Dengue Virus Nonstructural Protein 1 Protein Research Articles

Identification of Key Residues in Dengue Virus NS1 Protein That Are Essential for Its Secretion.

Dengue virus (DENV) non-structural protein 1 (NS1) is involved in multiple aspects of the DENV lifecycle. Importantly, it is secreted from infected cells as a hexameric lipoparticle that mediates vascular damage that is a hallmark of severe dengue. Although the secretion of NS1 is known to be important in DENV pathogenesis, the exact molecular features of NS1 that are required for its secretion from cells are not fully understood. In this study, we employed random point mutagenesis in the context of an NS1 expression vector encoding a C-terminal HiBiT luminescent peptide tag to identify residues within NS1 that are essential for its secretion. Using this approach, we identified 10 point mutations that corresponded with impaired NS1 secretion, with in silico analyses indicating that the majority of these mutations are located within the β-ladder domain. Additional studies on two of these mutants, V220D and A248V, revealed that they prevented viral RNA replication, while studies using a DENV NS1-NS5 viral polyprotein expression system demonstrated that these mutations resulted in a more reticular NS1 localisation pattern and failure to detect mature NS1 at its predicted molecular weight by Western blotting using a conformation-specific monoclonal antibody. Together, these studies demonstrate that the combination of a luminescent peptide tagged NS1 expression system with random point mutagenesis enables rapid identification of mutations that alter NS1 secretion. Two such mutations identified via this approach revealed residues that are essential for correct NS1 processing or maturation and viral RNA replication.

Dengue virus NS1 protein conveys pro-inflammatory signals by docking onto high-density lipoproteins.

The dengue virus nonstructural protein 1 (NS1) is a secreted virulence factor that modulates complement, activates immune cells and alters endothelial barriers. The molecular basis of these events remains incompletely understood. Here we describe a functional high affinity complex formed between NS1 and human high-density lipoproteins (HDL). Collapse of the soluble NS1 hexamer upon binding to the lipoprotein particle leads to the anchoring of amphipathic NS1 dimeric subunits into the HDL outer layer. The stable complex can be visualized by electron microscopy as a spherical HDL with rod-shaped NS1 dimers protruding from the surface. We further show that the assembly of NS1-HDL complexes triggers the production of pro-inflammatory cytokines in human primary macrophages while NS1 or HDL alone do not. Finally, we detect NS1 in complex with HDL and low-density lipoprotein (LDL) particles in the plasma of hospitalized dengue patients and observe NS1-apolipoprotein E-positive complexes accumulating overtime. The functional reprogramming of endogenous lipoprotein particles by NS1 as a means to exacerbate systemic inflammation during viral infection provides a new paradigm in dengue pathogenesis.

Platelet activation and aggregation response to dengue virus nonstructural protein 1 and domains

BackgroundPlatelets are now recognized as immunological sentries in the first line of defense that participate in the detection and response to pathogens. This frequently results in a decrease in the number of circulating platelets. Different mechanisms have been hypothesized to explain the thrombocytopenia in patients with severe dengue, one of them is the participation of the non‐structural protein 1 (NS1) of dengue virus (DENV), which can be secreted into circulation during DENV infection and promotes a more efficient infection. ObjectiveThe present study aimed to investigate the ability of platelet response to stimulation with full‐length DENV NS1 protein and its domains. MethodsDENV NS1 plasmid was transfected into HEK‐293T. Proteins were purified by Niquel Sepharose affinity chromatography. Secreted proteins were assessed by sodium dodecylsulfate polyacrylamide gel electrophoresis, Coomassie staining and western blot. Platelet‐rich plasma was directly incubated with DENV NS1 proteins. Platelet activation was confirmed by expression of αIIbβIII and P‐selectin by flow cytometry. Platelet aggregation was also assessed using DENV NS1 protein and its individual domains as agonists. ResultsDENV NS1 protein and its domains induce P‐selectin and αIIbβ3 complex expression on platelet surfaces. DENV NS1 induce a stable platelet aggregation after the addition of a minimal dose of adenosine diphosphate (ADP), epinephrine (EPI), or collagen. Interestingly, only EPI could induce the formation of platelet aggregates after incubation with the protein domains of NS1. ConclusionOur results suggest that the full DENV NS1 protein and also its domains promote platelet recognition, activation, and aggregation.

Dual targeting of dengue virus virions and NS1 protein with the heparan sulfate mimic PG545

Dengue virus (DENV) is the most prevalent mosquito-borne flavivirus that infects humans. At present, there are no specific antiviral drugs to treat DENV infection and vaccine development has met with challenges. DENV encodes two glycosaminoglycan (GAG) binding proteins; Envelope (E) and non-structural protein 1 (NS1). While previous work has validated the use of GAG analogues as inhibitors of E mediated virus-cell attachment, their potential for antiviral intervention in NS1 protein toxicity has not yet been explored. Here, we investigate the potential of the heparan sulfate mimetic PG545 as a dual purpose compound to target both DENV virion infectivity and NS1 function. In comparison to a non-sulfated analogue, we show that PG545 potently inhibits DENV infectivity with no cytotoxic effect. Against NS1, PG545 completely blocks the induction of cellular activation and abolishes NS1-mediated disruption of endothelial monolayer integrity. Furthermore, PG545 treatment moderately improves survival from lethal DENV challenge in a murine model. At peak disease, PG545-treated mice have lower viremia, circulating NS1 and serum TNF-α. Consistent with anti-NS1 activity, PG545 treatment also reduces systemic vascular leakage caused by DENV infection in vivo. Taken together, these findings demonstrate that the dual targeting of DENV virions and NS1 using GAG analogues offers a new avenue for DENV drug development.

Expression of soluble, glycosylated and correctly folded dengue virus NS1 protein in Pichia pastoris

The dengue virus (DENV) non structural protein 1 (NS1) is a 46–55 kDa protein that exists as homodimer inside cells and as hexamer in the extracellular milieu. Several lines of evidence have demonstrated that the biochemical and structural properties of recombinant NS1 (rNS1) vary depending on the protein expression system used. Aiming to improve current tools for studying NS1 multiple roles, a recombinant tag-free NS1 protein was expressed and purified from P. pastoris yeast cells. The best expression condition was achieved using GS115 strain and induction for 72 h with 0.7% methanol addition every 24 h. Total secreted rNS1 reached 2.18 mg in 1 L culture and the final yield of the purified protein was 1 mg per liter of culture (recovery yield of approximately 45.9%). Size-exclusion chromatography and treatment with EndoH and PNGase indicate that it exists as an N-glycosylated homodimer. Moreover, an ELISA assay with specific DENV anti-NS1 antibody that recognizes conformational epitopes revealed that rNS1 has most of its conformational epitopes preserved. The expression of rNS1 in its native conformation is an important tool for further studies of its role in DENV pathogenesis and replication.

Protein refolding based on high hydrostatic pressure and alkaline pH: Application on a recombinant dengue virus NS1 protein.

In this study we evaluated the association of high hydrostatic pressure (HHP) and alkaline pH as a minimally denaturing condition for the solubilization of inclusion bodies (IBs) generated by recombinant proteins expressed by Escherichia coli strains. The method was successfully applied to a recombinant form of the dengue virus (DENV) non-structural protein 1 (NS1). The minimal pH for IBs solubilization at 1 bar was 12 while a pH of 10 was sufficient for solubilization at HHP: 2.4 kbar for 90 min and 0.4 kbar for 14 h 30 min. An optimal refolding condition was achieved by compression of IBs at HHP and pH 10.5 in the presence of arginine, oxidized and reduced glutathiones, providing much higher yields (up to 8-fold) than association of HHP and GdnHCl via an established protocol. The refolded NS1, 109 ± 9.5 mg/L bacterial culture was recovered mainly as monomer and dimer, corresponding up to 90% of the total protein and remaining immunologically active. The proposed conditions represent an alternative for the refolding of immunologically active recombinant proteins expressed as IBs.

Salivary Detection of Dengue Virus NS1 Protein with a Label-Free Immunosensor for Early Dengue Diagnosis.

Dengue virus (DENV) is a highly pathogenic, arthropod-borne virus transmitted between people by Aedes mosquitoes. Despite efforts to prevent global spread, the potential for DENV epidemics is increasing world-wide. Annually, 3.6 billion people are at risk of infection. With no licensed vaccine, early diagnosis of dengue infection is critical for clinical management and patient survival. Detection of DENV non-structural protein 1 (NS1) is a clinically accepted biomarker for the early detection of DENV infection. Unfortunately, virtually all of the laboratory and commercial DENV NS1 diagnostic methods require a blood draw for sample analysis, limiting point-of-care diagnostics and decreases patient willingness. Alternatively, NS1 in human saliva has been identified for the potential early diagnosis of DENV infection. The collection of saliva is simple, non-invasive, painless, and inexpensive, even by minimally trained personnel. In this study, we present a label-free chemiresistive immunosensor for the detection of the DENV NS1 protein utilizing a network of single-walled carbon nanotubes functionalized with anti-dengue NS1 monoclonal antibodies. NS1 was successfully detected in adulterated artificial human saliva over the range of clinically relevant concentrations with high sensitivity and selectivity. It has potential application in clinical diagnosis and the ease of collection allows for self-testing, even within the home.

Epitope Sequences in Dengue Virus NS1 Protein Identified by Monoclonal Antibodies.

Dengue nonstructural protein 1 (NS1) is a multi-functional glycoprotein with essential functions both in viral replication and modulation of host innate immune responses. NS1 has been established as a good surrogate marker for infection. In the present study, we generated four anti-NS1 monoclonal antibodies against recombinant NS1 protein from dengue virus serotype 2 (DENV2), which were used to map three NS1 epitopes. The sequence 193AVHADMGYWIESALNDT209 was recognized by monoclonal antibodies 2H5 and 4H1BC, which also cross-reacted with Zika virus (ZIKV) protein. On the other hand, the sequence 25VHTWTEQYKFQPES38 was recognized by mAb 4F6 that did not cross react with ZIKV. Lastly, a previously unidentified DENV2 NS1-specific epitope, represented by the sequence 127ELHNQTFLIDGPETAEC143, is described in the present study after reaction with mAb 4H2, which also did not cross react with ZIKV. The selection and characterization of the epitope, specificity of anti-NS1 mAbs, may contribute to the development of diagnostic tools able to differentiate DENV and ZIKV infections.

Antibody Epitopes Identified in Critical Regions of Dengue Virus Nonstructural 1 Protein in Mouse Vaccination and Natural Human Infections

Dengue is a global public health problem and is caused by four dengue virus (DENV) serotypes (DENV1-4). A major challenge in dengue vaccine development is that cross-reactive anti-DENV Abs can be protective or potentially increase disease via Ab-dependent enhancement. DENV nonstructural protein 1 (NS1) has long been considered a vaccine candidate as it avoids Ab-dependent enhancement. In this study, we evaluated survival to challenge in a lethal DENV vascular leak model in mice immunized with NS1 combined with aluminum and magnesium hydroxide, monophosphoryl lipid A + AddaVax, or Sigma adjuvant system+CpG DNA, compared with mice infected with a sublethal dose of DENV2 and mice immunized with OVA (negative control). We characterized Ab responses to DENV1, 2, and 3 NS1 using an Ag microarray tiled with 20-mer peptides overlapping by 15 aa and identified five regions of DENV NS1 with significant levels of Ab reactivity in the NS1 + monophosphoryl lipid A + AddaVax group. Additionally, we profiled the Ab responses to NS1 of humans naturally infected with DENV2 or DENV3 in serum samples from Nicaragua collected at acute, convalescent, and 12-mo timepoints. One region in the wing domain of NS1 was immunodominant in both mouse vaccination and human infection studies, and two regions were identified only in NS1-immunized mice; thus, vaccination can generate Abs to regions that are not targeted in natural infection and could provide additional protection against lethal DENV infection. Overall, we identified a small number of immunodominant regions, which were in functionally important locations on the DENV NS1 protein and are potential correlates of protection.

Dengue virus NS1 protein activates immune cells via TLR4 but not TLR2 or TLR6.

The secreted hexameric form of the dengue virus (DENV) non-structural protein 1 (NS1) has recently been shown to elicit inflammatory cytokine release and disrupt endothelial cell monolayer integrity. This suggests that circulating NS1 contributes to the vascular leak that plays a major role in the pathology of dengue haemorrhagic fever and shock. Pathways activated by NS1 are thus of great interest as potential therapeutic targets. Recent works have separately implicated both toll-like receptor 4 (TLR4) and the TLR2/6 heterodimer in immune cell activation by NS1. Here we have used mouse gene knockout macrophages and antibodies blocking TLR function in human peripheral blood mononuclear cells to show that recombinant NS1, expressed and purified from eukaryotic cells, induces cytokine production via TLR4 but not TLR2/6. Furthermore, the commercial Escherichia coli-derived recombinant NS1 preparation used in other work to implicate TLR2/6 in the response is not correctly folded and appears to be contaminated by several microbial TLR ligands. Thus TLR4 remains a therapeutic target for DENV infections, with TLR4 antagonists holding promise for the treatment of dengue disease.

Electrical detection of dengue biomarker using egg yolk immunoglobulin as the biological recognition element.

Nonstructural protein 1 (NS1) is secreted by dengue virus in the first days of infection and acts as an excellent dengue biomarker. Here, the direct electrical detection of NS1 from dengue type 2 virus has been achieved by the measurement of variations in open circuit potential (OCP) between a reference electrode and a disposable Au electrode containing immobilized anti-NS1 antibodies acting as immunosensor. Egg yolk immunoglobulin (IgY) was utilized for the first time as the biological recognition element alternatively to conventional mammalian antibodies in the detection of dengue virus NS1 protein. NS1 protein was detected in standard samples in a 0.1 to 10 µg.mL−1 concentration range with (3.2 ± 0.3) mV/µg.mL−1 of sensitivity and 0.09 µg.mL−1 of detection limit. Therefore, the proposed system can be extended to detect NS1 in real samples and provide an early diagnosis of dengue.

Construction of recombinant Kluyveromyces marxianus UFV-3 to express dengue virus type 1 nonstructural protein 1 (NS1).

The yeast Kluyveromyces marxianus is a convenient host for industrial synthesis of biomolecules. However, despite its potential, there are few studies reporting the expression of heterologous proteins using this yeast. Here, we report expression of a dengue virus protein in K. marxianus for the first time. The dengue virus type 1 nonstructural protein 1 (NS1) was integrated into the K. marxianus UFV-3 genome at the LAC4 locus using an adapted integrative vector designed for high-level expression of recombinant protein in Kluyveromyces lactis. The NS1 gene sequence was codon-optimized to increase the level of protein expression in yeast. The synthetic gene was cloned in frame with K. lactis α-mating factor signal peptide, and the recombinant plasmid obtained was used to transform K. marxianus UFV-3 by electroporation. The transformed cells, selected in yeast extract peptone dextrose containing 200 μg mL(-1) Geneticin, were mitotically stable. Analysis of recombinant strains by RT-PCR and protein detection using blot analysis confirmed both transcription and expression of extracellular NS1 polypeptide. After induction with galactose, the NS1 protein was analyzed by sodium dodecyl sulfate-PAGE and immunogenic detection. Protein production was investigated under two conditions: with galactose and biotin pulses at 24-h intervals during 96 h of induction and without galactose and biotin supplementation. Protease activity was not detected in post-growth medium. Our results indicate that recombinant K. marxianus is a good host for the production of dengue virus NS1 protein, which has potential for diagnostic applications.

A thiophene-modified screen printed electrode for detection of dengue virus NS1 protein

A thiophene-modified screen printed electrode (SPE) for detection of the Dengue virus non-structural protein 1 (NS1), an important marker for acute phase diagnosis, is described. A sulfur-containing heterocyclic compound, the thiophene was incorporated to a carbon ink to prepare reproducible screen printed electrodes. After cured, the thiophene SPE was coated by gold nanoparticles conjugated to Protein A to form a nanostrutured surface. The Anti-NS1 antibodies immobilized via their Fc portions via Protein A, leaving their antigen specific sites free circumventing the problem of a random antibodies immobilization. Amperometric responses to the NS1 protein of dengue virus were obtained by cyclic voltammetries performed in presence of ferrocyanide/ferricyanide as redox probe. The calibration curve of immunosensor showed a linear response from 0.04µgmL−1 to 0.6µgmL−1 of NS1 with a good linear correlation (r=0.991, p<0.05). The detection limit (0.015µgmL−1 NS1) was lower than conventional analytical methods. In this work, thiophene monomers incorporated in the carbon ink enhanced the electroanalytical properties of the SPEs, increasing their reproducibility and sensitivity. This point-of-care testing represents a great potential for use in epidemic situations, facilitating the early diagnosis in acute phase of dengue virus.

Critical role of Dengue Virus NS1 protein in viral replication.

Dengue virus (DENV) nonstructural protein 1 (NS1) is a highly conserved 46-kDa protein that contains 2 glycosylation sites (Asn-130 and Asn-207) and 12 conserved cysteine (Cys) residues. Here, we performed site-directed mutagenesis to generate systematic mutants of viral strain TSV01. The results of the subsequent analysis showed that an alanine substitution at the second N-linked glycan Asn-207 in NS1 delayed viral RNA synthesis, reduced virus plaque size, and weakened the cytopathic effect. Three mutants at Cys sites (Cys-4, Cys-55, Cys-291) and a C-terminal deletion (ΔC) mutant significantly impaired RNA synthesis, and consequently abolished viral growth, whereas alanine mutations at Asn-130 and Glu-173 resulted in phenotypes that were similar to the wild-type (WT) virus. Further analysis showed that the Asn-207 mutation slightly delayed viral replication. These results suggest that the three conserved disulfide bonds and the second N-linked glycan in NS1 are required for DENV-2 replication.

Protection against Dengue Virus Infection in Mice by Administration of Antibodies against Modified Nonstructural Protein 1

BackgroundInfection with dengue virus (DENV) may cause life-threatening disease with thrombocytopenia and vascular leakage which are related to dysfunction of platelets and endothelial cells. We previously showed that antibodies (Abs) against DENV nonstructural protein 1 (NS1) cross-react with human platelets and endothelial cells, leading to functional disturbances. Based on sequence homology analysis, the C-terminal region of DENV NS1 protein contains cross-reactive epitopes. For safety in vaccine development, the cross-reactive epitopes of DENV NS1 protein should be deleted or modified.Methodology/Principal FindingsWe tested the protective effects of Abs against full-length DENV NS1, NS1 lacking the C-terminal amino acids (a.a.) 271-352 (designated ΔC NS1), and chimeric DJ NS1 consisting of N-terminal DENV NS1 (a.a. 1-270) and C-terminal Japanese encephalitis virus NS1 (a.a. 271-352). The anti-ΔC NS1 and anti-DJ NS1 Abs showed a lower binding activity to endothelial cells and platelets than that of anti-DENV NS1 Abs. Passive immunization with anti-ΔC NS1 and anti-DJ NS1 Abs reduced DENV-induced prolonged mouse tail bleeding time. Treatment with anti-DENV NS1, anti-ΔC NS1 and anti-DJ NS1 Abs reduced local skin hemorrhage, controlled the viral load of DENV infection in vivo, synergized with complement to inhibit viral replication in vitro, as well as abolished DENV-induced macrophage infiltration to the site of skin inoculation. Moreover, active immunization with modified NS1 protein, but not with unmodified DENV NS1 protein, reduced DENV-induced prolonged bleeding time, local skin hemorrhage, and viral load.Conclusions/SignificanceThese results support the idea that modified NS1 proteins may represent an improved strategy for safe and effective vaccine development against DENV infection.

Mapping the Interactions of Dengue Virus NS1 Protein with Human Liver Proteins Using a Yeast Two-Hybrid System: Identification of C1q as an Interacting Partner

Dengue constitutes a global health concern. The clinical manifestation of this disease varies from mild febrile illness to severe hemorrhage and/or fatal hypovolemic shock. Flavivirus nonstructural protein 1 (NS1) is a secreted glycoprotein that is displayed on the surface of infected cells but is absent in viral particles. NS1 accumulates at high levels in the plasma of dengue virus (DENV)-infected patients, and previous reports highlight its involvement in immune evasion, dengue severity, liver dysfunction and pathogenesis. In the present study, we performed a yeast two-hybrid screen to search for DENV2 NS1-interacting partners using a human liver cDNA library. We identified fifty genes, including human complement component 1 (C1q), which was confirmed by coimmunoprecipitation, ELISA and immunofluorescence assays, revealing for the first time the direct binding of this protein to NS1. Furthermore, the majority of the identified genes encode proteins that are secreted into the plasma of patients, and most of these proteins are classified as acute-phase proteins (APPs), such as plasminogen, haptoglobin, hemopexin, α-2-HS-glycoprotein, retinol binding protein 4, transferrin, and C4. The results presented here confirm the direct interaction of DENV NS1 with a key protein of the complement system and suggest a role for this complement protein in the pathogenesis of DENV infection.

A sensor tip based on carbon nanotube-ink printed electrode for the dengue virus NS1 protein

An immunosensor for the non-structural protein 1 (NS1) of the dengue virus based on carbon nanotube-screen printed electrodes (CNT-SPE) was successfully developed. A homogeneous mixture containing carboxylated carbon nanotubes was dispersed in carbon ink to prepare a screen printed working electrode. Anti-NS1 antibodies were covalently linked to CNT-SPE by an ethylenediamine film strategy. Amperometrical responses were generated at −0.5V vs. Ag/AgCl by hydrogen peroxide reaction with peroxidase (HRP) conjugated to the anti-NS1. An excellent detection limit (in the order of 12ngmL−1) and a sensitivity of 85.59μAmM−1cm−2 were achieved permitting dengue diagnostic according to the clinical range required. The matrix effect, as well as the performance of the assays, was successfully evaluated using spiked blood serum sample obtaining excellent recovery values in the results. Carbon nanotubes incorporated to the carbon ink improved the reproducibility and sensitivity of the CNT-SPE immunosensor. This point-of-care approach represents a great potential value for use in epidemic situations and can facilitate the early screening of patients in acute phase of dengue virus.

Celgosivir treatment misfolds dengue virus NS1 protein, induces cellular pro-survival genes and protects against lethal challenge mouse model

Dengue virus (DENV) infections continue to spread aggressively around the world. Here we demonstrate that celgosivir (6-O-butanoyl castanospermine), strongly inhibits all four DENV serotypes. We show by fluorescence microscopy that the antiviral mechanism of celgosivir, is in part, due to misfolding and accumulation of DENV non-structural protein 1 (NS1) in the endoplasmic reticulum. Moreover, celgosivir modulates the host’s unfolded protein response (UPR) for its antiviral action. Significantly, celgosivir is effective in lethal challenge mouse models that recapitulate primary or secondary antibody-dependent enhanced DENV infection. Celgosivir treated mice showed enhanced survival, reduced viremia and robust immune response, as reflected by serum cytokine analysis. Importantly, survival increased even after treatment was delayed till 2days post-infection. Together the present study suggests that celgosivir, which has been clinically determined to be safe in humans, may be a valuable candidate for clinical testing in dengue patients.

Super induction of dengue virus NS1 protein in E. coli

The non-structural protein 1 (NS1) of dengue virus is a useful target for diagnostics of dengue infection since the protein is abundantly circulating in blood during the acute phase of the disease. Prior work has established that secreted NS1 levels in plasma correlates with viremia levels and hence can also be used to diagnose patients at the risk for developing dengue hemorrhagic fever. Thus detection of non-structural dengue antigens may be of benefit for an early rapid diagnosis of dengue infection due to its long half life in the blood. Here we describe a simple and efficient method for the expression of NS1 in Escherichia coli, which could potentially be used to develop monoclonal and bispecific antibodies for point of care diagnostics. E. coli codon optimized synthetic full-length NS1 gene of dengue serotype 1 (DEN-1) was successfully cloned and expressed in very high-level as inclusion bodies. The NS1 protein was successfully affinity purified and refolded as a recombinant NS1 (rNS1) protein in E. coli and yield was 230–250 mg/L of bacterial culture. The rNS1 protein was used to immunize mice for hybridoma development. The polyclonal antiserum from animals immunized with this rNS1 protein was found to specifically recognize the rNS1, thus demonstrating the immunogenic nature of the protein. The rNS1 protein purified from E. coli could be useful for developing a sensitive serum diagnostic assay to monitor dengue outbreaks.

Liver injury caused by antibodies against dengue virus nonstructural protein 1 in a murine model

Clinical manifestations of severe dengue diseases include thrombocytopenia, vascular leakage, and liver damage. Evidence shows that hepatic injury is involved in the pathogenesis of dengue infection; however, the mechanisms are not fully resolved. Our previous in vitro studies suggested a mechanism of molecular mimicry in which antibodies directed against dengue virus (DV) nonstructural protein 1 (NS1) cross-reacted with endothelial cells and caused inflammatory activation and apoptosis. In this study, the pathogenic effects of anti-DV NS1 antibodies were further examined in a murine model. We found, in liver sections, that anti-DV NS1 antibodies bound to naive mouse vessel endothelium and the binding activity was inhibited by preabsorption of antibodies with DV NS1. Active immunization with DV NS1 resulted in antibody deposition to liver vessel endothelium, and also apoptotic cell death of liver endothelium. Liver tissue damage was observed in DV NS1-immunized mice by histological examination. The serum levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were increased in mice either actively immunized with DV NS1 protein or passively immunized with antibodies obtained from DV NS1-immunized mice. Furthermore, histological examination revealed mononuclear phagocyte infiltration and cell apoptosis in mice passively immunized with antibodies obtained from mice immunized with DV NS1. Increased AST and ALT levels were observed in mice passively immunized with purified immunoglobulin G (IgG) from dengue patients compared with normal control human IgG-immunized mice. The increased AST and ALT levels were inhibited when dengue patient serum IgG was preabsorbed with DV NS1. In conclusion, active immunization with DV NS1 protein causes immune-mediated liver injury in mice. Passive immunization provides additional evidence that anti-DV NS1 antibodies may play a role in liver damage, which is a pathologic manifestation in dengue virus disease.