[Show abstract][Hide abstract] ABSTRACT: Dengue virus (DENV) is the leading cause of mosquito-borne viral illness and death in humans. Like many viruses, DENV has evolved potent mechanisms that abolish the antiviral response within infected cells. Nevertheless, several in vivo studies have demonstrated a key role of the innate immune response in controlling DENV infection and disease progression. Here, we report that sensing of DENV infected cells by plasmacytoid dendritic cells (pDCs) triggers a robust TLR7-dependent production of IFNα, concomitant with additional antiviral responses, including inflammatory cytokine secretion and pDC maturation. We demonstrate that unlike the efficient cell-free transmission of viral infectivity, pDC activation depends on cell-to-cell contact, a feature observed for various cell types and primary cells infected by DENV, as well as West Nile virus, another member of the Flavivirus genus. We show that the sensing of DENV infected cells by pDCs requires viral envelope protein-dependent secretion and transmission of viral RNA. Consistently with the cell-to-cell sensing-dependent pDC activation, we found that DENV structural components are clustered at the interface between pDCs and infected cells. The actin cytoskeleton is pivotal for both this clustering at the contacts and pDC activation, suggesting that this structural network likely contributes to the transmission of viral components to the pDCs. Due to an evolutionarily conserved suboptimal cleavage of the precursor membrane protein (prM), DENV infected cells release uncleaved prM containing-immature particles, which are deficient for membrane fusion function. We demonstrate that cells releasing immature particles trigger pDC IFN response more potently than cells producing fusion-competent mature virus. Altogether, our results imply that immature particles, as a carrier to endolysosome-localized TLR7 sensor, may contribute to regulate the progression of dengue disease by eliciting a strong innate response.
[Show abstract][Hide abstract] ABSTRACT: Dengue virus infections are still increasing at an alarming rate in tropical and subtropical countries, underlying the need for a dengue vaccine. Although it is relatively easy to generate Ab responses to dengue virus, low avidity or low concentrations of Ab may enhance infection of FcR-bearing cells with clinical impact, posing a challenge to vaccine production. In this article, we report the characterization of a mAb, 2H12, which is cross-reactive to all four serotypes in the dengue virus group. Crystal structures of 2H12-Fab in complex with domain III of the envelope protein from three dengue serotypes have been determined. 2H12 binds to the highly conserved AB loop of domain III of the envelope protein that is poorly accessible in the mature virion. 2H12 neutralization varied between dengue serotypes and strains; in particular, dengue serotype 2 was not neutralized. Because the 2H12-binding epitope was conserved, this variation in neutralization highlights differences between dengue serotypes and suggests that significant conformational changes in the virus must take place for Ab binding. Surprisingly, 2H12 facilitated little or no enhancement of infection. These data provide a structural basis for understanding Ab neutralization and enhancement of infection, which is crucial for the development of future dengue vaccines.
The Journal of Immunology 04/2012; 188(10):4971-9. · 5.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The human C-type lectin-like molecule CLEC5A is a critical macrophage receptor for dengue virus. The binding of dengue virus
to CLEC5A triggers signaling through the associated adapter molecule DAP12, stimulating proinflammatory cytokine release.
We have crystallized an informative ensemble of CLEC5A structural conformers at 1.9-Å resolution and demonstrate how an on-off
extension to a β-sheet acts as a binary switch regulating the flexibility of the molecule. This structural information together
with molecular dynamics simulations suggests a mechanism whereby extracellular events may be transmitted through the membrane
and influence DAP12 signaling. We demonstrate that CLEC5A is homodimeric at the cell surface and binds to dengue virus serotypes
1–4. We used blotting experiments, surface analyses, glycan microarray, and docking studies to investigate the ligand binding
potential of CLEC5A with particular respect to dengue virus. This study provides a rational foundation for understanding the
dengue virus-macrophage interaction and the role of CLEC5A in dengue virus-induced lethal disease.
Journal of Biological Chemistry 07/2011; 286(27):24208-24218. · 4.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Dengue virus receptors are relatively poorly characterized, but there has been recent interest in 2 C-type lectin molecules, dendritic cell-specific intercellular adhesion molecule 3 (ICAM-3)-grabbing nonintegrin (DC-SIGN) and its close homologue liver/lymph node-specific ICAM-3-grabbing integrin (L-SIGN), which can both bind dengue and promote infection. In this report we have studied the interaction of dengue viruses produced in insect cells, tumor cell lines, and primary human dendritic cells (DCs) with DC-SIGN and L-SIGN. Virus produced in primary DCs is unable to interact with DC-SIGN but remains infectious for L-SIGN-expressing cells. Skin-resident DCs may thus be a site of initial infection by insect-produced virus, but DCs will likely not participate in large-scale virus replication during dengue infection. These results reveal that differential glycosylation of dengue virus envelope protein is highly dependent on cell state and suggest that studies of virus tropism using virus prepared in insect cells or tumor cell lines should be interpreted with caution.
The Journal of Infectious Diseases 06/2011; 203(12):1775-83. · 5.85 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The human C-type lectin-like molecule CLEC5A is a critical macrophage receptor for dengue virus. The binding of dengue virus to CLEC5A triggers signaling through the associated adapter molecule DAP12, stimulating proinflammatory cytokine release. We have crystallized an informative ensemble of CLEC5A structural conformers at 1.9-Å resolution and demonstrate how an on-off extension to a β-sheet acts as a binary switch regulating the flexibility of the molecule. This structural information together with molecular dynamics simulations suggests a mechanism whereby extracellular events may be transmitted through the membrane and influence DAP12 signaling. We demonstrate that CLEC5A is homodimeric at the cell surface and binds to dengue virus serotypes 1-4. We used blotting experiments, surface analyses, glycan microarray, and docking studies to investigate the ligand binding potential of CLEC5A with particular respect to dengue virus. This study provides a rational foundation for understanding the dengue virus-macrophage interaction and the role of CLEC5A in dengue virus-induced lethal disease.
Journal of Biological Chemistry 05/2011; 286(27):24208-18. · 4.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Dengue infections are increasing at an alarming rate in many tropical and subtropical countries, where epidemics can put health care systems under extreme pressure. The more severe infections lead to dengue hemorrhagic fever (DHF), which can be life threatening. A variety of viral and host factors have been associated with the severity of dengue infections. Because secondary dengue infection is more commonly associated with DHF than primary infections, the acquired immune response to dengue, both B cells and T cells have been implicated. In this study, we set out to study T-cell responses across the entire dengue virus proteome and to see whether these were related to disease severity in a cohort of dengue-infected children from Thailand. Robust responses were observed in most infected individuals against most viral proteins. Responses to NS3 were the most frequent, and there was a very strong association between the magnitude of the response and disease severity. Furthermore, in DHF, cytokine-high CD107a-negative cells predominated.
Proceedings of the National Academy of Sciences 09/2010; 107(39):16922-7. · 9.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: Severe dengue virus (DV) infections can cause the life-threatening condition dengue hemorrhagic fever, which is characterized by a severe plasma leak, thrombocytopenia, hemorrhage, and, in severe cases, circulatory collapse and death. There is now much evidence that pre-existing immunity to DV can enhance disease when an individual becomes infected on a second or sequential occasion. It has been shown that in contrast to infected dendritic cells (DC), noninfected bystander DC underwent maturation in dengue infection. In this study, we show that TNF-alpha and type I IFN contribute to the maturation of bystander DC, whereas the inhibition of DV-infected DC maturation can be overcome by activated T cells. Furthermore, IFN-gamma-inducible chemokines, CXCL9, 10, and 11 produced by infected DC are greatly amplified in the presence of DV-specific T cells. The chemokine secretion is also enhanced in coculture of HUVEC with either DV-infected DC or activated T cells. Finally, we found a close correlation between the serum level of these three chemokines and disease severity.
The Journal of Immunology 12/2008; 181(9):5865-74. · 5.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: T-cell recognition of the antigenic peptides presented by MHC class I molecules normally triggers protective immune responses, but can result in immune enhancement of disease. Cross-reactive T-cell responses may underlie immunopathology in dengue haemorrhagic fever. To analyze these effects at the molecular level, the functional MHC class I molecule HLA-A*1101 was crystallized bound to six naturally occurring peptide variants from the dengue virus NS3 protein. The crystals contained high levels of solvent and required optimization of the cryoprotectant and dehydration protocols for each complex to yield well ordered diffraction, a process that was facilitated by the use of a free-mounting system.
Acta Crystallographica Section F Structural Biology and Crystallization Communications 06/2007; 63(Pt 5):386-92. · 0.55 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Dengue virus infection poses a growing public health and economic burden in a number of tropical and subtropical countries. Dengue circulates as a number of quasispecies, which can be divided by serology into four groups or serotypes. An interesting feature of Dengue, recognized over five decades ago, is that most severe cases that show hemorrhagic fever are not suffering from a primary infection. Instead, they are reinfected with a virus of different serotype. This observation poses considerable problems in vaccine design, and it is therefore imperative to gain a full understanding of the mechanisms underlying this immunological enhancement of disease. In this study, we examined a T cell epitope restricted by HLA-A*24, a major MHC class I allele, in Southeast Asia in a cohort of children admitted to a hospital with acute Dengue infection. The cytokine profiles and the degranulation capacity of T cells generated to this epitope are defined and compared across different viral serotypes. Cross-reactive Dengue-specific T cells seem to show suboptimal degranulation but high cytokine production, which may contribute to the development of the vascular leak characteristic of Dengue hemorrhagic fever.
The Journal of Immunology 04/2006; 176(6):3821-9. · 5.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Dengue virus presents a growing threat to public health in the developing world. Four major serotypes of dengue virus have been characterized, and epidemiological evidence shows that dengue hemorrhagic fever (DHF), the more serious manifestation of the disease, occurs more frequently upon reinfection with a second serotype. We have studied dengue virus-specific T-cell responses in Thai children. During acute infection, few dengue-responsive CD8+ T cells were recovered; most of those present showed an activated phenotype and were undergoing programmed cell death. Many dengue-specific T cells were of low affinity for the infecting virus and showed higher affinity for other, probably previously encountered strains. Profound T-cell activation and death may contribute to the systemic disturbances leading to DHF, and original antigenic sin in the T-cell responses may suppress or delay viral elimination, leading to higher viral loads and increased immunopathology.
Nature Medicine 08/2003; 9(7):921-7. · 22.86 Impact Factor