Invariant NKT Cell Response to Dengue Virus Infection in Human

Background

Dengue viral infection is a global health threat without vaccine or specific treatment. The clinical outcome varies from asymptomatic, mild dengue fever (DF) to severe dengue hemorrhagic fever (DHF). While adaptive immune responses were found to be detrimental in the dengue pathogenesis, the roles of earlier innate events remain largely uninvestigated. Invariant natural killer T (iNKT) cells represent innate-like T cells that could dictate subsequent adaptive response but their role in human dengue virus infection is not known. We hypothesized that iNKT cells play a role in human dengue infection.

Methods

Blood samples from a well-characterized cohort of children with DF, DHF, in comparison to non-dengue febrile illness (OFI) and healthy controls at various time points were studied. iNKT cells activation were analyzed by the expression of CD69 by flow cytometry. Their cytokine production was then analyzed after α-GalCer stimulation. Further, the CD1d expression on monocytes, and CD69 expression on conventional T cells were measured.

Results

iNKT cells were activated during acute dengue infection. The level of iNKT cell activation associates with the disease severity. Furthermore, these iNKT cells had altered functional response to subsequent ex vivo stimulation with α-GalCer. Moreover, during acute dengue infection, monocytic CD1d expression was also upregulated and conventional T cells also became activated.

Conclusion

iNKT cells might play an early and critical role in the pathogenesis of severe dengue viral infection in human. Targeting iNKT cells and CD1d serve as a potential therapeutic strategy for severe dengue infection in the future.     

Classification of Dengue Fever Patients Based on Gene Expression Data Using Support Vector Machines

Background

Symptomatic infection by dengue virus (DENV) can range from dengue fever (DF) to dengue haemorrhagic fever (DHF), however, the determinants of DF or DHF progression are not completely understood. It is hypothesised that host innate immune response factors are involved in modulating the disease outcome and the expression levels of genes involved in this response could be used as early prognostic markers for disease severity.

Methodology/Principal Findings

mRNA expression levels of genes involved in DENV innate immune responses were measured using quantitative real time PCR (qPCR). Here, we present a novel application of the support vector machines (SVM) algorithm to analyze the expression pattern of 12 genes in peripheral blood mononuclear cells (PBMCs) of 28 dengue patients (13 DHF and 15 DF) during acute viral infection. The SVM model was trained using gene expression data of these genes and achieved the highest accuracy of ∼85% with leave-one-out cross-validation. Through selective removal of gene expression data from the SVM model, we have identified seven genes (MYD88, TLR7, TLR3, MDA5, IRF3, IFN-α and CLEC5A) that may be central in differentiating DF patients from DHF, with MYD88 and TLR7 observed to be the most important. Though the individual removal of expression data of five other genes had no impact on the overall accuracy, a significant combined role was observed when the SVM model of the two main genes (MYD88 and TLR7) was re-trained to include the five genes, increasing the overall accuracy to ∼96%.

Conclusions/Significance

Here, we present a novel use of the SVM algorithm to classify DF and DHF patients, as well as to elucidate the significance of the various genes involved. It was observed that seven genes are critical in classifying DF and DHF patients: TLR3, MDA5, IRF3, IFN-α, CLEC5A, and the two most important MYD88 and TLR7. While these preliminary results are promising, further experimental investigation is necessary to validate their specific roles in dengue disease.     

Dengue infection in children in ratchaburi, Thailand: a cohort study. I. Epidemiology of symptomatic acute dengue infection in children, 2006-2009

Background

There is an urgent need to field test dengue vaccines to determine their role in the control of the disease. Our aims were to study dengue epidemiology and prepare the site for a dengue vaccine efficacy trial.

Methods and Findings

We performed a prospective cohort study of children in primary schools in central Thailand from 2006 through 2009. We assessed the epidemiology of dengue by active fever surveillance for acute febrile illness as detected by school absenteeism and telephone contact of parents, and dengue diagnostic testing. Dengue accounted for 394 (6.74%) of the 5,842 febrile cases identified in 2882, 3104, 2717 and 2312 student person-years over the four years, respectively. Dengue incidence was 1.77% in 2006, 3.58% in 2007, 5.74% in 2008 and 3.29% in 2009. Mean dengue incidence over the 4 years was 3.6%. Dengue virus (DENV) types were determined in 333 (84.5%) of positive specimens; DENV serotype 1 (DENV-1) was the most common (43%), followed by DENV-2 (29%), DENV-3 (20%) and DENV-4 (8%). Disease severity ranged from dengue hemorrhagic fever (DHF) in 42 (10.5%) cases, dengue fever (DF) in 142 (35.5%) cases and undifferentiated fever (UF) in 210 (52.5%) cases. All four DENV serotypes were involved in all disease severity. A majority of cases had secondary DENV infection, 95% in DHF, 88.7% in DF and 81.9% in UF. Two DHF (0.5%) cases had primary DENV-3 infection.

Conclusion

The results illustrate the high incidence of dengue with all four DENV serotypes in primary school children, with approximately 50% of disease manifesting as mild clinical symptoms of UF, not meeting the 1997 WHO criteria for dengue. Severe disease (DHF) occurred in one tenth of cases. Data of this type are required for clinical trials to evaluate the efficacy of dengue vaccines in large scale clinical trials.     

Differential Expression of Toll-like Receptors in Dendritic Cells of Patients with Dengue during Early and Late Acute Phases of the Disease

Background

Dengue hemorrhagic fever (DHF) is observed in individuals that have pre-existing heterotypic dengue antibodies and is associated with increased viral load and high levels of pro-inflammatory cytokines early in infection. Interestingly, a recent study showed that dengue virus infection in the presence of antibodies resulted in poor stimulation of Toll-like receptors (TLRs), thereby facilitating virus particle production, and also suggesting that TLRs may contribute to disease pathogenesis.

Methodology/Principal Findings

We evaluated the expression levels of TLR2, 3, 4 and 9 and the co-stimulatory molecules CD80 and CD86 by flow cytometry. This was evaluated in monocytes, in myeloid and plasmacytoid dendritic cells (mDCs and pDCs) from 30 dengue patients with different clinical outcomes and in 20 healthy controls. Increased expression of TLR3 and TLR9 in DCs of patients with dengue fever (DF) early in infection was detected. In DCs from patients with severe manifestations, poor stimulation of TLR3 and TLR9 was observed. In addition, we found a lower expression of TLR2 in patients with DF compared to DHF. Expression levels of TLR4 were not affected. Furthermore, the expression of CD80 and CD86 was altered in mDCs and CD86 in pDCs of severe dengue cases. We show that interferon alpha production decreased in the presence of dengue virus after stimulation of PBMCs with the TLR9 agonist (CpG A). This suggests that the virus can affect the interferon response through this signaling pathway.

Conclusions/Significance

These results show that during dengue disease progression, the expression profile of TLRs changes depending on the severity of the disease. Changes in TLRs expression could play a central role in DC activation, thereby influencing the innate immune response.     

Serum Proteome and Cytokine Analysis in a Longitudinal Cohort of Adults with Primary Dengue Infection Reveals Predictive Markers of DHF

Background

Infections caused by dengue virus are a major cause of morbidity and mortality in tropical and subtropical regions of the world. Factors that control transition from mild forms of disease such as dengue fever (DF) to more life-threatening forms such as dengue hemorrhagic fever (DHF) are poorly understood. Consequently, there are no reliable methods currently available for early triage of DHF patients resulting in significant over-hospitalization.

Methodology/Principal Findings

We have systematically examined the proteome, cytokines and inflammatory markers in sera from 62 adult dengue patients (44 DF; 18 DHF) with primary DENV infection, at three different times of infection representing the early febrile, defervescence and convalescent stages. Using fluorescent bioplex assays, we measured 27 cytokines in these serum samples. Additionally, we used multiple mass spectrometry methods for iTRAQ-based comparative analysis of serum proteome as well as measurements of protein adducts- 3-nitrotyrosine and 3-chlorotyrosine as surrogate measures of free radical activity. Using multiple methods such as OPLS, MRMR and MSVM-RFE for multivariate feature selection and classification, we report molecular markers that allow prediction of primary DHF with sensitivity and specificity of >80%.

Conclusions/Significance

This report constitutes a comprehensive analysis of molecular signatures of dengue disease progression and will help unravel mechanisms of dengue disease progression. Our analysis resulted in the identification of markers that may be useful for early prediction of DHF during the febrile phase. The combination of highly sensitive analytical methods and novel statistical approaches described here forms a robust platform for biomarker discovery.     

A Prospective Nested Case-Control Study of Dengue in Infants: Rethinking and Refining the Antibody-Dependent Enhancement Dengue Hemorrhagic Fever Model

Background

Dengue hemorrhagic fever (DHF) is the severe and life-threatening syndrome that can develop after infection with any one of the four dengue virus (DENV) serotypes. DHF occurs almost exclusively in individuals with secondary heterologous DENV infections and infants with primary DENV infections born to dengue immune mothers. The widely accepted explanation for the pathogenesis of DHF in these settings, particularly during infancy, is antibody-dependent enhancement (ADE) of DENV infection.

Methods and Findings

We conducted a prospective nested case-control study of DENV infections during infancy. Clinical data and blood samples were collected from 4,441 mothers and infants in up to two pre-illness study visits, and surveillance was performed for symptomatic and inapparent DENV infections. Pre-illness plasma samples were used to measure the associations between maternally derived anti-DENV3 antibody-neutralizing and -enhancing capacities at the time of DENV3 infection and development of infant DHF.The study captured 60 infants with DENV infections across a wide spectrum of disease severity. DENV3 was the predominant serotype among the infants with symptomatic (35/40) and inapparent (15/20) DENV infections, and 59/60 infants had a primary DENV infection. The estimated in vitro anti-DENV3 neutralizing capacity at birth positively correlated with the age of symptomatic primary DENV3 illness in infants. At the time of symptomatic DENV3 infection, essentially all infants had low anti-DENV3 neutralizing activity (50% plaque reduction neutralizing titers [PRNT₅₀] ≤50) and measurable DENV3 ADE activity. The infants who developed DHF did not have significantly higher frequencies or levels of DENV3 ADE activity compared to symptomatic infants without DHF. A higher weight-for-age in the first 3 mo of life and at illness presentation was associated with a greater risk for DHF from a primary DENV infection during infancy.

Conclusions

This prospective nested case-control study of primarily DENV3 infections during infancy has shown that infants exhibit a full range of disease severity after primary DENV infections. The results support an initial in vivo protective role for maternally derived antibody, and suggest that a DENV3 PRNT₅₀ >50 is associated with protection from symptomatic DENV3 illness. We did not find a significant association between DENV3 ADE activity at illness onset and the development of DHF compared with less severe symptomatic illness. The results of this study should encourage rethinking or refinement of the current ADE pathogenesis model for infant DHF and stimulate new directions of research into mechanisms responsible for the development of DHF during infancy.

Trial registration

ClinicalTrials.gov {"type":"clinical-trial","attrs":{"text":"NCT00377754","term_id":"NCT00377754"}}NCT00377754 Please see later in the article for the Editors'' Summary     

Metabolomics-Based Discovery of Small Molecule Biomarkers in Serum Associated with Dengue Virus Infections and Disease Outcomes

Background

Epidemic dengue fever (DF) and dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS) are overwhelming public health capacity for diagnosis and clinical care of dengue patients throughout the tropical and subtropical world. The ability to predict severe dengue disease outcomes (DHF/DSS) using acute phase clinical specimens would be of enormous value to physicians and health care workers for appropriate triaging of patients for clinical management. Advances in the field of metabolomics and analytic software provide new opportunities to identify host small molecule biomarkers (SMBs) in acute phase clinical specimens that differentiate dengue disease outcomes.

Methodology/Principal Findings

Exploratory metabolomic studies were conducted to characterize the serum metabolome of patients who experienced different dengue disease outcomes. Serum samples from dengue patients from Nicaragua and Mexico were retrospectively obtained, and hydrophilic interaction liquid chromatography (HILIC)-mass spectrometry (MS) identified small molecule metabolites that were associated with and statistically differentiated DHF/DSS, DF, and non-dengue (ND) diagnosis groups. In the Nicaraguan samples, 191 metabolites differentiated DF from ND outcomes and 83 differentiated DHF/DSS and DF outcomes. In the Mexican samples, 306 metabolites differentiated DF from ND and 37 differentiated DHF/DSS and DF outcomes. The structural identities of 13 metabolites were confirmed using tandem mass spectrometry (MS/MS). Metabolomic analysis of serum samples from patients diagnosed as DF who progressed to DHF/DSS identified 65 metabolites that predicted dengue disease outcomes. Differential perturbation of the serum metabolome was demonstrated following infection with different DENV serotypes and following primary and secondary DENV infections.

Conclusions/Significance

These results provide proof-of-concept that a metabolomics approach can be used to identify metabolites or SMBs in serum specimens that are associated with distinct DENV infections and disease outcomes. The differentiating metabolites also provide insights into metabolic pathways and pathogenic and immunologic mechanisms associated with dengue disease severity.     

Predictive Value of Proteinuria in Adult Dengue Severity

Background

Dengue is an important viral infection with different presentations. Predicting disease severity is important in triaging patients requiring hospital care. We aim to study the value of proteinuria in predicting the development of dengue hemorrhagic fever (DHF), utility of urine dipstick test as a rapid prognostic tool.

Methodology and principal findings

Adult patients with undifferentiated fever (n = 293) were prospectively enrolled at the Infectious Disease Research Clinic at Tan Tock Seng Hospital, Singapore from January to August 2012. Dengue infection was confirmed in 168 (57%) by dengue RT-PCR or NS1 antigen detection. Dengue cases had median fever duration of 6 days at enrolment. DHF was diagnosed in 34 cases according to the WHO 1997 guideline. Dengue fever (DF) patients were predominantly younger and were mostly seen in the outpatient setting with higher platelet level. Compared to DF, DHF cases had significantly higher peak urine protein creatinine ratio (UPCR) during clinical course (26 vs. 40 mg/mmol; p<0.001). We obtained a UPCR cut-off value of 29 mg/mmol based on maximum AUC in ROC curves of peak UPCR for DF versus DHF, corresponding to 76% sensitivity and 60% specificity. Multivariate analysis with other readily available clinical and laboratory variables increased the AUC to 0.91 with 92% sensitivity and 80% specificity. Neither urine dipstick at initial presentation nor peak urine dipstick value during the entire illness was able to discriminate between DF and DHF.

Conclusions

Proteinuria measured by a laboratory-based UPCR test may be sensitive and specific in prognosticating adult dengue patients.     

Autophagy Facilitates Antibody-Enhanced Dengue Virus Infection in Human Pre-Basophil/Mast Cells

Background

Dengue virus (DENV) infection can cause severe hemorrhagic disease in humans. Although the pathogenic mechanisms underlying severe DENV disease remain unclear, one of the possible contributing factors is antibody-dependent enhancement (ADE) which occurs when sub-neutralizing antibodies derived from a previous DENV infection enhance viral infection through interaction between virus-antibody complexes and FcR-bearing cells, such as macrophages and basophil/mast cells. Although recent reports showed that DENV induces autophagy, the relationship between antibody-enhanced DENV infection and autophagy is not clear.

Methodology/Principal Findings

We showed that sub-neutralizing antibodies derived from dengue patient sera enhanced DENV infection and autophagy in the KU812 pre-basophil-like cell line as well as the HMC-1 immature mast cell line. Antibody-enhanced DENV infection of KU812 cells increased the number of autophagosome vesicles, LC3 punctation, LC3-II accumulation, and p62 degradation over that seen in cells infected with DENV alone. The percentages of DENV envelope (E) protein-positive cells and LC3 puncta following antibody-enhanced DENV infection of KU812 cells were reduced by the autophagy inhibitor 3-MA. Antibody-enhanced DENV infection of HMC-1 cells showed co-localization of DENV E protein and dsRNA with autophagosomes, which was inhibited by 3-MA treatment. Furthermore, DENV infection and replication were reduced when KU812 cells were transfected with the autophagy-inhibiting Atg4B^C74A mutant.

Conclusions/Significance

Our results demonstrate a significant induction of autophagy in antibody-enhanced DENV infection of pre-basophil-like KU812 and immature mast cell-like HMC-1 cells. Also, autophagy plays an important role in DENV infection and replication in these cells. Given the importance of ADE and FcR-bearing cells such as monocytes, macrophages and basophil/mast cells in dengue disease, the results provide insights into dengue pathogenesis and therapeutic means of control.     

Arterial Hypertension and Skin Allergy Are Risk Factors for Progression from Dengue to Dengue Hemorrhagic Fever: A Case Control Study

Background

Currently, knowledge does not allow early prediction of which cases of dengue fever (DF) will progress to dengue hemorrhagic fever (DHF), to allow early intervention to prevent progression or to limit severity. The objective of this study is to investigate the hypothesis that some specific comorbidities increase the likelihood of a DF case progressing to DHF.

Methods

A concurrent case-control study, conducted during dengue epidemics, from 2009 to 2012. Cases were patients with dengue fever that progressed to DHF, and controls were patients of dengue fever who did not progress to DHF. Logistic regression was used to estimate the association between DHF and comorbidities.

Results

There were 490 cases of DHF and 1,316 controls. Among adults, progression to DHF was associated with self-reported hypertension (OR = 1.6; 95% CI 1.1-2.1) and skin allergy (OR = 1.8; 95% CI 1.1-3.2) with DHF after adjusting for ethnicity and socio-economic variables. There was no statistically significant association between any chronic disease and progression to DHF in those younger than 15 years.

Conclusions

Physicians attending patients with dengue fever should keep those with hypertension or skin allergies in health units to monitor progression for early intervention. This would reduce mortality by dengue.     

Serum Metabolome and Lipidome Changes in Adult Patients with Primary Dengue Infection

Background

Dengue virus (DENV) is the most widespread arbovirus with an estimated 100 million infections occurring every year. Endemic in the tropical and subtropical areas of the world, dengue fever/dengue hemorrhagic fever (DF/DHF) is emerging as a major public health concern. The complex array of concurrent host physiologic changes has hampered a complete understanding of underlying molecular mechanisms of dengue pathogenesis.

Methodology/Principle Findings

Systems level characterization of serum metabolome and lipidome of adult DF patients at early febrile, defervescence, and convalescent stages of DENV infection was performed using liquid chromatography- and gas chromatography-mass spectrometry. The tractability of following metabolite and lipid changes in a relatively large sample size (n = 44) across three prominent infection stages allowed the identification of critical physiologic changes that coincided with the different stages. Sixty differential metabolites were identified in our metabolomics analysis and the main metabolite classes were free fatty acids, acylcarnitines, phospholipids, and amino acids. Major perturbed metabolic pathways included fatty acid biosynthesis and β-oxidation, phospholipid catabolism, steroid hormone pathway, etc., suggesting the multifactorial nature of human host responses. Analysis of phospholipids and sphingolipids verified the temporal trends and revealed association with lymphocytes and platelets numbers. These metabolites were significantly perturbed during the early stages, and normalized to control levels at convalescent stage, suggesting their potential utility as prognostic markers.

Conclusions/Significance

DENV infection causes temporally distinct serum metabolome and lipidome changes, and many of the differential metabolites are involved in acute inflammatory responses. Our global analyses revealed early anti-inflammatory responses working in concert to modulate early pro-inflammatory processes, thus preventing the host from development of pathologies by excessive or prolonged inflammation. This study is the first example of how an omic- approach can divulge the extensive, concurrent, and dynamic host responses elicited by DENV and offers plausible physiological insights to why DF is self limiting.     

Dengue infection in children in Ratchaburi, Thailand: a cohort study. II. Clinical manifestations

Background

Dengue infection is one of the most important mosquito-borne diseases. More data regarding the disease burden and the prevalence of each clinical spectrum among symptomatic infections and the clinical manifestations are needed. This study aims to describe the incidence and clinical manifestations of symptomatic dengue infection in Thai children during 2006 through 2008.

Study Design

This study is a school-based prospective open cohort study with a 9,448 person-year follow-up in children aged 3–14 years. Active surveillance for febrile illnesses was done in the studied subjects. Subjects who had febrile illness were asked to visit the study hospital for clinical and laboratory evaluation, treatment, and serological tests for dengue infection. The clinical data from medical records, diary cards, and data collection forms were collected and analyzed.

Results

Dengue infections were the causes of 12.1% of febrile illnesses attending the hospital, including undifferentiated fever (UF) (49.8%), dengue fever (DF) (39.3%) and dengue hemorrhagic fever (DHF) (10.9%). Headache, anorexia, nausea/vomiting and myalgia were common symptoms occurring in more than half of the patients. The more severe dengue spectrum (i.e., DHF) had higher temperature, higher prevalence of nausea/vomiting, abdominal pain, rash, diarrhea, petechiae, hepatomegaly and lower platelet count. DHF cases also had significantly higher prevalence of anorexia, nausea/vomiting and abdominal pain during day 3–6 and diarrhea during day 4–6 of illness. The absence of nausea/vomiting, abdominal pain, diarrhea, petechiae, hepatomegaly and positive tourniquet test may predict non-DHF.

Conclusion

Among symptomatic dengue infection, UF is most common followed by DF and DHF. Some clinical manifestations may be useful to predict the more severe disease (i.e., DHF). This study presents additional information in the clinical spectra of symptomatic dengue infection.     

Antibody-Dependent Enhancement Infection Facilitates Dengue Virus-Regulated Signaling of IL-10 Production in Monocytes

Background

Interleukin (IL)-10 levels are increased in dengue virus (DENV)-infected patients with severe disorders. A hypothetical intrinsic pathway has been proposed for the IL-10 response during antibody-dependent enhancement (ADE) of DENV infection; however, the mechanisms of IL-10 regulation remain unclear.

Principle Finding

We found that DENV infection and/or attachment was sufficient to induce increased expression of IL-10 and its downstream regulator suppressor of cytokine signaling 3 in human monocytic THP-1 cells and human peripheral blood monocytes. IL-10 production was controlled by activation of cyclic adenosine monophosphate response element-binding (CREB), primarily through protein kinase A (PKA)- and phosphoinositide 3-kinase (PI3K)/PKB-regulated pathways, with PKA activation acting upstream of PI3K/PKB. DENV infection also caused glycogen synthase kinase (GSK)-3β inactivation in a PKA/PI3K/PKB-regulated manner, and inhibition of GSK-3β significantly increased DENV-induced IL-10 production following CREB activation. Pharmacological inhibition of spleen tyrosine kinase (Syk) activity significantly decreased DENV-induced IL-10 production, whereas silencing Syk-associated C-type lectin domain family 5 member A caused a partial inhibition. ADE of DENV infection greatly increased IL-10 expression by enhancing Syk-regulated PI3K/PKB/GSK-3β/CREB signaling. We also found that viral load, but not serotype, affected the IL-10 response. Finally, modulation of IL-10 expression could affect DENV replication.

Significance

These results demonstrate that, in monocytes, IL-10 production is regulated by ADE through both an extrinsic and an intrinsic pathway, all involving a Syk-regulated PI3K/PKB/GSK-3β/CREB pathway, and both of which impact viral replication.     

DC-SIGN (CD209) Promoter -336 A/G polymorphism is associated with dengue hemorrhagic fever and correlated to DC-SIGN expression and immune augmentation

Background

The C-type lectin DC-SIGN (CD209) is known to be the major dengue receptor on human dendritic cells, and a single nucleotide polymorphism (SNP) in the promoter region of CD209 (−336 A/G; rs4804803) is susceptible to many infectious diseases. We reason that variations in the DC-SIGN gene might have a broad influence on viral replication and host immune responses.

Methods and Findings

We studied whether the rs4804803 SNP was associated with a susceptibility to dengue fever (DF) and/or dengue hemorrhagic fever (DHF) through genotyping analysis in a Taiwanese cohort. We generated monocyte-derived dendritic cells (MDDCs) from individuals with AA or AG genotype of rs4804803 to study the viral replication and immune responses for functional validation. A total of 574 DNA samples were genotyped, including 176 DF, 135 DHF, 143 other non-dengue febrile illnesses (OFI) and 120 population controls. A strong association between GG/AG genotypes of rs4804803 and risk of DHF was found when compared among DF, OFI and controls (p = 0.004, 3×10⁻⁵ and 0.001, respectively). The AA genotype was associated with protection against dengue infection compared with OFI and controls (p = 0.002 and 0.020, respectively). Moreover, MDDCs from individuals with AG genotype with a higher cell surface DC-SIGN expression had a significantly higher TNFα, IL-12p40, and IP-10 production than those with AA genotype in response to dengue infection. However, the viral replication in MDDCs with AG genotype was significantly lower than those with AA genotype. With both genotypes, MDDCs revealed an increase in viral replication following the addition of anti-IP-10 neutralizing antibody.

Conclusions/Significance

The rs4804803 SNP in the CD209 promoter contributed to susceptibility to dengue infection and complication of DHF. This SNP with AG genotype affects the cell surface DC-SIGN expression related to immune augmentation and less viral replication.     

Alternative Complement Pathway Deregulation Is Correlated with Dengue Severity

Background

The complement system, a key component that links the innate and adaptive immune responses, has three pathways: the classical, lectin, and alternative pathways. In the present study, we have analyzed the levels of various complement components in blood samples from dengue fever (DF) and dengue hemorrhagic fever (DHF) patients and found that the level of complement activation is associated with disease severity.

Methods and Results

Patients with DHF had lower levels of complement factor 3 (C3; p = 0.002) and increased levels of C3a, C4a and C5a (p<0.0001) when compared to those with the less severe form, DF. There were no significant differences between DF and DHF patients in the levels of C1q, immunocomplexes (CIC-CIq) and CRP. However, small but statistically significant differences were detected in the levels of MBL. In contrast, the levels of two regulatory proteins of the alternative pathway varied widely between DF and DHF patients: DHF patients had higher levels of factor D (p = 0.01), which cleaves factor B to yield the active (C3bBb) C3 convertase, and lower levels of factor H (p = 0.03), which inactivates the (C3bBb) C3 convertase, than did DF patients. When we considered the levels of factors D and H together as an indicator of (C3bBb) C3 convertase regulation, we found that the plasma levels of these regulatory proteins in DHF patients favored the formation of the (C3bBb) C3 convertase, whereas its formation was inhibited in DF patients (p<0.0001).

Conclusion

The data suggest that an imbalance in the levels of regulatory factors D and H is associated with an abnormal regulation of complement activity in DHF patients.