Prida Malasit

Original antigenic sin and apoptosis in the pathogenesis of dengue hemorrhagic fever

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.

Cross-Reacting Antibodies Enhance Dengue Virus Infection in Humans

Dangerous Dengue Provocation One problem with dengue virus is that one infection does not protect against a subsequent infection; secondary infections can result in the severe immunopathology of dengue hemorrhagic fever. Dejnirattisai et al. (p. 745) derived a panel of monoclonal antibodies specific for dengue viruses. These antibodies were mainly directed against the dengue virus precursor membrane protein (prM), and most cross-reacted with all four dengue serotypes. The antibodies were not capable of fully neutralizing the virus, but instead promoted immune responses over a wide range of concentrations. During virus production and virion assembly, maturation of prm is often incomplete, and, consequently, a major part of the hosts natural antibody response recognizes a component that is present in variable numbers on the virion. Thus, rather than resulting in complete neutralization, the antibody response promotes virus infection of cells that carry receptors for antibodies. Variable maturation of a dengue viral antigen results in incomplete neutralization and promotes secondary pathology. 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.

Arrhythmogenic Marker for the Sudden Unexplained Death Syndrome in Thai Men

BACKGROUND Between 1981 and 1988, the Centers for Disease Control and Prevention reported a very high incidence of sudden death among young male Southeast Asians who died unexpectedly during sleep. The pattern of death has long been prevalent in Southeast Asia. We carried out a study to identify the clinical markers for patients at high risk of developing sudden unexplained death syndrome (SUDS) and long-term outcomes. METHODS AND RESULTS We studied 27 Thai men (mean age, 39.7+/-11 years) referred because they had cardiac arrest due to ventricular fibrillation, usually occurring at night while asleep (n=17), or were suspected to have had symptoms similar to the clinical presentation of SUDS (n=10). We performed cardiac testing, including EPS and cardiac catheterization. The patients were then followed at approximately 3-month intervals; our primary end points were death, ventricular fibrillation, or cardiac arrest. A distinct ECG abnormality divided our patients who had no structural heart disease (except 3 patients with mild left ventricular hypertrophy) into two groups: group 1 (n=16) patients had right bundle-branch block and ST-segment elevation in V1 through V3, and group 2 (n=11) had a normal ECG. Group 1 patients had well-defined electrophysiological abnormalities: group 1 had an abnormally prolonged His-Purkinje conduction time (HV interval, 63+/-11 versus 49+/-6 ms; P=.007). Group 1 had a higher incidence of inducible ventricular fibrillation (93% for group 1 versus 11% for group 2; P=.0002) and a positive signal-averaged ECG (92% for group 1 versus 11% for group 2; P=.002), which was associated with a higher incidence of ventricular fibrillation or death (P=.047). The life-table analysis showed that the group 1 patients had a much greater risk of dying suddenly (P=.05). CONCLUSIONS Right bundle-branch block and precordial injury pattern in V1 through V3 is common in SUDS patients and represents an arrhythmogenic marker that identifies patients who face an inordinate risk of ventricular fibrillation or sudden death.

Dengue virus sero-cross-reactivity drives antibody-dependent enhancement of infection with zika virus

Zika virus (ZIKV) was discovered in 1947 and was thought to lead to relatively mild disease. The recent explosive outbreak of ZIKV in South America has led to widespread concern, with reports of neurological sequelae ranging from Guillain Barré syndrome to microcephaly. ZIKV infection has occurred in areas previously exposed to dengue virus (DENV), a flavivirus closely related to ZIKV. Here we investigated the serological cross-reaction between the two viruses. Plasma immune to DENV showed substantial cross-reaction to ZIKV and was able to drive antibody-dependent enhancement (ADE) of ZIKV infection. Using a panel of human monoclonal antibodies (mAbs) to DENV, we showed that most antibodies that reacted to DENV envelope protein also reacted to ZIKV. Antibodies to linear epitopes, including the immunodominant fusion-loop epitope, were able to bind ZIKV but were unable to neutralize the virus and instead promoted ADE. Our data indicate that immunity to DENV might drive greater ZIKV replication and have clear implications for disease pathogenesis and future vaccine programs for ZIKV and DENV.

A variant in the CD209 promoter is associated with severity of dengue disease

Dengue fever and dengue hemorrhagic fever are mosquito-borne viral diseases. Dendritic cell–specific ICAM-3 grabbing nonintegrin (DC-SIGN1, encoded by CD209), an attachment receptor of dengue virus, is essential for productive infection of dendritic cells. Here, we report strong association between a promoter variant of CD209, DCSIGN1-336, and risk of dengue fever compared with dengue hemorrhagic fever or population controls. The G allele of the variant DCSIGN1-336 was associated with strong protection against dengue fever in three independent cohorts from Thailand, with a carrier frequency of 4.7% in individuals with dengue fever compared with 22.4% in individuals with dengue hemorrhagic fever (odds ratio for risk of dengue hemorrhagic fever versus dengue fever: 5.84, P = 1.4 × 10−7) and 19.5% in controls (odds ratio for protection: 4.90, P = 2 × 10−6). This variant affects an Sp1-like binding site and transcriptional activity in vitro. These results indicate that CD209 has a crucial role in dengue pathogenesis, which discriminates between severe dengue fever and dengue hemorrhagic fever. This may have consequences for therapeutic and preventive strategies.

T Cell Responses in Dengue Hemorrhagic Fever: Are Cross-Reactive T Cells Suboptimal?

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.

A new class of highly potent, broadly neutralizing antibodies isolated from viremic patients infected with dengue virus

Dengue is a rapidly emerging, mosquito-borne viral infection, with an estimated 400 million infections occurring annually. To gain insight into dengue immunity, we characterized 145 human monoclonal antibodies (mAbs) and identified a previously unknown epitope, the envelope dimer epitope (EDE), that bridges two envelope protein subunits that make up the 90 repeating dimers on the mature virion. The mAbs to EDE were broadly reactive across the dengue serocomplex and fully neutralized virus produced in either insect cells or primary human cells, with 50% neutralization in the low picomolar range. Our results provide a path to a subunit vaccine against dengue virus and have implications for the design and monitoring of future vaccine trials in which the induction of antibody to the EDE should be prioritized.

Secreted NS1 of dengue virus attaches to the surface of cells via interactions with heparan sulfate and chondroitin sulfate E.

Dengue virus (DENV) nonstructural protein-1 (NS1) is a secreted glycoprotein that is absent from viral particles but accumulates in the supernatant and on the plasma membrane of cells during infection. Immune recognition of cell surface NS1 on endothelial cells has been hypothesized as a mechanism for the vascular leakage that occurs during severe DENV infection. However, it has remained unclear how NS1 becomes associated with the plasma membrane, as it contains no membrane-spanning sequence motif. Using flow cytometric and ELISA-based binding assays and mutant cell lines lacking selective glycosaminoglycans, we show that soluble NS1 binds back to the surface of uninfected cells primarily via interactions with heparan sulfate and chondroitin sulfate E. DENV NS1 binds directly to the surface of many types of epithelial and mesenchymal cells yet attaches poorly to most peripheral blood cells. Moreover, DENV NS1 preferentially binds to cultured human microvascular compared to aortic or umbilical cord vein endothelial cells. This binding specificity was confirmed in situ as DENV NS1 bound to lung and liver but not intestine or brain endothelium of mouse tissues. Differential binding of soluble NS1 by tissue endothelium and subsequent recognition by anti-NS1 antibodies could contribute to the selective vascular leakage syndrome that occurs during severe secondary DENV infection.

Immunodominant T-cell responses to dengue virus NS3 are associated with DHF

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.

An In-Depth Analysis of Original Antigenic Sin in Dengue Virus Infection

ABSTRACT The evolution of dengue viruses has resulted in four antigenically similar yet distinct serotypes. Infection with one serotype likely elicits lifelong immunity to that serotype, but generally not against the other three. Secondary or sequential infections are common, as multiple viral serotypes frequently cocirculate. Dengue infection, although frequently mild, can lead to dengue hemorrhagic fever (DHF) which can be life threatening. DHF is more common in secondary dengue infections, implying a role for the adaptive immune response in the disease. There is currently much effort toward the design and implementation of a dengue vaccine but these efforts are made more difficult by the challenge of inducing durable neutralizing immunity to all four viruses. Domain 3 of the dengue virus envelope protein (ED3) has been suggested as one such candidate because it contains neutralizing epitopes and it was originally thought that relatively few cross-reactive antibodies are directed to this domain. In this study, we performed a detailed analysis of the anti-ED3 response in a cohort of patients suffering either primary or secondary dengue infections. The results show dramatic evidence of original antigenic sin in secondary infections both in terms of binding and enhancement activity. This has important implications for dengue vaccine design because heterologous boosting is likely to maintain the immunological footprint of the first vaccination. On the basis of these findings, we propose a simple in vitro enzyme-linked immunosorbent assay (ELISA) to diagnose the original dengue infection in secondary dengue cases.