Trai Ming Yeh

Immunopathogenesis of dengue virus infection

Dengue virus infection causes dengue fever (DF), dengue hemorrhagic fever (DHF), and dengue shock syndrome (DSS), whose pathogeneses are not clearly understood. Current hypotheses of antibody-dependent enhancement, virus virulence, and IFN-gamma/TNFalpha-mediated immunopathogenesis are insufficient to explain clinical manifestations of DHF/DSS such as thrombocytopenia and hemoconcentration. Dengue virus infection induces transient immune aberrant activation of CD4/CD8 ratio inversion and cytokine overproduction, and infection of endothelial cells and hepatocytes causes apoptosis and dysfunction of these cells. The coagulation and fibrinolysis systems are also activated after dengue virus infection. We propose a new hypothesis for the immunopathogenesis for dengue virus infection. The aberrant immune responses not only impair the immune response to clear the virus, but also result in overproduction of cytokines that affect monocytes, endothelial cells, and hepatocytes. Platelets are destroyed by crossreactive anti-platelet autoantibodies. Dengue-virus-induced vasculopathy and coagulopathy must be involved in the pathogenesis of hemorrhage, and the unbalance between coagulation and fibrinolysis activation increases the likelihood of severe hemorrhage in DHF/DSS. Hemostasis is maintained unless the dysregulation of coagulation and fibrinolysis persists. The overproduced IL-6 might play a crucial role in the enhanced production of anti-platelet or anti-endothelial cell autoantibodies, elevated levels of tPA, as well as a deficiency in coagulation. Capillary leakage is triggered by the dengue virus itself or by antibodies to its antigens. This immunopathogenesis of DHF/DSS can account for specific characteristics of clinical, pathologic, and epidemiological observations in dengue virus infection.

Dengue Hemorrhagic Fever in Infants: A Study of Clinical and Cytokine Profiles

A prospective study of clinical and cytokine profiles of 107 infants with dengue hemorrhagic fever (DHF)/dengue shock syndrome (DSS) was conducted. Fever, petechiae on the skin, and hepatomegaly were the most common clinical findings associated with DHF/DSS in infants. DSS occurred in 20.5% of the patients. Hemoconcentration and thrombocytopenia were observed in 91.5% and 92.5% of the patients, respectively. Serologic testing revealed that almost all of the patients (95.3%) had primary dengue virus infections. These data demonstrate that clinical and laboratory findings of DHF/DSS in infants are compatible with the World Health Organizations clinical diagnostic criteria for pediatric DHF. The present study is the first to report evidence of production of cytokines in infants with DHF/DSS and to describe the difference between the cytokine profile of infants with primary dengue virus infections and children with secondary infections. Overproduction of both proinflammatory cytokines (interferon-gamma and tumor necrosis factor-alpha) and anti-inflammatory cytokines (interleukin-10 and -6) may play a role in the pathogenesis of DHF/DSS in infants.

Autophagic machinery activated by dengue virus enhances virus replication

Abstract Autophagy is a cellular response against stresses which include the infection of viruses and bacteria. We unravel that Dengue virus-2 (DV2) can trigger autophagic process in various infected cell lines demonstrated by GFP-LC3 dot formation and increased LC3-II formation. Autophagosome formation was also observed under the transmission electron microscope. DV2-induced autophagy further enhances the titers of extracellular and intracellular viruses indicating that autophagy can promote viral replication in the infected cells. Moreover, our data show that ATG5 protein is required to execute DV2-induced autophagy. All together, we are the first to demonstrate that DV can activate autophagic machinery that is favorable for viral replication.

A Mouse-Adapted Enterovirus 71 Strain Causes Neurological Disease in Mice after Oral Infection

ABSTRACT A mouse-adapted enterovirus 71 (EV71) strain with increased virulence in mice, MP4, was generated after four serial passages of the parental EV71 strain 4643 in mice. Strain MP4 exhibited a larger plaque size, grew more rapidly, and was more cytotoxic in vitro than strain 4643. Although strains 4643 and MP4 both induced apoptosis of SK-N-SH human neuroblastoma cells, MP4 was more virulent than 4643 in 1-day-old mice (50% lethal doses, 102 and 104 PFU/mouse, respectively). Strain MP4 (5 × 106 PFU/mouse), but not 4643, could orally infect 7-day-old mice, resulting in rear-limb paralysis followed by death 5 to 9 days after inoculation with the virus. Histopathologically, neuronal loss and apoptosis were evident in the spinal cords as well as the brain stems of the infected mice. The limb muscles displayed massive necrosis. There was early and transient virus replication in the intestines, whereas the spinal cord, brain, and muscle became the sites of viral replication during the late phase of the infection. Virus transmission occurred among infected and noninfected cagemates, as demonstrated by the occurrence of seroconversion and the presence of viable viruses in the stool samples of the latter. Protection against EV71 challenge was demonstrated following administration of hyperimmune serum 1 day after inoculation with the virus. Nucleotide sequence analysis of the genome of EV71 strain MP4 revealed four nucleotide changes on the 5′ untranslated region, three on the VP2 region, and eight on the 2C region, resulting in one and four amino acid substitutions in the VP2 and 2C proteins, respectively.

Endothelial Cell Apoptosis Induced by Antibodies Against Dengue Virus Nonstructural Protein 1 Via Production of Nitric Oxide

The onset of vascular leakage and hemorrhagic diathesis is one of the life-threatening complications occurring in dengue patients, yet the pathogenic mechanisms are not well understood. In this study, we demonstrated that Abs against dengue virus nonstructural protein 1 (NS1) generated in mice cross-reacted with human endothelial cells and mouse vessel endothelium. After binding, mouse anti-NS1 Abs induced endothelial cell apoptosis in a caspase-dependent manner. Inducible NO synthase expression could be observed; it showed a time- and dose-dependent correlation with NO production. Endothelial cell apoptosis, characterized by exposure of phosphatidylserine on the cell surface and nuclear DNA fragmentation, was blocked by treatment with the NO synthase inhibitor Nω-nitro-l-arginine methyl ester. Further studies demonstrated that the expression of Bcl-2 and Bcl-xL decreased in both mRNA and protein levels, whereas p53 and Bax increased after anti-NS1 treatment. Cytochrome c release was also observed. All of these effects could be inhibited by Nω-nitro-l-arginine methyl ester. Taken together, anti-NS1 Abs act as autoantibodies that cross-react with noninfected endothelial cells and trigger the intracellular signaling leading to the production of NO and to apoptosis. Endothelial cell damage may cause vascular leakage that contributes to the pathogenesis of dengue disease.

The Dual-Specific Binding of Dengue Virus and Target Cells for the Antibody-Dependent Enhancement of Dengue Virus Infection

Using flow cytometric assay and monoclonal anti-dengue Ab, we observed that both anti-E and anti-prM Abs could enhance dengue virus infection in a concentration-dependent but serotype-independent manner. Increases were found in both the percentage of dengue-infected cells and the expression of dengue E and NS1 protein per cell. Dengue virion binding and infection were enhanced on FcR-bearing cells via the Fc-FcγRII pathway. Furthermore, anti-prM Ab also enhanced dengue virion binding and infection on cells lacking FcR, such as BHK-21 or A549 cells, by the mechanism of peptide (CPFLKQNEPEDIDCW)-specific binding. Anti-prM Ab cross-reacted with BHK-21 or A549 cells and recognized self-Ags such as heat shock protein 60. In summary, a novel mechanism of anti-prM Ab-mediated enhancement on dengue virus infection was found to be mediated by dual specific binding to dengue virion and to target cells, in addition to the traditional enhancement on FcR-bearing cells.

Generation of IgM anti‐platelet autoantibody in dengue patients

Dengue virus infection causes a wide range of diseases from dengue fever to life‐threatening dengue hemorrhagic fever and dengue shock syndrome (DHF/DSS). The mechanisms involved in DHF/DSS pathogenesis remain unclear. Patient sera collected from an outbreak in southern Taiwan from November 1998 to January 1999 were studied. The presence of antibodies which cross‐reacted with platelets could be detected in patient sera, and the isotype of these autoantibodies was IgM. The anti‐platelet IgM levels were higher in DHF/DSS than in dengue fever patient sera in disease acute phase. These autoantibodies were still detectable in convalescent stage (1–3 weeks after acute phase) and even eight to nine months after illness. The platelet binding activity was not observed in other virus‐infected patient sera tested. Further investigation showed that dengue patient sera caused platelet lysis in the presence of complement. The platelet cytotoxicity induced by DHF/DSS patient sera was higher than that by dengue fever sera. Dengue patient sera also inhibited platelet aggregation which, however, appeared to be not related to DHF/DSS development. J. Med. Virol. 63:143–149, 2001.

Expression of Cytokine, Chemokine, and Adhesion Molecules during Endothelial Cell Activation Induced by Antibodies against Dengue Virus Nonstructural Protein 1

Vascular dysfunction is a hallmark associated with disease onset in dengue hemorrhagic fever and dengue shock syndrome. In addition to direct viral damage, immune responses to dengue virus (DV) infection may also underlie the pathogenesis of disease. We have proposed a mechanism of molecular mimicry in which Abs directed against DV nonstructural protein 1 (NS1) cross-react with endothelial cells and induce damage. In this study, we demonstrated the inflammatory endothelial cell activation induced by anti-DV NS1 via the transcription factor NF-κB-regulated pathway. Protein phosphorylation and NF-κB activation were observed after anti-DV NS1 stimulation in a human microvascular endothelial cell line-1. The cytokine and chemokine production, including IL-6, IL-8, and MCP-1, but not RANTES, in endothelial cells increased after treatment with anti-DV NS1 Abs. The expression of IL-6, IL-8, and MCP-1 was blocked by the preabsorption of anti-DV NS1 with DV NS1 or by the inhibition of NF-κB activation. Furthermore, the increases in both ICAM-1 expression and the ability of human PBMC to adhere to endothelial cells were also observed, and these effects were inhibited by pretreatment with anti-ICAM-1 or anti-MCP-1 Abs. Therefore, in addition to endothelial cell apoptosis, as previously reported, inflammatory activation occurs in endothelial cells after stimulation by anti-DV NS1 Abs. These results suggest the involvement of anti-DV NS1 Abs in the vasculopathy of DV infection.

Manifestation of thrombocytopenia in dengue-2-virus-infected mice.

Dengue virus infection causes dengue fever, dengue haemorrhagic fever and dengue shock syndrome. No animal model is available that mimics these clinical manifestations. In this study, the establishment is reported of a murine model for dengue virus infection that resembles the thrombocytopenia manifestation. Dengue-2 virus (dengue virus type 2) can infect murine cells either in vitro (primary cell culture) or in vivo. Viraemia detected by RT-PCR was found transiently at 2 days after intravenous injection of dengue-2 virus. Transient thrombocytopenia developed at 10-13 days after primary or secondary infection. Anti-platelet antibody was generated after dengue-2 virus infection. There was strain variation in dengue-2 virus infection; the A/J strain was more sensitive than BALB/c or B6 mice. This dengue-2-virus-infected mouse system accompanied by thrombocytopenia and anti-platelet antibody will be a valuable model to study the pathogenicity of dengue virus infection.

Heparin inhibits dengue-2 virus infection of five human liver cell lines

Liver is suggested to be the major target of dengue virus infection and plays an important role in the immunopathogenesis of dengue hemorrhagic fever. Previously, we reported that five human liver cell lines (HuH-7, HA22T, Hep3B, PLC, and Chang liver) with various degrees of differentiation and tumorigenicity showed different susceptibility for dengue virus infection. Here, we demonstrate that heparin, an analogue of heparan sulfate (HS), can compete with HS on cell membrane for virus binding and subsequently inhibits the replication of dengue-2 and Japanese encephalitis viruses in hepatoma and BHK-21 cells, respectively. It indicates that the binding of these viruses with HS is an important process for their invasion. Moreover, the inhibitory effect of heparin correlates with the infectivity of the virus in the cells. All together, our results suggest that HS is an important host component for dengue and Japanese encephalitis virus replication, which can be effectively blocked by heparin.