Production of anti-dengue NS1 monoclonal antibodies by DNA immunization

Domperidone inhibits dengue virus infection by targeting the viral envelope protein and nonstructural protein 1

Dengue is a mosquito-borne disease caused by dengue virus (DENV) infection, which remains a major public health concern worldwide owing to the lack of specific treatments or antiviral drugs available. This study investigated the potential repurposing of domperidone, an antiemetic and gastrokinetic agent, to control DENV infection. Domperidone was identified by pharmacophore-based virtual screening as a small molecule that can bind to both the viral envelope (E) and the nonstructural protein 1 (NS1) of DENV. Molecular dynamics (MD) simulations and surface plasmon resonance (SPR) analysis were subsequently performed to determine specific interactions of domperidone with the DENV E and NS1 proteins and their binding affinity. Treatment of immortalized human hepatocyte-like cells (imHC) with domperidone could inhibit DENV production and NS1 secretion in a dose-dependent manner following infection with DENV serotype 2. These inhibitory effects were mediated by reduction in viral RNA replication and viral E and NS1 protein expression, but not by interference with virus entry into cells or NS1 oligomerization. The suppression of DENV production and NS1 secretion by domperidone was observed across all four DENV serotypes to varying degrees between different virus strains. The findings from our study suggest viral target-based repurposing of domperidone for modulating DENV.

Whole-blood model reveals granulocytes as key sites of dengue virus propagation, expanding understanding of disease pathogenesis

Dengue virus (DENV) infection poses a significant global health threat, yet our understanding of its immunopathogenesis remains incomplete due to limitations of existing models. Here, we establish an in vitro whole-blood model using hirudin, an anticoagulant that preserves complement activity and cellular interactions, to study DENV infection. Our model reveals the susceptibility of all major leukocyte populations to DENV infection, with monocytes and granulocytes demonstrating high permissiveness and production of infectious virus progeny. Notably, granulocytes emerge as previously unrecognized targets of DENV infection, highlighting the importance of studying viral tropism within a physiologically relevant context. We also observed efficient DENV binding to B cells, but limited production of infectious virus, suggesting a potential role in viral sequestration or immune dysregulation. Interestingly, both NK and T cells, while less permissive, were also found to be susceptible to DENV infection. Our ex vivo analysis of whole blood from DENV-infected patients confirms the susceptibility of granulocytes, monocytes, B cells, natural killer cells, and T cells to infection, further validating the clinical relevance of our model. Additionally, we observed dynamic changes in circulating blood cell populations during acute dengue, potentially reflecting both direct virus-mediated effects and immune responses. This whole-blood model offers a valuable tool for investigating the complex interplay between DENV and host factors, facilitating a deeper understanding of dengue pathogenesis and ultimately contributing to the development of novel therapeutic strategies.IMPORTANCEDengue virus (DENV) infection is a significant global health threat, with increasing incidence in endemic regions and expanding geographic range due to factors like global warming. Current models for studying DENV pathogenesis often lack the complexity of the human immune system, hindering the development of effective therapies and vaccines. To address this, we have established the first in vitro whole-blood model using hirudin, preserving critical immune components and cellular interactions. This model reveals granulocytes as previously unrecognized targets of productive DENV infection, challenging existing paradigms of viral tropism. Our ex vivo analysis of patient blood samples confirms the clinical relevance of this finding and validates our model's utility. This unique model offers a powerful platform for future studies to dissect the complex interactions between DENV and the host immune system, including the roles of different leukocyte populations, ultimately informing the development of novel therapeutic strategies to combat this devastating disease.

Optical Control of TRPV1 Channels In Vitro with Tethered Photopharmacology

Transient receptor potential vanilloid 1 (TRPV1) is a nonselective cation channel that is important for nociception and inflammatory pain and is activated by a variety of nociceptive stimuli─including lipids such as capsaicin (CAP) and endocannabinoids. TRPV1's role in physiological systems is often studied by activating it with externally perfused ligands; however, this approach is plagued by poor spatiotemporal resolution. Lipid agonists are insoluble in physiological buffers and can permeate membranes to accumulate nonselectively inside cells, where they can have off-target effects. To increase the spatiotemporal precision with which we can activate lipids on cells and tissues, we previously developed optically cleavable targeted (OCT) ligands, which use protein tags (SNAP-tags) to localize a photocaged ligand on a target cellular membrane. After enrichment, the active ligand is released on a flash of light to activate nearby receptors. In our previous work, we developed an OCT-ligand to control a cannabinoid-sensitive GPCR. Here, we expand the scope of OCT-ligand technology to target TRPV1 ion channels. We synthesize a probe, OCT-CAP, that tethers to membrane-bound SNAP-tags and releases a TRPV1 agonist when triggered by UV-A irradiation. Using Ca2+ imaging and electrophysiology in HEK293T cells expressing TRPV1, we demonstrate that OCT-CAP uncaging activates TRPV1 with superior spatiotemporal precision when compared to standard diffusible ligands or photocages. This study is the first example of an OCT-ligand designed to manipulate an ion-channel target. We anticipate that these tools will find many applications in controlling lipid signaling pathways in various cells and tissues.

Differential critical residues on the overlapped region of the non-structural protein-1 recognized by flavivirus and dengue virus cross-reactive monoclonal antibodies

The non-structural protein-1 (NS1) of dengue virus (DENV) contributes to several functions related to dengue disease pathogenesis as well as diagnostic applications. Antibodies against DENV NS1 can cross-react with other co-circulating flaviviruses, which may lead to incorrect diagnosis. Herein, five anti-DENV NS1 monoclonal antibodies (mAbs) were investigated. Four of them (1F11, 2E3, 1B2, and 4D2) cross-react with NS1 of all four DENV serotypes (pan-DENV mAbs), whereas the other (2E11) also reacts with NS1 of other flaviviruses (flavi-cross-reactive mAb). The binding epitopes recognized by these mAbs were found to overlap a region located on the disordered loop of the NS1 wing domain (amino acid residues 104 to 123). Fine epitope mapping employing phage display technology and alanine-substituted DENV2 NS1 mutants indicates the critical binding residues W115, K116, and K120 for the 2E11 mAb, which are conserved among flaviviruses. In contrast, the critical binding residues of four pan-DENV mAbs include both flavi-conserved residues (W115 to G119) and DENV-conserved flanking residues (K112, Y113, S114 and A121, K122). Our results highlight DENV-conserved residues in cross-reactive epitopes that distinguish pan-DENV antibodies from the flavi-cross-reactive antibody. These antibodies can be potentially applied to differential diagnosis of DENV from other flavivirus infections.

A replication competent luciferase-secreting DENV2 reporter for sero-epidemiological surveillance of neutralizing and enhancing antibodies

Dengue virus (DENV) specific neutralizing and enhancing antibodies play crucial roles in dengue disease prevention and pathogenesis. DENV reporters are gaining popularity in the evaluation of these antibodies; their accessibility and acceptance may improve with more efficient production systems and indications of their antigenic equivalence to the wild-type virus. This study aimed to generate a replication competent luciferase-secreting DENV reporter (LucDENV2) and evaluate its feasibility in neutralizing and infection-enhancing antibody assays in comparison with wild-type DENV2, strain 16681, and a luciferase-secreting, single-round infectious DENV2 reporter (LucSIP). LucDENV2 replicated to similarly high levels as that of the parent 16681 virus in a commonly used mosquito cell line. LucDENV2 was neutralized in an antibody concentration-dependent manner by a monoclonal antibody specific to the flavivirus fusion loop and two antibodies specific to the E domain III, which closely resembled the neutralization patterns employing the LucSIP and wild-type DENV2. Parallel analysis of LucDENV2 and wild-type DENV2 revealed good agreement between the luciferase-based and focus-based neutralization and enhancement assays in a 96-well microplate format when employed against a set of clinical sera, suggesting comparable antigenic properties of LucDENV2 with those of the parent virus. The high-titer, replication competent, luciferase-secreting DENV reporter presented here should be a useful tool for fast and reliable quantitation of neutralizing and infection-enhancing antibodies in populations living in DENV-endemic areas.

Cross-reactive antibodies targeting surface-exposed non-structural protein 1 (NS1) of dengue virus-infected cells recognize epitopes on the spaghetti loop of the β-ladder domain

Non-structural protein 1 (NS1) is a glycoprotein component of dengue virus (DENV) that is essential for viral replication, infection and immune evasion. Immunization with NS1 has been shown to elicit antibody-mediated immune responses which protect mice against DENV infections. Here, we obtained peripheral blood mononuclear cells from human subjects with secondary dengue infections, which were used to construct a dengue immune phage library displaying single-chain variable fragments. Phage selective for DENV NS1 were obtained by biopanning. Twenty-one monoclonal antibodies (mAbs) against DENV NS1 were generated from the selected phage and characterized in detail. We found most anti-NS1 mAbs used IGHV1 heavy chain antibody genes. The mAbs were classified into strongly and weakly-reactive groups based on their binding to NS1 expressed in dengue virus 2 (DENV2)-infected cells. Antibody binding experiments with recombinant NS1 proteins revealed that the mAbs recognize conformational epitopes on the β-ladder domain (amino acid residues 178–273) of DENV NS1. Epitope mapping studies on alanine-substituted NS1 proteins identified distinct but overlapping epitopes. Protruding amino acids distributed around the spaghetti loop are required for the binding of the strongly-reactive mAbs, whereas the recognition residues of the weakly-reactive mAbs are likely to be located in inaccessible sites facing toward the cell membrane. This information could guide the design of an NS1 epitope-based vaccine that targets cross-reactive conserved epitopes on cell surface-associated DENV NS1.

Increased capsid oligomerization is deleterious to dengue virus particle production

The capsid protein (C) of dengue virus is required for viral infectivity as it packages viral RNA genome into infectious particles. C exists as a homodimer that forms via hydrophobic interactions between the α2 and α4 helices of monomers. To identify C region(s) important for virus particle production, a complementation system was employed in which single-round infectious particles are generated by trans-encapsidation of a viral C-deleted genome by recombinant C expressed in mosquito cells. Mutants harbouring a complete α3 deletion, or a dual Ile65-/Trp69-to-Ala substitution in the α3 helix, exhibited reduced production of infectious virus. Unexpectedly, higher proportions of oligomeric C were detected in cells expressing both mutated forms as compared with the wild-type counterpart, indicating that the α3 helix, through its internal hydrophobic residues, may down-modulate oligomerization of C during particle formation. Compared with wild-type C, the double Ile65-/Trp69 to Ala mutations appeared to hamper viral infectivity but not C and genomic RNA incorporation into the pseudo-infectious virus particles, suggesting that increased C oligomerization may impair DENV replication at the cell entry step.

Potential Phosphorylation of Viral Nonstructural Protein 1 in Dengue Virus Infection

Dengue virus (DENV) infection causes a spectrum of dengue diseases that have unclear underlying mechanisms. Nonstructural protein 1 (NS1) is a multifunctional protein of DENV that is involved in DENV infection and dengue pathogenesis. This study investigated the potential post-translational modification of DENV NS1 by phosphorylation following DENV infection. Using liquid chromatography-tandem mass spectrometry (LC-MS/MS), 24 potential phosphorylation sites were identified in both cell-associated and extracellular NS1 proteins from three different cell lines infected with DENV. Cell-free kinase assays also demonstrated kinase activity in purified preparations of DENV NS1 proteins. Further studies were conducted to determine the roles of specific phosphorylation sites on NS1 proteins by site-directed mutagenesis with alanine substitution. The T27A and Y32A mutations had a deleterious effect on DENV infectivity. The T29A, T230A, and S233A mutations significantly decreased the production of infectious DENV but did not affect relative levels of intracellular DENV NS1 expression or NS1 secretion. Only the T230A mutation led to a significant reduction of detectable DENV NS1 dimers in virus-infected cells; however, none of the mutations interfered with DENV NS1 oligomeric formation. These findings highlight the importance of DENV NS1 phosphorylation that may pave the way for future target-specific antiviral drug design.

Melatonin Inhibits Dengue Virus Infection via the Sirtuin 1-Mediated Interferon Pathway

Dengue virus (DENV) is the causative pathogen in the life-threatening dengue hemorrhagic fever and dengue shock syndrome. DENV is transmitted to humans via the bite of an infected Aedes mosquito. Approximately 100 million people are infected annually worldwide, and most of those live in tropical and subtropical areas. There is still no effective drug or vaccine for treatment of DENV infection. In this study, we set forth to investigate the effect of melatonin, which is a natural hormone with multiple pharmacological functions, against DENV infection. Treatment with subtoxic doses of melatonin dose-dependently inhibited DENV production. Cross-protection across serotypes and various cell types was also observed. Time-of-addition assay suggested that melatonin exerts its influence during the post-entry step of viral infection. The antiviral activity of melatonin partly originates from activation of the sirtuin pathway since co-treatment with melatonin and the sirtuin 1 (SIRT1) inhibitor reversed the effect of melatonin treatment alone. Moreover, melatonin could modulate the transcription of antiviral genes that aid in suppression of DENV production. This antiviral mechanism of melatonin suggests a possible new strategy for treating DENV infection.

High performance dengue virus antigen-based serotyping-NS1-ELISA (plus): A simple alternative approach to identify dengue virus serotypes in acute dengue specimens

Dengue hemorrhagic fever (DHF) is caused by infection with dengue virus (DENV). Four different serotypes (DENV1-4) co-circulate in dengue endemic areas. The viral RNA genome-based reverse-transcription PCR (RT-PCR) is the most widely used method to identify DENV serotypes in patient specimens. However, the non-structural protein 1 (NS1) antigen as a biomarker for DENV serotyping is an emerging alternative method. We modified the serotyping-NS1-enzyme linked immunosorbent assay (stNS1-ELISA) from the originally established assay which had limited sensitivity overall and poor specificity for the DENV2 serotype. Here, four biotinylated serotype-specific antibodies were applied, including an entirely new design for detection of DENV2. Prediction of the infecting serotype of retrospective acute-phase plasma from dengue patients revealed 100% concordance with the standard RT-PCR method for all four serotypes and 78% overall sensitivity (156/200). The sensitivity of DENV1 NS1 detection was greatly improved (from 62% to 90%) by the addition of a DENV1/DENV3 sub-complex antibody pair. Inclusive of five antibody pairs, the stNS1-ELISA (plus) method showed an overall increased sensitivity to 85.5% (171/200). With the same clinical specimens, a commercial NS1 rapid diagnostic test (NS1-RDT) showed 72% sensitivity (147/200), significantly lower than the stNS1-ELISA (plus) performance. In conclusion, the stNS1-ELISA (plus) is an improved method for prediction of DENV serotype and for overall sensitivity. It could be an alternative assay not only for early dengue diagnosis, but also for serotype identification especially in remote resource-limited dengue endemic areas.

Four serotypes of DENV co-circulate in dengue endemic areas. Secondary infection with a different DENV serotype is beleived to involve with severe dengue disease. Standard laboratory diagnosis to identify DENV serotypes in dengue patient specimens is performed by sophisticated genome-based RT-PCR method with serotype-specific oligoprimers. We have previously established an alternative protein-based NS1 assay for DENV serotyping namely, a serotyping-NS1-ELISA (stNS1-ELISA), with the use of serotype-specific monoclonal antibodies (Mabs) to NS1 protein. Due to its unsatisfactory performance, the stNS1-ELISA was modified in this study. The biotinylated serotype-specific detection Mabs were introduced to enhance the overall sensitivity. A new DENV2-specific antibody was applied to improve DENV serotype identification. Prediction of infecting serotype from NS1-positive samples by our modified assay was 100% concordant with the standard RT-PCR method for all four serotypes. The overall sensitivity was greatly improved by an additional DENV1/DENV3 sub-complex antibody. This modified assay is efficient not only for early dengue diagnosis, but also for serotype identification in epidemiological studies and disease surveillance.

Peptides targeting dengue viral nonstructural protein 1 inhibit dengue virus production

Viruses manipulate the life cycle in host cells via the use of viral properties and host machineries. Development of antiviral peptides against dengue virus (DENV) infection has previously been concentrated on blocking the actions of viral structural proteins and enzymes in virus entry and viral RNA processing in host cells. In this study, we proposed DENV NS1, which is a multifunctional non-structural protein indispensable for virus production, as a new target for inhibition of DENV infection by specific peptides. We performed biopanning assays using a phage-displayed peptide library and identified 11 different sequences of 12-mer peptides binding to DENV NS1. In silico analyses of peptide-protein interactions revealed 4 peptides most likely to bind to DENV NS1 at specific positions and their association was analysed by surface plasmon resonance. Treatment of Huh7 cells with these 4 peptides conjugated with N-terminal fluorescent tag and C-terminal cell penetrating tag at varying time-of-addition post-DENV infection could inhibit the production of DENV-2 in a time- and dose-dependent manner. The inhibitory effects of the peptides were also observed in other virus serotypes (DENV-1 and DENV-4), but not in DENV-3. These findings indicate the potential application of peptides targeting DENV NS1 as antiviral agents against DENV infection.

The ER Membrane Protein Complex Promotes Biogenesis of Dengue and Zika Virus Non-structural Multi-pass Transmembrane Proteins to Support Infection

Although flaviviruses co-opt the function of the host endoplasmic reticulum (ER) membrane protein complex (EMC) during infection, a mechanistic explanation for this observation remains unclear. Here, we show that the EMC promotes biogenesis of dengue virus (DENV) and Zika virus (ZIKV) non-structural multi-pass transmembrane proteins NS4A and NS4B, which are necessary for viral replication. The EMC binds to NS4B and colocalizes with the DENV replication organelle. Mapping analysis reveals that the two N-terminal marginally hydrophobic domains of NS4B confer EMC dependency. Furthermore, altering the hydrophobicity of these two marginally hydrophobic domains relieves NS4B’s EMC dependency. We demonstrate that NS4B biogenesis, but not its stability, is reduced in EMC-depleted cells. Our data suggest that the EMC acts as a multi-pass transmembrane chaperone required for expression of at least two virally encoded proteins essential for flavivirus infection and point to a shared vulnerability during the viral life cycle that could be exploited for antiviral therapy.

Multiple genetic screens have identified the ER membrane protein complex (EMC) as essential for infection by dengue and Zika flaviviruses. Lin et al. demonstrate that efficient biogenesis of the viral non-structural proteins NS4A and NS4B requires the EMC.

The induction and characterization of monoclonal antibodies specific to GP of Ebola virus

The Ebola virus is highly infectious and characterized by hemorrhagic fever, headache, and so on with a high mortality rate. Currently, there are neither therapeutic drugs or vaccines against the Ebola virus nor fast diagnostic methods for the detection of Ebola virus infection. This study reported the induction and isolation of two monoclonal antibodies that specifically recognized the glycoprotein (GP) and secreted glycoprotein (sGP) of the Ebola virus. Plasmids encoding either GP or sGP were constructed and immunized BALB/c mice, accordingly purified sGP was boosted. The antisera were analyzed for binding activity against sGP protein in enzyme-linked immunosorbent assay (ELISA) and neutralization activity in a pseudotyped virus neutralization assay. A number of reactive clones were isolated and two monoclonal antibodies T231 and T242 were identified to react with both GP and sGP. Western blot and ELISA assays showed that the monoclonal antibodies could react with GP and sGP, respectively. Moreover, they could recognize Ebola pseudovirus by cellular immunochemistry assay. We labeled the monoclonal antibody T231 with biotin and analyzed the competitiveness of the two antibodies by the ELISA test. The results showed that the binding epitopes of the two monoclonal antibodies to sGP were partially overlapped. In summary, two GP-specific mAbs were identified, which will be used to detect the Ebola virus or investigate GP.

Human glucose-regulated protein 78 modulates intracellular production and secretion of nonstructural protein 1 of dengue virus

Virus-host interactions play important roles in virus infection and host cellular response. Several viruses, including dengue virus (DENV), usurp host chaperones to support their amplification and survival in the host cell. We investigated the interaction of nonstructural protein 1 (NS1) of DENV with three endoplasmic reticulum-resident chaperones (i.e. GRP78, calnexin and calreticulin) to delineate their functional roles and potential binding sites for protein complex formation. GRP78 protein showed prominent association with DENV NS1 in virus-infected Huh7 cells as evidenced by co-localization and co-immunoprecipitation assays. Further studies on the functional interaction of GRP78 protein were performed by using siRNA-mediated gene knockdown in a DENV replicon transfection system. GRP78 knockdown significantly decreased intracellular NS1 production and delayed NS1 secretion but had no effect on viral RNA replication. Dissecting the important domain of GRP78 required for DENV NS1 interaction showed co-immunoprecipitation of DENV NS1 with a full-length and substrate-binding domain (SBD), but not an ATPase domain, of GRP78, confirming their interaction through SBD binding. Molecular dynamics simulations of DENV NS1 and human GRP78 complex revealed their potential binding sites through hydrogen and hydrophobic bonding. The majority of GRP78-binding sites were located in a β-roll domain and connector subdomains on the DENV NS1 structure involved in hydrophobic surface formation. Taken together, our findings demonstrated the roles of human GRP78 in facilitating the intracellular production and secretion of DENV NS1 as well as predicted potential binding sites between the DENV NS1 and GRP78 complex, which could have implications in the future development of target-based antiviral drugs.

Coat protein complex I facilitates dengue virus production

Dengue hemorrhagic fever is a life-threatening disease caused by the dengue virus (DENV). After DENV enters into host cells, it replicates to generate viral particles to infect other cells. DENV exploits components of the cellular trafficking pathway to achieve effective virion production. Understanding of the proteins required for this trafficking process is essential for revealing the pathogenesis of DENV infection. Coat protein complex and soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs), two host protein families in the cellular trafficking pathway, were investigated to elucidate their respective roles during DENV infection. Coat proteins (COPI and COPII) and SNAREs (STX 5 and NSF) were knocked down in a DENV-infected Huh7 cells by RNA interference. Depletion of COPI and COPII, but not of STX5 and NSF, decreased DENV production in DENV-infected Huh7 cells. DENV proteins, including DENV C, prM, E, and NS1, were significantly reduced in COPI-silenced DENV-infected Huh7 cells, when compared to those of control cells. COPI also facilitated DENV production in an endothelial cell line and in all DENV serotypes, indicating the importance of coat protein complex in facilitating DENV infection.

Dengue and Zika viruses: lessons learned from the similarities between these Aedes mosquito-vectored arboviruses

The currently spreading arbovirus epidemic is having a severe impact on human health worldwide. The two most common flaviviruses, dengue virus (DENV) and Zika virus (ZIKV), are transmitted through the same viral vector, Aedes spp. mosquitoes. Since the discovery of DENV in 1943, this virus has been reported to cause around 390 million human infections per year, approximately 500,000 of which require hospitalization and over 20,000 of which are lethal. The present DENV epidemic is primarily concentrated in Southeast Asia. ZIKV, which was discovered in 1952, is another important arthropod-borne flavivirus. The neurotropic role of ZIKV has been reported in infected newborns with microcephaly and in adults with Guillain-Barre syndrome. Despite DENV and ZIKV sharing the same viral vector, their complex pathogenic natures are poorly understood, and the infections they cause do not have specific treatments or effective vaccines. Therefore, this review will describe what is currently known about the clinical characteristics, pathogenesis mechanisms, and transmission of these two viruses. Better understanding of the interrelationships between DENV and ZIKV will provide a useful perspective for developing an effective strategy for controlling both viruses in the future.

Secreted NS1 Protects Dengue Virus from Mannose-Binding Lectin-Mediated Neutralization

Flavivirus nonstructural protein 1 (NS1) is a unique secreted nonstructural glycoprotein. Although it is absent from the flavivirus virion, intracellular and extracellular forms of NS1 have essential roles in viral replication and the pathogenesis of infection. The fate of NS1 in insect cells has been more controversial, with some reports suggesting it is exclusively cell associated. In this study, we confirm NS1 secretion from cells of insect origin and characterize its physical, biochemical, and functional properties in the context of dengue virus (DENV) infection. Unlike mammalian cell-derived NS1, which displays both high mannose and complex type N-linked glycans, soluble NS1 secreted from DENV-infected insect cells contains only high mannose glycans. Insect cell-derived secreted NS1 also has different physical properties, including smaller and more heterogeneous sizes and the formation of less stable NS1 hexamers. Both mammalian and insect cell-derived NS1 bind to complement proteins C1s, C4, and C4-binding protein, as well as to a novel partner, mannose-binding lectin. Binding of NS1 to MBL protects DENV against mannose-binding lectin-mediated neutralization by the lectin pathway of complement activation. As we detected secreted NS1 and DENV together in the saliva of infected Aedes aegypti mosquitoes, these findings suggest a mechanism of viral immune evasion at the very earliest phase of infection.

Synergistic Effect of TNF-α and Dengue Virus Infection on Adhesion Molecule Reorganization in Human Endothelial Cells

Dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS) is a severe pathological manifestation of dengue virus (DENV) infection. Enhanced production of cytokines in dengue patients is proposed to induce endothelial barrier instability resulting in increased vascular leakage. Tumor necrosis factor (TNF)-α is an inflammatory cytokine that activates endothelial cells and enhances vascular permeability and plasma leakage in DHF/DSS. The present study investigated the in vitro effect of TNF-α and DENV infection on the expression of adherence junction proteins, tight junction proteins, and membrane integrity of human endothelial cell lines. Immunofluorescence staining and western blot analysis demonstrated platelet endothelial cell adhesion molecule-1 (PECAM-1) reorganization and decreased levels of the tight junction protein occludin in human endothelial cells treated with TNF-α and DENV, compared to mock, DENV, or TNF-α-treated cells. Permeability assessed by FITC-dextran as a transport molecule was increased and correlated with the unusual reorganization of PECAM-1. The altered distribution of PECAM-1 and low occludin protein levels in human endothelial cells treated with TNF-α and DENV correlated with increased permeability. In conclusion, the synergistic effect of TNF-α and DENV induced permeability changes in endothelial cells. These results contribute to the understanding of the mechanisms underlying enhanced vascular permeability in DENV infection.

Mass spectrometric analysis of host cell proteins interacting with dengue virus nonstructural protein 1 in dengue virus-infected HepG2 cells

Dengue virus (DENV) infection is a leading cause of the mosquito-borne infectious diseases that affect humans worldwide. Virus-host interactions appear to play significant roles in DENV replication and the pathogenesis of DENV infection. Nonstructural protein 1 (NS1) of DENV is likely involved in these processes; however, its associations with host cell proteins in DENV infection remain unclear. In this study, we used a combination of techniques (immunoprecipitation, in-solution trypsin digestion, and LC-MS/MS) to identify the host cell proteins that interact with cell-associated NS1 in an in vitro model of DENV infection in the human hepatocyte HepG2 cell line. Thirty-six novel host cell proteins were identified as potential DENV NS1-interacting partners. A large number of these proteins had characteristic binding or catalytic activities, and were involved in cellular metabolism. Coimmunoprecipitation and colocalization assays confirmed the interactions of DENV NS1 and human NIMA-related kinase 2 (NEK2), thousand and one amino acid protein kinase 1 (TAO1), and component of oligomeric Golgi complex 1 (COG1) proteins in virus-infected cells. This study reports a novel set of DENV NS1-interacting host cell proteins in the HepG2 cell line and proposes possible roles for human NEK2, TAO1, and COG1 in DENV infection.

DNA immunization as a technology platform for monoclonal antibody induction

To combat the threat of many emerging infectious diseases, DNA immunization offers a unique and powerful approach to the production of high-quality monoclonal antibodies (mAbs) against various pathogens. Compared with traditional protein-based immunization approaches, DNA immunization is efficient for testing novel immunogen designs, does not require the production or purification of proteins from a pathogen or the use of recombinant protein technology and is effective at generating mAbs against conformation-sensitive targets. Although significant progress in the use of DNA immunization to generate mAbs has been made over the last two decades, the literature does not contain an updated summary of this experience. The current review provides a comprehensive analysis of the literature, including our own work, describing the use of DNA immunization to produce highly functional mAbs, in particular, those against emerging infectious diseases. Critical factors such as immunogen design, delivery approach, immunization schedule, use of immune modulators and the role of final boost immunization are discussed in detail.

Expression of NS3/NS4A Proteins of Hepatitis C Virus in Huh7 Cells Following Engineering Its Eukaryotic Expression Vector

BACKGROUND

Although the development of novel therapeutic regimens to combat hepatitis C virus (HCV) infection have been speeded up with successful results, no efficient vaccines exist yet.

OBJECTIVES

This study aimed to construct a eukaryotic expression vector encoding nonstructural proteins, NS3/NS4A, of HCV genotype 3a, and evaluate its expression on Huh7 cell surface.

MATERIALS AND METHODS

The NS3/NS4A sequence was isolated from a patient with HCV-3a chronic infection, cloned into intermediate vector pTZ57R/T, and then used for engineering a mammalian expression vector, pDisplay, to direct the respective protein to the secretory pathway and anchor it to the plasma membrane. The expression of the protein in Huh7 cell, which was transiently transfected with the vector using Lipofectamine, was determined by immunocytochemical staining assay with fluorescein isothiocyanate (FITC)-conjugated antibodies to the HA/myc tags located besides the fusion fragment.

RESULTS

The results showed that the fragment was successfully amplified and cloned into a eukaryotic expression vector. Sequencing and enzyme digestion analysis confirmed the cloned gene completion and its correct position in the pDisply-NS3/NS4A plasmid. Immunocytochemical staining revealed that the target protein was expressed as a membrane-anchored protein in the Huh7 cells.

CONCLUSIONS

This study can serve as a fundamental experiment for the construction of a NS3/NS4A eukaryotic expression vector and its expression in mammalian cells. Further research is underway to evaluate the fragment immunogenicity in lab animal models.

Adaptor Protein 1A Facilitates Dengue Virus Replication

Rearrangement of membrane structure induced by dengue virus (DENV) is essential for replication, and requires host cellular machinery. Adaptor protein complex (AP)-1 is a host component, which can be recruited to components required for membrane rearrangement. Therefore, dysfunction of AP-1 may affect membrane organization, thereby decreasing replication of virus in infected cells. In the present study, AP-1-dependent traffic inhibitor inhibited DENV protein expression and virion production. We further clarified the role of AP-1A in the life cycle of DENV by RNA interference. AP-1A was not involved in DENV entry into cells. However, it facilitated DENV RNA replication. Viral RNA level was reduced significantly in Huh7 cells transfected with AP-1A small interfering RNA (siRNA) compared with control siRNA. Transfection of naked DENV viral RNA into Huh7 cells transfected with AP-1A siRNA resulted in less viral RNA and virion production than transfection into Huh7 cells transfected with control siRNA. Huh7 cells transfected with AP-1A siRNA showed greater modification of membrane structures and fewer vesicular packets compared with cells transfected with control siRNA. Therefore, AP-1A may partly control DENV-induced rearrangement of membrane structures required for viral replication.

Role of human heterogeneous nuclear ribonucleoprotein C1/C2 in dengue virus replication

BACKGROUND

Host and viral proteins are involved in dengue virus (DENV) replication. Heterogeneous ribonucleoprotein (hnRNP) C1/C2 are abundant host cellular proteins that exhibit RNA binding activity and play important roles in the replication of positive-strand RNA viruses such as poliovirus and hepatitis C virus. hnRNP C1/C2 have previously been shown to interact with vimentin and viral NS1 in DENV-infected cells; however, their functional role in DENV replication is not clearly understood. In the present study, we investigated the role of hnRNP C1/C2 in DENV replication by using an in vitro model of DENV infection in a hepatocyte cell line (Huh7) and siRNA-mediated knockdown of hnRNP C1/C2.

METHODS

Huh7 cells were transfected with hnRNP C1/C2-specific siRNA or irrelevant siRNA (control) followed by infection with DENV. Mock and DENV-infected knockdown cells were processed for immunoprecipitation using hnRNP C1/C2-specific antibody or their isotype-matched control antibody. The immunoprecipitated samples were subjected to RNA extraction and reverse transcriptase polymerase chain reaction (RT-PCR) for detection of DENV RNA. In addition, the knockdown cells harvested at varying time points after the infection were assessed for cell viability, cell proliferation, percentage of DENV infection, amount of viral RNA, and viral E and NS1 expression. Culture supernatants were subjected to focus forming unit assays to determine titers of infectious DENV. DENV luciferase reporter assay was also set up to determine viral translation.

RESULTS

Immunoprecipitation with the anti-hnRNP C1/C2 antibody and subsequent RT-PCR revealed the presence of DENV RNA in the immunoprecipitated complex containing hnRNP C1/C2 proteins. Transfection with hnRNP C1/C2-specific siRNA resulted in a significant reduction of hnRNP C1/C2 mRNA and protein levels but did not induce cell death during DENV infection. The reduced hnRNP C1/C2 expression decreased the percentage of DENV antigen-positive cells as well as the amount of DENV RNA and the relative levels of DENV E and NS1 proteins; however, it had no direct effect on DENV translation. In addition, a significant reduction of DENV titers was observed in the supernatant from DENV-infected cells following the knockdown of hnRNP C1/C2.

CONCLUSIONS

Our findings suggest that hnRNP C1/C2 is involved in DENV replication at the stage of viral RNA synthesis.

Microparticles provide a novel biomarker to predict severe clinical outcomes of dengue virus infection

Shedding of microparticles (MPs) is a consequence of apoptotic cell death and cellular activation. Low levels of circulating MPs in blood help maintain homeostasis, whereas increased MP generation is linked to many pathological conditions. Herein, we investigated the role of MPs in dengue virus (DENV) infection. Infection of various susceptible cells by DENV led to apoptotic death and MP release. These MPs harbored a viral envelope protein and a nonstructural protein 1 (NS1) on their surfaces. Ex vivo analysis of clinical specimens from patients with infections of different degrees of severity at multiple time points revealed that MPs generated from erythrocytes and platelets are two major MP populations in the circulation of DENV-infected patients. Elevated levels of red blood cell-derived MPs (RMPs) directly correlated with DENV disease severity, whereas a significant decrease in platelet-derived MPs was associated with a bleeding tendency. Removal by mononuclear cells of complement-opsonized NS1-anti-NS1 immune complexes bound to erythrocytes via complement receptor type 1 triggered MP shedding in vitro, a process that could explain the increased levels of RMPs in severe dengue. These findings point to the multiple roles of MPs in dengue pathogenesis. They offer a potential novel biomarker candidate capable of differentiating dengue fever from the more serious dengue hemorrhagic fever.

IMPORTANCE

Dengue is the most important mosquito-transmitted viral disease in the world. No vaccines or specific treatments are available. Rapid diagnosis and immediate treatment are the keys to achieve a positive outcome. Dengue virus (DENV) infection, like some other medical conditions, changes the level and composition of microparticles (MPs), tiny bag-like structures which are normally present at low levels in the blood of healthy individuals. This study investigated how MPs in culture and patients' blood are changed in response to DENV infection. Infection of cells led to programmed cell death and MP release. In patients' blood, the majority of MPs originated from red blood cells and platelets. Decreased platelet-derived MPs were associated with a bleeding tendency, while increased levels of red blood cell-derived MPs (RMPs) correlated with more severe disease. Importantly, the level of RMPs during the early acute phase could serve as a biomarker to identify patients with potentially severe disease who require immediate care.

An improved and robust DNA immunization method to develop antibodies against extracellular loops of multi-transmembrane proteins

Multi-transmembrane proteins are especially difficult targets for antibody generation largely due to the challenge of producing a protein that maintains its native conformation in the absence of a stabilizing membrane. Here, we describe an immunization strategy that successfully resulted in the identification of monoclonal antibodies that bind specifically to extracellular epitopes of a 12 transmembrane protein, multi-drug resistant protein 4 (MRP4). These monoclonal antibodies were developed following hydrodynamic tail vein immunization with a cytomegalovirus (CMV) promoter-based plasmid expressing MRP4 cDNA and were characterized by flow cytometry. As expected, the use of the immune modulators fetal liver tyrosine kinase 3 ligand (Flt3L) and granulocyte-macrophage colony-stimulating factor positively enhanced the immune response against MRP4. Imaging studies using CMV-based plasmids expressing luciferase showed that the in vivo half-life of the target antigen was less than 48 h using CMV-based plasmids, thus necessitating frequent boosting with DNA to achieve an adequate immune response. We also describe a comparison of plasmids, which contained MRP4 cDNA with either the CMV or CAG promoters, used for immunizations. The observed luciferase activity in this comparison demonstrated that the CAG promoter-containing plasmid pCAGGS induced prolonged constitutive expression of MRP4 and an increased anti-MRP4 specific immune response even when the plasmid was injected less frequently. The method described here is one that can be broadly applicable as a general immunization strategy to develop antibodies against multi-transmembrane proteins, as well as target antigens that are difficult to express or purify in native and functionally active conformation.

An optimized expression vector for improving the yield of dengue virus-like particles from transfected insect cells

Recombinant virus-like particles (rVLPs) of flaviviruses are non-infectious particles released from cells expressing the envelope glycoproteins prM and E. Dengue virus rVLPs are recognized as a potential vaccine candidate, but large scale production of these particles is hindered by low yields and the occurrence of cytopathic effects. In an approach to improve the yield of rVLPs from transfected insect cells, several components of a dengue serotype 2 virus prM+E expression cassette were modified and the effect of these modifications was assessed during transient expression. Enhancement of extracellular rVLP levels by simultaneous substitutions of the prM signal peptide and the stem-anchor region of E with homologous cellular and viral counterparts, respectively, was further augmented by codon optimization. Extensive formation of multinucleated cells following transfection with the codon-optimized expression cassette was abrogated by introducing an E fusion loop mutation. This mutation also helped restore the extracellular E levels affected negatively by alteration of a charged residue at the pr-M junction, which was intended to promote maturation of rVLPs during export. Optimized expression cassettes generated in this multiple add-on modification approach should be useful in the generation of stably expressing clones and production of dengue virus rVLPs for immunogenicity studies.

Non-structural protein-1 is required for West Nile virus replication complex formation and viral RNA synthesis

Background

Flavivirus NS1 is a non-structural glycoprotein that is expressed on the cell surface and secreted into the extracellular space, where it acts as an antagonist of complement pathway activation. Despite its transit through the secretory pathway and intracellular localization in the lumen of the endoplasmic reticulum and Golgi vesicles, NS1 is as an essential gene for flavivirus replication. How NS1 modulates infection remains uncertain given that the viral RNA replication complex localizes to the cytosolic face of the endoplasmic reticulum.

Methods and Results

Using a trans-complementation assay, we show that viruses deleted for NS1 (∆-NS1) can be rescued by transgenic expression of NS1 from West Nile virus (WNV) or heterologous flaviviruses in the absence of adaptive mutations. In viral lifecycle experiments, we demonstrate that WNV NS1 was not required for virus attachment or input strand translation of the infectious viral RNA, but was necessary for negative and positive strand RNA synthesis and formation of the endoplasmic reticulum-associated replication complex.

Conclusions

WNV RNA lacking intact NS1 genes was efficiently translated but failed to form canonical replication complexes at early times after infection, which resulted in an inability to replicate viral RNA. These results expand on prior studies with yellow fever and Kunjin viruses to show that flavivirus NS1 has an essential co-factor role in regulating replication complex formation and viral RNA synthesis.

Molecular Localization Techniques in the Diagnosis and Characterization of Nonhuman Primate Infectious Diseases

Molecular localization techniques remain important diagnostic and research tools for the pathologist evaluating nonhuman primate tissues. In situ hybridization and immunohistochemistry protocols have been developed for many important pathogens of nonhuman primates, including RNA and DNA viruses, prions, and bacterial, protozoal, and fungal pathogens. Such techniques will remain critical in defining the impact and relevance of novel agents on animal health and disease. A comparative pathology perspective often provides valuable insight to the best strategy for reagent development and can also facilitate interpretation of molecular localization patterns. Such a perspective is grounded in a firm understanding of microbe-host pathobiology. This review summarizes current molecular localization protocols used in the diagnosis of selected primate infectious diseases.

Potent monoclonal antibodies against Clostridium difficile toxin A elicited by DNA immunization

Recent studies have demonstrated that DNA immunization is effective in eliciting antigen-specific antibody responses against a wide range of infectious disease targets. The polyclonal antibodies elicited by DNA vaccination exhibit high sensitivity to conformational epitopes and high avidity. However, there have been limited reports in literature on the production of monoclonal antibodies (mAb) by DNA immunization. Here, by using Clostridium difficile (C. diff) toxin A as a model antigen, we demonstrated that DNA immunization was effective in producing a panel of mAb that are protective against toxin A challenge and can also be used as sensitive reagents to detect toxin A from various testing samples. The immunoglobulin (Ig) gene usage for such mAb was also investigated. Further studies should be conducted to fully establish DNA immunization as a unique platform to produce mAb in various hosts.

Establishment of a stable cell line coexpressing dengue virus-2 and green fluorescent protein for screening of antiviral compounds

This study aimed to generate a stable cell line harboring subgenomic dengue virus replicon and a green fluorescent gene (DENV/GFP) for a cell-based model to screen anti-DENV compounds. The gene-encoding envelope protein of DENV-2 was deleted and then replaced with fragments of the GFP gene and a foot-and-mouth-disease virus 2A-derived cleavage site. The human cytomegalovirus immediate early and antisense hepatitis delta virus ribozyme sequences were added at the 5'- and 3'-ends. An internal ribosome entry site and neomycin resistance genes were placed upstream and next to the NS1 gene. The recombinant plasmids were propagated in a mammalian cell line. A stable cell line with the brightest green fluorescent protein and the highest viral protein and RNA expression was selected from six clones. The clone was then examined for effectiveness in an antiviral drug screening assay with compounds isolated from the local plants using two known antiviral agents as controls. Two novel flavones, PMF and TMF, were discovered having DENV-inhibitory properties. The data were validated by a conventional plaque titration assay. The results indicate that this newly developed cell line is efficient for use as a cell-based model for primary screening of anti-DENV compounds.

Development of Dengue type-2 virus replicons expressing GFP reporter gene in study of viral RNA replication

Insertion of green fluorescent protein (GFP) encoding-gene into virus genes has provided a valuable tool for flavivirus research. This study aimed to develop dengue virus (DENV) replicons expressing GFP reporter that would provide a fast in vitro system to analyze functional roles of specific DENV sequences in viral replication. Two classes of recombinant replicon constructs were generated; one was a RNA-launched replicon with a GFP gene directly inserted into a full-length DENV genome (FL-DENV/GFP), and the other consisted of 4 types of DNA-launched DENV subgenomic replicons with GFP replacement at various structural genes (Δ-DENV/GFP). The FL-DENV/GFP resulted in GFP expression in transfected cells with no viable DENV being recovered from the transfection. The Δ-DENV/GFP constructs with partial structural gene deletion (ΔC-, ΔCprM/M-, ΔprM/M-, or ΔE-) expressed bright and long lasting GFP. The GFP expression intensity in living cells correlated well with the level of RNA replication. Various mutations in the 5'noncoding region of DENV-2 previously shown to be important genetic determinants for virus replication and mouse virulence were incorporated into the 5 different replicon constructs. Characterizations of 29 mutants demonstrated that these replicons can provide a useful platform for a quick and powerful in vitro system to analyze genetic determinants of DENV replication. These constructs can also be useful for development of vectors expressing foreign genes for various researches.

Induced autophagy reduces virus output in dengue infected monocytic cells

While several studies have shown a role for autophagy in the replication of dengue virus (DENV), these studies have been performed in directly infected cells. However, in severe cases of DENV infection the critical cell in the disease is believed to be monocytes which are poorly infected directly, but are highly susceptible to antibody enhanced infection. This study sought to determine the involvement of autophagy in the DENV infection of monocytic cells, using U937 cells as a model system. While the induction of autophagy was seen in response to DENV-2 infection, biochemical induction of autophagy resulted in a significant decrease in virus output. Down regulation of autophagy resulted in only a very slight increase in intracellular virus levels. In monocytic cells autophagy is not a significant part of the DENV replication mechanism, and there are distinct cell type specific differences in the DENV-autophagy interaction.

Binding of flavivirus nonstructural protein NS1 to C4b binding protein modulates complement activation

The complement system plays a pivotal protective role in the innate immune response to many pathogens including flaviviruses. Flavivirus nonstructural protein 1 (NS1) is a secreted nonstructural glycoprotein that accumulates in plasma to high levels and is displayed on the surface of infected cells but absent from viral particles. Previous work has defined an immune evasion role of flavivirus NS1 in limiting complement activation by forming a complex with C1s and C4 to promote cleavage of C4 to C4b. In this study, we demonstrate a second mechanism, also involving C4 and its active fragment C4b, by which NS1 antagonizes complement activation. Dengue, West Nile, or yellow fever virus NS1 directly associated with C4b binding protein (C4BP), a complement regulatory plasma protein that attenuates the classical and lectin pathways. Soluble NS1 recruited C4BP to inactivate C4b in solution and on the plasma membrane. Mapping studies revealed that the interaction sites of NS1 on C4BP partially overlap with the C4b binding sites. Together, these studies further define the immune evasion potential of NS1 in reducing the functional capacity of C4 in complement activation and control of flavivirus infection.

N-linked glycosylation of dengue virus NS1 protein modulates secretion, cell-surface expression, hexamer stability, and interactions with human complement

Dengue virus (DENV) NS1 is a versatile non-structural glycoprotein that is secreted as a hexamer, binds to the cell surface of infected and uninfected cells, and has immune evasive functions. DENV NS1 displays two conserved N-linked glycans at N130 and N207. In this study, we examined the role of these two N-linked glycans on NS1 secretion, stability, and function. Because some groups have reported reduced yields of infectious DENV when N130 and N207 are changed, we analyzed glycosylation-deficient NS1 phenotypes using a transgenic expression system. We show that the N-linked glycan at position 130 is required for stabilization of the secreted hexamer whereas the N-linked glycan at residue 207 facilitates secretion and extracellular protein stability. Moreover, NS1 mutants lacking an N-linked glycan at N130 did not interact efficiently with complement components C1s and C4. In summary, our results elucidate the contribution of N-linked glycosylation to the function of DENV NS1.

Antibody production by injection of living cells expressing non self antigens as cell surface type II transmembrane fusion protein

Antigen expression and purification are laborious, time consuming and frequently difficult steps in the process of antibody production. In the present study, we developed a method avoiding these two steps. This method relies on the injection of histocompatible living cells stably expressing the antigen as a cell surface type II transmembrane fusion protein. A vector, nicknamed pCD1-CD134L, was constructed to express the antigen fused at the carboxyterminal end of the human CD134 ligand (CD134L) type II transmembrane protein on the surface of eucaryotic cells. This vector was shown to induce cell surface expression of epitopes from human c-Myc (soluble protein), uterogloblin-related protein 1 (secreted protein) and CD94 (type II transmembrane protein). Using this vector, we developed a method to produce antibodies without antigen production. The flowchart of this method is as follows: (i) cloning of the antigen in the pCD1-CD134L vector; (ii) production of a histocompatible cell line stably expressing the CD134L-antigen fusion protein; (iii) testing for cell surface expression of the fusion protein by targeting the CD134L carrier; and (iv) prime-boost immunisation with living cells expressing the fusion protein. This method was successfully used for production of polyclonal antibodies raised against Ixodes ricinus calreticulin (secreted protein) in mice and for production of monoclonal antibodies raised against an epitope of Vaccinia virus A56 (type I transmembrane protein) protein in rat. The present study is the first to demonstrate the use of a type II transmembrane protein as a carrier for cell surface display of antigens.

Development of retinol-binding protein 4 immunocolloidal gold fast test strip using high-sensitivity monoclonal antibodies generated by DNA immunization

DNA immunization is an efficient method for high-affinity monoclonal antibody generation. Here, we describe the generation of several high-quality monoclonal antibodies (mAbs) against retinol-binding protein 4 (RBP4), an important marker for kidney abnormality and dysfunction, with a combination method of DNA priming and protein boost. The mAbs generated could bind to RBP4 with high sensitivity and using these mAbs, an immunocolloidal gold fast test strip was constructed. The strip can give a result in <5 min and is very sensitive with a detection limit of about 1 ng/ml. A small-scale clinical test revealed that the result of this strip was well in accordance with that of an enzyme-labeled immunosorbent assay kit currently available on the market. Consequently, it could be useful for more convenient and faster RBP4 determination in the clinic.

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

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

Cross-reacting antibodies enhance dengue virus infection in humans

Dengue virus co-circulates as four serotypes, and sequential infections with more than one serotype are common. One hypothesis for the increased severity seen in secondary infections is antibody-dependent enhancement (ADE) leading to increased replication in Fc receptor-bearing cells. In this study, we have generated a panel of human monoclonal antibodies to dengue virus. Antibodies to the structural precursor-membrane protein (prM) form a major component of the response. These antibodies are highly cross-reactive among the dengue virus serotypes and, even at high concentrations, do not neutralize infection but potently promote ADE. We propose that the partial cleavage of prM from the viral surface reduces the density of antigen available for viral neutralization, leaving dengue viruses susceptible to ADE by antibody to prM, a finding that has implications for future vaccine design.

Antagonism of the complement component C4 by flavivirus nonstructural protein NS1

The complement system plays an essential protective role in the initial defense against many microorganisms. Flavivirus NS1 is a secreted nonstructural glycoprotein that accumulates in blood, is displayed on the surface of infected cells, and has been hypothesized to have immune evasion functions. Herein, we demonstrate that dengue virus (DENV), West Nile virus (WNV), and yellow fever virus (YFV) NS1 attenuate classical and lectin pathway activation by directly interacting with C4. Binding of NS1 to C4 reduced C4b deposition and C3 convertase (C4b2a) activity. Although NS1 bound C4b, it lacked intrinsic cofactor activity to degrade C4b, and did not block C3 convertase formation or accelerate decay of the C3 and C5 convertases. Instead, NS1 enhanced C4 cleavage by recruiting and activating the complement-specific protease C1s. By binding C1s and C4 in a complex, NS1 promotes efficient degradation of C4 to C4b. Through this mechanism, NS1 protects DENV from complement-dependent neutralization in solution. These studies define a novel immune evasion mechanism for restricting complement control of microbial infection.

Generation of monoclonal antibodies against human recombinant interferon beta using genetic immunization with simultaneous expression of IgM and IgG isotypes

Monoclonal antibodies (MAbs) against human recombinant interferon beta (hrIFNbeta) were generated by genetic immunization (GI). In order to test two viral promoters frequently used in mammalian expression plasmid vectors, mice were inoculated four times by intramuscular injection, without adjuvant, with 100 microg of either pcDNA 3.1hrIFNbeta or pZeoSV2IFNbeta containing the entire human interferon beta gene and under the control of, respectively, human cytomegalovirus (HCMV) immediate-early promoter or early SV-40 enhancer/promoter. Only serum samples from mice immunized with pZeoSV2IFNbeta were positive to anti-hrIFNbeta. The spleens of the immunized mice were fused with myeloma Sp2/0 cells and the hybridoma clones generated screened by an in house enzyme-linked immunosorbent assay (ELISA). Fourteen MAbs were selected as reactive with hrIFNbeta. Western blot analysis was performed and only one recognized the 18 kDa isoform (non-glycosylated) of hrIFNbeta. All MAbs were subjected to antibody isotype characterization with a commercial ELISA and showed unusual profile with simultaneous expression of both IgM and IgG2a isotypes. This observation is further supported by RT-PCR amplification of the IgM CH4 domain using total RNA from hybridomas.

Three different immunogen preparation strategies for production of CD4 monoclonal antibodies

Monoclonal antibodies (MAb) specific to the protein of interest can be achieved following the classical hybridoma technique. However, obtaining a desired MAb is not always straightforward. The intrinsic quality of immunogen is one of the critical success factors. In this study, three sources of immunogens were compared for CD4 MAb production. CD4 proteins were isolated by immunoprecipitation and the CD4 immunoprecipitated (CD4-IP) beads were used as an immunogen. Recombinant CD4 protein-biotin carboxyl carrier protein (BCCP) fusion proteins (CD4-BCCP) were produced in Escherichia coli, isolated by streptavidin-coated beads, and the CD4-BCCP beads were used as an immunogen. CD4 expressing COS (CD4-COS) cells were generated, enriched by immunosorting, and used as an immunogen. After three immunizations, anti-CD4 antibodies could be observed in all immunized mice. The CD4 MAbs that were generated from CD4-IP bead and CD4-COS cell immunizations reacted with both CD4 expressed on transfected COS cells and lymphocytes. These MAbs could be used for immunoprecipitation of CD4 molecules from lymphocyte lysate and for enumerating CD4+ lymphocytes by flow cytometry. In contrast, the MAb generated from CD4-BCCP bead immunization reacted only with recombinant CD4-BCCP proteins but not with native CD4 expressed on CD4+ lymphocytes. Our results indicate that the proposed methods can facilitate the production of desired MAbs where the purified protein antigens are not available or difficult to prepare, but either the encoding cDNA or specific MAb is available.

Production and characterization of anti-dengue capsid antibodies suggesting the N terminus region covering the first 20 amino acids of dengue virus capsid protein is predominantly immunogenic in mice

We produced monoclonal and polyclonal antibodies to the capsid (C) protein of dengue serotype 2 virus (DV2 C). First, a maltose-binding protein fused to DV2 C protein (MBP-C) was overproduced in E. coli. The affinity-purified MBP-C protein was cleaved by factor Xa protease to obtain a recombinant DV2 C protein, which was then used for mouse immunizations. Two hybridoma cell lines producing anti-C Mabs as well as anti-C polyclonal antibody were successfully generated and characterized. Interestingly, all of the generated antibodies specifically recognized the first 20 amino acids of the DV2 C protein, as determined by peptide epitope mapping and via a recombinant DV2 C protein in which this region was deleted. The results suggested that this region is predominantly immunogenic in mice.

Co-localization of constituents of the dengue virus translation and replication machinery with amphisomes

Infections with dengue virus (DENV) are a significant public health concern in tropical and subtropical regions. However, little detail is known about how DENV interacts with the host-cell machinery to facilitate its translation and replication. In DENV-infected HepG2 cells, an increase in the level of LC3-II (microtubule-associated protein 1 light chain 3 form II), the autophagosomal membrane-bound form of LC3, was observed, and LC3 was found to co-localize with dsRNA and DENV NS1 protein, as well as ribosomal protein L28, indicating the presence of at least some of the DENV translation/replication machinery on autophagic vacuoles. Inhibition of fusion of autophagic vacuoles with lysosomes resulted in an increase in both intracellular and extracellular virus, and co-localization observed between mannose-6-phosphate receptor (MPR) and dsRNA and between MPR and LC3 identified the autophagic vacuoles as amphisomes. Amphisomes are formed as a result of fusion between endosomal and autophagic vacuoles, and as such provide a direct link between virus entry and subsequent replication and translation.

A role for autophagolysosomes in dengue virus 3 production in HepG2 cells

We have recently proposed that amphisomes act as a site for translation and replication of dengue virus (DENV)-2 and that DENV-2 entry and replication are linked through an ongoing association with membranes of an endosomal-autophagosomal lineage. In this report, we present the results of an investigation into the interaction between DENV-3 and the autophagy machinery. Critically, treatment with the lysosomal fusion inhibitor l-asparagine differentiated the interaction of DENV-3 from that of DENV-2. Inhibition of fusion of autophagosomes and amphisomes with lysosomes resulted in decreased DENV-3 production, implying a role for the autophagolysosome in the DENV-3 life cycle. Evidence based upon the co-localization of LC3 and cathepsin D with double stranded RNA and NS1 protein, as assessed by confocal microscopy, support a model in which DENV-3 interacts with both amphisomes and autophagolysosomes. These results demonstrate that the interactions between DENV and the host cell autophagy machinery are complex and may be determined in part by virus-encoded factors.

The Aedes aegypti cell line CCL-125 is dengue virus permissive

While the majority of dengue infections worldwide are transmitted by the Aedes aegypti mosquito, the majority of research into the interaction between dengue and insect cells is undertaken in the Aedes albopictus derived cell line C6/36. The CCL-125 cell line is a long established A. aegypti derived cell line that was originally characterized as not susceptible to infection by the dengue virus. The present study establishes that CCL-125 is permissive to dengue virus infection and is able to be infected productively as determined by both plaque assay and immunocytochemistry. Infection occurred without observable cytopathic effect. This study demonstrates the utility of the A. aegypti derived cell line CCL-125 as a dengue permissive cell line and suggests that it may be a useful alternative to C6/36 cells in dissecting out the dengue virus-insect cell interaction.