Immunomodulation in dengue: towards deciphering dengue severity markers

BACKGROUND

Dengue is a vector-borne debilitating disease that is manifested as mild dengue fever, dengue with warning signs, and severe dengue. Dengue infection provokes a collective immune response; in particular, the innate immune response plays a key role in primary infection and adaptive immunity during secondary infection. In this review, we comprehensively walk through the various markers of immune response against dengue pathogenesis and outcome.

MAIN BODY

Innate immune response against dengue involves a collective response through the expression of proinflammatory cytokines, such as tumor necrosis factors (TNFs), interferons (IFNs), and interleukins (ILs), in addition to anti-inflammatory cytokines and toll-like receptors (TLRs) in modulating viral pathogenesis. Monocytes, dendritic cells (DCs), and mast cells are the primary innate immune cells initially infected by DENV. Such immune cells modulate the expression of various markers, which can influence disease severity by aiding virus entry and proinflammatory responses. Adaptive immune response is mainly aided by B and T lymphocytes, which stimulate the formation of germinal centers for plasmablast development and antibody production. Such antibodies are serotype-dependent and can aid in virus entry during secondary infection, mediated through a different serotype, such as in antibody-dependent enhancement (ADE), leading to DENV severity. The entire immunological repertoire is exhibited differently depending on the immune status of the individual.

SHORT CONCLUSION

Dengue fever through severe dengue proceeds along with the modulated expression of several immune markers. In particular, TLR2, TNF-α, IFN-I, IL-6, IL-8, IL-17 and IL-10, in addition to intermediate monocytes (CD14+CD16+) and Th17 (CD4+IL-17+) cells are highly expressed during severe dengue. Such markers could assist greatly in severity assessment, prompt diagnosis, and treatment.

The ApoA1-mimetic peptide 4F blocks flavivirus NS1-triggered endothelial dysfunction and protects against lethal dengue virus challenge

Flavivirus infections result in a variety of outcomes, from clinically inapparent infections to severe, sometimes fatal cases characterized by hemorrhagic manifestations and vascular leakage leading to shock (dengue), meningomyeloencephalitis (West Nile), and congenital abnormalities (Zika). Although there are approved vaccines against several flaviviruses, potentially enhancing cross-reactive immune responses have complicated the development and implementation of vaccines against dengue and Zika viruses, and no specific therapeutics currently exist. The flavivirus nonstructural protein 1 (NS1) is a promising antiviral target because it is a conserved multifunctional virulence factor that directly triggers vascular leak. We previously showed that interactions between NS1 and the ApoA1 lipoprotein modulate DENV infection. Here, we evaluated the potential of the ApoA1-mimetic peptide, 4F, to interfere with endothelial dysfunction mediated by the NS1 protein of dengue, Zika, and West Nile flaviviruses. In an in vitro model consisting of human endothelial cell monolayers, 4F inhibited NS1-induced hyperpermeability, as measured by a transendothelial electrical resistance assay, and prevented NS1-triggered disruption of the endothelial glycocalyx layer. We also demonstrate that treatment with 4F inhibited NS1 interaction with endothelial cells. Finally, we show that 4F protects against lethal DENV challenge in a mouse model, reducing morbidity and mortality in a dose-dependent manner. Our data demonstrate the potential of 4F to inhibit flavivirus NS1-mediated pathology and severe dengue disease in mice and suggest that 4F can also serve as a molecular tool to probe different NS1 functions in vitro and in vivo.

Pirarubicin combined with TLR3 or TLR4 agonists enhances anti-tumor efficiency

BACKGROUND

Triple-negative breast cancer (TNBC) is prone to relapse due to the lack of effective therapeutic targets. Macrophages are the most abundant immune cells in the tumor microenvironment (TME) of breast cancer. Targeting the cross-talk between macrophages and cancer cells provides a more efficient strategy for anti-tumor therapy. Toll-like receptors (TLRs) are important players involved in macrophage activation, and TLR agonists are known to play roles in cancer therapy. However, the combination strategy of TLR agonists with chemotherapy drugs is still not well characterized.

METHODS

RT-PCR and Western blot were used to detect the expression of TLRs. The communication between breast cancer cells and macrophages were determined by co-culture in vitro. Tumor cells proliferation and migration were investigated by MTT assay and scratch wound assay. The effects of drug combinations and toxic side effects were assessed by immunohistochemistry and Hematoxylin & Eosin staining.

RESULTS

Expression of TLR3 and TLR4 were lower in breast tumor tissues compared with adjacent normal tissues. Patients with higher TLR3 or TLR4 expression levels had a better prognosis than those with lower expression levels. TLR3/4 expression was significantly inhibited when breast cancer cells MDA-MB-231 and E0771 were conditioned-cultured with macrophages in vitro and was also inhibited by pirarubicin (THP). However, the combination of TLR agonists and THP could reverse this response and inhibit the proliferation and migration of breast cancer cells. Additionally, this combination significantly reduced the tumor volume and weight in the murine model, increased the expression of TLR3/4 in mouse breast tumors.

CONCLUSIONS

Our results provide new ideas for the combination strategy of THP with TLR agonists which improves prognosis of breast cancer.

Dengue NS1 interaction with lipids alters its pathogenic effects on monocyte derived macrophages

BACKGROUND

While dengue NS1 antigen has been shown to be associated with disease pathogenesis in some studies, it has not been linked in other studies, with the reasons remaining unclear. NS1 antigen levels in acute dengue are often associated with increased disease severity, but there has been a wide variation in results based on past dengue infection and infecting dengue virus (DENV) serotype. As NS1 engages with many host lipids, we hypothesize that the type of NS1-lipid interactions alters its pathogenicity.

METHODS

Primary human monocyte derived macrophages (MDMs) were co-cultured with NS1 alone or with HDL, LDL, LPS and/or platelet activating factor (PAF) from individuals with a history of past dengue fever (DF = 8) or dengue haemorrhagic fever (DHF = 8). IL-1β levels were measured in culture supernatants, and gene expression analysis carried out in MDMs. Monocyte subpopulations were assessed by flow cytometry. Hierarchical cluster analysis with Euclidean distance calculations were used to differentiate clusters. Differentially expressed variables were extracted and a classifier model was developed to differentiate between past DF and DHF.

RESULTS

Significantly higher levels of IL-1β were seen in culture supernatants when NS1 was co-cultured with LDL (p = 0.01, median = 45.69 pg/ml), but lower levels when NS1 was co-cultured with HDL (p = 0.05, median = 4.617 pg/ml). MDMs of those with past DHF produced higher levels of IL-1β when NS1 was co-cultured with PAF (p = 0.02). MDMs of individuals with past DHF, were significantly more likely to down-regulate RPLP2 gene expression when macrophages were co-cultured with either PAF alone, or NS1 combined with PAF, or NS1 combined with LDL. When NS1 was co-cultured with PAF, HDL or LDL two clusters were detected based on IL10 expression, but these did not differentiate those with past DF or DHF.

CONCLUSIONS

As RPLP2 is important in DENV replication, regulating cellular stress responses and immune responses and IL-10 is associated with severe disease, it would be important to further explore how differential expression of RPLP2 and IL-10 could lead to disease pathogenesis based on NS1 and lipid interactions.

Toll-like receptor 4 - a multifunctional virus recognition receptor

Since the initial description of Toll receptors in Drosophila and their mammalian counterparts Toll-like receptors (TLRs), numerous fundamental and applied studies have explored their crucial role as sensors of pathogen-associated molecular patterns (PAMPs). Among the ten human TLRs, TLR4 is particularly well known for its ability to detect lipopolysaccharides (LPS), a component of the Gram-negative bacterial cell wall. In addition to its archetypal functions, TLR4 is also a versatile virus sensor. This review provides a background on the discovery of TLR4 and how this knowledge laid a foundation for characterization of its diverse roles in antiviral responses, examined through genetic, biochemical, structural, and immunological approaches. These advances have led to a deeper understanding of the molecular functions that enable TLR4 to orchestrate multi-nodal control by professional antigen-presenting cells (APCs) to initiate appropriate and regulated antiviral immune responses.

The N and C-terminal deleted variant of the dengue virus NS1 protein is a potential candidate for dengue vaccine development

NS1 is an elusive dengue protein, involved in viral replication, assembly, pathogenesis, and immune evasion. Its levels in blood plasm are positively related to disease severity like thrombocytopenia, hemorrhage, and vascular leakage. Despite its pathogenic roles, NS1 is being used in various vaccine formulations due to its sequence conservancy, ability to produce protective antibodies and low risk for inducing antibody-dependent enhancement. In this study, we have used bioinformatics tools and reported literature to develop an NS1 variant (dNS1). Molecular docking studies were performed to evaluate the receptor-binding ability of the NS1 and dNS1 with TLR4. NS1 and dNS1 (153 to 312 amino acid region) genes were cloned, expressed and protein was purified followed by refolding. Docking studies showed the binding of NS1 and dNS1 with the TLR4 receptor which suggests that N and C-terminal sequences of NS1 are not critical for receptor binding. Antibodies against NS1 and dNS1 were raised in rabbits and binding affinity of anti-dNS1 anti-NS1 sera was evaluated against both NS1 and dNS1. Similar results were observed through western blotting which highlight that N and C-terminal deletion of NS1 does not compromise the immunogenic potential of dNS1 hence, supports its use in future vaccine formulations as a substitute for NS1.

The Flavivirus Non-Structural Protein 5 (NS5): Structure, Functions, and Targeting for Development of Vaccines and Therapeutics

Flaviviruses, including dengue (DENV), Zika (ZIKV), West Nile (WNV), Japanese encephalitis (JEV), yellow fever (YFV), and tick-borne encephalitis (TBEV) viruses, pose a significant global emerging threat. With their potential to cause widespread outbreaks and severe health complications, the development of effective vaccines and antiviral therapeutics is imperative. The flaviviral non-structural protein 5 (NS5) is a highly conserved and multifunctional protein that is crucial for viral replication, and the NS5 protein of many flaviviruses has been shown to be a potent inhibitor of interferon (IFN) signalling. In this review, we discuss the functions of NS5, diverse NS5-mediated strategies adopted by flaviviruses to evade the host antiviral response, and how NS5 can be a target for the development of vaccines and antiviral therapeutics.

Proteomic investigations of dengue virus infection: key discoveries over the last 10 years

INTRODUCTION

Dengue virus (DENV) infection remains one of the most significant infectious diseases in humans. Several efforts have been made to address its molecular mechanisms. Over the last 10 years, proteomics has been widely applied to investigate various aspects of DENV infection.

AREAS COVERED

In this review, we briefly introduce common proteomics approaches using various mass spectrometric modalities followed by summarizing all the discoveries obtained from proteomic investigations of DENV infection over the last 10 years. These include the data on DENV-vector interactions and host responses to address the DENV biology and disease mechanisms. Moreover, applications of proteomics to disease prevention, diagnosis, vaccine design, development of anti-DENV agents and other new treatment strategies are discussed.

EXPERT OPINION

Despite efforts on disease prevention, DENV infection is still a significant global healthcare burden that affects the general population. As summarized herein, proteomic technologies with high-throughput capabilities have provided more in-depth details of protein dynamics during DENV infection. More extensive applications of proteomics and other powerful research tools would provide a promise to better cope and prevent this mosquito-borne infectious disease.

Structural biology of flavivirus NS1 protein and its antibody complexes

The genus of flavivirus includes many mosquito-borne human pathogens, such as Zika (ZIKV) and the four serotypes of dengue (DENV1-4) viruses, that affect billions of people as evidenced by epidemics and endemicity in many countries and regions in the world. Among the 10 viral proteins encoded by the viral genome, the nonstructural protein 1 (NS1) is the only secreted protein and has been used as a diagnostic biomarker. NS1 has also been an attractive target for its biotherapeutic potential as a vaccine antigen. This review focuses on the recent advances in the structural landscape of the secreted NS1 (sNS1) and its complex with monoclonal antibodies (mAbs). NS1 forms an obligatory dimer, and upon secretion, it has been reported to be hexametric (trimeric dimers) that could dissociate and bind to the epithelial cell membrane. However, high-resolution structural information has been missing about the high-order oligomeric states of sNS1. Several cryoEM studies have since shown that DENV and ZIKV recombinant sNS1 (rsNS1) are in dynamic equilibrium of dimer-tetramer-hexamer states, with tetramer being the predominant form. It was recently revealed that infection-derived sNS1 (isNS1) forms a complex of the NS1 dimer partially embedded in a High-Density Lipoprotein (HDL) particle. Structures of NS1 in complexes with mAbs have also been reported which shed light on their protective roles during infection. The biological significance of the diversity of NS1 oligomeric states remains to be further studied, to inform future research on flaviviral pathogenesis and the development of therapeutics and vaccines. Given the polymorphism of flavivirus NS1 across sample types with variations in antigenicity, we propose a nomenclature to accurately define NS1 based on the localization and origin.

Differences in the Membrane-Binding Properties of Flaviviral Nonstructural 1 (NS1) Protein: Comparative Simulations of Zika and Dengue Virus NS1 Proteins in Explicit Bilayers

NS1 in flaviviruses is the only nonstructural protein that is secretory and interacts with different cellular components of the host cell membrane. NS1 is localized in the ER as a dimer to facilitate viral replication. Crystal structures of NS1 homologues from zika (ZIKV) and dengue (DENV) viruses have revealed the organization of different domains in NS1 dimers. The β-roll and the connector and intertwined loop regions of wing domains of NS1 have been shown to interact with the membranes. In this study, we have performed multiple molecular dynamics (MD) simulations of ZIKV and DENV NS1 systems in apo and in POPE bilayers with different cholesterol concentrations (0, 20 and 40%). The NS1 protein was placed just above the membrane surface, and for each NS1-membrane system two to three independent simulations with 600 ns production run were performed. At the end of the production runs, ZIKV NS1 inserts deeper inside the membrane compared to the DENV counterpart. Unlike ZIKV NS1, the orientation of DENV NS1 is asymmetric in which one of the chains in the dimer interacts with the membrane while the other is more exposed to the solvent. The β-roll region in ZIKV NS1 penetrates beyond the headgroup region and interacts with the lipid acyl chains while the C-terminal region barely interacts with the headgroup. Specific residues in the intertwined region deeply penetrate inside the membrane. The role of charged and aromatic residues of ZIKV NS1 in strongly interacting with the membrane components is revealed. The presence of cholesterol affects the extent of insertion in the membrane and interaction of individual residues. Overall, membrane-binding properties of ZIKV NS1 significantly differ from its counterpart in DENV. The differences found in the binding and insertion of NS1 can be used to design drugs and novel antibodies that can be flavivirus specific.

Recent Insights into the Molecular Mechanisms of the Toll-like Receptor Response to Influenza Virus Infection

Influenza A viruses (IAVs) pose a significant global threat to human health. A tightly controlled host immune response is critical to avoid any detrimental effects of IAV infection. It is critical to investigate the association between the response of Toll-like receptors (TLRs) and influenza virus. Because TLRs may act as a double-edged sword, a balanced TLR response is critical for the overall benefit of the host. Consequently, a thorough understanding of the TLR response is essential for targeting TLRs as a novel therapeutic and prophylactic intervention. To date, a limited number of studies have assessed TLR and IAV interactions. Therefore, further research on TLR interactions in IAV infection should be conducted to determine their role in host-virus interactions in disease causation or clearance of the virus. Although influenza virus vaccines are available, they have limited efficacy, which should be enhanced to improve their efficacy. In this study, we discuss the current status of our understanding of the TLR response in IAV infection and the strategies adopted by IAVs to avoid TLR-mediated immune surveillance, which may help in devising new therapeutic or preventive strategies. Furthermore, recent advances in the use of TLR agonists as vaccine adjuvants to enhance influenza vaccine efficacy are discussed.

Dengue NS1 interaction with lipids alters its pathogenic effects on monocyte derived macrophages

Background

While dengue NS1 antigen has been shown to be associated with disease pathogenesis in some studies, it has not been linked in other studies, with the reasons remaining unclear. NS1 antigen levels in acute dengue are often associated with increased disease severity, but there have been a wide variation in results based on past dengue infection and infecting dengue virus (DENV) serotype. As NS1 engages with many host lipids, we hypothesize that the type of NS1-lipid interactions alters its pathogenicity.

Methods

Primary human monocyte derived macrophages (MDMs) were co-cultured with NS1 alone or with HDL, LDL, LPS and/or platelet activating factor (PAF) from individuals with a history of past dengue fever (DF=8) or dengue haemorrhagic fever (DHF=8). IL-1β levels were measured in culture supernatants, and gene expression analysis carried out in MDMs. Monocyte subpopulations were assessed by flow cytometry. Hierarchical cluster analysis with Euclidean distance calculations were used to differentiate clusters. Differentially expressed variables were extracted and a classifier model was developed to differentiate between past DF and DHF.

Results

Significantly higher levels of IL-1β were seen in culture supernatants when NS1 was co-cultured with LDL (p=0.01), but with lower levels with HDL (p=0.05). MDMs of those past DHF produced more IL-1β when NS1 with PAF (p=0.02). MDMs of individuals with past DHF, were significantly more likely to down-regulate RPLP2 gene expression when macrophages were co-cultured with either PAF alone, or NS1 combined with PAF, or NS1 combined with LDL. When NS1 was co-cultured with PAF, HDL or LDL two clusters were detected based on IL10 expression, but these did not differentiate those with past DF or DHF.

Conclusions

As RPLP2 is important in DENV replication and in regulating cellular stress responses and immune responses and IL-10 is associated with severe disease, it would be important to further explore how differential expression of RPLP2 and IL-10 could lead to disease pathogenesis based on NS1 and lipid interactions.

Secreted dengue virus NS1 from infection is predominantly dimeric and in complex with high-density lipoprotein

Severe dengue infections are characterized by endothelial dysfunction shown to be associated with the secreted nonstructural protein 1 (sNS1), making it an attractive vaccine antigen and biotherapeutic target. To uncover the biologically relevant structure of sNS1, we obtained infection-derived sNS1 (isNS1) from dengue virus (DENV)-infected Vero cells through immunoaffinity purification instead of recombinant sNS1 (rsNS1) overexpressed in insect or mammalian cell lines. We found that isNS1 appeared as an approximately 250 kDa complex of NS1 and ApoA1 and further determined the cryoEM structures of isNS1 and its complex with a monoclonal antibody/Fab. Indeed, we found that the major species of isNS1 is a complex of the NS1 dimer partially embedded in a high-density lipoprotein (HDL) particle. Crosslinking mass spectrometry studies confirmed that the isNS1 interacts with the major HDL component ApoA1 through interactions that map to the NS1 wing and hydrophobic domains. Furthermore, our studies demonstrated that the sNS1 in sera from DENV-infected mice and a human patient form a similar complex as isNS1. Our results report the molecular architecture of a biological form of sNS1, which may have implications for the molecular pathogenesis of dengue.

Sex-related immunity: could Toll-like receptors be the answer in acute inflammatory response?

An increasing number of studies have highlighted the existence of a sex-specific immune response, wherein men experience a worse prognosis in cases of acute inflammatory diseases. Initially, this sex-dependent inflammatory response was attributed to the influence of sex hormones. However, a growing body of evidence has shifted the focus toward the influence of chromosomes rather than sex hormones in shaping these inflammatory sex disparities. Notably, certain pattern recognition receptors, such as Toll-like receptors (TLRs), and their associated immune pathways have been implicated in driving the sex-specific immune response. These receptors are encoded by genes located on the X chromosome. TLRs are pivotal components of the innate immune system, playing crucial roles in responding to infectious diseases, including bacterial and viral pathogens, as well as trauma-related conditions. Importantly, the TLR-mediated inflammatory responses, as indicated by the production of specific proteins and cytokines, exhibit discernible sex-dependent patterns. In this review, we delve into the subject of sex bias in TLR activation and explore its clinical implications relatively to both the X chromosome and the hormonal environment. The overarching objective is to enhance our understanding of the fundamental mechanisms underlying these sex differences.

Japanese encephalitis virus NS1 and NS1' protein disrupts the blood-brain barrier through macrophage migration inhibitory factor-mediated autophagy

Flaviviruses in the Japanese encephalitis virus (JEV) serogroup, such as JEV, West Nile virus, and St. Louis encephalitis virus, can cause severe neurological diseases. The nonstructural protein 1 (NS1) is a multifunctional protein of flavivirus that can be secreted by infected cells and circulate in the host bloodstream. NS1' is an additional form of NS1 protein with 52 amino acids extension at its carboxy-terminal and is produced exclusively by flaviviruses in the JEV serogroup. In this study, we demonstrated that the secreted form of both NS1 and NS1' can disrupt the blood-brain barrier (BBB) of mice, with NS1' exhibiting a stronger effect. Using the in vitro BBB model, we found that treatment of soluble recombinant JEV NS1 or NS1' protein increases the permeability of human brain microvascular endothelial cells (hBMECs) and leads to the degradation of tight junction proteins through the autophagy-lysosomal pathway. Consistently, NS1' protein exhibited a more pronounced effect compared to NS1 in these cellular processes. Further research revealed that the increased expression of macrophage migration inhibitory factor (MIF) is responsible for triggering autophagy after NS1 or NS1' treatment in hBMECs. In addition, TLR4 and NF-κB signaling was found to be involved in the activation of MIF transcription. Moreover, administering the MIF inhibitor has been shown to decrease viral loads and mitigate inflammation in the brains of mice infected with JEV. This research offers a novel perspective on the pathogenesis of JEV. In addition, the stronger effect of NS1' on disrupting the BBB compared to NS1 enhances our understanding of the mechanism by which flaviviruses in the JEV serogroup exhibit neurotropism.IMPORTANCEJapanese encephalitis (JE) is a significant viral encephalitis worldwide, caused by the JE virus (JEV). In some patients, the virus cannot be cleared in time, leading to the breach of the blood-brain barrier (BBB) and invasion of the central nervous system. This invasion may result in cognitive impairment, behavioral disturbances, and even death in both humans and animals. However, the mechanism by which JEV crosses the BBB remains unclear. Previous studies have shown that the flavivirus NS1 protein plays an important role in causing endothelial dysfunction. The NS1' protein is an elongated form of NS1 protein that is particularly produced by flaviviruses in the JEV serogroup. This study revealed that both the secreted NS1 and NS1' of JEV can disrupt the BBB by breaking down tight junction proteins through the autophagy-lysosomal pathway, and NS1' is found to have a stronger effect compared to NS1 in this process. In addition, JEV NS1 and NS1' can stimulate the expression of MIF, which triggers autophagy via the ERK signaling pathway, leading to damage to BBB. Our findings reveal a new function of JEV NS1 and NS1' in the disruption of BBB, thereby providing the potential therapeutic target for JE.

The step-by-step assembly mechanism of secreted flavivirus NS1 tetramer and hexamer captured at atomic resolution

Flaviviruses encode a conserved, membrane-associated nonstructural protein 1 (NS1) with replication and immune evasion functions. The current knowledge of secreted NS1 (sNS1) oligomers is based on several low-resolution structures, thus hindering the development of drugs and vaccines against flaviviruses. Here, we revealed that recombinant sNS1 from flaviviruses exists in a dynamic equilibrium of dimer-tetramer-hexamer states. Two DENV4 hexameric NS1 structures and several tetrameric NS1 structures from multiple flaviviruses were solved at atomic resolution by cryo-EM. The stacking of the tetrameric NS1 and hexameric NS1 is facilitated by the hydrophobic β-roll and connector domains. Additionally, a triacylglycerol molecule located within the central cavity may play a role in stabilizing the hexamer. Based on differentiated interactions between the dimeric NS1, two distinct hexamer models (head-to-head and side-to-side hexamer) and the step-by-step assembly mechanisms of NS1 dimer into hexamer were proposed. We believe that our study sheds light on the understanding of the NS1 oligomerization and contributes to NS1-based therapies.

Molecular mechanisms in the pathogenesis of dengue infections

Dengue is the most rapidly emerging climate-sensitive infection, and morbidity/mortality and disease incidence are rising markedly, leading to healthcare systems being overwhelmed. There are currently no specific treatments for dengue or prognostic markers to identify those who will progress to severe disease. Owing to an increase in the burden of illness and a change in epidemiology, many patients experience severe disease. Our limited understanding of the complex mechanisms of disease pathogenesis has significantly hampered the development of safe and effective treatments, vaccines, and biomarkers. We discuss the molecular mechanisms of dengue pathogenesis, the gaps in our knowledge, and recent advances, as well as the most crucial questions to be answered to enable the development of therapeutics, biomarkers, and vaccines.

Dual action effects of ethyl-p-methoxycinnamate against dengue virus infection and inflammation via NF-κB pathway suppression

Dengue virus (DENV) infection can lead to severe outcomes through a virus-induced cytokine storm, resulting in vascular leakage and inflammation. An effective treatment strategy should target both virus replication and cytokine storm. This study identified Kaempferia galanga L. (KG) extract as exhibiting anti-DENV activity. The major bioactive compound, ethyl-p-methoxycinnamate (EPMC), significantly reduced DENV-2 infection, virion production, and viral protein synthesis in HepG2 and A549 cells, with half-maximal effective concentration (EC50) values of 22.58 µM and 6.17 µM, and impressive selectivity indexes (SIs) of 32.40 and 173.44, respectively. EPMC demonstrated efficacy against all four DENV serotypes, targeting the replication phase of the virus life cycle. Importantly, EPMC reduced DENV-2-induced cytokines (IL-6 and TNF-α) and chemokines (RANTES and IP-10), as confirmed by immunofluorescence and immunoblot analyses, indicating inhibition of NF-κB activation. EPMC's role in preventing excessive inflammatory responses suggests it as a potential candidate for dengue treatment. Absorption, distribution, metabolism, excretion, and toxicity (ADMET) and drug-likeness for EPMC were predicted using SwissADME and ProTox II servers, showing good drug-like properties without toxicity. These findings highlight KG extract and EPMC as promising candidates for future anti-dengue therapeutics, offering a dual-action approach by inhibiting virus replication and mitigating inflammatory reactions.

Dengue virus pathogenesis and host molecular machineries

Dengue viruses (DENV) are positive-stranded RNA viruses belonging to the Flaviviridae family. DENV is the causative agent of dengue, the most rapidly spreading viral disease transmitted by mosquitoes. Each year, millions of people contract the virus through bites from infected female mosquitoes of the Aedes species. In the majority of individuals, the infection is asymptomatic, and the immune system successfully manages to control virus replication within a few days. Symptomatic individuals may present with a mild fever (Dengue fever or DF) that may or may not progress to a more critical disease termed Dengue hemorrhagic fever (DHF) or the fatal Dengue shock syndrome (DSS). In the absence of a universally accepted prophylactic vaccine or therapeutic drug, treatment is mostly restricted to supportive measures. Similar to many other viruses that induce acute illness, DENV has developed several ways to modulate host metabolism to create an environment conducive to genome replication and the dissemination of viral progeny. To search for new therapeutic options, understanding the underlying host-virus regulatory system involved in various biological processes of the viral life cycle is essential. This review aims to summarize the complex interaction between DENV and the host cellular machinery, comprising regulatory mechanisms at various molecular levels such as epigenetic modulation of the host genome, transcription of host genes, translation of viral and host mRNAs, post-transcriptional regulation of the host transcriptome, post-translational regulation of viral proteins, and pathways involved in protein degradation.

The inflammasome pathway is activated by dengue virus non-structural protein 1 and is protective during dengue virus infection

Dengue virus (DENV) is a medically important flavivirus causing an estimated 50-100 million dengue cases annually, some of whom progress to severe disease. DENV non-structural protein 1 (NS1) is secreted from infected cells and has been implicated as a major driver of dengue pathogenesis by inducing endothelial barrier dysfunction. However, less is known about how DENV NS1 interacts with immune cells and what role these interactions play. Here we report that DENV NS1 can trigger activation of inflammasomes, a family of cytosolic innate immune sensors that respond to infectious and noxious stimuli, in mouse and human macrophages. DENV NS1 induces the release of IL-1β in a caspase-1 dependent manner. Additionally, we find that DENV NS1-induced inflammasome activation is independent of the NLRP3, Pyrin, and AIM2 inflammasome pathways, but requires CD14. Intriguingly, DENV NS1-induced inflammasome activation does not induce pyroptosis and rapid cell death; instead, macrophages maintain cellular viability while releasing IL-1β. Lastly, we show that caspase-1/11-deficient, but not NLRP3-deficient, mice are more susceptible to lethal DENV infection. Together, these results indicate that the inflammasome pathway acts as a sensor of DENV NS1 and plays a protective role during infection.

Approaches of dengue control: vaccine strategies and future aspects

Dengue, caused by the dengue virus (DENV), affects millions of people worldwide every year. This virus has two distinct life cycles, one in the human and another in the mosquito, and both cycles are crucial to be controlled. To control the vector of DENV, the mosquito Aedes aegypti, scientists employed many techniques, which were later proved ineffective and harmful in many ways. Consequently, the attention shifted to the development of a vaccine; researchers have targeted the E protein, a surface protein of the virus and the NS1 protein, an extracellular protein. There are several types of vaccines developed so far, such as live attenuated vaccines, recombinant subunit vaccines, inactivated virus vaccines, viral vectored vaccines, DNA vaccines, and mRNA vaccines. Along with these, scientists are exploring new strategies of developing improved version of the vaccine by employing recombinant DNA plasmid against NS1 and also aiming to prevent the infection by blocking the DENV life cycle inside the mosquitoes. Here, we discussed the aspects of research in the field of vaccines until now and identified some prospects for future vaccine developments.

Roles of NS1 Protein in Flavivirus Pathogenesis

Flaviviruses such as dengue, Zika, and West Nile viruses are highly concerning pathogens that pose significant risks to public health. The NS1 protein is conserved among flaviviruses and is synthesized as a part of the flavivirus polyprotein. It plays a critical role in viral replication, disease progression, and immune evasion. Post-translational modifications influence NS1's stability, secretion, antigenicity, and interactions with host factors. NS1 protein forms extensive interactions with host cellular proteins allowing it to affect vital processes such as RNA processing, gene expression regulation, and cellular homeostasis, which in turn influence viral replication, disease pathogenesis, and immune responses. NS1 acts as an immune evasion factor by delaying complement-dependent lysis of infected cells and contributes to disease pathogenesis by inducing endothelial cell damage and vascular leakage and triggering autoimmune responses. Anti-NS1 antibodies have been shown to cross-react with host endothelial cells and platelets, causing autoimmune destruction that is hypothesized to contribute to disease pathogenesis. However, in contrast, immunization of animal models with the NS1 protein confers protection against lethal challenges from flaviviruses such as dengue and Zika viruses. Understanding the multifaceted roles of NS1 in flavivirus pathogenesis is crucial for effective disease management and control. Therefore, further research into NS1 biology, including its host protein interactions and additional roles in disease pathology, is imperative for the development of strategies and therapeutics to combat flavivirus infections successfully. This Review provides an in-depth exploration of the current available knowledge on the multifaceted roles of the NS1 protein in the pathogenesis of flaviviruses.

Vav proteins do not influence dengue virus replication but are associated with induction of phospho-ERK, IL-6, and viperin mRNA following DENV infection in vitro

IMPORTANCE

Dengue disease is characterized by an inflammatory-mediated immunopathology, with elevated levels of circulating factors including TNF-α and IL-6. If the damaging inflammatory pathways could be blocked without loss of antiviral responses or exacerbating viral replication, then this would be of potential therapeutic benefit. The study here has investigated the Vav guanine exchange factors as a potential alternative signaling pathway that may drive dengue virus (DENV)-induced inflammatory responses, with a focus on Vav1 and 2. While Vav proteins were positively associated with mRNA for inflammatory cytokines, blocking Vav signaling didn't affect DENV replication but prevented DENV-induction of p-ERK and enhanced IL-6 (inflammatory) and viperin (antiviral) mRNA. These initial data suggest that Vav proteins could be a target that does not compromise control of viral replication and should be investigated further for broader impact on host inflammatory responses, in settings such as antibody-dependent enhancement of infection and in different cell types.

Platelet derived exosomes disrupt endothelial cell monolayer integrity and enhance vascular inflammation in dengue patients

Background

Thrombocytopenia is the most notable phenomenon in dengue. Activation status of platelets and interaction of platelets with endothelium contribute towards dengue disease pathogenesis. Platelets are the major cell types known to release extracellular vesicles, especially exosomes in circulation. However, the role of platelet derived exosomes (PLT-EXOs) in endothelial dysfunction during dengue infection remains unknown.

Methods

In this study, we recruited 28 healthy subjects and 69 dengue patients categorized as WS- (n=31), WS+ (n=29) and SD (n=9). Platelets were isolated from platelet rich plasma of dengue patients and their activation was assessed by flow cytometry. PLT-EXOs were isolated by ultracentrifugation method. Western blot analyses were performed to characterize the exosomes. Exosome uptake experiment was carried out to see the internalization of exosomes inside endothelial cells (HUVECs). To observe the effect of exosomes on endothelial cells, exosomes were added on HUVECs and expression of adherens and tight junctional proteins were examined by immunofluorescence assay and western blot. Expression levels of vascular injury markers were measured in the culture supernatants of Exosome-HUVEC coculture and sera of dengue patients by MSD-multiplex assay.

Results

As compared to healthy subjects, CD41/CD61 expression was significantly reduced (p<0.0001) and CD62p expression was significantly increased (p<0.0001) on platelets in dengue patients. PLT-EXOs isolated from the dengue patients showed higher expression of CD63 and CD9 proteins than the healthy subjects. With in-vitro immunofluorescence assays, we illustrated the internalization of PLT-EXOs by the HUVECs and observed disruption of endothelial cell monolayer integrity in the presence of PLT-EXOs from WS+ and SD patients. Furthermore, the significant reduction in the expressions of ZO-2, VE-Cadherin and CD31 in endothelial cells following exposure to PLT-EXOs from the dengue patients provide direct evidence of PLT-EXOs mediated vascular permeability. PLT-EXOs stimulated the release of inflammatory markers CRP, SAA, sVCAM-1 and sICAM-1 in the supernatants of HUVEC cells. Importantly, significantly higher levels of CRP, sVCAM-1 and sICAM-1 in the sera of severe than mild dengue patients (p<0.0001) suggest their role in disease severity.

Conclusions

In summary, our data suggest that PLT-EXOs promote vascular leakage via release of proinflammatory mediators and compromise vascular barrier integrity in dengue patients.

The dangerous liaisons in innate immunity involving recombinant proteins and endotoxins: Examples from the literature and the Leptospira field

Endotoxins, also known as lipopolysaccharides (LPS), are essential components of cell walls of diderm bacteria such as Escherichia coli. LPS are microbe-associated molecular patterns that can activate pattern recognition receptors. While trying to investigate the interactions between proteins and host innate immunity, some studies using recombinant proteins expressed in E. coli reported interaction and activation of immune cells. Here, we set out to provide information on endotoxins that are highly toxic to humans and bind to numerous molecules, including recombinant proteins. We begin by outlining the history of the discovery of endotoxins, their receptors and the associated signaling pathways that confer extreme sensitivity to immune cells, acting alone or in synergy with other microbe-associated molecular patterns. We list the various places where endotoxins have been found. Additionally, we warn against the risk of data misinterpretation due to endotoxin contamination in recombinant proteins, which is difficult to estimate with the Limulus amebocyte lysate assay, and cannot be completely neutralized (e.g., treatment with polymyxin B or heating). We further illustrate our point with examples of recombinant heat-shock proteins and viral proteins from severe acute respiratory syndrome coronavirus 2, dengue and HIV, for which endotoxin contamination has eventually been shown to be responsible for the inflammatory roles previously ascribed. We also critically appraised studies on recombinant Leptospira proteins regarding their putative inflammatory roles. Finally, to avoid these issues, we propose alternatives to express recombinant proteins in nonmicrobial systems. Microbiologists wishing to undertake innate immunity studies with their favorite pathogens should be aware of these difficulties.

Integrated control strategies for dengue, Zika, and Chikungunya virus infections

Arboviruses are a major threat to public health in tropical regions, encompassing over 534 distinct species, with 134 capable of causing diseases in humans. These viruses are transmitted through arthropod vectors that cause symptoms such as fever, headache, joint pains, and rash, in addition to more serious cases that can lead to death. Among the arboviruses, dengue virus stands out as the most prevalent, annually affecting approximately 16.2 million individuals solely in the Americas. Furthermore, the re-emergence of the Zika virus and the recurrent outbreaks of chikungunya in Africa, Asia, Europe, and the Americas, with one million cases reported annually, underscore the urgency of addressing this public health challenge. In this manuscript we discuss the epidemiology, viral structure, pathogenicity and integrated control strategies to combat arboviruses, and the most used tools, such as vaccines, monoclonal antibodies, treatment, etc., in addition to presenting future perspectives for the control of arboviruses. Currently, specific medications for treating arbovirus infections are lacking, and symptom management remains the primary approach. However, promising advancements have been made in certain treatments, such as Chloroquine, Niclosamide, and Isatin derivatives, which have demonstrated notable antiviral properties against these arboviruses in vitro and in vivo experiments. Additionally, various strategies within vector control approaches have shown significant promise in reducing arbovirus transmission rates. These encompass public education initiatives, targeted insecticide applications, and innovative approaches like manipulating mosquito bacterial symbionts, such as Wolbachia. In conclusion, combatting the global threat of arbovirus diseases needs a comprehensive approach integrating antiviral research, vaccination, and vector control. The continued efforts of research communities, alongside collaborative partnerships with public health authorities, are imperative to effectively address and mitigate the impact of these arboviral infections on public health worldwide.

Kinetics of severe dengue virus infection and development of gut pathology in mice

IMPORTANCE

Dengue virus, an arbovirus, causes an estimated 100 million symptomatic infections annually and is an increasing threat as the mosquito range expands with climate change. Dengue epidemics are a substantial strain on local economies and health infrastructure, and an understanding of what drives severe disease may enable treatments to help reduce hospitalizations. Factors exacerbating dengue disease are debated, but gut-related symptoms are much more frequent in severe than mild cases. Using mouse models of dengue infection, we have shown that inflammation and damage are earlier and more severe in the gut than in other tissues. Additionally, we observed impairment of the gut mucus layer and propose that breakdown of the barrier function exacerbates inflammation and promotes severe dengue disease. This idea is supported by recent data from human patients showing elevated bacteria-derived molecules in dengue patient serum. Therapies aiming to maintain gut integrity may help to abrogate severe dengue disease.

Toll-like receptor 4 (TLR4): new insight immune and aging

TLR4, a transmembrane receptor, plays a central role in the innate immune response. TLR4 not only engages with exogenous ligands at the cellular membrane's surface but also interacts with intracellular ligands, initiating intricate intracellular signaling cascades. Through MyD88, an adaptor protein, TLR4 activates transcription factors NF-κB and AP-1, thereby facilitating the upregulation of pro-inflammatory cytokines. Another adapter protein linked to TLR4, known as TRIF, autonomously propagates signaling pathways, resulting in heightened interferon expression. Recently, TLR4 has garnered attention as a significant factor in the regulation of symptoms in aging-related disorders. The persistent inflammatory response triggered by TLR4 contributes to the onset and exacerbation of these disorders. In addition, alterations in TLR4 expression levels play a pivotal role in modifying the manifestations of age-related diseases. In this review, we aim to consolidate the impact of TLR4 on cellular senescence and aging-related ailments, highlighting the potential of TLR4 as a novel therapeutic target that extends beyond immune responses.

Role of toll-like receptor-mediated pyroptosis in sepsis-induced cardiomyopathy

Sepsis, a life-threatening dysregulated status of the host response to infection, can cause multiorgan dysfunction and mortality. Sepsis places a heavy burden on the cardiovascular system due to the pathological imbalance of hyperinflammation and immune suppression. Myocardial injury and cardiac dysfunction caused by the aberrant host responses to pathogens can lead to cardiomyopathy, one of the most critical complications of sepsis. However, many questions about the specific mechanisms and characteristics of this complication remain to be answered. The causes of sepsis-induced cardiac dysfunction include abnormal cardiac perfusion, myocardial inhibitory substances, autonomic dysfunction, mitochondrial dysfunction, and calcium homeostasis dysregulation. The fight between the host and pathogens acts as the trigger for sepsis-induced cardiomyopathy. Pyroptosis, a form of programmed cell death, plays a critical role in the progress of sepsis. Toll-like receptors (TLRs) act as pattern recognition receptors and participate in innate immune pathways that recognize damage-associated molecular patterns as well as pathogen-associated molecular patterns to mediate pyroptosis. Notably, pyroptosis is tightly associated with cardiac dysfunction in sepsis and septic shock. In line with these observations, induction of TLR-mediated pyroptosis may be a promising therapeutic approach to treat sepsis-induced cardiomyopathy. This review focuses on the potential roles of TLR-mediated pyroptosis in sepsis-induced cardiomyopathy, to shed light on this promising therapeutic approach, thus helping to prevent and control septic shock caused by cardiovascular disorders and improve the prognosis of sepsis patients.

Dengue Vaccination: Towards a New Dawn of Curbing Dengue Infection

Dengue is an infectious disease caused by dengue virus (DENV) and is a serious global burden. Antibody-dependent enhancement and the ability of DENV to infect immune cells, along with other factors, lead to fatal Dengue Haemorrhagic Fever and Dengue Shock Syndrome. This necessitates the development of a robust and efficient vaccine but vaccine development faces a number of hurdles. In this review, we look at the epidemiology, genome structure and cellular targets of DENV and elaborate upon the immune responses generated by human immune system against DENV infection. The review further sheds light on various challenges in development of a potent vaccine against DENV which is followed by presenting a current account of different vaccines which are being developed or have been licensed.

Making sense of flavivirus non-strctural protein 1 in innate immune evasion and inducing tissue-specific damage

Flaviviruses include medically important mosquito-borne pathogens, such as Zika virus (ZIKV), Japanese encephalitis virus (JEV), dengue virus (DENV) and West Nile virus (WNV), that cause hundreds of millions of infections each year. Currently, there are no approved effect therapies against mosquito-borne flaviviruses. The flaviviruses encoded nonstructural protein 1 (NS1) is a secreted glycoprotein widely involved in viral replication, immune evasion, and directly causing tissue-specific damage during flaviviruses infection. Upon viral infection of host cell, NS1 can be found in multiple oligomeric forms and include a dimer on the cell surface, and a soluble secreted hexameric lipoparticle. In the recent decade, the detailed crystal structure of several flaviviruses NS1 have been determined and unraveled its broader and deeper functions. Consistent with the potential immune function revealed by its structure, NS1 is involved in the escaping of host signal immune pathway mediated by pattern recognition receptors (PRRs), including RIG-I-like receptors (RLRS) and Toll-like receptors (TLRs). Moreover, the flavivirus NS1 is efficiently secreted by infected cells and circulates in the blood of the host to directly induce specific tissues damage. The NS1 of ZIKV, JEV and WNV changes the permeability of brain microvascular endothelial cell to cause endothelial cell dysfunction and promote virus pathogenesis. DENV NS1 can induce systemic tissues damage in humans through multiple strategies. Mutations of several key amino acids in NS1 can reduce the neurovirulence of the flavivirus. In this article, we provide an overview of the latest research on this fascinating protein in these disparate areas.

DENV-2 NS1 promotes AMPK-LKB1 interaction to activate AMPK/ERK/mTOR signaling pathway to induce autophagy

The global incidence of dengue fever has gradually increased in recent years, posing a serious threat to human health. In the absence of specific anti-dengue drugs, understanding the interaction of Dengue virus (DENV) with the host is essential for the development of effective therapeutic measures. Autophagy is often activated during DENV infection to promote viral replication, but the mechanism of how DENV's own proteins induce autophagy has not been clarified. In this study, we first preliminarily identified DENV-2 NS1 as the most likely viral protein for DENV-2-induced autophagy with the help of molecular docking techniques. Further experimental results confirmed that DENV-2 NS1 regulates DENV-2 infection of HUVEC-induced autophagy through the AMPK/ERK/mTOR signaling pathway. Mechanistically, DENV-2 NS1 mainly interacted with AMPK by means of its Wing structural domain, and NS1 bound to all three structural domains on the AMPKα subunit. Finally, the experimental results showed that DENV-2 NS1 promoted the interaction between LKB1 and AMPKα1 and thus activated AMPK by both increasing the expression of LKB1 and binding LKB1. In conclusion, the results of this study revealed that DENV-2 NS1 protein served as a platform for the interaction between AMPK and LKB1 after DENV-2 infection with HUVEC, and pulled AMPK and LKB1 together to form a complex. LKB1 to form a complex, promoting LKB1 action on the kinase structural domain of AMPKα1, which in turn promotes phosphorylation of the Thr172 site on the AMPK kinase structural domain and activates AMPK, thereby positively regulating the AMPK/ERK/mTOR signaling pathway and inducing autophagy. The present discovery improves our understanding of DENV-2-induced host autophagy and contributes to the development of anti-dengue drugs.

The Inflammasome Pathway is Activated by Dengue Virus Non-structural Protein 1 and is Protective During Dengue Virus Infection

Dengue virus (DENV) is a medically important flavivirus causing an estimated 50-100 million dengue cases annually, some of whom progress to severe disease. DENV non-structural protein 1 (NS1) is secreted from infected cells and has been implicated as a major driver of dengue pathogenesis by inducing endothelial barrier dysfunction. However, less is known about how DENV NS1 interacts with immune cells and what role these interactions play. Here we report that DENV NS1 can trigger activation of inflammasomes, a family of cytosolic innate immune sensors that respond to infectious and noxious stimuli, in mouse and human macrophages. DENV NS1 induces the release of IL-1β in a caspase-1 dependent manner. Additionally, we find that DENV NS1-induced inflammasome activation is independent of the NLRP3, Pyrin, and AIM2 inflammasome pathways, but requires CD14. Intriguingly, DENV NS1-induced inflammasome activation does not induce pyroptosis and rapid cell death; instead, macrophages maintain cellular viability while releasing IL-1β. Lastly, we show that caspase-1/11-deficient, but not NLRP3-deficient, mice are more susceptible to lethal DENV infection. Together, these results indicate that the inflammasome pathway acts as a sensor of DENV NS1 and plays a protective role during infection.

Genetic differences of dengue virus 2 in patients with distinct clinical outcome

The genetic diversity of the dengue virus is characterized by four circulating serotypes, several genotypes, and an increasing number of existing lineages that may have differences in the potential to cause epidemics and disease severity. Accurate identification of the genetic variability of the virus is essential to identify lineages responsible for an epidemic and understanding the processes of virus spread and virulence. Here, we characterize, using portable nanopore genomic sequencing, different lineages of dengue virus 2 (DENV-2) detected in 22 serum samples from patients with and without dengue warning signs attended at Hospital de Base of São José do Rio Preto (SJRP) in 2019, during a DENV-2 outbreak. Demographic, epidemiological, and clinical data were also analyzed. The phylogenetic reconstruction and the clinical data showed that two lineages belonging to the American/Asian genotype of DENV-2-BR3 and BR4 (BR4L1 and BR4L2)-were co-circulating in SJRP. Although preliminary, these results indicate no specific association between clinical form and phylogenetic clustering at the virus consensus sequence level. Studies with larger sample sizes and which explore single nucleotide variants are needed. Therefore, we showed that portable nanopore genome sequencing could generate quick and reliable sequences for genomic surveillance to monitor viral diversity and its association with disease severity as an epidemic unfolds.

Antibody and memory B cell responses to the dengue virus NS1 antigen in individuals with varying severity of past infection

To further understand the role of NS1-specific antibodies (Abs) in disease pathogenesis, we compared neutralizing antibody levels (Nabs), NS1-Ab levels, IgG antibody subclass profiles and NS1-specific memory B-cell responses (Bmems) in individuals, with varying severity of past dengue. Nabs (Neut50 titres) were assessed using the Foci Reduction Neutralization Test (FRNT) and in-house ELISAs were used to assess NS1-Abs and NS1-Ab subclasses for all four DENV serotypes in individuals with past DF (n = 22), those with past DHF (n = 14) and seronegative (SN) individuals (n = 7). B-cell ELISpot assays were used to assess NS1-specific Bmem responses. 15/22 (68.18%) individuals with past DF and 9/14 (64.29%) individuals with past DHF had heterotypic infections. Neut50 titres were found to be significantly higher for DENV1 than DENV2 (p = 0.0006) and DENV4 (p = 0.0127), in those with past DHF, whereas there was no significant difference seen in titres for different DENV serotypes in those with past DF. Overall NS1-Ab to all serotypes and NS1-specific IgG1 responses for DENV1, 2 and 4 serotypes were significantly higher in those with past DHF than individuals with past DF. Those with past DHF also had higher IgG1 than IgG3 for DENV1 and DENV3, whereas no differences were seen in those with past DF. Over 50% of those with past DF or DHF had NS1-specific Bmem responses to >2 DENV serotypes. There was no difference in the frequency of Bmem responses to any of the DENV serotypes between individuals with past DF and DHF. Although the frequency of Bmem responses to DENV1 correlated with DENV1-specific NS1-Abs levels (Spearman r = 0.35, p = 0.02), there was no correlation with other DENV serotypes. We found that those with past DF had broadly cross-reactive Nabs, while those with past DHF had higher NS1-Ab responses possibly with a different functionality profile than those with past DF. Therefore, it would be important to further evaluate the functionality of NS1-specific antibody and Bmem responses to find out the type of antibody repertoire that is associated with protection against severe disease.

Ophthalmic complications during the dengue epidemic in Reunion Island in 2020: a case series and review of the literature

INTRODUCTION

Dengue is an arboviral disease transmitted by the dengue virus, whose vectors are Aedes aegypti and Aedes albopictus. The acute phase with its cohort of well-known symptoms is usually spontaneously favorable. Since 2020 in Reunion Island, a new symptom has appeared: the ocular damage of dengue fever, which has already been described in South Asia and South-East Asia. We therefore decided to describe the clinical, biological, ophthalmological, therapeutic, and outcomes of patients with ocular manifestations during dengue fever in Reunion Island in 2020.

PATIENTS AND METHODS

This was a retrospective observational study. Patients were included from January 2020 to August 2020 and then reassessed by teleconsultation 1 year later. The patients were identified from the French public health surveillance network by all ophthalmologists on the island. Medical data were collected directly from medical records.

RESULTS

Twenty-eight patients were included. The mean age was 41.9 years. Ocular involvement occurred approximately 9.2 days after the onset of dengue symptoms. The main symptoms were scotoma (71.4%) and sudden decrease of visual acuity (39.2%). Eighteen patients (64.2%) had macular involvement. Fourteen patients were treated with oral or intravenous corticosteroids. Twenty-two (78.5%) patients were evaluated by telephone one year later. Scotoma and decreased visual acuity persisted in 15 patients. Thirteen patients (59%) were bothered by night driving, 32% of patients had reading difficulties and 27% of patients became sensitive to prolonged exposure to screens.

CONCLUSION

Ocular complications of dengue require early and collegial management to limit the risk of long-term sequelae. Further studies on the characteristics and complications of dengue fever are needed to better understand this disease.

A comprehensive protein interaction map and druggability investigation prioritized dengue virus NS1 protein as promising therapeutic candidate

Dengue Virus (DENV) is a serious threat to human life worldwide and is one of the most dangerous vector-borne diseases, causing thousands of deaths annually. We constructed a comprehensive PPI map of DENV with its host Homo sapiens and performed various bioinformatics analyses. We found 1195 interactions between 858 human and 10 DENV proteins. Pathway enrichment analysis was performed on the two sets of gene products, and the top 5 human proteins with the maximum number of interactions with dengue viral proteins revealed noticeable results. The non-structural protein NS1 in DENV had the maximum number of interactions with the host protein, followed by NS5 and NS3. Among the human proteins, HBA1 and UBE2I were associated with 7 viral proteins, and 3 human proteins (CSNK2A1, RRP12, and HSP90AB1) were found to interact with 6 viral proteins. Pharmacophore-based virtual screening of millions of compounds in the public databases was performed to identify potential DENV-NS1 inhibitors. The lead compounds were selected based on RMSD values, docking scores, and strong binding affinities. The top ten hit compounds were subjected to ADME profiling which identified compounds C2 (MolPort-044-180-163) and C6 (MolPort-001-742-737) as lead inhibitors against DENV-NS1. Molecular dynamics trajectory analysis and intermolecular interactions between NS1 and the ligands displayed the molecular stability of the complexes in the cellular environment. The in-silico approaches used in this study could pave the way for the development of potential specie-specific drugs and help in eliminating deadly viral infections. Therefore, experimental and clinical assays are required to validate the results of this study.

Experimental infection of Artibeus lituratus bats and no detection of Zika virus in neotropical bats from French Guiana, Peru, and Costa Rica suggests a limited role of bats in Zika transmission

Bats are important natural reservoir hosts of a diverse range of viruses that can be transmitted to humans and have been suggested to play an important role in the Zika virus (ZIKV) transmission cycle. However, the exact role of these animals as reservoirs for flaviviruses is still controversial. To further expand our understanding of the role of bats in the ZIKV transmission cycle in Latin America, we carried out an experimental infection in wild-caught Artibeus lituratus bats and sampled several free-living neotropical bats across three countries of the region. Experimental ZIKV infection was performed in wild-caught adult bats (4 females and 5 males). The most relevant findings were hemorrhages in the bladder, stomach and patagium. Significant histological findings included inflammatory infiltrate consisting of a predominance of neutrophils and lymphocytes, in addition to degeneration in the reproductive tract of males and females. This suggests that bat reproduction might be at some level affected by ZIKV. Leukopenia was also observed in some inoculated animals. Hemorrhages, genital alterations, and leukopenia are suggested to be caused by ZIKV; however, since these were wild-caught bats, we cannot exclude other agents. Detection of ZIKV by qPCR was observed at low concentrations in only two urine samples in two inoculated animals. All other animals and tissues tested were negative. Finally, no virus-neutralizing antibodies were found in any animal. To determine ZIKV infection in nature, the blood of a total of 2056 bats was sampled for ZIKV detection by qPCR. Most of the sampled individuals belonged to the genus Pteronotus sp. (23%), followed by the species Carollia sp. (17%), Anoura sp. (14%), and Molossus sp. (13.7%). No sample of any tested species was positive for ZIKV by qPCR. These results together suggest that bats are not efficient amplifiers or reservoirs of ZIKV and may not have an important role in ZIKV transmission dynamics.

Secretory pathways and multiple functions of nonstructural protein 1 in flavivirus infection

The genus Flavivirus contains a wide variety of viruses that cause severe disease in humans, including dengue virus, yellow fever virus, Zika virus, West Nile virus, Japanese encephalitis virus and tick-borne encephalitis virus. Nonstructural protein 1 (NS1) is a glycoprotein that encodes a 352-amino-acid polypeptide and has a molecular weight of 46-55 kDa depending on its glycosylation status. NS1 is highly conserved among multiple flaviviruses and occurs in distinct forms, including a dimeric form within the endoplasmic reticulum, a cell-associated form on the plasma membrane, or a secreted hexameric form (sNS1) trafficked to the extracellular matrix. Intracellular dimeric NS1 interacts with other NSs to participate in viral replication and virion maturation, while extracellular sNS1 plays a critical role in immune evasion, flavivirus pathogenesis and interactions with natural vectors. In this review, we provide an overview of recent research progress on flavivirus NS1, including research on the structural details, the secretory pathways in mammalian and mosquito cells and the multiple functions in viral replication, immune evasion, pathogenesis and interaction with natural hosts, drawing together the previous data to determine the properties of this protein.

Toll-like Receptor Response to Human Immunodeficiency Virus Type 1 or Co-Infection with Hepatitis B or C Virus: An Overview

Toll-like receptors (TLRs) are evolutionarily conserved pattern recognition receptors that play important roles in the early detection of pathogen-associated molecular patterns and shaping innate and adaptive immune responses, which may influence the consequences of infection. Similarly to other viral infections, human immunodeficiency virus type 1 (HIV-1) also modulates the host TLR response; therefore, a proper understanding of the response induced by human HIV-1 or co-infection with hepatitis B virus (HBV) or hepatitis C virus (HCV), due to the common mode of transmission of these viruses, is essential for understanding HIV-1 pathogenesis during mono- or co-infection with HBV or HCV, as well as for HIV-1 cure strategies. In this review, we discuss the host TLR response during HIV-1 infection and the innate immune evasion mechanisms adopted by HIV-1 for infection establishment. We also examine changes in the host TLR response during HIV-1 co-infection with HBV or HCV; however, this type of study is extremely scarce. Moreover, we discuss studies investigating TLR agonists as latency-reverting agents and immune stimulators towards new strategies for curing HIV. This understanding will help develop a new strategy for curing HIV-1 mono-infection or co-infection with HBV or HCV.

Characterization of soluble TLR2 and CD14 levels during acute dengue virus infection

Dengue virus infection results in a broad spectrum of diseases ranging from mild dengue fever (DF) to severe dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). Hitherto, there is no consensus biomarker for the prediction of severe dengue disease in patients. Yet, early identification of patients who progress to severe dengue is pivotal for better clinical management. We have recently reported that an increased frequency of classical (CD14 ⁺⁺CD16^-) monocytes with sustained high TLR2 expression in acutely infected dengue patients correlates with severe dengue development. Here, we hypothesized that the relatively lower TLR2 and CD14 expression in mild dengue patients is due to the shedding of their soluble forms (sTLR2 and sCD14) and that these could be used as indicators of disease progression. Therefore, using commercial sandwich ELISAs, we evaluated the release of sTLR2 and sCD14 by peripheral blood mononuclear cells (PBMCs) in response to in vitro dengue virus (DENV) infection and assessed their levels in acute-phase plasma of 109 dengue patients. We show that while both sTLR2 and sCD14 are released by PBMCs in response to DENV infection in vitro, their co-circulation in an acute phase of the disease is not always apparent. In fact, sTLR2 was found only in 20% of patients irrespective of disease status. In contrast, sCD14 levels were detected in all patients and were significantly elevated in DF patients when compared to DHF patients and age-matched healthy donors. Altogether, our results suggest that sCD14 may help in identifying patients at risk of severe dengue at hospital admittance.

Experimental Dengue Virus Type 4 Infection Increases the Expression of MicroRNAs-15/16, Triggering a Caspase-Induced Apoptosis Pathway

The World Health Organization has estimated the annual occurrence of approximately 392 million dengue virus (DENV) infections in more than 100 countries where the virus is endemic, which represents a serious threat to humanity. DENV is a serologic group with four distinct serotypes (DENV-1, DENV-2, DENV-3, and DENV-4) belonging to the genus Flavivirus, in the family Flaviviridae. Dengue is the most widespread mosquito-borne disease in the world. The ~10.7 kb DENV genome encodes three structural proteins (capsid (C), pre-membrane (prM), and envelope (E)) and seven non-structural (NS) proteins (NS1, NS2A, NS2B, NS3, NS4A, NS4B, and NS5). The NS1 protein is a membrane-associated dimer and a secreted, lipid-associated hexamer. Dimeric NS1 is found on membranes both in cellular compartments and cell surfaces. Secreted NS1 (sNS1) is often present in patient serum at very high levels, which correlates with severe dengue symptoms. This study was conducted to discover how the NS1 protein, microRNAs-15/16 (miRNAs-15/16), and apoptosis are related during DENV-4 infection in human liver cell lines. Huh 7.5 and HepG2 cells were infected with DENV-4, and miRNAs-15/16, viral load, NS1 protein, and caspases-3/7 were quantified after different durations of infection. This study demonstrated that miRNAs-15/16 were overexpressed during the infection of HepG2 and Huh 7.5 cells with DENV-4 and had a relationship with NS1 protein expression, viral load, and the activity of caspases-3/7, thus making these miRNAs potential injury markers during DENV infection in human hepatocytes.

Orthohantavirus Replication in the Context of Innate Immunity

Orthohantaviruses are rodent-borne, negative-sense RNA viruses that are capable of causing severe vascular disease in humans. Over the course of viral evolution, these viruses have tailored their replication cycles in such a way as to avoid and/or antagonize host innate immune responses. In the rodent reservoir, this results in life long asymptomatic infections. However, in hosts other than its co-evolved reservoir, the mechanisms for subduing the innate immune response may be less efficient or absent, potentially leading to disease and/or viral clearance. In the case of human orthohantavirus infection, the interaction of the innate immune response with viral replication is thought to give rise to severe vascular disease. The orthohantavirus field has made significant advancements in understanding how these viruses replicate and interact with host innate immune responses since their identification by Dr. Ho Wang Lee and colleagues in 1976. Therefore, the purpose of this review, as part of this special issue dedicated to Dr. Lee, was to summarize the current knowledge of orthohantavirus replication, how viral replication activates innate immunity, and how the host antiviral response, in turn, impacts viral replication.

Comparative Analysis of Human Hepatic Lesions in Dengue, Yellow Fever, and Chikungunya: Revisiting Histopathological Changes in the Light of Modern Knowledge of Cell Pathology

Arboviruses, such as yellow fever virus (YFV), dengue virus (DENV), and chikungunya virus (CHIKV), present wide global dissemination and a pathogenic profile developed in infected individuals, from non-specific clinical conditions to severe forms, characterised by the promotion of significant lesions in different organs of the harbourer, culminating in multiple organ dysfunction. An analytical cross-sectional study was carried out via the histopathological analysis of 70 samples of liver patients, collected between 2000 and 2017, with confirmed laboratory diagnoses, who died due to infection and complications due to yellow fever (YF), dengue fever (DF), and chikungunya fever (CF), to characterise, quantify, and compare the patterns of histopathological alterations in the liver between the samples. Of the histopathological findings in the human liver samples, there was a significant difference between the control and infection groups, with a predominance of alterations in the midzonal area of the three cases analysed. Hepatic involvement in cases of YF showed a greater intensity of histopathological changes. Among the alterations evaluated, cell swelling, microvesicular steatosis, and apoptosis were classified according to the degree of tissue damage from severe to very severe. Pathological abnormalities associated with YFV, DENV, and CHIKV infections showed a predominance of changes in the midzonal area. We also noted that, among the arboviruses studied, liver involvement in cases of YFV infection was more intense.

In vitro evidence against productive SARS-CoV-2 infection of human testicular cells: Bystander effects of infection mediate testicular injury

The hallmark of severe COVID-19 involves systemic cytokine storm and multi-organ injury including testicular inflammation, reduced testosterone, and germ cell depletion. The ACE2 receptor is also expressed in the resident testicular cells, however, SARS-CoV-2 infection and mechanisms of testicular injury are not fully understood. The testicular injury could be initiated by direct virus infection or exposure to systemic inflammatory mediators or viral antigens. We characterized SARS-CoV-2 infection in different human testicular 2D and 3D culture systems including primary Sertoli cells, Leydig cells, mixed seminiferous tubule cells (STC), and 3D human testicular organoids (HTO). Data shows that SARS-CoV-2 does not productively infect any testicular cell type. However, exposure of STC and HTO to inflammatory supernatant from infected airway epithelial cells and COVID-19 plasma decreased cell viability and resulted in the death of undifferentiated spermatogonia. Further, exposure to only SARS-CoV-2 Envelope protein caused inflammatory response and cytopathic effects dependent on TLR2, while Spike 1 or Nucleocapsid proteins did not. A similar trend was observed in the K18-hACE2 transgenic mice which demonstrated a disrupted tissue architecture with no evidence of virus replication in the testis that correlated with peak lung inflammation. Virus antigens including Spike 1 and Envelope proteins were also detected in the serum during the acute stage of the disease. Collectively, these data strongly suggest that testicular injury associated with SARS-CoV-2 infection is likely an indirect effect of exposure to systemic inflammation and/or SARS-CoV-2 antigens. Data also provide novel insights into the mechanism of testicular injury and could explain the clinical manifestation of testicular symptoms associated with severe COVID-19.

Identification of Key Residues in Dengue Virus NS1 Protein That Are Essential for Its Secretion

Dengue virus (DENV) non-structural protein 1 (NS1) is involved in multiple aspects of the DENV lifecycle. Importantly, it is secreted from infected cells as a hexameric lipoparticle that mediates vascular damage that is a hallmark of severe dengue. Although the secretion of NS1 is known to be important in DENV pathogenesis, the exact molecular features of NS1 that are required for its secretion from cells are not fully understood. In this study, we employed random point mutagenesis in the context of an NS1 expression vector encoding a C-terminal HiBiT luminescent peptide tag to identify residues within NS1 that are essential for its secretion. Using this approach, we identified 10 point mutations that corresponded with impaired NS1 secretion, with in silico analyses indicating that the majority of these mutations are located within the β-ladder domain. Additional studies on two of these mutants, V220D and A248V, revealed that they prevented viral RNA replication, while studies using a DENV NS1-NS5 viral polyprotein expression system demonstrated that these mutations resulted in a more reticular NS1 localisation pattern and failure to detect mature NS1 at its predicted molecular weight by Western blotting using a conformation-specific monoclonal antibody. Together, these studies demonstrate that the combination of a luminescent peptide tagged NS1 expression system with random point mutagenesis enables rapid identification of mutations that alter NS1 secretion. Two such mutations identified via this approach revealed residues that are essential for correct NS1 processing or maturation and viral RNA replication.

Intrinsic B cell TLR-BCR linked coengagement induces class-switched, hypermutated, neutralizing antibody responses in absence of T cells

Maturation of antibody responses entails somatic hypermutation (SHM), class-switch DNA recombination (CSR), plasma cell differentiation, and generation of memory B cells, and it is thought to require T cell help. We showed that B cell Toll-like receptor 4 (TLR4)-B cell receptor (BCR) (receptor for antigen) coengagement by 4-hydroxy-3-nitrophenyl acetyl (NP)-lipopolysaccharide (LPS) (Escherichia coli lipid A polysaccharide O-antigen) or TLR5-BCR coengagement by Salmonella flagellin induces mature antibody responses to NP and flagellin in Tcrβ-/-Tcrδ-/- and NSG/B mice. TLR-BCR coengagement required linkage of TLR and BCR ligands, "linked coengagement." This induced B cell CSR/SHM, germinal center-like differentiation, clonal expansion, intraconal diversification, plasma cell differentiation, and an anamnestic antibody response. In Tcrβ-/-Tcrδ-/- mice, linked coengagement of TLR4-BCR by LPS or TLR5-BCR by flagellin induced protective antibodies against E. coli or Salmonella Typhimurium. Our findings unveiled a critical role of B cell TLRs in inducing neutralizing antibody responses, including those to microbial pathogens, without T cell help.

Mechanism of Immune Evasion in Mosquito-Borne Diseases

In recent decades, mosquito-borne illnesses have emerged as a major health burden in many tropical regions. These diseases, such as malaria, dengue fever, chikungunya, yellow fever, Zika virus infection, Rift Valley fever, Japanese encephalitis, and West Nile virus infection, are transmitted through the bite of infected mosquitoes. These pathogens have been shown to interfere with the host's immune system through adaptive and innate immune mechanisms, as well as the human circulatory system. Crucial immune checkpoints such as antigen presentation, T cell activation, differentiation, and proinflammatory response play a vital role in the host cell's response to pathogenic infection. Furthermore, these immune evasions have the potential to stimulate the human immune system, resulting in other associated non-communicable diseases. This review aims to advance our understanding of mosquito-borne diseases and the immune evasion mechanisms by associated pathogens. Moreover, it highlights the adverse outcomes of mosquito-borne disease.