Alteration of cytokines and chemokines during febrile episodes associated with endothelial cell damage and plasma leakage in dengue hemorrhagic fever

Severity of Plasma Leakage Is Associated With High Levels of Interferon γ-Inducible Protein 10, Hepatocyte Growth Factor, Matrix Metalloproteinase 2 (MMP-2), and MMP-9 During Dengue Virus Infection

BACKGROUND

 Dengue virus infection typically causes mild dengue fever, but, in severe cases, life-threatening dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS) occur. The pathophysiological hallmark of DHF and DSS is plasma leakage that leads to enhanced vascular permeability, likely due to a cytokine storm.

METHODS

 Ninety patients with dengue during 2010-2012 in Singapore were prospectively recruited and stratified according to their disease phase, primary and secondary infection status, and disease severity, measured by plasma leakage. Clinical parameters were recorded throughout the disease progression. The levels of various immune mediators were quantified using comprehensive multiplex microbead-based immunoassays for 46 immune mediators.

RESULTS

 Associations between clinical parameters and immune mediators were analyzed using various statistical methods. Potential immune markers, including interleukin 1 receptor antagonist, interferon γ-inducible protein 10, hepatocyte growth factor, soluble p75 tumor necrosis factor α receptor, vascular cell adhesion molecule 1, and matrix metalloproteinase 2, were significantly associated with significant plasma leakage. Secondary dengue virus infections were also shown to influence disease outcome in terms of disease severity.

CONCLUSIONS

 This study identified several key markers for exacerbated dengue pathogenesis, notably plasma leakage. This will allow a better understanding of the molecular mechanisms of DHF and DSS in patients with dengue.

West Nile virus-infected human dendritic cells fail to fully activate invariant natural killer T cells

West Nile virus (WNV) infection is a mosquito-borne zoonosis with increasing prevalence in the United States. WNV infection begins in the skin, and the virus replicates initially in keratinocytes and dendritic cells (DCs). In the skin and cutaneous lymph nodes, infected DCs are likely to interact with invariant natural killer T cells (iNKTs). Bidirectional interactions between DCs and iNKTs amplify the innate immune response to viral infections, thus controlling viral load and regulating adaptive immunity. iNKTs are stimulated by CD1d-bound lipid antigens or activated indirectly by inflammatory cytokines. We exposed human monocyte-derived DCs to WNV Kunjin and determined their ability to activate isolated blood iNKTs. DCs became infected as judged by synthesis of viral mRNA and Envelope and NS-1 proteins, but did not undergo significant apoptosis. Infected DCs up-regulated the co-stimulatory molecules CD86 and CD40, but showed decreased expression of CD1d. WNV infection induced DC secretion of type I interferon (IFN), but no or minimal interleukin (IL)-12, IL-23, IL-18 or IL-10. Unexpectedly, we found that the WNV-infected DCs stimulated human iNKTs to up-regulate CD69 and produce low amounts of IL-10, but not proinflammatory cytokines such as IFN-γ or tumour necrosis factor (TNF)-α. Both CD1d and IFNAR blockade partially abrogated this iNKT response, suggesting involvement of a T cell receptor (TCR)-CD1d interaction and type I interferon receptor (IFNAR) signalling. Thus, WNV infection interferes with DC-iNKT interactions by preventing the production of proinflammatory cytokines. iNKTs may be a source of IL-10 observed in human flavivirus infections and initiate an anti-inflammatory innate response that limits adaptive immunity and immune pathology upon WNV infection.

Cytokine Profile of Children Hospitalized with Virologically-Confirmed Dengue during Two Phase III Vaccine Efficacy Trials

Background

Two large-scale efficacy studies with the recombinant yellow fever-17D–dengue virus, live-attenuated, tetravalent dengue vaccine (CYD-TDV) candidate undertaken in Asia (NCT01373281) and Latin America (NCT01374516) demonstrated significant protection against dengue disease during two years’ active surveillance (active phase). Long-term follow up of participants for breakthrough disease leading to hospitalization is currently ongoing (hospital phase).

Methodology/Principal findings

We assessed the cytokine profile in acute sera from selected participants hospitalized (including during the active phase) up to the beginning of the second year of long-term follow up for both studies. The serum concentrations of 38 cytokines were measured in duplicate using the Milliplex Human Cytokine MAGNETIC BEAD Premixed 38 Plex commercial kit (Millipore, Billerica, MA, USA). Partial least squares discriminant analyses did not reveal any difference in the overall cytokine profile of CYD-TDV and placebo recipients hospitalized for breakthrough dengue regardless of stratification used. In addition, there was no difference in the cytokine profile for breakthrough dengue among those aged <9 years versus those aged ≥ 9 years.

Conclusions/Significance

These exploratory findings show that CYD-TDV does not induce a particular immune profile versus placebo, corroborating the clinical profile observed.

A live-attenuated, tetravalent dengue vaccine (CYD-TDV) has been shown to provide protection against dengue disease in two large-scale, placebo-controlled, phase III efficacy studies. Continued surveillance of study participants was subsequently undertaken to better define longer term vaccine efficacy and safety. A yet unexplained higher incidence of hospitalization for dengue disease was observed among children aged <9 years in year 3 of follow up. While the clinical outcome of the hospitalized cases was similar between CYD-TDV and placebo recipients, it was important to further investigate whether the immune profile induced by breakthrough infection differed between the two study groups. We compared the profile of 38 cytokines, chemokines and growth factors in acute phase sera collected from participants with breakthrough disease in the two groups. No difference in overall profile was observed between CYD-TDV and placebo recipients. Similarly, no difference in the cytokine profile for breakthrough dengue was observed between those aged <9 years and those aged ≥ 9 years. Based on these analyzed factors, our study shows that CYD-TDV does not induce an overall altered immunological profile with breakthrough disease compared with placebo, in agreement with the similar clinical pictures and viremia observed in the two groups.

Slow resolution of inflammation in severe adult dengue patients

BACKGROUND

The pathogenesis of severe dengue has not been fully elucidated. The inflammatory response plays a critical role in the outcome of dengue disease.

METHODS

In this study, we investigated the levels of 17 important inflammation mediators in plasma collected from mild or severe adult dengue patients at different time points to understand the contribution of inflammation to disease severity and to seek experimental evidence to optimize the existing clinical treatment strategies. Patients were simply classified as mild and severe dengue according to the 2009 WHO classification. Plasma was collected on day 3-5, 6-7, 8-10 and 14-17 of illness. Levels of 17 inflammation mediators including TNF-α, IL-1α, IFN-γ, IL-6, IFN-α, MIF, IL-10, IL-1RA, IL-8, IP-10, MCP-1, RANTES, GRO, eotaxin-1, sICAM-1 and sVCAM-1 were determined by a multiplex Luminex® system. Different trends of inflammation mediators throughout the disease were compared between mild and severe patients.

RESULTS

Inflammation mediators including IL-1α, IFN-γ, IL-10, IL-8, IP-10, MCP-1 and sVCAM-1 displayed significant differences on day 8-10 of illness between mild and severe dengue patients. Their concentrations were higher in severe patients than mild ones at the same time points. Moreover, those cytokines decreased gradually in mild patients but not in severe patients.

CONCLUSION

Our results revealed the coexistence of excessive inflammatory response and slow resolution of inflammation in severe adult dengue patients. Hence suppression and/or pro-resolution of inflammation could be a potential therapeutic approach for treatment of severe dengue.

Isolation of dengue virus serotype 4 genotype II from a patient with high viral load and a mixed Th1/Th17 inflammatory cytokine profile in South Brazil

Background

We report the isolation and characterization of dengue virus (DENV) serotype 4 from a resident of Santa Fé, state of Paraná, South Brazil, in March 2013. This patient presented with hemorrhagic manifestations, high viral load and, interestingly, a mixed Th1/Th17 cytokine profile.

Case presentation

The patient presented with classical dengue symptoms, such as fever, rash, myalgia, arthralgia, and hemorrhagic manifestations including petechiae, gum bleeding and a positive tourniquet test result. A serum sample obtained 1 day after the initial appearance of clinical symptoms was positive for NS1 viral antigen, but this sample was negative for both IgM and IgG against DENV. Dengue virus infection was confirmed by isolation of the virus from C6/36 cells, and dengue virus serotyping was performed via one-step RT-PCR. The infection was confirmed to be caused by a serotype 4 dengue virus. Additionally, based on multiple alignment and phylogeny analyses of its complete genome sequence, the viral strain was classified as genotype II (termed LRV13/422). Moreover, a mixed Th1/Th17 cytokine profile was detected in the patient’s serum, and this result demonstrated significant inflammation. Biological characterization of the virus via in vitro assays comparing LRV13/422 with a laboratory-adapted reference strain of dengue virus serotype 4 (TVP/360) showed that LRV13/422 infects both vertebrate and invertebrate cell lines more efficiently than TVP/360. However, LRV13/422 was unable to inhibit type I interferon responses, as suggested by the results obtained for other dengue virus strains. Furthermore, LRV13/422 is the first completely sequenced serotype 4 dengue virus isolated in South Brazil.

Conclusion

The high viral load and mixed Th1/Th17 cytokine profile observed in the patient’s serum could have implications for the development of the hemorrhagic signs observed, and these potential relationships can now be further studied using suitable animal models and/or in vitro systems.

Electronic supplementary material

The online version of this article (doi:10.1186/s12985-016-0548-9) contains supplementary material, which is available to authorized users.

Demethylation profile of the TNF-α promoter gene is associated with high expression of this cytokine in Dengue virus patients

Dengue is the most prevalent arthropod-borne viral illness in humans. The overexpression of cytokines by Dengue virus (DENV) infected cells is associated with the most severe forms of the disease. Unmethylated CpG islands are related to a transcriptionally active structure, whereas methylated DNA recruits methyl-binding proteins that inhibit gene expression. Several studies have described the importance of epigenetic events in the regulation and expression of many cytokines. The purpose of the present study was to evaluate the methylation status of the IFN-γ and TNF-α promoters in DNA extracted from dengue infected patients using methylation-specific polymerase chain reaction. A high frequency of demethylation was observed in the TNF-α promoter of DENV infected patients when compared to non-infected controls. The patients with an unmethylated profile showed higher expression of TNF-α mRNA than patients with the methylated status. No difference was found in the methylation frequency between the two analyzed groups regarding the IFN-γ promoter or in the expression of IFN-γ transcripts. The present study provides the first association of TNF-α promoter demethylation in DENV infected individuals and demonstrates a correlation between the methylation status of the region analyzed and the expression of TNF-α transcripts in DENV infected patients. J. Med. Virol. 88:1297-1302, 2016. © 2016 Wiley Periodicals, Inc.

Recent advances in understanding dengue

Dengue is an emerging threat to billions of people worldwide. In the last 20 years, the incidence has increased four-fold and this trend appears to be continuing. Caused by one of four viral serotypes, dengue can present as a wide range of clinical phenotypes with the severe end of the spectrum being defined by a syndrome of capillary leak, coagulopathy, and organ impairment. The pathogenesis of severe disease is thought to be in part immune mediated, but the exact mechanisms remain to be defined. The current treatment of dengue relies on supportive measures with no licensed therapeutics available to date. There have been recent advances in our understanding of a number of areas of dengue research, of which the following will be discussed in this review: the drivers behind the global dengue pandemic, viral structure and epitope binding, risk factors for severe disease and its pathogenesis, as well as the findings of recent clinical trials including therapeutics and vaccines. We conclude with current and future dengue control measures and key areas for future research.

Upregulation of the Suppressors of Cytokine Signaling 1 and 3 Is Associated with Arrest of Phosphorylated-STAT1 Nuclear Importation and Reduced Innate Response in Denguevirus-Infected Macrophages

To clarify whether the suppressors of cytokine signaling (SOCS) are associated with denguevirus (DENV) evasion of the antiviral response, we analyzed the expression kinetics of SOCS1 and SOCS3 and of the antiviral genes MxA and OAS during DENV infection of U937 macrophages that were or not treated with interferon (IFN)-α. DENV infection produced a viral titer three times higher in untreated than in IFN-α-treated cells (p < 0.001 at 72 h postinfection [p.i.]). Partial inhibition of DENV replication was associated with reduced expression of MxA and OAS antiviral genes as well as higher SOCS1 and SOCS3 expression in DENV-infected cells than in cells treated only with IFN-α. Complete loss of phosphorylated-signal transducer and activator of transcription (p-STAT)2 and reduced nuclear importation of p-STAT1 were observed in DENV-infected cells compared to IFN-α treatment that induced p-STAT1 and p-STAT2. Our data thus suggest that overexpression of SOCS1 and SOCS3 induced by DENV infection leads to impairment of antiviral response through the inhibition of STAT functionality.

Differential proteomic analysis of virus-enriched fractions obtained from plasma pools of patients with dengue fever or severe dengue

Background

Dengue is the most widespread mosquito-borne viral disease of public health concern. In some patients, endothelial cell and platelet dysfunction lead to life-threatening hemorrhagic dengue fever or dengue shock syndrome. Prognostication of disease severity is urgently required to improve patient management. The pathogenesis of severe dengue has not been fully elucidated, and the role of host proteins associated with viral particles has received little exploration.

Methods

The proteomes of virion-enriched fractions purified from plasma pools of patients with dengue fever or severe dengue were compared. Virions were purified by ultracentrifugation combined with a water-insoluble polyelectrolyte-based technique. Following in-gel hydrolysis, peptides were analyzed by nano-liquid chromatography coupled to ion trap mass spectrometry and identified using data libraries.

Results

Both dengue fever and severe dengue viral-enriched fractions contained identifiable viral envelope proteins and host cellular proteins. Canonical pathway analysis revealed the identified host proteins are mainly involved in the coagulation cascade, complement pathway or acute phase response signaling pathway. Some host proteins were over- or under-represented in plasma from patients with severe dengue compared to patients with dengue fever. ELISAs were used to validate differential expression of a selection of identified host proteins in individual plasma samples of patients with dengue fever compared to patients with severe dengue. Among 22 host proteins tested, two could differentiate between dengue fever and severe dengue in two independent cohorts (olfactomedin-4: area under the curve (AUC), 0.958; and platelet factor-4: AUC, 0.836).

Conclusion

A novel technique of virion-enrichment from plasma has allowed to identify two host proteins that have prognostic value for classifying patients with acute dengue who are more likely to develop a severe dengue. The impact of these host proteins on pathogenicity and disease outcome are discussed.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-015-1271-7) contains supplementary material, which is available to authorized users.

Circulating cytokines and chemokines associated with plasma leakage and hepatic dysfunction in Brazilian children with dengue fever

Dengue fever is usually a benign acute viral infection transmitted by arthropods but may evolve to severe clinical manifestations such as coagulation and/or hemodynamic disorders, caused mainly by an increase of vascular permeability. Deregulated circulating immunological factors have been associated with severity. In Brazil severe cases appeared in children only recently and we evaluated the profile of cytokine/chemokine kinetics in 134 hospitalized young patients during the epidemic in Rio de Janeiro in 2008. Inflammatory cytokines TNF and IFNγ were found elevated during the acute phase in children as well as the anti-inflammatory IL10 and chemokines MIF and CXCL10/IP10, all last three persisting longer during the recovery phase. Severe disease fitting the dengue hemorrhagic fever pattern (WHO, 1997) was associated with higher IL10 and CXCL10/IP10 circulating levels (peak levels at seven days with P<0.01 and P<0.001 respectively as compared to DF). These factors were higher in patients pulmonary effusion or ascites (P<0.05 for IL10 and P<0.01 for CXCL10/IP10). Both factors were also associated with liver changes such as AST increase correlated with CXCL10/IP10 (r=0.4300 with P<0.0001) and patients presenting painful hepatomegaly showed higher circulating levels of IL10 (P<0.01, at 7-9 days) and of CXCL10/IP10 (P<0.05, 4-6 days and P<0.001, 7-9 days) when compared to patients without apparent liver alterations. Most cases presented a history of prior infection (93%). This is the first study demonstrating cytokine and chemokine association with severity during dengue fever in Brazilian children. IL10 and CXCL10/IP10 play a role in the disease severity associated with induction of vascular leakage and a novel association with changes in liver dysfunction.

Minimal within-host dengue models highlight the specific roles of the immune response in primary and secondary dengue infections

In recent years, the within-host viral dynamics of dengue infections have been increasingly characterized, and the relationship between aspects of these dynamics and the manifestation of severe disease has been increasingly probed. Despite this progress, there are few mathematical models of within-host dengue dynamics, and the ones that exist focus primarily on the general role of immune cells in the clearance of infected cells, while neglecting other components of the immune response in limiting viraemia. Here, by considering a suite of mathematical within-host dengue models of increasing complexity, we aim to isolate the critical components of the innate and the adaptive immune response that suffice in the reproduction of several well-characterized features of primary and secondary dengue infections. By building up from a simple target cell limited model, we show that only the innate immune response is needed to recover the characteristic features of a primary symptomatic dengue infection, while a higher rate of viral infectivity (indicative of antibody-dependent enhancement) and infected cell clearance by T cells are further needed to recover the characteristic features of a secondary dengue infection. We show that these minimal models can reproduce the increased risk of disease associated with secondary heterologous infections that arises as a result of a cytokine storm, and, further, that they are consistent with virological indicators that predict the onset of severe disease, such as the magnitude of peak viraemia, time to peak viral load, and viral clearance rate. Finally, we show that the effectiveness of these virological indicators to predict the onset of severe disease depends on the contribution of T cells in fuelling the cytokine storm.

Vascular leakage in dengue hemorrhagic Fever is associated with dengue infected monocytes, monocyte activation/exhaustion, and cytokines production

The vascular leakage was shown by the increment of hematocrit (Hct), dengue viral infected monocyte, monocyte status, and cytokines production in patients infected with dengue virus. Dengue viral antigens were demonstrated in monocytes (CD14+) from peripheral blood mononuclear cells. The increased levels of Hct, interleukin- (IL-) 10, and tumor necrosis factor-alpha (TNF-α) were detected in dengue fever (DF), dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS) patients as compared with other febrile illnesses (OFIs). The highest levels of Hct and IL-10 were detected in DSS patients as compared with other groups (P < 0.05) especially on one day before and after defervescence. The unstimulated and lipopolysaccharide- (LPS-) stimulated monocytes from DSS patients showed the significantly decreased of intracellular IL-1β and TNF-α. In addition, the lowest level of mean fluorescence intensity (MFI) of CD11b expression on monocytes surface in DSS patients was also demonstrated. Furthermore, the negative correlations between IL-10 levels and intracellular IL-1β and MFI of CD11b expression in unstimulated and LPS-stimulated monocytes were also detected. Nevertheless, not only were the relationships between the prominent IL-10 and the suppression of intracellular monocyte secretion, namely, IL-1β, TNF-α, demonstrated but also the effect of vascular leakage was observed.

Platelet activating factor contributes to vascular leak in acute dengue infection

Background

Although plasma leakage is the hallmark of severe dengue infections, the factors that cause increased vascular permeability have not been identified. As platelet activating factor (PAF) is associated with an increase in vascular permeability in other diseases, we set out to investigate its role in acute dengue infection.

Materials and Methods

PAF levels were initially assessed in 25 patients with acute dengue infection to determine if they were increased in acute dengue. For investigation of the kinetics of PAF, serial PAF values were assessed in 36 patients. The effect of dengue serum on tight junction protein ZO-1 was determined by using human endothelial cell lines (HUVECs). The effect of dengue serum on and trans-endothelial resistance (TEER) was also measured on HUVECs.

Results

PAF levels were significantly higher in patients with acute dengue (n = 25; p = 0.001) when compared to healthy individuals (n = 12). In further investigation of the kinetics of PAF in serial blood samples of patients (n = 36), PAF levels rose just before the onset of the critical phase. PAF levels were significantly higher in patients with evidence of vascular leak throughout the course of the illness when compared to those with milder disease. Serum from patients with dengue significantly down-regulated expression of tight junction protein, ZO-1 (p = 0.004), HUVECs. This was significantly inhibited (p = 0.004) by use of a PAF receptor (PAFR) blocker. Serum from dengue patients also significantly reduced TEER and this reduction was also significantly (p = 0.02) inhibited by prior incubation with the PAFR blocker.

Conclusion

Our results suggest the PAF is likely to be playing a significant role in inducing vascular leak in acute dengue infection which offers a potential target for therapeutic intervention.

Although plasma leakage is the hallmark of severe dengue infections, the factors that cause increased vascular permeability have not been identified. As platelet activating factor (PAF) is associated with an increase in vascular permeability in other diseases, we set out to investigate its role in acute dengue infection. In this study, we found that PAF was significantly increased in patients with DHF, and the PAF levels rose just before the onset of the critical phase of dengue, during which vascular leak is thought to occur. PAF in serum of dengue patients was associated with reduced expression of tight junction proteins (ZO-1) and reduction in trans-endothelial resistance (TEER) of human endothelial cells. Use of PAFR blockers significantly reduced the down regulation of ZO-1 by serum of dengue patients and also the reduction of TEER, suggesting that PAF plays a significant role in inducing vascular leak in acute dengue infections.

Elevated erythropoietin and cytokines levels are related to impaired reticulocyte maturation in thalassemic patients

Serum EPO concentration is related primarily to the rate of erythrocyte production and, under the stimulation of hypoxia, increases exponentially as hemoglobin (Hb) decreased. The level of EPO was determined in 141 subjects including 43 normal, 44 thalassemic patients and 54 thalassemic trait subjects. The EPO level was significantly higher in the thalassemic patients (54.8mU/ml in HbH disease [α thal1/α thal2;], 78.1mU/ml in HbH with Hb CS [α thal 1/CS]; 95.6mU/ml in β-thal/HbE splenectomized [BE(S)]; and 114.8mU/ml in β-thal/HbE non-splenectomized [BE(NS)]as compared with 12.0mU/ml in normal subjects. No significant differences were detected in thalassemic trait subjects. In addition, the levels of EPO in thalassemic patients is correlated significantly with the number of reticulocytes and the reticulocyte fractions especially the fraction of immature reticulocytes. Interestingly, the highest level of EPO/% retic ratio as indicated for EPO non-responder was detected in BE(NS) patients. However, the impaired reticulocytes maturation was found to be related significantly with the levels of TNF-α,IFN-γ,IL-10, and VEGF. Since, TNF-α, IFN-γ, IL-10 and VEGF are reported as the cytokines with erythropoietic inhibitory mediators, the variation of these cytokines in thalassemic environments may be associated to the anemic crisis in these patients.

Predicting outcome from dengue

Dengue is emerging as one of the most abundant vector-borne disease globally. Although the majority of infections are asymptomatic or result in only a brief systemic viral illness, a small proportion of patients develop potentially fatal complications. These severe manifestations, including a unique plasma leakage syndrome, a coagulopathy sometimes accompanied by bleeding, and organ impairment, occur relatively late in the disease course, presenting a window of opportunity to identify the group of patients likely to progress to these complications. However, as yet, differentiating this group from the thousands of milder cases seen each day during outbreaks remains challenging, and simple and inexpensive strategies are urgently needed in order to improve case management and to facilitate appropriate use of limited resources. This review will cover the current understanding of the risk factors associated with poor outcome in dengue. We focus particularly on the clinical features of the disease and on conventional investigations that are usually accessible in mid-level healthcare facilities in endemic areas, and then discuss a variety of viral, immunological and vascular biomarkers that have the potential to improve risk prediction. We conclude with a description of several novel methods of assessing vascular function and intravascular volume status non-invasively.

The association of cytokines with severe dengue in children

Background: Dengue virus infection is a major public health problem. A hypothesis put forward for severe dengue is the cytokine storm, a sudden increase in cytokines that induces vascular permeability. Previous studies and our recent meta-analysis showed that IL-6, IL-8, IFNγ, TNFα, VEGF-A and VCAM-1 are associated with dengue shock syndrome. Therefore, in this study we aim to validate the association of these cytokines with severe dengue.

Methods & Findings: In a hospital based-case control study in Vietnam, children with dengue fever, other febrile illness and healthy controls were recruited. Dengue virus infection was confirmed by several diagnostic tests. Multiplex immunoassay using Luminex technology was used to measure cytokines simultaneously. A positive association with dengue shock syndrome was found for VCAM-1, whereas a negative association was found for IFNγ. Furthermore, multivariate logistic analysis also showed that VCAM-1 and IFNγ were independently correlated with dengue shock syndrome.

Conclusion: IFNγ and VCAM-1 were associated with dengue shock syndrome, although their role in the severe dengue pathogenesis remains unclear. Additional studies are required to shed further light on the function of these cytokines in severe dengue.

Differential induction of cytokines by human neonatal, adult, and elderly monocyte/macrophages infected with dengue virus

Immunosuppressive status against infections in monocytes from neonates and elderly subjects has been reported. The interaction between dengue virus and monocytes/macrophages plays an important role during dengue disease. The aim of this study was to determine the cytokine response of monocytes from individuals with different ages after infection with dengue virus. Monocyte/macrophage cultures from neonatal, adult, and elderly subjects (n=10 each group) were incubated with all four dengue virus types (DENV-1 to -4). After 1 and 3 days of culture, cytokine concentrations (TNF-α, IL-6, and IL-1β) were determined in culture supernatants by enzyme-linked immunosorbant assay. Increased production of all studied cytokines was induced by the different viral types in monocyte/macrophage cultures regardless of their source. However, lower cytokine concentrations were found in neonatal and elderly monocytes. The relative monocyte/macrophage immunosuppressive status observed in neonates and the elderly could be relevant during dengue infection in those age groups and important in innate and adaptive immunity responses against this virus.

The pathology of severe dengue in multiple organs of human fatal cases: histopathology, ultrastructure and virus replication

Dengue is a public health problem, with several gaps in understanding its pathogenesis. Studies based on human fatal cases are extremely important and may clarify some of these gaps. In this work, we analyzed lesions in different organs of four dengue fatal cases, occurred in Brazil. Tissues were prepared for visualization in optical and electron microscopy, with damages quantification. As expected, we observed in all studied organ lesions characteristic of severe dengue, such as hemorrhage and edema, although other injuries were also detected. Cases presented necrotic areas in the liver and diffuse macro and microsteatosis, which were more accentuated in case 1, who also had obesity. The lung was the most affected organ, with hyaline membrane formation associated with mononuclear infiltrates in patients with pre-existing diseases such as diabetes and obesity (cases 1 and 2, respectively). These cases had also extensive acute tubular necrosis in the kidney. Infection induced destruction of cardiac fibers in most cases, with absence of nucleus and loss of striations, suggesting myocarditis. Spleens revealed significant destruction of the germinal centers and atrophy of lymphoid follicles, which may be associated to decrease of T cell number. Circulatory disturbs were reinforced by the presence of megakaryocytes in alveolar spaces, thrombus formation in glomerular capillaries and loss of endothelium in several tissues. Besides histopathological and ultrastructural observations, virus replication were investigated by detection of dengue antigens, especially the non-structural 3 protein (NS3), and confirmed by the presence of virus RNA negative strand (in situ hybridization), with second staining for identification of some cells. Results showed that dengue had broader tropism comparing to what was described before in literature, replicating in hepatocytes, type II pneumocytes and cardiac fibers, as well as in resident and circulating monocytes/macrophages and endothelial cells.

Vascular events in viral hemorrhagic fevers: a comparative study of dengue and hantaviruses

Viral hemorrhagic diseases are a group of systemic viral infections with worldwide distribution and are significant causes of global mortality and morbidity. The hallmarks of viral hemorrhagic fevers are plasma leakage, thrombocytopenia, coagulopathy and hemorrhagic manifestations. The molecular mechanisms leading to plasma leakage in viral hemorrhagic fevers are not well understood. A common theme has emerged in which a complex interplay between pathogens, host immune response, and endothelial cells leads to the activation of endothelial cells and perturbation of barrier integrity. In this article, two clinically distinct viral hemorrhagic fevers caused by dengue viruses and hantaviruses are discussed to highlight their similarities and differences that may provide insights into the pathogenesis and therapeutic approach.

Increased expression of cytokines, soluble cytokine receptors, soluble apoptosis ligand and apoptosis in dengue

Several studies have been performed to determine biomarkers that define the risk factors to developing severe forms of dengue. In this study, the levels of TNF-α, IL-6, IL-1, IL-17, soluble interleukin-1 receptor like 1 protein (sST2), soluble TNF-related apoptosis-inducing ligand (sTRAIL), IL-12 and soluble receptors for TNF (sTNF-RI and sTNF-RII) were determined by ELISA in dengue patients and monocyte/macrophage cultures. Dengue was classified as dengue without warning symptoms (DNWS), with warning symptoms (DWWS) and severe dengue (SD). High values of IL-6, sTNFRI, sTNFRII and sST2 were observed in DWWS and/or SD and IL-12 and sTRAIL in DNWS. TNF-α and IL-17 were increased not associated to the disease severity. High production of TNF-α, IL-1β, IL-12, IL-17, sST2 and sTRAIL and apoptosis expression were observed in dengue monocyte/macrophage cultures. This study shows that beneficial or deleterious biomarkers can be present in dengue regardless the disease severity and that monocytes may be in part the source of studied molecules.

Host biomarkers distinguish dengue from leptospirosis in Colombia: a case-control study

BACKGROUND

Dengue fever and leptospirosis have partially overlapping geographic distributions, similar clinical presentations and potentially life-threatening complications but require different treatments. Distinguishing between these cosmopolitan emerging pathogens represents a diagnostic dilemma of global importance. We hypothesized that perturbations in host biomarkers can differentiate between individuals with dengue fever and leptospirosis during the acute phase of illness.

METHODS

We randomly selected subjects from a prospective cohort study of acute febrile illness in Bucaramanga, Colombia and tested 19 serum biomarkers by ELISA in dengue fever (DF, n = 113) compared to subjects with leptospirosis (n = 47). Biomarkers were selected for further analysis if they had good discriminatory ability (area under the ROC curve (AUC) >0.80) and were beyond a reference range (assessed using local healthy controls).

RESULTS

Nine biomarkers differed significantly between dengue fever and leptospirosis, with higher levels of Angptl3, IL-18BP, IP-10/CXCL10, Platelet Factor 4, sICAM-1, Factor D, sEng and sKDR in dengue and higher levels of sTie-2 in leptospirosis (p < 0.001 for all comparisons). Two biomarkers, sEng and IL18BP, showed excellent discriminatory ability (AUROC >0.90). When incorporated into multivariable models, sEng and IL18BP improved the diagnostic accuracy of clinical information alone.

CONCLUSIONS

These results suggest that host biomarkers may have utility in differentiating between dengue and leptospirosis, clinically similar conditions of different etiology.

Association of IL1B -31C/T and IL1RA variable number of an 86-bp tandem repeat with dengue shock syndrome in Thailand

BACKGROUND

Dengue patients present a range of symptoms: dengue fever (DF), dengue hemorrhagic fever (DHF), and dengue shock syndrome (DSS). It is not clear whether this variability is due to their genetic background. Here we tested polymorphisms of interleukin 1 beta (IL1B) and interleukin 1 receptor antagonist (IL1RA) genes for association with DSS in the Thai population.

METHODS

Polymorphisms of IL1B -31C/T (rs1143627) and IL1RA 86-base-pair tandem repeat were analyzed in 871 patients (DF = 384, DHF = 413, and DSS = 74).

RESULTS

IL1B -31C and IL1RA 2/4 genotype were associated with DSS (IL1B -31C: DSS vs DHF: P = .0061, odds ratio [OR, 95% confidence interval {CI}], 3.49 [1.36-8.95]; DSS vs DF: P = .027, OR [95% CI], 2.81 [1.12-7.06]; IL1RA 2/4: DSS vs DHF: P = .017, OR [95% CI], 1.94 [1.12-3.40]; DSS vs DF: P = .024, OR [95% CI], 1.90 [1.07-3.4]). No difference was found between DF and DHF. Logistic regression analysis revealed that IL1B -31C and IL1RA 2/4 genotypes were each independently associated with DSS.

CONCLUSIONS

Patients with IL1B -31C carrier, or IL1RA 2/4 genotype carry a risk for DSS, implying that IL1B may play a role in pathogenesis of DSS.

T cell responses in dengue viral infections

Dengue viral infections are the commonest mosquito borne viral infection in the world, affecting more than 100 countries and 390 million individuals annually. Currently, there are no effective antiviral drugs or an effective vaccine to prevent infection. A main hurdle in developing a safe and effective vaccine has been our poor understanding of the complex nature of the protective immune response in acute dengue infection and the presence of four dengue virus (DV) serotypes that are highly homologous. The role of DV specific T cells in the pathogenesis of severe clinical disease in not clear. It has been speculated that highly cross reactive T cells for the previous infecting heterologous DV serotype, which produce pro-inflammatory cytokines, contribute to disease pathogenesis. These cross reactive T cells are believed to be suboptimal in clearing the infection with the current DV-serotype. However, other studies have shown that cross-reactive DV-specific T cells are absent or present in very low frequency during acute infection, appearing only during the convalescent period in the majority of patients. Furthermore, significant apoptosis of T cells occurs in severe acute clinical disease. Overall therefore, it is unclear what role T cells play in contributing to disease pathogenesis during acute dengue infection. Existing data have been complicated by cross-reactivity in T cells assays. These findings can now be re-evaluated in the light of novel technologies to identify serotype-specific T cell responses.

Role of CC chemokine receptor 1 and two of its ligands in human dengue infection. Three approaches under the Cuban situation

Any of the four dengue serotypes can cause a severe disease, partly due to systemic inflammation orchestrated by mediators like cytokines and chemokines. We addressed the role of CCR1 and its ligands CCL3/MIP-1α and CCL5/RANTES in dengue infection using three different approaches: an ex vivo model exploring memory immune response in subjects with a well characterized dengue immune background, an in vivo study in patients with primary or secondary dengue infection, and an approach in fatal dengue. CCR1 and CCL3/MIP-1α gene expression showed differences after homotypic and heterotypic challenge according to dengue immune background of subjects, in correspondence with previous observations in Cuban dengue outbreaks. CCL5/RANTES gene expression was higher after homotypic challenge. CCR1 and CCL3/MIP-1α gene expression was higher in patients with secondary infection during critical days of the dengue disease, while the increase in RANTES expression started earlier than the observed for CCR1 and CCL3/MIP-1α. CCR1 and CCL3/MIP-1α gene expression was as high in brain as in spleen tissue from necropsy. Our results confirm the strong influence of previous immunity in subsequent dengue infections, and confer a possible pathogenic role to CCR1 and CCL3/MIP-1α in dengue disease and a possible protective role for CCL5/RANTES, probably through CCR5 interaction.

Hemostatic derangement in dengue hemorrhagic fever

Dengue hemorrhagic fever (DHF) is a more severe manifestation of dengue virus infection. Patients with DHF exhibit abnormal hematological indices, including high hematocrit, low white blood cells, low neutrophils, high lymphocytes, increased atypical lymphocytes, low platelets, slightly prolonged activated partial thromboplastin time, prothrombin time, and thrombin time. Abnormal platelet functions manifest as impaired platelet aggregation to ADP, and concurrent increases in plasma thromboglobulin and platelet factor 4 levels are also seen. Variable reductions in the activities of coagulation factors including prothrombin, V, VII, VIII, IX, and X may be present. The plasma level of antithrombin is typically normal, but protein C and protein S are modestly reduced. Within the fibrinolytic system, slightly increased levels of tissue-plasminogen activator accompanied by slightly increased plasminogen activator inhibitor-1 and decreased thrombin activatable fibrinolysis inhibitor have been demonstrated. These derangements are prominent in patients with DHF grades III and IV, collectively known as dengue shock syndrome. Moreover, patients with excessive depletion of intravascular volume from plasma leakage and/or massive bleeding from endothelial dysfunction, thrombocytopenia, platelet dysfunction, and coagulopathy may exhibit shock, prolonged shock and repeated shock. DIC is also commonly found in these complicated patients. However, most patients recover spontaneously with normalization of abnormal laboratory profiles during the convalescent stage or within one to two weeks after defervescence.

Suppression of virus specific immune responses by IL-10 in acute dengue infection

BACKGROUND

Elevated IL-10 has been shown to be associated with severe dengue infection (DI). We proceeded to investigate the role of IL-10 in the pathogenesis of acute DI.

MATERIALS AND METHODS

Ex vivo and cultured IFNγ ELISpot assays for dengue virus (DENV) NS3 protein and non dengue viral proteins were carried out in 26 patients with acute DI (16 with dengue haemorrhagic fever) and 12 healthy dengue seropositive individuals from Sri Lanka. DENV serotype specific (SS) responses were determined by using a panel of SS peptides.

RESULTS

Serum IL-10 level were significantly higher (p = 0.02) in those who did not have in vitro responses to DENV-SS peptides (mean 144.2 pg/ml) when compared to those who responded (mean 75.7 pg/ml). DENV-NS3 specific ex vivo IFNγ ELISpot responses were also significantly lower (p = 0.0001) in those who did not respond to DENV-SS peptides (mean 42 SFU/million PBMCs) when compared to those who responded to DENV-SS peptides (mean 1024 SFU/million PBMCs). Serum IL-10 levels correlated significantly (p = 0.03) and inversely (Spearmans R = -0.45) with ex vivo DENV-NS3 specific responses but not with ex vivo non DENV specific responses (Spearmans R = -014, p = 0.52). Blockage of IL-10 in vitro significantly increased (p = 0.04) the ex vivo IFNγ ELISpot DENV-NS3 specific responses but had no effect on responses to non DENV proteins.

CONCLUSION

IL-10 appears to contribute to the pathogenesis of acute dengue infections by inhibiting DENV-specific T cell responses, which can be restored by blocking IL-10.

Dengue vaccines: recent developments, ongoing challenges and current candidates

Dengue is among the most prevalent and important arbovirus diseases of humans. To effectively control this rapidly spreading disease, control of the vector mosquito and a safe and efficacious vaccine are critical. Despite considerable efforts, the development of a successful vaccine has remained elusive. Multiple factors have complicated the creation of a successful vaccine, not the least of which are the complex, immune-mediated responses against four antigenically distinct serotypes necessitating a tetravalent vaccine providing long-lasting protective immunity. Despite the multiple impediments, there are currently many promising vaccine candidates in preclinical and clinical development. Here, the recent advances in dengue virus vaccine development are reviewed and the challenges associated with the use of these vaccines as a public health tool are briefly discussed.

Serum IL-10 as a marker of severe dengue infection

Background

Several studies have shown that serum IL-10, IFNγ and MIF are elevated in patients in severe dengue (SD) and could be used as potential biomarkers. We proceeded to determine if these cytokines could be used as biomarkers in a large cohort of adult dengue patients with varying severity of dengue infection.

Methods

Serum IL-10 levels were determined in 259 of whom 40 had severe dengue infection. Serum IFNγ and IFNα levels were done in 78 and MIF levels were done in 65 patients with acute dengue infection. Clinical features and laboratory investigations were undertaken during the febrile and critical phase.

Results

We found that serum IL-10 levels were significantly higher (p = 0.001) in patients with SD, when compared to those with non SD. Serum IL-10 levels significantly and inversely correlated with white cell counts (R = −0.23, p = 0.0002) and lymphocyte counts (R = −0.29, p < 0.0001) but significantly and positively correlated with aspartate tranaminase levels (R = 0.16, p = 0.01) and alanine transaminase levels (R = 0.22, p = 0.007). However, IL-10 levels did not have a good predictive value in discriminating those who were likely to develop SD (AUC = 0.66). Serum IFNγ levels were also significantly higher (p = 0.04) in patients with SD when compared to non SD. There was no difference (p = 0.34) in serum IFNα levels and serum MIF levels (p = 0.15) in patients with SD and non SD.

Conclusion

Although serum IL-10 was significantly elevated in patients with SD it had a poor discriminatory value in identifying those with SD and non SD and therefore, is unsuitable to be used as a robust biomarker in this cohort.

The role of endothelial activation in dengue hemorrhagic fever and hantavirus pulmonary syndrome

The loss of the endothelium barrier and vascular leakage play a central role in the pathogenesis of hemorrhagic fever viruses. This can be caused either directly by the viral infection and damage of the vascular endothelium, or indirectly by a dysregulated immune response resulting in an excessive activation of the endothelium. This article briefly reviews our knowledge of the importance of the disruption of the vascular endothelial barrier in two severe disease syndromes, dengue hemorrhagic fever and hantavirus pulmonary syndrome. Both viruses cause changes in vascular permeability without damaging the endothelium. Here we focus on our understanding of the virus interaction with the endothelium, the role of the endothelium in the induced pathogenesis, and the possible mechanisms by which each virus causes vascular leakage. Understanding the dynamics between viral infection and the dysregulation of the endothelial cell barrier will help us to define potential therapeutic targets for reducing disease severity.

An emerging role for the anti-inflammatory cytokine interleukin-10 in dengue virus infection

Infection with dengue virus (DENV) causes both mild dengue fever and severe dengue diseases, such as dengue hemorrhagic fever and dengue shock syndrome. The pathogenic mechanisms for DENV are complicated, involving viral cytotoxicity, immunopathogenesis, autoimmunity, and underlying host diseases. Viral load correlates with disease severity, while the antibody-dependent enhancement of infection largely determines the secondary effects of DENV infection. Epidemiological and experimental studies have revealed an association between the plasma levels of interleukin (IL)-10, which is the master anti-inflammatory cytokine, and disease severity in patients with DENV infection. Based on current knowledge of IL-10-mediated immune regulation during infection, researchers speculate an emerging role for IL-10 in clinical disease prognosis and dengue pathogenesis. However, the regulation of dengue pathogenesis has not been fully elucidated. This review article discusses the regulation and implications of IL-10 in DENV infection. For future strategies against DENV infection, manipulating IL-10 may be an effective antiviral treatment in addition to the development of a safe dengue vaccine.

The pathogenesis of dengue

PURPOSE OF REVIEW

Dengue is one of the most rapidly spreading vector-borne diseases in the world, with the incidence increasing 30-fold in the past 50 years. There are currently no licensed treatments or vaccines for dengue. This review covers the recent advances in our understanding of dengue pathogenesis, including host and viral determinants.

RECENT FINDINGS

The pathogenesis of severe dengue is thought to be immune-mediated due to the timing of the clinical manifestations and higher incidence in secondary infections with a heterologous serotype. Recent evidence has provided further information of neutralizing versus enhancing monoclonal antibodies and their target epitopes on the dengue virion, which has major implications for vaccine design. The role of T-cell immunopathology has also been advanced with recent evidence of cross-reactive high pro-inflammatory cytokine producing T cells predominating in severe dengue. Recent large genome-wide association studies have identified specific susceptibility loci associated with severe disease. Epidemiological studies have served to define certain at-risk groups and specific viral virulence factors have recently been described.

SUMMARY

The pathogenesis of dengue is likely to be a complex interplay of host immunity and genetic predisposition combined with certain viral virulence factors. Better understanding of the underlying mechanisms leading to severe dengue is crucial if we are to develop prognostic markers, novel diagnostics and therapeutics and ultimately a balanced and safe vaccine.

High plasma levels of soluble ST2 but not its ligand IL-33 is associated with severe forms of pediatric dengue

Identification of early determinants of dengue disease progression, which could potentially enable individualized patient care are needed at present times. Soluble ST2 (sST2) has been recently reported to be elevated in the serum of children older than 2 years old and adults with dengue infection and it was correlated with secondary infections as well as with severe presentations of the disease. The mechanism by which secreted ST2 is linked to severe dengue and plasma leakage remains unclear. One possibility is that IL-33 ligand may be elevated, contributing to membrane bound ST2 as part of the immune activation in dengue infection. We determined plasma levels of sST2 and the ligand IL-33 in 66 children with acute secondary dengue infections clinically classified using the guidelines of the World Health Organization, 2009. Dengue infection showed significant increases in cytokines IL-12p70, IL-10, IL-8, IL-6, IL-1β and TNFα measured by flow cytometry based assay compared to uninfected individuals. In contrast, IL-33 levels remained unchanged between infected and uninfected individuals. The levels of sST2 positively correlated with values of IL-6 and IL-8 and inversely correlated with number of median value of platelet levels. In addition to circulating cytokine positive correlations we found that sST2 and isoenzyme creatine kinase-MB (CK-MB), a marker of myocardial muscle damage present in severe dengue cases were associated. Our pediatric study concluded that in dengue infections sST2 elevation does not involve concomitant changes of IL-33 ligand. We propose a study to assess its value as a predictor factor of disease severity.