Tumor necrosis factor alpha levels in plasma and whole-blood culture in dengue-infected patients: relationship between virus detection and pre-existing specific antibodies

Subneutralizing antibodies to enterovirus 71 induce antibody-dependent enhancement of infection in newborn mice

Antibody-dependent enhancement (ADE) of virus infections can be induced by subneutralizing concentrations of specific antibodies. We recently demonstrated ADE in human monocytes infected with enterovirus 71 (EV71). The current study was designed to extend these observations by determining the effect of ADE on the pathogenesis of EV71 infection in newborn mice. We compared the clinical manifestations, mortality, virus titer, histopathology, and serum levels of cytokines and chemokines in newborn mice pretreated with subneutralizing antibodies to EV71 or normal mouse IgG with and without virus. Seven-day-old ICR mice were pretreated with a wide range of mouse anti-EV71 IgG 24 h prior to intraperitoneal injection of EV71. Mice were protected from infection by neutralizing doses of anti-EV71 IgG ranging from 6.43 × 10⁻¹ to 329.6 μg/ml. Subneutralizing doses ranging from 2.01 × 10⁻² to 3.21 × 10⁻¹ μg/ml were found to significantly increase 14-day mortality compared to virus alone. The ADE effect was not evident at lower doses. Histopathological examination of mice given a subneutralizing dose of 8.04 × 10⁻² μg/ml revealed extensive neuronal and muscular damage compared to untreated infected controls. Higher serum levels of interferon (IFN)-γ and monocyte chemoattractant protein (MCP)-1 were noted in mice pretreated with subneutralizing doses than untreated infected controls. These findings support the concept that subneutralizing antibodies directed enhance EV71 induce ADE in newborn mice.

Autoimmunity in dengue pathogenesis

Dengue is one of the most important vector-borne viral diseases. With climate change and the convenience of travel, dengue is spreading beyond its usual tropical and subtropical boundaries. Infection with dengue virus (DENV) causes diseases ranging widely in severity, from self-limited dengue fever to life-threatening dengue hemorrhagic fever and dengue shock syndrome. Vascular leakage, thrombocytopenia, and hemorrhage are the major clinical manifestations associated with severe DENV infection, yet the mechanisms remain unclear. Besides the direct effects of the virus, immunopathogenesis is also involved in the development of dengue disease. Antibody-dependent enhancement increases the efficiency of virus infection and may suppress type I interferon-mediated antiviral responses. Aberrant activation of T cells and overproduction of soluble factors cause an increase in vascular permeability. DENV-induced autoantibodies against endothelial cells, platelets, and coagulatory molecules lead to their abnormal activation or dysfunction. Molecular mimicry between DENV proteins and host proteins may explain the cross-reactivity of DENV-induced autoantibodies. Although no licensed dengue vaccine is yet available, several vaccine candidates are under development. For the development of a safe and effective dengue vaccine, the immunopathogenic complications of dengue disease need to be considered.

Dengue virus infection mediates HMGB1 release from monocytes involving PCAF acetylase complex and induces vascular leakage in endothelial cells

High mobility group box 1 (HMGB1) protein is released from cells as a pro-inflammatory cytokine in response to an injury or infection. During dengue hemorrhagic fever (DHF)/dengue shock syndrome (DSS), a number of pro-inflammatory cytokines are released, contributing to disease pathogenesis. In this study, the release of HMGB1 from human myelogenous leukemia cell line K562 and primary peripheral blood monocytes (PBM) cells was examined during dengue virus (DV)-infection. HMGB1 was shown to translocate from cell nuclei to the cytoplasm in both K562- and PBM-infected cells. The translocation of HMGB1 from the nucleus to the cytoplasm was shown to be mediated by the host cell p300/CBP-associated factor (PCAF) acetylase complex in K562 cells. In addition, DV capsid protein was observed to be the putative viral protein in actuating HMGB1 migration from the nucleus to cytoplasm through the involvement of PCAF acetylase. HMGB1 was released from DV-infected K562 cells into the extracellular milieu in a multiplicity of infection (M.O.I.)-independent manner and its release can be inhibited by the addition of 1–5 mM of ethyl pyruvate (EP) in a dose-dependent manner. Application of DV-infected K562 cell culture supernatants to primary endothelial cells induced vascular permeability. In contrast, supernatants from DV-infected K562 cells treated with EP or HMGB1 neutralizing antibody were observed to maintain the structural integrity of the vascular barrier.

Variation in inflammatory/regulatory cytokines in secondary, tertiary, and quaternary challenges with dengue virus

Secondary heterologous dengue infection is a risk factor for severe disease manifestations because of the immune-enhancement phenomenon. Succeeding clinical infections are seldom reported, and the clinical course of tertiary and quaternary dengue infections is not clear. Cuba represents a unique environment to study tertiary/quaternary dengue infections in a population with known clinical and serologic dengue markers and no dengue endemicity. We took advantage of this exceptional epidemiologic condition to study the effect of primary, secondary, tertiary, and quaternary dengue infection exposure on the expression of pro-inflammatory and regulatory cytokines, critical in dengue infection pathogenesis, by using a dengue infection ex vivo model. Whereas secondary exposure induced a high cytokine response, we found a significantly lower expression of tumor necrosis factor-α, interferon-γ, interleukin-10, and tumor growth factor-β after tertiary and quaternary infectious challenge. Significant differences in expression of the cytokines were seen between the dengue immune profiles, suggesting that the sequence in which the immune system encounters serotypes may be important in determining the nature of the immune response to subsequent infections.

Dengue: A Clinicohaematological Profile

BACKGROUND

Fifty cases of fever, clinically suspected to be dengue were studied.

METHODS

Complete clinical, haematological evaluation and IgM capture assay was done.

RESULT

54% of patients clinically suspected to have dengue were positive for IgM antibodies by enzyme-linked immunosorbent assay (ELISA). The commonest clinical feature was fever with rash (85%). Thrombocytopenia was seen in 19% of patients only. One patient died of dengue shock syndrome (DSS).

CONCLUSION

Out of the 27 cases of seropositive dengue there was one death due to dengue shock syndrome. Thrombocytopenia may not always be a feature of dengue.

Cells in dengue virus infection in vivo

Dengue has been recognized as one of the most important vector-borne emerging infectious diseases globally. Though dengue normally causes a self-limiting infection, some patients may develop a life-threatening illness, dengue hemorrhagic fever (DHF)/dengue shock syndrome (DSS). The reason why DHF/DSS occurs in certain individuals is unclear. Studies in the endemic regions suggest that the preexisting antibodies are a risk factor for DHF/DSS. Viremia and thrombocytopenia are the key clinical features of dengue virus infection in patients. The amounts of virus circulating in patients are highly correlated with severe dengue disease, DHF/DSS. Also, the disturbance, mainly a transient depression, of hematological cells is a critical clinical finding in acute dengue patients. However, the cells responsible for the dengue viremia are unresolved in spite of the intensive efforts been made. Dengue virus appears to replicate and proliferate in many adapted cell lines, but these in vitro properties are extremely difficult to be reproduced in primary cells or in vivo. This paper summarizes reports on the permissive cells in vitro and in vivo and suggests a hematological cell lineage for dengue virus infection in vivo, with the hope that a new focus will shed light on further understanding of the complexities of dengue disease.

TNF and LTA gene, allele, and extended HLA haplotype associations with severe dengue virus infection in ethnic Thais

Severe dengue virus (DENV) infection is characterized by a cascade of cytokine production, including the production of tumor necrosis factor-alpha (TNF-alpha) and lymphotoxin-alpha (LT-alpha). We have analyzed a variety of polymorphisms in the TNF and LTA genes of 435 ethnic Thais who had subclinical DENV infection, primary or secondary dengue fever (DF), or primary or secondary dengue hemorrhagic fever (DHF). The TNF -238A polymorphism marking the TNF-4,LTA-3 haplotype occurred in a significantly greater number of patients with secondary DHF (20 [15.2%] of 132) than patients with secondary DF (7 [4.1%] of 169) (P < .001; P corrected by use of Bonferroni adjustment, .022; odds ratio, 4.13 [95% confidence interval, 1.59-11.17]). In a subset of patients, the LTA-3 haplotype was associated with in vivo intracellular production of LT-alpha and TNF-alpha during the acute viremic phase of infection. Two extended human major histocompatibility complex (MHC) haplotypes containing TNF-4 and LTA-3, together with HLA-B48, HLA-B57, and HLA-DPB1*0501, were detected only in patients with secondary DHF. These observations indicate that polymorphism in functionally distinct MHC-encoded proteins contributes to the risk of developing severe secondary DENV infection and warrants further investigation.

Mechanisms and results of the antibody-dependent enhancement of viral infections and role in the pathogenesis of coxsackievirus B-induced diseases

The mechanisms of the antibody-dependent enhancement (ADE) of viral infection are presented, particularly within the Picornaviridae family. The ADE of infection has been described in both human and animal models, worsens viral infections and compromises vaccine safety. The ADE of coxsackievirus B infection can also be implied in the pathogenesis of diseases like chronic dilated cardiomyopathy or insulin-dependent type 1 diabetes.

Serum levels of interleukin-6, tumor necrosis factor-alpha and interferon-gamma in infants with and without dengue

This study compared the serum levels of IL-6, TNF-alpha and IFN-gamma, in children under 1 year of age with and without dengue. Sera were collected from a total of 41 children living in the Department of Antioquia, Colombia (27 patients with dengue and 14 controls). The results showed higher cytokine levels in children with dengue than without dengue, with statistically significant differences for IL-6 and IFN-gamma. No statistically significant differences were found between clinical forms, although IL-6 and IFN-gamma levels were higher in dengue fever cases than in dengue hemorrhagic fever cases. On the other hand, TNF-alpha levels were higher in dengue hemorrhagic fever than in dengue fever. The levels of IL-6 and TNF-alpha were higher in secondary infection than in primary infection, although IFN-gamma levels were higher in primary infection. These results suggest that IL-6, TNF-alpha and IFN-gamma are involved in dengue infection independently of the clinical form.

Secreted NS1 of dengue virus attaches to the surface of cells via interactions with heparan sulfate and chondroitin sulfate E

Dengue virus (DENV) nonstructural protein-1 (NS1) is a secreted glycoprotein that is absent from viral particles but accumulates in the supernatant and on the plasma membrane of cells during infection. Immune recognition of cell surface NS1 on endothelial cells has been hypothesized as a mechanism for the vascular leakage that occurs during severe DENV infection. However, it has remained unclear how NS1 becomes associated with the plasma membrane, as it contains no membrane-spanning sequence motif. Using flow cytometric and ELISA-based binding assays and mutant cell lines lacking selective glycosaminoglycans, we show that soluble NS1 binds back to the surface of uninfected cells primarily via interactions with heparan sulfate and chondroitin sulfate E. DENV NS1 binds directly to the surface of many types of epithelial and mesenchymal cells yet attaches poorly to most peripheral blood cells. Moreover, DENV NS1 preferentially binds to cultured human microvascular compared to aortic or umbilical cord vein endothelial cells. This binding specificity was confirmed in situ as DENV NS1 bound to lung and liver but not intestine or brain endothelium of mouse tissues. Differential binding of soluble NS1 by tissue endothelium and subsequent recognition by anti-NS1 antibodies could contribute to the selective vascular leakage syndrome that occurs during severe secondary DENV infection.

Dengue virus (DENV) is a mosquito-transmitted virus that infects humans and has become a global emerging infectious disease threat. Four serotypes of DENV exist, and the most severe cases are associated with secondary infection with a different virus serotype. Clinical deterioration is characterized by bleeding and selective vascular leakage from endothelium in specific tissue sites. An increased understanding of how DENV proteins contribute to this phenotype is vital to developing novel vaccines and identifying individuals at risk for severe disease. DENV nonstructural protein-1 (NS1) is one such protein: during infection, it is secreted and accumulates in the supernatant and on the surface of cells. In this study, we demonstrate that soluble DENV NS1 attaches to subsets of cells, including some but not all endothelial cells, primarily via an interaction with specific glycosaminoglycans (heparan sulfate and chondroitin sulfate E). This was confirmed in tissue binding studies as DENV NS1 bound to lung and liver but not intestine or brain endothelium. Our findings suggest that the selective vascular leakage that occurs in severe DENV infection may be related to the relative ability of endothelial cells in different tissues to bind soluble NS1 and to be targeted by cross-reactive anti-NS1 antibodies during secondary infection.

High pro-inflammatory cytokine secretion and loss of high avidity cross-reactive cytotoxic T-cells during the course of secondary dengue virus infection

Background

Dengue is one of the most important human diseases transmitted by an arthropod vector and the incidence of dengue virus infection has been increasing – over half the world's population now live in areas at risk of infection. Most infections are asymptomatic, but a subset of patients experience a potentially fatal shock syndrome characterised by plasma leakage. Severe forms of dengue are epidemiologically associated with repeated infection by more than one of the four dengue virus serotypes. Generally attributed to the phenomenon of antibody-dependent enhancement, recent observations indicate that T-cells may also influence disease phenotype.

Methods and Findings

Virus-specific cytotoxic T lymphocytes (CTL) showing high level cross reactivity between dengue serotypes could be expanded from blood samples taken during the acute phase of secondary dengue infection. These could not be detected in convalescence when only CTL populations demonstrating significant serotype specificity were identified. Dengue cross-reactive CTL clones derived from these patients were of higher avidity than serotype-specific clones and produced much higher levels of both type 1 and certain type 2 cytokines, many previously implicated in dengue pathogenesis.

Conclusion

Dengue serotype cross-reactive CTL clones showing high avidity for antigen produce higher levels of inflammatory cytokines than serotype-specific clones. That such cells cannot be expanded from convalescent samples suggests that they may be depleted, perhaps as a consequence of activation-induced cell death. Such high avidity cross-reactive memory CTL may produce inflammatory cytokines during the course of secondary infection, contributing to the pathogenesis of vascular leak. These cells appear to be subsequently deleted leaving a more serotype-specific memory CTL pool. Further studies are needed to relate these cellular observations to disease phenotype in a large group of patients. If confirmed they have significant implications for understanding the role of virus-specific CTL in pathogenesis of dengue disease.

Transcriptional activation of interferon-stimulated genes but not of cytokine genes after primary infection of rhesus macaques with dengue virus type 1

Macaques are the only animal model used to test dengue virus (DENV) vaccine candidates. Nevertheless, the pathogenesis of DENV in macaques is not well understood. In this work, by using Affymetrix oligonucleotide microarrays, we studied the broad transcriptional modifications and cytokine expression profile after infecting rhesus macaques with DENV serotype 1. Five days after infection, these animals produced a potent, innate antiviral immune response by inducing the transcription of signature genes from the interferon (IFN) pathway with demonstrated antiviral activity, such as myxoprotein, 2',5'-oligoadenylate synthetase, phospholipid scramblase 1, and viperin. Also, IFN regulatory element 7, IFN-stimulated gene 15, and protein ligases linked to the ISGylation process were up-regulated. Unexpectedly, no up-regulation of IFN-alpha, -beta, or -gamma genes was detected. Transcription of the genes of interleukin-10 (IL-10), IL-8, IL-6, and tumor necrosis factor alpha was neither up-regulated nor down-regulated. Results were confirmed by real-time PCR and by multiplex cytokine detection in serum samples.

Dengue illness: clinical features and pathogenesis

The incidence and geographical distribution of dengue has gradually increased during the past decade. This review is an update on dengue virus infections, based on our clinical and laboratory experiences in the Philippines and on other relevant literature. The differential diagnosis of this disease is discussed, especially for use by clinicians where dengue is not endemic. The complex pathogenesis of thrombocytopenia and increased vascular permeability in dengue illness is also discussed. Our recent data suggest that platelet-associated immunoglobulins involving anti-dengue virus activity play a pivotal role in the development of dengue hemorrhagic fever (DHF), as well as thrombocytopenia in secondary dengue virus infections. Further elucidation is needed on the involvement of platelet-associated immunoglobulins on the molecular mechanisms of thrombocytopenia and the increased vascular permeability.

Role of T cells, cytokines and antibody in dengue fever and dengue haemorrhagic fever

Dengue infections are a major cause of morbidity and mortality in the tropical and sub-tropical regions of the world. There is no vaccine for dengue and also there are no anti-viral drugs to treat the infection. Some patients, typically those experiencing a secondary infection with a different dengue serotype, may progress from an acute febrile disease to the more severe forms of disease, dengue haemorrhagic fever and dengue shock syndrome. Here we discuss the significant immunopathological component to severe disease and how T cells, cytokines and cross-reactive antibody combine to contribute to the progression to dengue haemorrhagic fever. These events are thought to lead to vascular leakage, the signature event in dengue haemorrhagic fever, and are addressed in this review by incorporating the concept of heterologous T cell immunity. The need for effective measures against dengue and dengue-related illness is clear. We propose that drugs against dengue virus, or the symptoms of severe dengue disease, are a viable goal.

The role of tumor necrosis factor in modulating responses of murine embryo fibroblasts by flavivirus, West Nile

Murine embryo fibroblasts (MEF) transcribe tumor necrosis factor (TNF) mRNA and secrete soluble TNF in response to infection by West Nile virus (WNV) and TNF was demonstrated to be protective against WNV infection in vitro. TNF is not required for the WNV-induced upregulation of MHC-I expression on MEF, as TNF deficiency did not affect the upregulation of major histocompatibility complex class I (MHC-I) by WNV. Furthermore, NF-kappaB was activated by WNV in TNF-deficient MEF, demonstrating that WNV induces NF-kappaB activation in a TNF-independent manner. The subunits of NF-kappaB activated by TNF and WNV differed, WNV-activated a p65/p50 NF-kappaB complex while TNF-activated NF-kappaB was composed of p65, p50, and c-Rel. Furthermore, TNF-induced activation of NF-kappaB occurred earlier than WNV-induced NF-kappaB activation. The data demonstrate that WNV infection of MEF is associated with TNF production, but the WNV-induced activation of NF-kappaB and subsequent upregulation of MHC-I by WNV is TNF-independent.

Anti-TNF antibody treatment reduces mortality in experimental dengue virus infection

Here we describe a lethal mouse model infected with dengue virus type 2 with several similarities to human DEN-2 infection. Clinically animals demonstrated anemia, thrombocytopenia, pre-terminal paralysis and shock. The most impressive changes were seen with tumor necrosis factor (TNF)-alpha, which abruptly and steeply increased 24 h before the exitus (mean at day 6). Serum levels of IL-1beta, IL-6, IL-10, IL-1 receptor antagonist and soluble TNF receptor I continuously increased during the time of infection. A 100% mortality rate was noted in that group of animals. Treating animals with anti-TNF-alpha serum reduced mortality rate down to 40% (P<0.05). Our model supports the view that activation of innate immune response is at least partially responsible for mortality in DEN-2 infection, and in line with this concept, anti-TNF treatment significantly reduces mortality rates.

Dengue: an update

This review is an update of dengue and dengue haemorrhagic fever (DHF) based on international and Cuban experience. We describe the virus characteristics and risk factors for dengue and DHF, and compare incidence and the case fatality rates in endemic regions (southeast Asia, western Pacific, and the Americas). The clinical picture and the pathogenesis of the severe disease are explained. We also discuss the viral, individual, and environmental factors that determine severe disease. Much more research is necessary to clarify these mechanisms. Also reviewed are methods for viral isolation and the serological, immunohistochemical, and molecular methods applied in the diagnosis of the disease. We describe the status of vaccine development and emphasise that the only alternative that we have today to control the disease is through control of its vector Aedes aegypti.

Dengue fever and dengue haemorrhagic fever: challenges of controlling an enemy still at large

Dengue virus infections are a serious cause of morbidity and mortality in most tropical and subtropical areas of the world: mainly Southeast and South Asia, Central and South America, and the Caribbean. Understanding the pathogenesis of dengue haemorrhagic fever (DHF), the severe form of dengue illness, is a very important and challenging research subject. Viral virulence and immune responses have been considered as two major factors responsible for the pathogenesis. Virological studies are attempting to define the molecular basis of viral virulence. The immunopathological mechanisms appear to include a complex series of immune responses. A rapid increase in the levels of cytokines and chemical mediators apparently plays a key role in inducing plasma leakage, shock and haemorrhagic manifestations. It is likely that the entire process is initiated by infection with a so-called virulent dengue virus, often with the help of enhancing antibodies in secondary infection, and then triggered by rapidly elevated cytokines and chemical mediators produced by intense immune activation. However, understanding of the DHF pathogenesis is not complete. We still have a long way to go.

Detection of circulant tumor necrosis factor-alpha, soluble tumor necrosis factor p75 and interferon-gamma in Brazilian patients with dengue fever and dengue hemorrhagic fever

Pro-inflammatory cytokines are believed to play an important role in the pathogenesis of dengue infection. This study reports cytokine levels in a total of 54 patients examined in Recife, State of Pernambuco, Brazil. Five out of eight patients who had hemorrhagic manifestations presented tumor necrosis factor-alpha (TNF-alpha) levels in sera which were statistically higher than those recorded for controls. In contrast, only one out of 16 patients with mild manifestations had elevated TNF-alpha levels. The levels of interleukin-6 (IL), IL-1beta tested in 24 samples and IL-12 in 30 samples were not significantly increased. Interferon-g was present in 10 out of 30 patients with dengue. The data support the concept that the increased level of TNF-alpha is related to the severity of the disease. Soluble TNF receptor p75 was found in most patients but it is unlikely to be related to severity since it was found with an equivalent frequency and levels in 15 patients with dengue fever and another 15 with dengue hemorrhagic fever.

Involvement of oxidative stress, NF-IL-6, and RANTES expression in dengue-2-virus-infected human liver cells

The liver has been suspected to be one of the major targets of dengue virus infection. Here, we detected increasing secretion of the chemokine RANTES (regulated upon activation, normal T cell expressed and secreted), which functions to recruit the immune cells, in dengue-virus-infected liver cells and patients. Three luciferase reporter genes with various deletions at the 5'-end of the RANTES promoter were constructed to explore the RANTES activation mechanism in human liver cells. The reporter gene was optimally activated by dengue-2 virus when the RANTES promoter contains the region from the transcription starting site (+1) to the nucleotide at the -181 position. NF-IL-6 and an undefined factor forming DNA-protein complexes in the RANTES promoter E and A/B regions in the infected cells were demonstrated by electrophoretic mobility shift assay. Further analysis showed that oxidative stress was an upstream inducer of NF-IL-6 and RANTES signaling in dengue-virus-infected liver cells. This finding was demonstrated by three antioxidants (N-acetyl-l-cysteine, nitro-l-arginine methyl ester, and pyrrolidine dithiocarbamate) used to suppress the activation. In contrast, the DNA binding activity of the undefined factor was not affected by the antioxidant treatment, indicating the existence of an oxidant-independent pathway. We hypothesize that dengue virus infection of the liver cells may trigger both an oxidant-dependent and an oxidant-independent pathway to up-regulate RANTES mRNA expression through activating NF-IL-6 and an undefined factor, respectively. In conclusion, the present study suggests a new direction for the study of liver pathogenesis involving RANTES in host immune responses during dengue virus infection.

Determination of tumor necrosis factor-alpha levels in dengue virus infected patients by sensitive biotin-streptavidin enzyme-linked immunosorbent assay

A modified sandwich enzyme-linked immunosorbent assay using biotin-streptavidin system (BS-ELISA) was developed to determine levels of tumor necrosis factor-alpha (TNF-alpha) in serum samples of children infected with dengue virus (n=99) and healthy controls (n=41). The minimum detectable concentration of TNF-alpha by the BS-ELISA was 3.3 pg/ml. The mean TNF-alpha level was highest in those patients with dengue shock syndrome (DSS) or dengue hemorrhagic fever (DHF) grade III (37.44+/-42.0 pg/ml). Lower levels were found in DHF grade I (28.44+/-42.7 pg/ml), DHF grade II (24. 21+/-25.4 pg/ml) and dengue fever (DF) (14.10+/-24.0 pg/ml). TNF-alpha in the sera of DF and DHF patients could be detected on days 2-6 after the onset of fever, the high level occurring on day 5. TNF-alpha was detected in 41.4% (24.01+/-35.2 pg/ml) of dengue virus infected patients and 7.3% (4.2+/-15.6 pg/ml) of control subjects. The sera of patients contained significantly higher levels of TNF-alpha than the sera of controls, P-value<0.001. DHF patients had significantly higher levels of TNF-alpha than DF patients (P-value=0.020) but no difference in the TNF-alpha levels from sera of DHF grades I-III patients was observed (P-value=0.295). The results indicate that the BS-ELISA is a very sensitive method for determining TNF-alpha in serum samples of DF and DHF patients. The TNF-alpha levels might be associated with dengue virus infection and related to disease severity of DHF.

Potential dengue virus-triggered apoptotic pathway in human neuroblastoma cells: arachidonic acid, superoxide anion, and NF-kappaB are sequentially involved

Direct in vivo evidence for the susceptibility of human neuronal cells to dengue virus has not been reported. In this study, we demonstrated that type 2 dengue (DEN-2) virus infection induced extensive apoptosis in the human neuroblastoma cell line SK-N-SH. Phospholipase A(2) (PLA(2)) was activated by DEN-2 infection, which led to the generation of arachidonic acid (AA). Inhibition of PLA(2) activity by the PLA(2) inhibitors, AACOCF(3) and ONO-RS-082, diminished DEN-2 virus-induced apoptosis. In contrast, the cyclooxygenase inhibitors aspirin and indomethacin, thought to increase AA accumulation by blocking AA catabolism, enhanced apoptosis. Exogenous AA induced apoptosis in a dose-dependent manner. Superoxide anion, which is thought to be generated through the AA-activated NADPH oxidase, was increased after infection. Pretreatment with superoxide dismutase (SOD) protected cells against DEN-2 virus-induced apoptosis. Furthermore, generation of superoxide anion was blocked by AACOCF(3). In addition, the transcription factors, NF-kappaB and c-Jun, were found to be activated after DEN-2 virus infection. However, pretreatment of cells with oligodeoxynucleotides containing NF-kappaB, but not c-Jun, binding sites (transcription factor decoy) strongly prevented dengue virus-induced apoptosis. The finding that AACOCF(3) and SOD significantly block activation of NF-kappaB suggests that this activation is derived from the AA-superoxide anion pathway. Our results indicate that DEN-2 virus infection of human neuroblastoma cells triggers an apoptotic pathway through PLA(2) activation to superoxide anion generation and subsequently to NF-kappaB activation. This apoptotic effect can be either directly derived from the action of AA and superoxide anion on mitochondria or indirectly derived from the products of apoptosis-related genes activated by NF-kappaB.

Release of vasoactive cytokines by antibody-enhanced dengue virus infection of a human mast cell/basophil line

We report here the first demonstration of dengue virus infection and vasoactive cytokine response of a cell of the mast cell/basophil lineage. Infection of KU812 cells was dependent on dengue-specific antibody and gave rise to infectious virions. This antibody-enhanced dengue virus infection triggered a four- to fivefold increase in the release of interleukin-1beta (IL-1beta) and a modest increase for IL-6 but not for an alternate cytokine, granulocyte-macrophage colony-stimulating factor. The results suggest a potential role for mast cells/basophils in the pathogenesis of dengue virus-induced disease.

Cytokine cascade in dengue hemorrhagic fever: implications for pathogenesis

Dengue virus produces a mild acute febrile illness, dengue fever (DF) and a severe illness, dengue hemorrhagic fever (DHF). The characteristic feature of DHF is increased capillary permeability leading to extensive plasma leakage in serous cavities resulting in shock. The pathogenesis of DHF is not fully understood. This paper presents a cascade of cytokines, that in our view, may lead to DHF. The main feature is the early generation of a unique cytokine, human cytotoxic factor (hCF) that initiates a series of events leading to a shift from Th1-type response in mild illness to a Th2-type response resulting in severe DHF. The shift from Th1 to Th2 is regulated by the relative levels of interferon-gamma and interleukin (IL)-10 and between IL-12 and transforming growth factor-beta, which showed an inverse relationship in patients with DF.

Sequential production of cytokines by dengue virus-infected human peripheral blood leukocyte cultures

The study was undertaken to elucidate the sequence of appearance of T helper (Th)1- and Th2-type cytokines in human peripheral blood leucocyte cultures infected in vitro with dengue type 2 virus. Commercial sandwich enzyme-linked immunosorbent assay kits were used to assay the levels of tumour necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), interleukin (IL)-2, IL-4, IL-5, IL-6, and IL-10 in culture supernatants. Culture supernatants were also screened for the cytotoxic factor and the dengue virus titres determined. The cytokines that appeared in the culture supernatants on the first day post-infection (p.i.) were cytotoxic factor, TNF-alpha, IL-2, and IL-6; their levels were highest on the second day p.i. IFN-gamma appeared on the second day with a peak on the third day p.i. The levels of these cytokines declined quickly, except for human cytotoxic factor (hCF) and IL-2. The cytokines that appeared later were IL-10 and IL-5 on the fourth day and IL-4 on the sixth day p.i. Dengue virus replicated in the peripheral blood leucocyte (PBL) cultures and was present throughout the course of the study. The findings of the present study show that dengue virus induced a predominant Th1-type cytokine response during the first 3 days of infection of PBL cultures that was replaced by a Th2-type response later.

Increased pro-inflammatory cytokines (TNF-alpha and IL-6) and anti-inflammatory compounds (sTNFRp55 and sTNFRp75) in Brazilian patients during exanthematic dengue fever

Pro-inflammatory cytokines, tumor necrosis factor (TNF-alpha), interleukin-6 (IL-6) and interleukin-1beta (IL-1beta) as well as anti-inflammatory compounds, soluble TNF-Receptor p55 (sTNFRp55), sTNFRp75 and IL-1 receptor antagonist (sIL-1Ra), were investigated in 34 Brazilian cases of dengue fever (DF) originated from a study of exanthematic virosis. The presence of pro-inflammatory cytokines was detected in sera from these patients by ELISA. TNF-alpha and IL-6 levels were significantly higher than control subjects in 32% and 52% patients, respectively. To our knowledge this was the first time a receptor antagonist and soluble receptors for cytokines were detected in sera obtained during exanthematic DF without hemorrhagic manifestations. Both sTNFRp55 and sTNFRp75 were consistently elevated in 42% and 84% patients, respectively. Most patients had IL-1beta levels not different from those of normal subjects, except for one case. Only 16% patients had altered levels of IL-1Ra. Previous studies in dengue hemorrhagic fever patients demonstrated production of these soluble factors; here we observed that they are found in absence of hemorrhagic manifestations. The possible role of these anti-inflammatory compounds in immune cell activation and in regulating cytokine-mediated pathogenesis during dengue infection is discussed.

Apoptotic cell death in response to dengue virus infection: the pathogenesis of dengue haemorrhagic fever revisited

BACKGROUND

Dengue virus infection may be asymptomatic or lead to undifferentiated febrile illness or dengue haemorrhagic fever and dengue shock syndrome (DHF/DSS). The major clinical manifestations of DHF/DSS are high fever, haemorrhage, hepatomegaly and circulatory failure.

OBJECTIVES

The relatively high level of viraemia only a few days after infection may reflect a large number of replication sites. However, the degree of cell injury in fatal cases of DHF/DSS is not sufficient to explain death and suggests metabolic disturbance rather than tissue destruction. This theory was investigated in this study.

RESULTS

We demonstrated that replication of dengue virus in infected cells induces stress leading to apoptotic cell death in vitro and in vivo.

CONCLUSIONS

The elimination of apoptotic bodies by phagocytic cells is a previously unsuspected pathway of dengue virus clearance from infected tissues. However, the mechanisms of host defence involving apoptosis and phagocytic cell activation may cause local tissue injury or transient homeostasis imbalance and may trigger further deleterious events.