Molecular profiling of T-helper immune genes during dengue virus infection

Scratching the Surface Takes a Toll: Immune Recognition of Viral Proteins by Surface Toll-like Receptors

Early innate viral recognition by the host is critical for the rapid response and subsequent clearance of an infection. Innate immune cells patrol sites of infection to detect and respond to invading microorganisms including viruses. Surface Toll-like receptors (TLRs) are a group of pattern recognition receptors (PRRs) that can be activated by viruses even before the host cell becomes infected. However, the early activation of surface TLRs by viruses can lead to viral clearance by the host or promote pathogenesis. Thus, a plethora of research has attempted to identify specific viral ligands that bind to surface TLRs and mediate progression of viral infection. Herein, we will discuss the past two decades of research that have identified specific viral proteins recognized by cell surface-associated TLRs, how these viral proteins and host surface TLR interactions affect the host inflammatory response and outcome of infection, and address why controversy remains regarding host surface TLR recognition of viral proteins.

What is the association between the IL6-174 G > C (rs1800795) polymorphism and the risk of dengue? Evidence from a meta-analysis

The association of polymorphisms in genes responsible for immunological mediators with dengue allows the identification of certain genetic alterations that increase or decrease the development risk of the disease. A few number of studies that correlate the interleukin 6-174 G > C (IL6-174 G > C) polymorphism (rs1800795) with dengue. However, there is an inconsistency on the polymorphism influence on the disease which motivated this meta-analysis. So, this study aimed to evaluate the rs1800795 polymorphism with protection or susceptibility for development of dengue. A search of the literature was performed for studies published before 05 September 2020 in various databases. Calculations of Odds Ratio (OR) with 95% of Confidence Intervals (CI) and heterogeneity (I²) were assessed and publication bias was done by Begg' and Egger's test. The value of P < 0.05 was considered as significant. As results, five case-control studies were identified and included in the results. The analysis showed that the heterozygous genotype has a protective role against dengue without warning signs (DWOS) (OR = 0.57, p = 0.001), as well as the polymorphic C allele (OR = 0.77, p = 0.04). When unifying the data from the included studies, the GG genotype was more prevalent among individuals with dengue with warning signs (DWWS) when compared to the control group (p = 0.0221). GC genotype was more prevalent in the control group than in the DWWS group (p = 0.0119). Therefore, in our study we observed that the GC genotype and the C allele have a protective role against DWOS. Since this polymorphism is associated with low IL-6 expression, thus it is expected that there will be a decreased pro-inflammatory response. However, more studies regarding this thematic are necessary to have a consensus about this polymorphism and dengue.

Use of Animal Models in Studying Roles of Antibodies and Their Secretion Cells in Dengue Vaccine Development

The cardinal feature of adaptive immunity is its ability to form memory responses that can be rapidly recalled to contain pathogens upon reencountering. Conferring a robust memory immune response to an infection is a key feature for a successful vaccination program. The plasmablasts are cells that not only can secret non-neutralizing antibodies but also can secrete the specific antibodies essential to neutralize and inactivate the invading pathogens. Dengue has been recognized as one of the most important vector-borne human viral diseases globally. Currently, supportive care with vigilant monitoring is the standard practice since there is as yet no approved therapeutic modality to treat dengue. Even though the approved vaccine has become available, its low efficacy with the potential to cause harm is the major hurdle to promote the widespread usage of the vaccine. Despite the decades of research on dengue, the major challenge in dengue vaccine development is the absence of suitable experimental animal models that reflect the pathological features and clinical symptoms, as seen in humans. Dengue is transmitted by the bite of mosquitoes carrying infectious dengue virus (DENV), which has four distinct serotypes. Recently, cases resulting from unconventional transmission routes, such as blood transfusion, organs as well as stem cells and bone marrow transplantations, and mother-to-infant vertical transmission, have been reported, suggesting an alternate route of DENV transmission exists in nature. This review discusses issues and challenges needing to be resolved to develop an effective dengue vaccine. Development of a robust and reliable dengue animal model that can reflect not only dynamic human clinical symptoms but also can answer around why preexisting neutralizing antibodies do not confer protection upon re-infection and immune protection marker for dengue vaccine efficacy evaluation.

Fatal Dengue Cases Reveal Brain Injury and Viral Replication in Brain-Resident Cells Associated with the Local Production of Pro-Inflammatory Mediators

Dengue is an arboviral disease caused by dengue virus (DENV), which is transmitted to humans by Aedes aegypti mosquitoes. Infection by DENV most commonly results in a mild flu-like illness; however, the disease has been increasingly associated with neurological symptomatology. This association draws attention to further investigations on the impact of DENV infection in the host's central nervous system. Here, we analyzed brain samples of three fatal dengue cases that occurred in 2002 during an outbreak in Rio de Janeiro, Brazil. Brain tissues of these cases were marked by histopathological alterations, such as degenerated neurons, demyelination, hemorrhage, edema, and increased numbers of astrocytes and microglial cells. Samples were also characterized by lymphocytic infiltrates mainly composed of CD8 T cells. DENV replication was evidenced in neurons, microglia and endothelial cells through immunohistochemistry and in situ hybridization techniques. Pro-inflammatory cytokines, such as TNF-α and IFN-γ were detected in microglia, while endothelial cells were marked by the expression of RANTES/CCL5. Cytoplasmic HMGB1 and the production of nitric oxide were also found in neurons and microglial cells. This work highlights the possible participation of several local pro-inflammatory mediators in the establishment of dengue neuropathogenesis.

Expression Pattern of Selected Toll-like Receptors (TLR's) in the PBMC's of Severe and Non-severe Dengue Cases

Objective: The role of TLR's in the pathogenesis of dengue is not explored well. Differential expression of TLR2 and TLR4 was reported in dengue cases. In the present study in order to understand the expression pattern of various TLR's, including TLR2, TLR3, TLR4 and TLR9, mRNA levels were determined in various dengue study groups compared to control groups, at the time of admission and around defervescence using quantitative real-time PCR (RT-PCR).Methods: A total of 88 dengue cases with 32 severe and 56 non-severe cases were involved in the study. Gene expression pattern of the study groups was compared with 31 other febrile illness (OFI) cases and 63 healthy controls. Transcript levels of the target genes were estimated from the peripheral blood mononuclear cells (PBMC) samples collected from cases and controls using quantitative real-time PCR.Results: We have noted a significant alteration in the levels of all TLR's in dengue and OFI cases compared to healthy controls at the time of admission. Interestingly we have noted a significant alteration in the levels of TLR9 in severe and non-severe cases during defervescence. The same was not detected in the OFI group.Conclusion: The present study found a change in TLR's during dengue infection. This suggests us to explore the TLR's as therapeutic candidate for anti-dengue virus strategies. However, in order to ascertain the involvement of TLR's in the disease pathology and its role as biomarkers for prognosis, a complete dynamics of TLR's expression needs to be studied.

Placental Inflammation and Fetal Injury in a Rare Zika Case Associated With Guillain-Barré Syndrome and Abortion

Zika virus (ZIKV) is an emerging virus involved in recent outbreaks in Brazil. The association between the virus and Guillain-Barré syndrome (GBS) or congenital disorders has raised a worldwide concern. In this work, we investigated a rare Zika case, which was associated with GBS and spontaneous retained abortion. Using specific anti-ZIKV staining, the virus was identified in placenta (mainly in Hofbauer cells) and in several fetal tissues, such as brain, lungs, kidneys, skin and liver. Histological analyses of the placenta and fetal organs revealed different types of tissue abnormalities, which included inflammation, hemorrhage, edema and necrosis in placenta, as well as tissue disorganization in the fetus. Increased cellularity (Hofbauer cells and TCD8⁺ lymphocytes), expression of local pro-inflammatory cytokines such as IFN-γ and TNF-α, and other markers, such as RANTES/CCL5 and VEGFR2, supported placental inflammation and dysfunction. The commitment of the maternal-fetal link in association with fetal damage gave rise to a discussion regarding the influence of the maternal immunity toward the fetal development. Findings presented in this work may help understanding the ZIKV immunopathogenesis under the rare contexts of spontaneous abortions in association with GBS.

Animal models for dengue vaccine development and testing

Dengue fever is a tropical endemic disease; however, because of climate change, it may become a problem in South Korea in the near future. Research on vaccines for dengue fever and outbreak preparedness are currently insufficient. In addition, because there are no appropriate animal models, controversial results from vaccine efficacy assessments and clinical trials have been reported. Therefore, to study the mechanism of dengue fever and test the immunogenicity of vaccines, an appropriate animal model is urgently needed. In addition to mouse models, more suitable models using animals that can be humanized will need to be constructed. In this report, we look at the current status of model animal construction and discuss which models require further development.

Peripheral Organs of Dengue Fatal Cases Present Strong Pro-Inflammatory Response with Participation of IFN-Gamma-, TNF-Alpha- and RANTES-Producing Cells

Dengue disease is an acute viral illness caused by dengue virus (DENV) that can progress to hemorrhagic stages leading to about 20000 deaths every year worldwide. Despite many clinical investigations regarding dengue, the immunopathogenic process by which infected patients evolve to the severe forms is not fully understood. Apart from differences in virulence and the antibody cross reactivity that can potentially augment virus replication, imbalanced cellular immunity is also seen as a major concern in the establishment of severe dengue. In this context, the investigation of cellular immunity and its products in dengue fatal cases may provide valuable data to help revealing dengue immunopathogenesis. Here, based in four dengue fatal cases infected by the serotype 3 in Brazil, different peripheral organs (livers, lungs and kidneys) were studied to evaluate the presence of cell infiltrates and the patterns of local cytokine response. The overall scenario of the studied cases revealed a considerable systemic involvement of infection with mononuclear cells targeted to all of the evaluated organs, as measured by immunohistochemistry (IHC). Quantification of cytokine-expressing cells in peripheral tissues was also performed to characterize the ongoing inflammatory process by the severe stage of the disease. Increased levels of IFN-γ- and TNF-α-expressing cells in liver, lung and kidney samples of post-mortem subjects evidenced a strong pro-inflammatory induction in these tissues. The presence of increased RANTES-producing cell numbers in all analyzed organs suggested a possible link between the clinical status and altered vascular permeability. Co-staining of DENV RNA and IFN-γ or TNF-α using in situ hibridization and IHC confirmed the virus-specific trigger of the pro-inflammatory response. Taken together, this work provided additional evidences that corroborated with the traditional theories regarding the “cytokine storm” and the occurrence of uneven cellular immunity in response to DENV as major reasons for progress to severe disease.

Activation of TLR2 and TLR6 by Dengue NS1 Protein and Its Implications in the Immunopathogenesis of Dengue Virus Infection

Dengue virus (DV) infection is the most prevalent mosquito-borne viral disease and its manifestation has been shown to be contributed in part by the host immune responses. In this study, pathogen recognition receptors, Toll-like receptor (TLR) 2 and TLR6 were found to be up-regulated in DV-infected human PBMC using immunofluorescence staining, flow cytometry and Western blot analyses. Using ELISA, IL-6 and TNF-α, cytokines downstream of TLR2 and TLR6 signaling pathways were also found to be up-regulated in DV-infected PBMC. IL-6 and TNF-α production by PBMC were reduced when TLR2 and TLR6 were blocked using TLR2 and TLR6 neutralizing antibodies during DV infection. These results suggested that signaling pathways of TLR2 and TLR6 were activated during DV infection and its activation contributed to IL-6 and TNF-α production. DV NS1 protein was found to significantly increase the production of IL-6 and TNF-α when added to PBMC. The amount of IL-6 and TNF-α stimulated by DV NS1 protein was reduced when TLR2 and TLR6 were blocked, suggesting that DV NS1 protein is the viral protein responsible for the activation of TLR2 and TLR6 during DV infection. Secreted alkaline phosphatase (SEAP) reporter assay was used to further confirm activation of TLR2 and TLR6 by DV NS1 protein. In addition, DV-infected and DV NS1 protein-treated TLR6^-/- mice have higher survivability compared to DV-infected and DV NS1 protein-treated wild-type mice. Hence, activation of TLR6 via DV NS1 protein could potentially play an important role in the immunopathogenesis of DV infection.

Despite the prevalence of dengue virus infection and the heavy economic burden it puts on the endemic countries, the immunopathogenesis of dengue virus infection remains unclear. Plasma leakage in dengue hemorrhagic fever (DHF) develops not when the viremia is at its peak in infected patients but when viremia has been significantly reduced or cleared. This suggests that host immune response is responsible for the development DHF. The interactions of the viral factors with host factors which trigger the host immune responses are likely to play a significant role in the development of dengue diseases, thus are of great interests. In this study, we found that dengue NS1 protein activates TLR2 and TLR6, leading to increase proinflammatory cytokine production. In addition, the interaction of viral factor with TLR6 was found to play an important role in the manifestation of dengue virus infection. Our study provides new insights into the involvement of TLR6 in dengue virus infection and the potential of using TLR6 anatagonist in therapeutic treatment for DV infection.

Gene cloning and induced expression pattern of IRF4 and IRF10 in the Asian swamp eel (Monopterus albus)

The Asian swamp eel (Monopterus albus) is one of the most economically important freshwater fish in East Asia, but data on the immune genes of M. albus are scarce compared to other commercially important fish. A better understanding of the eel's immune responses may help in developing strategies for disease management, potentially improving yields and mitigating losses. In mammals, interferon regulatory factors (IRFs) play a vital role in both the innate and adaptive immune system; though among teleosts IRF4 and IRF10 have seldom been studied. In this study, we characterized IRF4 and IRF10 from M. albus (maIRF4 and maIRF10) and found that maIRF4 cDNA consists of 1 716 nucleotides encoding a 451 amino acid (aa) protein, while maIRF10 consists of 1 744 nucleotides including an open reading frame (ORF) of 1 236 nt encoding 411 aa. The maIRF10 gene was constitutively expressed at high levels in a variety of tissues, while maIRF4 showed a very limited expression pattern. Expression of maIRF4 and maIRF10 in head kidney, and spleen tissues was significantly up-regulated from 12 h to 48 h post-stimulation with polyinosinic: polycytidylic acid (poly I:C), lipopolysaccharide (LPS) and a common pathogenic bacteria Aeromonas hydrophila. These results suggest that IRF4 and IRF10 play roles in immune responses to both viral and bacterial infections in M. albus.

Overcoming tumor immune evasion with an unique arbovirus

Combining dendritic cell vaccination with the adjuvant effect of a strain of dengue virus may be a way to overcome known tumor immune evasion mechanisms. Dengue is unique among viruses as primary infections carry lower mortality than the common cold, but secondary infections carry significant risk of hypovolemic shock. While current immuno-therapies rely on a single axis of attack, this approach combines physiological (hyperthermic reduction of tumor perfusion), immunological (activation of effector cells of the adaptive and innate immune system), and apoptosis-inducing pathways (sTRAIL) to destroy tumor cells. The premise of using multiple mechanisms of action in synergy with a decline in the ability of the tumor cells to employ resistance methods suggests the potential of this combination approach in cancer immunotherapy.

Cytokine expression profile of dengue patients at different phases of illness

BACKGROUND

Dengue is an important medical problem, with symptoms ranging from mild dengue fever to severe forms of the disease, where vascular leakage leads to hypovolemic shock. Cytokines have been implicated to play a role in the progression of severe dengue disease; however, their profile in dengue patients and the synergy that leads to continued plasma leakage is not clearly understood. Herein, we investigated the cytokine kinetics and profiles of dengue patients at different phases of illness to further understand the role of cytokines in dengue disease.

METHODS AND FINDINGS

Circulating levels of 29 different types of cytokines were assessed by bead-based ELISA method in dengue patients at the 3 different phases of illness. The association between significant changes in the levels of cytokines and clinical parameters were analyzed. At the febrile phase, IP-10 was significant in dengue patients with and without warning signs. However, MIP-1β was found to be significant in only patients with warning signs at this phase. IP-10 was also significant in both with and without warning signs patients during defervescence. At this phase, MIP-1β and G-CSF were significant in patients without warning signs, whereas MCP-1 was noted to be elevated significantly in patients with warning signs. Significant correlations between the levels of VEGF, RANTES, IL-7, IL-12, PDGF and IL-5 with platelets; VEGF with lymphocytes and neutrophils; G-CSF and IP-10 with atypical lymphocytes and various other cytokines with the liver enzymes were observed in this study.

CONCLUSIONS

The cytokine profile patterns discovered between the different phases of illness indicate an essential role in dengue pathogenesis and with further studies may serve as predictive markers for progression to dengue with warning signs.

Dengue virus infection mediates HMGB1 release from monocytes involving PCAF acetylase complex and induces vascular leakage in endothelial cells

High mobility group box 1 (HMGB1) protein is released from cells as a pro-inflammatory cytokine in response to an injury or infection. During dengue hemorrhagic fever (DHF)/dengue shock syndrome (DSS), a number of pro-inflammatory cytokines are released, contributing to disease pathogenesis. In this study, the release of HMGB1 from human myelogenous leukemia cell line K562 and primary peripheral blood monocytes (PBM) cells was examined during dengue virus (DV)-infection. HMGB1 was shown to translocate from cell nuclei to the cytoplasm in both K562- and PBM-infected cells. The translocation of HMGB1 from the nucleus to the cytoplasm was shown to be mediated by the host cell p300/CBP-associated factor (PCAF) acetylase complex in K562 cells. In addition, DV capsid protein was observed to be the putative viral protein in actuating HMGB1 migration from the nucleus to cytoplasm through the involvement of PCAF acetylase. HMGB1 was released from DV-infected K562 cells into the extracellular milieu in a multiplicity of infection (M.O.I.)-independent manner and its release can be inhibited by the addition of 1–5 mM of ethyl pyruvate (EP) in a dose-dependent manner. Application of DV-infected K562 cell culture supernatants to primary endothelial cells induced vascular permeability. In contrast, supernatants from DV-infected K562 cells treated with EP or HMGB1 neutralizing antibody were observed to maintain the structural integrity of the vascular barrier.