data suggest that T cells may be involved in the clearance of virus from the target organ bursa and peripheral tissues such as spleen. The findings of these studies provide new insights into the pathogenesis of IBD and provide mechanistic evidence that the cytotoxic T cells may act through both Fas-FasL and perforin-granzyme pathways in mediating the clearance of virus-infected cells.

Antigen presentation by endothelial cells: what role in the pathophysiology of malaria?

Disruption of the endothelial cell (EC) barrier leads to pathology via edema and inflammation. During infections, pathogens are known to invade the EC barrier and modulate vascular permeability. However, ECs are semi-professional antigen-presenting cells, triggering T-cell costimulation and specific immune-cell activation. This in turn leads to the release of inflammatory mediators and the destruction of infected cells by effectors such as CD8(+) T-cells. During malaria, transfer of parasite antigens to the EC surface is now established. At the same time, CD8 activation seems to play a major role in cerebral malaria. We summarize here some of the pathways leading to antigen presentation by ECs and address the involvement of these mechanisms in the pathophysiology of cerebral malaria.

Oncolytic poxvirus armed with Fas ligand leads to induction of cellular Fas receptor and selective viral replication in FasR-negative cancer

The TNF superfamily members including Fas ligand and TRAIL have been studied extensively for cancer therapy, including as components of gene therapy. We examined the use of FasL expression to achieve tumor selective replication of an oncolytic poxvirus (vFasL) and explored its biology and therapeutic efficacy for FasR− and FasR+ cancers. Infection of FasR+ normal and MC38 cancer cells by vFasL led to abortive viral replication due to acute apoptosis and subsequently displayed both reduced pathogenicity in non-tumor bearing mice and reduced efficacy in FasR+ tumor-bearing mice. Infection of FasR− B16 cancer cells by vFasL led to efficient viral replication, followed by late induction of FasR and subsequent apoptosis. Treatment with vFasL compared to its parental virus (vJS6) led to increased tumor regression and prolonged survival of mice with FasR− cancer (B16), but not with FasR+ cancer (MC38). The delayed induction of FasR by viral infection in FasR− cells provides for potential increased efficacy beyond the limit of the direct oncolytic effect. FasR induction provides one mechanism for tumor selective replication of oncolytic poxviruses in FasR− cancers with enhanced safety. The overall result is both a safer and more effective oncolytic virus for FasR− cancer.

A detrimental role for invariant natural killer T cells in the pathogenesis of experimental dengue virus infection

Dengue virus (DENV), a member of the mosquito-borne flaviviruses, is a serious public health problem in many tropical countries. We assessed the in vivo physiologic contribution of invariant natural killer T (iNKT) cells, a population of nonconventional lipid-reactive αβ T lymphocytes, to the host response during experimental DENV infection. We used a mouse-adapted DENV serotype 2 strain that causes a disease that resembles severe dengue in humans. On DENV challenge, splenic and hepatic iNKT cells became activated insofar as CD69 and Fas ligand up-regulation and interferon-γ production. C57BL/6 mice deficient in iNKT cells (Jα18(-/-)) were more resistant to lethal infection than were wild-type animals, and the phenotype was reversed by adoptive transfer of iNKT cells to Jα18(-/-) animals. The absence of iNKT cells in Jα18(-/-) mice was associated with decreased systemic and local inflammatory responses, less liver injury, diminished vascular leak syndrome, and reduced activation of natural killer cells and neutrophils. iNKT cell functions were not necessary for control of primary DENV infection, after either natural endogenous activation or exogenous activation with the canonical iNKT cell agonist α-galactosylceramide. Together, these data reveal a novel and critical role for iNKT cells in the pathogenesis of severe experimental dengue disease.

Productive dengue virus infection of human endothelial cells is directed by heparan sulfate-containing proteoglycan receptors

Dengue virus causes leakage of the vascular endothelium, resulting in dengue hemorrhagic fever and dengue shock syndrome. The endothelial cell lining of the vasculature regulates capillary permeability and is altered by immune and chemokine responses which affect fluid barrier functions of the endothelium. Our findings indicate that human endothelial cells are highly susceptible to infection by dengue virus (type 4). We found that dengue virus productively infects ∼80% of primary human endothelial cells, resulting in the rapid release of ∼10(5) virions 1 day postinfection. Analysis of potential inhibitors of dengue virus entry demonstrated that antibodies and ligands to integrins and cellular receptors were unable to inhibit dengue virus infection of endothelial cells. In contrast, pretreating cells with heparin or heparan sulfate resulted in a 60 to 80% reduction in dengue virus-infected cells, and pretreatment of endothelial cells with heparinase III or protease reduced dengue infectivity by >80%. Dengue virus bound specifically to resin immobilized heparin, and binding was competitively inhibited by excess heparin but not other ligands. Collectively, these findings suggest that dengue virus specifically attaches to heparan sulfate-containing proteoglycan receptors on endothelial cells. Following attachment to human endothelial cell receptors, dengue virus causes a highly productive infection that has the potential to increase viral dissemination and viremia. This provides the potential for dengue virus-infected endothelial cells to directly alter barrier functions of the endothelium, contribute to enhancement of immune cell activation, and serve as potential targets of immune responses which play a central role in dengue pathogenesis.

Role of CD137 signaling in dengue virus-mediated apoptosis

Hepatic dysfunction is a well recognized feature of dengue virus (DENV) infection. However, molecular mechanisms of hepatic injury are still poorly understood. A complex interaction between DENV and the host immune response contributes to DENV-mediated tissue injury. DENV capsid protein (DENV C) physically interacts with the human death domain-associated protein Daxx. A double substitution mutation in DENV C (R85A/K86A) abrogates Daxx interaction, nuclear localization and apoptosis. Therefore we compared the expression of cell death genes between HepG2 cells expressing DENV C and DENV C (R85A/K86A) using a real-time PCR array. Expression of CD137, which is a member of the tumor necrosis factor receptor family, increased significantly in HepG2 cells expressing DENV C compared to HepG2 cells expressing DENV C (R85A/K86A). In addition, CD137-mediated apoptotic activity in HepG2 cells expressing DENV C was significantly increased by anti-CD137 antibody compared to that of HepG2 cells expressing DENV C (R85A/K86A). In DENV-infected HepG2 cells, CD137 mRNA and CD137 positive cells significantly increased and CD137-mediated apoptotic activity was increased by anti-CD137 antibody. This work is the first to demonstrate the contribution of CD137 signaling to DENV-mediated apoptosis.

Dengue infection of monocytic cells activates ER stress pathways, but apoptosis is induced through both extrinsic and intrinsic pathways

Monocytic cells are believed to be an important mediator of the pathology of dengue disease in cases of secondary infection where pre-existing antibodies from a first infection facilitate virus entry to Fc receptor bearing cells. In this study we assessed the induction of the ER stress in response to infection of monocytic U937 cells with all four DENV serotypes as well as the induction of apoptosis. Clear evidence of ER stress and the production of pro-apoptotic signals were observed, together with activation of caspase 9. Surprisingly, caspase 8 was also activated, independently of caspase 9, and this was accompanied by an increase in the expression of TNF-α, suggesting the simultaneous but independent activation of both extrinsic and intrinsic apoptosis pathways. Both the induction of ER stress and apoptosis were shown to be serotype independent.