Cytotoxic T lymphocytes in dengue virus infection

Aminotransferases in Relation to the Severity of Dengue: A Systematic Review

A systematic review was conducted to investigate the relationship between aminotransferases and the severity of dengue infection, which is a prevalent and significant infection in tropical and subtropical regions. Aminotransferases are enzymes that are often elevated in dengue due to the liver's physiological and immunological response to the infection. This review focused on analyzing various studies that examined the correlation between aminotransferase levels and the severity of dengue. Extensive literature searches were performed using ("dengue*" OR "dengue fever*" OR "dengue haemorrhagic fever*" OR "dengue shock syndrome*") AND ("alanine aminotransferase*" OR "aspartate aminotransferase*") on PubMed. The selected articles were thoroughly reviewed, encompassing epidemiology, pathogenesis, and clinical manifestations of dengue. The consistent findings across the studies indicated that aminotransferases can serve as predictive markers for dengue severity. Therefore, early assessment of liver enzyme levels is crucial in dengue cases, and elevated levels should be closely monitored to prevent adverse outcomes.

The Good, the Bad, and the Shocking: The Multiple Roles of Dengue Virus Nonstructural Protein 1 in Protection and Pathogenesis

Dengue virus (DENV) is the most prevalent medically important mosquito-borne virus in the world. Upon DENV infection of a host cell, DENV nonstructural protein 1 (NS1) can be found intracellularly as a monomer, associated with the cell surface as a dimer, and secreted as a hexamer into the bloodstream. NS1 plays a variety of roles in the viral life cycle, particularly in RNA replication and immune evasion of the complement pathway. Over the past several years, key roles for NS1 in the pathogenesis of severe dengue disease have emerged, including direct action of the protein on the vascular endothelium and triggering release of vasoactive cytokines from immune cells, both of which result in endothelial hyperpermeability and vascular leak. Importantly, the adaptive immune response generates a robust response against NS1, and its potential contribution to dengue vaccines is also discussed.

Synergistic interactions between the NS3(hel) and E proteins contribute to the virulence of dengue virus type 1

Background

Dengue includes a broad range of symptoms, ranging from fever to hemorrhagic fever and may occasionally have alternative clinical presentations. Many possible viral genetic determinants of the intrinsic virulence of dengue virus (DENV) in the host have been identified, but no conclusive evidence of a correlation between viral genotype and virus transmissibility and pathogenicity has been obtained.

Methodology/Principal Findings

We used reverse genetics techniques to engineer DENV-1 viruses with subsets of mutations found in two different neuroadapted derivatives. The mutations were inserted into an infectious clone of DENV-1 not adapted to mice. The replication and viral production capacity of the recombinant viruses were assessed in vitro and in vivo. The results demonstrated that paired mutations in the envelope protein (E) and in the helicase domain of the NS3 (NS3_hel) protein had a synergistic effect enhancing viral fitness in human and mosquito derived cell lines. E mutations alone generated no detectable virulence in the mouse model; however, the combination of these mutations with NS3_hel mutations, which were mildly virulent on their own, resulted in a highly neurovirulent phenotype.

Conclusions/Significance

The generation of recombinant viruses carrying specific E and NS3_hel proteins mutations increased viral fitness both in vitro and in vivo by increasing RNA synthesis and viral load (these changes being positively correlated with central nervous system damage), the strength of the immune response and animal mortality. The introduction of only pairs of amino acid substitutions into the genome of a non-mouse adapted DENV-1 strain was sufficient to alter viral fitness substantially. Given current limitations to our understanding of the molecular basis of dengue neuropathogenesis, these results could contribute to the development of attenuated strains for use in vaccinations and provide insights into virus/host interactions and new information about the mechanisms of basic dengue biology.

Dengue virus constitutes a significant public health problem in tropical regions of the world. Despite the high morbidity and mortality of this infection, no effective antiviral drugs or vaccines are available for the treatment or prevention of dengue infections. The profile of clinical signs associated with dengue infection has changed in recent years with an increase in the number of episodes displaying unusual signs. We use reverse genetics technology to engineer DENV-1 viruses with subsets of mutations previously identified in highly neurovirulent strains to provide insights into the molecular mechanisms underlying dengue neuropathogenesis. We found that single mutations affecting the E and NS3_hel proteins, introduced in a different genetic context, had a synergistic effect increasing DENV replication capacity in human and mosquito derived cells in vitro. We also demonstrated correlations between the presence of these mutations and viral replication efficiency, viral loads, the induction of innate immune response genes and pathogenesis in a mouse model. These results should improve our understanding of the DENV-host cell interaction and contribute to the development of effective antiviral strategies.

Conserved MHC class I-presented dengue virus epitopes identified by immunoproteomics analysis are targets for cross-serotype reactive T-cell response

Dengue fever and dengue hemorrhagic fever are significant global public health problems, and understanding the overall immune response to infection will contribute to appropriate management of the disease and its potentially severe complications. Live attenuated and subunit vaccine candidates, which are under clinical evaluation, induce primarily an antibody response to the virus and minimal cross-reactive T-cell responses. Currently, there are no available tools to assess protective T-cell responses during infection or after vaccination. In this study, we utilize an immunoproteomics process to uncover novel HLA-A2-specific epitopes derived from dengue virus (DV)-infected cells. These epitopes are conserved, and we report that epitope-specific cytotoxic lymphocytes (CTLs) are cross-reactive against all 4 DV serotypes. These epitopes have potential as new informational and diagnostic tools to characterize T-cell immunity in DV infection and may serve as part of a universal vaccine candidate complementary to current vaccines in trial.

Cross-reactive T-cell responses to the nonstructural regions of dengue viruses among dengue fever and dengue hemorrhagic fever patients in Malaysia

Dengue virus infections are a major cause of morbidity and mortality in tropical and subtropical areas in the world. Attempts to develop effective vaccines have been hampered by the lack of understanding of the pathogenesis of the disease and the absence of suitable experimental models for dengue viral infection. The magnitude of T-cell responses has been reported to correlate with dengue disease severity. Sixty Malaysian adults with dengue viral infections were investigated for their dengue virus-specific T-cell responses to 32 peptides antigens from the structural and nonstructural regions from a dengue virus isolate. Seventeen different peptides from the C, E, NS2B, NS3, NS4A, NS4B, and NS5 regions were found to evoke significant responses in a gamma interferon enzyme-linked immunospot (ELISPOT) assay of samples from 13 selected patients with dengue fever (DF) and dengue hemorrhagic fever (DHF). NS3 and predominantly NS3(422-431) were found to be important T-cell targets. The highest peaks of T-cell responses observed were in responses to NS3(422-431) and NS5(563-571) in DHF patients. We also found almost a sevenfold increase in T-cell response in three DHF patients compared to three DF patient responses to peptide NS3(422-431). A large number of patients' T cells also responded to the NS2B(97-106) region. The ELISPOT analyses also revealed high frequencies of T cells that recognize both serotype-specific and cross-reactive dengue virus antigens in patients with DHF.

Progress for dengue virus diseases

Transmitted by the Aedes aegypti mosquito, the dengue virus is the etiological agent of dengue fever, dengue hemorrhagic fever and dengue shock syndrome, and, as such, is a significant factor in the high death rate found in most tropical and subtropical areas of the world. Dengue diseases are not only a health burden to developing countries, but pose an emerging problem worldwide. The immunopathological mechanisms appear to include a complex series of immune responses. A rapid increase in the levels of cytokines and chemical mediators during dengue disease plays a key role in inducing plasma leakage, shock and hemorrhagic manifestations. Currently, there are no vaccines available against dengue virus, although several tetravalent live-attenuated dengue vaccines are in clinical phases I or II, and prevention through vaccination has become a major priority on the agendas of the World Health Organization and of national ministries of health and military organizations. An alternative to vaccines is found in therapeutic-based approaches. Understanding the molecular mechanisms of viral replication has led to the development of potential drugs, and new molecular viral targets for therapy are emerging. The NS3 protease domain of the NS3 protein is responsible for processing the viral polyprotein and its inhibition is one of the principal aims of pharmacological therapy. This review is an overview of the progress made against dengue virus; in particular, it examines the unique properties--structural and functional--of the NS3 protease for the treatment of dengue virus infections by the inhibition of viral polyprotein processing.

Role of CD8+ T cells in control of West Nile virus infection

Infection with West Nile virus (WNV) causes fatal encephalitis more frequently in immunocompromised humans than in those with a healthy immune system. Although a complete understanding of this increased risk remains unclear, experiments with mice have begun to define how different components of the adaptive and innate immune response function to limit infection. Previously, we demonstrated that components of humoral immunity, particularly immunoglobulin M (IgM) and IgG, have critical roles in preventing dissemination of WNV infection to the central nervous system. In this study, we addressed the function of CD8(+) T cells in controlling WNV infection. Mice that lacked CD8(+) T cells or classical class Ia major histocompatibility complex (MHC) antigens had higher central nervous system viral burdens and increased mortality rates after infection with a low-passage-number WNV isolate. In contrast, an absence of CD8(+) T cells had no effect on the qualitative or quantitative antibody response and did not alter the kinetics or magnitude of viremia. In the subset of CD8(+)-T-cell-deficient mice that survived initial WNV challenge, infectious virus was recovered from central nervous system compartments for several weeks. Primary or memory CD8(+) T cells that were generated in vivo efficiently killed target cells that displayed WNV antigens in a class I MHC-restricted manner. Collectively, our experiments suggest that, while specific antibody is responsible for terminating viremia, CD8(+) T cells have an important function in clearing infection from tissues and preventing viral persistence.

Evasion of innate and adaptive immunity by flaviviruses

After a virus infects an animal, antiviral responses are generated that attempt to prevent dissemination. Interferons, antibody, complement, T and natural killer cells all contribute to the control and eradication of viral infections. Most flaviviruses, with the exception of some of the encephalitic viruses, cause acute disease and do not establish persistent infection. The outcome of flavivirus infection in an animal is determined by a balance between the speed of viral replication and spread, and the immune system response. Although many of the mechanistic details require further elucidation, flaviviruses have evolved specific tactics to evade the innate and adaptive immune response. A more thorough understanding of these principles could lead to improved models for viral pathogenesis and to strategies for the development of novel antiviral agents.

Activation of terminally differentiated human monocytes/macrophages by dengue virus: productive infection, hierarchical production of innate cytokines and chemokines, and the synergistic effect of lipopolysaccharide

Dengue virus (DV) primarily infects blood monocytes (MO) and tissue macrophages (M phi). We have shown in the present study that DV can productively infect primary human MO/M phi regardless of the stage of cell differentiation. After DV infection, the in vitro-differentiated MO/M phi secreted multiple innate cytokines and chemokines, including tumor necrosis factor alpha, alpha interferon (IFN-alpha), interleukin-1 beta (IL-1 beta), IL-8, IL-12, MIP-1 alpha, and RANTES but not IL-6, IL-15, or nitric oxide. Secretion of these mediators was highlighted by distinct magnitude, onset, kinetics, duration, and induction potential. A chemokine-to-cytokine hierarchy was noted in the magnitude and induction potential of secretion, and a chemokine-to-cytokine-to-chemokine/Th1 cytokine cascade could be seen in the production kinetics. Furthermore, we found that terminally differentiated MO/M phi cultured for more than 45 days could support productive DV infection and produce innate cytokines and chemokines, indicating that these mature cells were functionally competent in the context of a viral infection. In addition, DV replication in primary differentiated human MO/M phi was enhanced and prolonged in the presence of lipopolysaccharide (LPS), and LPS-mediated synergistic production of IFN-alpha could be seen in DV-infected MO/M phi. The secretion of innate cytokines and chemokines by differentiated MO/M phi suggests that regional accumulation of these mediators may occur in various tissues to which DV has disseminated and may thus result in local inflammation. The LPS-mediated enhancement of virus replication and synergistic IFN-alpha production suggests that concurrent bacterial infection may modulate cytokine-mediated disease progression during DV infection.

Bystander target cell lysis and cytokine production by dengue virus-specific human CD4(+) cytotoxic T-lymphocyte clones

Dengue hemorrhagic fever, the severe form of dengue virus infection, is believed to be an immunopathological response to a secondary infection with a heterologous serotype of dengue virus. Dengue virus capsid protein-specific CD4(+) cytotoxic T-lymphocyte (CTL) clones were shown to be capable of mediating bystander lysis of non-antigen-presenting target cells. After activation by anti-CD3 or in the presence of unlabeled antigen-presenting target cells, these clones could lyse both Jurkat cells and HepG2 cells as bystander targets. Lysis of HepG2 cells suggests a potential role for CD4(+) CTL in the liver involvement observed during dengue virus infection. Three CD4(+) CTL clones were demonstrated to lyse cognate, antigen-presenting target cells by a mechanism that primarily involves perforin, while bystander lysis occurred through Fas/Fas ligand interactions. In contrast, one clone used a Fas/Fas ligand mechanism to lyse both cognate and bystander targets. Cytokine production by the CTL clones was also examined. In response to stimulation with D2 antigen, CD4(+) T-cell clones produced gamma interferon, tumor necrosis factor alpha (TNF-alpha) and TNF-beta. The data suggest that CD4(+) CTL clones may contribute to the immunopathology observed upon secondary dengue virus infections through direct cytolysis and/or cytokine production.