Shed GP of Ebola virus triggers immune activation and increased vascular permeability

The Utilization and Development of Viral Vectors in Vaccines as a Prophylactic Treatment Against Ebola Virus as an Emerging and Zoonotic Infectious Disease

Alongside the prescription of commonly used antivirals, such as acyclovir, remdesivir, oseltamivir, and ciprofloxacin, the most efficient way to prevent or treat communicable diseases is by vaccination. Vaccines have been the most efficient way to prevent or treat highly transmissible infectious agents, such as Ebola, Anthrax, and Dengue Fever. Most epidemics of these highly transmissible infectious agents occur in places, such as South America, Central America, Tropical Asia, and Africa, where the availability of resources and access to adequate healthcare are limited. However, recent events in history have proven that even with access to resources and proper healthcare, those in firstworld countries are not invincible when it comes to infectious diseases and epidemics. The Ebola virus outbreak in West Africa highlighted the gaps in therapeutic advancement and readiness and led to the rapid development of novel vaccine approaches. Viral vectors, in the case of the Ebola vaccine the Vesicular Stomatitis Virus (VSV), can be safely used to activate or initiate the innate adaptive immune response to protect against viral infection. When developed properly and with extensive study, novel vaccine approaches allow physicians and health experts to control the rate at which viruses spread or prevent transmission. This review will discuss the advantages of viral vector vaccines, their chemistry and development, and the pathophysiology of the Ebola virus to develop advantageous and efficacious treatments.

Extracellular vesicle storm during the course of Ebola virus infection in primates

Introduction

Ebola virus (EBOV) is an RNA virus of the Filoviridae family that is responsible for outbreaks of hemorrhagic fevers in primates with a lethality rate as high as 90%. EBOV primarily targets host macrophages leading to cell activation and systemic cytokine storm, and fatal infection is associated with an inhibited interferon response, and lymphopenia. The EBOV surface glycoprotein (GP) has been shown to directly induce T cell depletion and can be secreted outside the virion via extracellular vesicles (EVs), though most studies are limited to epithelial cells and underlying mechanisms remain poorly elucidated.

Methods

To assess the role of GP on EBOV-induced dysregulation of host immunity, we first utilized EBOV virus-like particles (VLPs) expressing VP40 and NP either alone (Bald-VLP) or in conjunction with GP (VLP-GP) to investigate early inflammatory responses in THP-1 macrophages and in a murine model. We then sought to decipher the role of non-classical inflammatory mediators such as EVs over the course of EBOV infection in two EBOV-infected rhesus macaques by isolating and characterizing circulatory EVs throughout disease progression using size exclusion chromatography, nanoparticle tracking-analysis, and LC-MS/MS.

Results

While all VLPs could induce inflammatory mediators and recruit small peritoneal macrophages, pro-inflammatory cytokine and chemokine gene expression was exacerbated by the presence of GP. Further, quantification of EVs isolated from infected rhesus macaques revealed that the concentration of vesicles peaked in circulation at the terminal stage, at which time EBOV GP could be detected in host-derived exosomes. Moreover, comparative proteomics conducted across EV populations isolated from serum at various time points before and after infection revealed differences in host-derived protein content that were most significantly pronounced at the endpoint of infection, including significant expression of mediators of TLR4 signaling.

Discussion

These results suggest a dynamic role for EVs in the modification of disease states in the context of EBOV. Overall, our work highlights the importance of viral factors, such as the GP, and host derived EVs in the inflammatory cascade and pathogenesis of EBOV, which can be collectively further exploited for novel antiviral development.

Ebola virus shed glycoprotein is toxic to human T, B, and natural killer lymphocytes

Lymphocyte depletion is a distinctive feature of Ebola virus (EBOV) disease. The ectodomain of EBOV glycoprotein (GP) is cleaved off the surface of infected cells into circulation as shed GP. To test the hypothesis that shed GP induces lymphocyte death, we cultured primary human B, NK, or T cells with shed GP in vitro. We found that shed GP dependably decreased B, NK, and T cell viability across donors. B and NK cells exhibited higher susceptibility than T cells. Continuous monitoring revealed shed GP began to kill B and NK cells by 4 h and T cells by 5 h. We also demonstrated that shed GP-induced lymphocyte death can be both caspase dependent and caspase independent. Our data are evidence that the cytotoxic effect of shed GP on lymphocytes may contribute to EBOV disease and highlight the need for further research to clarify mechanisms of shed GP-induced death.

Antibodies against the Ebola virus soluble glycoprotein are associated with long-term vaccine-mediated protection of non-human primates

The 2013 Ebola epidemic in Central and West Africa heralded the emergence of wide-spread, highly pathogenic viruses. The successful recombinant vector vaccine against Ebola (rVSVΔG-ZEBOV-GP) will limit future outbreaks, but identifying mechanisms of protection is essential to protect the most vulnerable. Vaccine-induced antibodies are key determinants of vaccine efficacy, yet the mechanism by which vaccine-induced antibodies prevent Ebola infection remains elusive. Here, we exploit a break in long-term vaccine efficacy in non-human primates to identify predictors of protection. Using unbiased humoral profiling that captures neutralization and Fc-mediated functions, we find that antibodies specific for soluble glycoprotein (sGP) drive neutrophil-mediated phagocytosis and predict vaccine-mediated protection. Similarly, we show that protective sGP-specific monoclonal antibodies have elevated neutrophil-mediated phagocytic activity compared with non-protective antibodies, highlighting the importance of sGP in vaccine protection and monoclonal antibody therapeutics against Ebola virus.

Role of Siglecs in viral infections: A double-edged sword interaction

Sialic-acid-binding immunoglobulin-like lectins are cell surface immune receptors known as Siglecs that play a paramount role as modulators of immunity. In recent years, research has underscored how the underlaying biology of this family of receptors influences the outcome of viral infections. While Siglecs are needed to promote effective antiviral immune responses, they can also pave the way to viral dissemination within tissues. Here, we review how recent preclinical findings focusing on the interplay between Siglecs and viruses may translate into promising broad-spectrum therapeutic interventions or key biomarkers to monitor the course of viral infections.

Ebola virus-like particles reprogram cellular metabolism

Ebola virus can trigger a release of pro-inflammatory cytokines with subsequent vascular leakage and impairment of clotting finally leading to multiorgan failure and shock after entering and infecting patients. Ebola virus is known to directly target endothelial cells and macrophages, even without infecting them, through direct interactions with viral proteins. These interactions affect cellular mechanics and immune processes, which are tightly linked to other key cellular functions such as metabolism. However, research regarding metabolic activity of these cells upon viral exposure remains limited, hampering our understanding of its pathophysiology and progression. Therefore, in the present study, an untargeted cellular metabolomic approach was performed to investigate the metabolic alterations of primary human endothelial cells and M1 and M2 macrophages upon exposure to Ebola virus-like particles (VLP). The results show that Ebola VLP led to metabolic changes among endothelial, M1, and M2 cells. Differential metabolite abundance and perturbed signaling pathway analysis further identified specific metabolic features, mainly in fatty acid-, steroid-, and amino acid-related metabolism pathways for all the three cell types, in a host cell specific manner. Taken together, this work characterized for the first time the metabolic alternations of endothelial cells and two primary human macrophage subtypes after Ebola VLP exposure, and identified the potential metabolites and pathways differentially affected, highlighting the important role of those host cells in disease development and progression. KEY MESSAGES: • Ebola VLP can lead to metabolic alternations in endothelial cells and M1 and M2 macrophages. • Differential abundance of metabolites, mainly including fatty acids and sterol lipids, was observed after Ebola VLP exposure. • Multiple fatty acid-, steroid-, and amino acid-related metabolism pathways were observed perturbed.

Structurally Different Yet Functionally Similar: Aptamers Specific for the Ebola Virus Soluble Glycoprotein and GP1,2 and Their Application in Electrochemical Sensing

The Ebola virus glycoprotein (GP) gene templates several mRNAs that produce either the virion-associated transmembrane protein or one of two secreted glycoproteins. Soluble glycoprotein (sGP) is the predominant product. GP1 and sGP share an amino terminal sequence of 295 amino acids but differ in quaternary structure, with GP1 being a heterohexamer with GP2 and sGP a homodimer. Two structurally different DNA aptamers were selected against sGP that also bound GP1,2. These DNA aptamers were compared with a 2'FY-RNA aptamer for their interactions with the Ebola GP gene products. The three aptamers have almost identical binding isotherms for sGP and GP1,2 in solution and on the virion. They demonstrated high affinity and selectivity for sGP and GP1,2. Furthermore, one aptamer, used as a sensing element in an electrochemical format, detected GP1,2 on pseudotyped virions and sGP with high sensitivity in the presence of serum, including from an Ebola-virus-infected monkey. Our results suggest that the aptamers interact with sGP across the interface between the monomers, which is different from the sites on the protein bound by most antibodies. The remarkable similarity in functional features of three structurally distinct aptamers suggests that aptamers, like antibodies, have preferred binding sites on proteins.

Self-amplifying RNA vaccine protects mice against lethal Ebola virus infection

Emerging and re-emerging viruses, such as Zaire Ebola virus (EBOV), pose a global threat and require immediate countermeasures, including the rapid development of effective vaccines that are easy to manufacture. Synthetic self-amplifying RNAs (saRNAs) attend to these needs, being safe and strong immune stimulators that can be inexpensively produced in large quantities, using cell-free systems and good manufacturing practice. Here, the first goal was to develop and optimize an anti-EBOV saRNA-based vaccine in terms of its antigen composition and route of administration. Vaccinating mice with saRNAs expressing the EBOV glycoprotein (GP) alone or in combination with the nucleoprotein (NP) elicited antigen-specific immune responses. GP-specific antibodies showed neutralizing activity against EBOV. Strong CD4+ T cell response against NP and GP and CD8+ T cell response against NP were detected by ELISpot assays. Intramuscular vaccination with saRNAs conferred better immune response than intradermal. Finally, mice vaccinated in a prime-boost regimen with saRNAs encoding both GP and NP or with GP alone survived an EBOV infection. In addition, a single dose of GP and NP saRNAs was also protective against fatal EBOV infection. Overall, saRNAs expressing viral antigens represent a promising vaccine platform.

Immune correlates of protection for SARS-CoV-2, Ebola and Nipah virus infection

Correlates of protection (CoP) are biological parameters that predict a certain level of protection against an infectious disease. Well-established correlates of protection facilitate the development and licensing of vaccines by assessing protective efficacy without the need to expose clinical trial participants to the infectious agent against which the vaccine aims to protect. Despite the fact that viruses have many features in common, correlates of protection can vary considerably amongst the same virus family and even amongst a same virus depending on the infection phase that is under consideration. Moreover, the complex interplay between the various immune cell populations that interact during infection and the high degree of genetic variation of certain pathogens, renders the identification of immune correlates of protection difficult. Some emerging and re-emerging viruses of high consequence for public health such as SARS-CoV-2, Nipah virus (NiV) and Ebola virus (EBOV) are especially challenging with regards to the identification of CoP since these pathogens have been shown to dysregulate the immune response during infection. Whereas, virus neutralising antibodies and polyfunctional T-cell responses have been shown to correlate with certain levels of protection against SARS-CoV-2, EBOV and NiV, other effector mechanisms of immunity play important roles in shaping the immune response against these pathogens, which in turn might serve as alternative correlates of protection. This review describes the different components of the adaptive and innate immune system that are activated during SARS-CoV-2, EBOV and NiV infections and that may contribute to protection and virus clearance. Overall, we highlight the immune signatures that are associated with protection against these pathogens in humans and could be used as CoP.

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.

Filoviruses: Innate Immunity, Inflammatory Cell Death, and Cytokines

Filoviruses are a group of single-stranded negative sense RNA viruses. The most well-known filoviruses that affect humans are ebolaviruses and marburgviruses. During infection, they can cause life-threatening symptoms such as inflammation, tissue damage, and hemorrhagic fever, with case fatality rates as high as 90%. The innate immune system is the first line of defense against pathogenic insults such as filoviruses. Pattern recognition receptors (PRRs), including toll-like receptors, retinoic acid-inducible gene-I-like receptors, C-type lectin receptors, AIM2-like receptors, and NOD-like receptors, detect pathogens and activate downstream signaling to induce the production of proinflammatory cytokines and interferons, alert the surrounding cells to the threat, and clear infected and damaged cells through innate immune cell death. However, filoviruses can modulate the host inflammatory response and innate immune cell death, causing an aberrant immune reaction. Here, we discuss how the innate immune system senses invading filoviruses and how these deadly pathogens interfere with the immune response. Furthermore, we highlight the experimental difficulties of studying filoviruses as well as the current state of filovirus-targeting therapeutics.

Activation of Toll-like receptor 4 by Ebola virus-shed glycoprotein is direct and requires the internal fusion loop but not glycosylation

Infection by the Ebola virus, a member of the Filoviridae family of RNA viruses, leads to acute viral hemorrhagic fever. End-stage Ebola virus disease is characterized by a cytokine storm that causes tissue damage, vascular disintegration, and multi-organ failure. Previous studies showed that a shed form of the viral spike glycoprotein (sGP1,2) drives this hyperinflammatory response by activating Toll-like receptor 4 (TLR4). Here, we find that glycosylation is not required for activation of TLR4 by sGP1,2 and identify the internal fusion loop (IFL) as essential for inflammatory signaling. sGP1,2 competes with lipid antagonists of TLR4, and the IFL interacts directly with TLR4 and co-receptor MD2. Together, these findings indicate that sGP1,2 activates TLR4 analogously to bacterial agonist lipopolysaccharide (LPS) by binding into a hydrophobic pocket in MD2 and promoting the formation of an active heterotetramer. This conclusion is supported by docking studies that predict binding sites for sGP1,2 on TLR4 and MD2.

Activation of TLR4 by viral glycoproteins: A double-edged sword?

Recognition of viral infection by pattern recognition receptors is paramount for a successful immune response to viral infection. However, an unbalanced proinflammatory response can be detrimental to the host. Recently, multiple studies have identified that the SARS-CoV-2 spike protein activates Toll-like receptor 4 (TLR4), resulting in the induction of proinflammatory cytokine expression. Activation of TLR4 by viral glycoproteins has also been observed in the context of other viral infection models, including respiratory syncytial virus (RSV), dengue virus (DENV) and Ebola virus (EBOV). However, the mechanisms involved in virus-TLR4 interactions have remained unclear. Here, we review viral glycoproteins that act as pathogen-associated molecular patterns to induce an immune response via TLR4. We explore the current understanding of the mechanisms underlying how viral glycoproteins are recognized by TLR4 and discuss the contribution of TLR4 activation to viral pathogenesis. We identify contentious findings and research gaps that highlight the importance of understanding viral glycoprotein-mediated TLR4 activation for potential therapeutic approaches.

Acquisition of Furin Cleavage Site and Further SARS-CoV-2 Evolution Change the Mechanisms of Viral Entry, Infection Spread, and Cell Signaling

Circulation of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the human population leads to further viral evolution. The new variants that arise during this evolution are more infectious. Our data suggest that newer variants have shifted from utilizing both cathepsin/endosome- and TMPRSS2-mediated entry mechanisms to rely on a TMPRSS2-dependent entry pathway. Accordingly, only the early lineages of SARS-CoV-2 are capable of infecting and forming syncytia in Vero/ACE2 cells which lack TMPRSS2 expression. The presence of an intact multibasic furin cleavage site (FCS) in the S protein was a key requirement for cell-to-cell fusion. Deletion of FCS makes SARS-CoV-2 more infectious in vitro but renders it incapable of syncytium formation. Cell-to-cell fusion likely represents an alternative means of virus spread and is resistant to the presence of high levels of neutralizing monoclonal antibodies (MAbs) and immune sera in the media. In this study, we also noted that cells infected with SARS-CoV-2 with an intact FCS or alphavirus replicon expressing S protein (VEErep/S) released high levels of free S1 subunit. The released S1 is capable of activating the TLR4 receptor and inducing a pro-inflammatory response. Thus, S1 activation of TLR4 may be an important contributor to SARS-CoV-2-induced COVID-19 disease and needs to be considered in the design of COVID mRNA vaccines. Lastly, a VEErep/S-replicon was shown to produce large amounts of infectious, syncytium-forming pseudoviruses and thus could represent alternative experimental system for screening inhibitors of virus entry and syncytium formation.

IMPORTANCE The results of this study demonstrate that the late lineages of SARS-CoV-2 evolved to more efficient use of the TMPRSS2-mediated entry pathway and gradually lost an ability to employ the cathepsins/endosome-mediated entry. The acquisition of a furin cleavage site (FCS) by SARS-CoV-2-specific S protein made the virus a potent producer of syncytia. Their formation is also determined by expression of ACE2 and TMPRSS2 and is resistant to neutralizing human MAbs and immune sera. Syncytium formation appears to be an alternative means of infection spread following the development of an adaptive immune response. Cells infected with SARS-CoV-2 with an intact FCS secrete high levels of the S1 subunit. The released S1 demonstrates an ability to activate the TLR4 receptor and induce pro-inflammatory cytokines, which represent a hallmark of SARS-CoV-2 pathogenesis. Alphavirus replicons encoding SARS-CoV-2 S protein cause spreading, syncytium-forming infection, and they can be applied as an experimental tool for studying the mechanism of syncytium formation.

Ebola virus protein VP40 stimulates IL-12- and IL-18-dependent activation of human natural killer cells

Accumulation of activated natural killer (NK) cells in tissues during Ebola virus infection contributes to Ebola virus disease (EVD) pathogenesis. Yet, immunization with Ebola virus-like particles (VLPs) comprising glycoprotein and matrix protein VP40 provides rapid, NK cell–mediated protection against Ebola challenge. We used Ebola VLPs as the viral surrogates to elucidate the molecular mechanism by which Ebola virus triggers heightened NK cell activity. Incubation of human peripheral blood mononuclear cells with Ebola VLPs or VP40 protein led to increased expression of IFN-γ, TNF-α, granzyme B, and perforin by CD3^–CD56⁺ NK cells, along with increases in degranulation and cytotoxic activity of these cells. Optimal activation required accessory cells like CD14⁺ myeloid and CD14^– cells and triggered increased secretion of numerous inflammatory cytokines. VP40-induced IFN-γ and TNF-α secretion by NK cells was dependent on IL-12 and IL-18 and suppressed by IL-10. In contrast, their increased degranulation was dependent on IL-12 with little influence of IL-18 or IL-10. These results demonstrate that Ebola VP40 stimulates NK cell functions in an IL-12– and IL-18–dependent manner that involves CD14⁺ and CD14^– accessory cells. These potentially novel findings may help in designing improved intervention strategies required to control viral transmission during Ebola outbreaks.

Could a Lower Toll-like Receptor (TLR) and NF-κB Activation Due to a Changed Charge Distribution in the Spike Protein Be the Reason for the Lower Pathogenicity of Omicron?

The novel SARS-CoV-2 Omicron variant B.1.1.529, which emerged in late 2021, is currently active worldwide, replacing other variants, including the Delta variant, due to an enormously increased infectivity. Multiple substitutions and deletions in the N-terminal domain (NTD) and the receptor binding domain (RBD) in the spike protein collaborate with the observed increased infectivity and evasion from therapeutic monoclonal antibodies and vaccine-induced neutralizing antibodies after primary/secondary immunization. In contrast, although three mutations near the S1/S2 furin cleavage site were predicted to favor cleavage, observed cleavage efficacy is substantially lower than in the Delta variant and also lower compared to the wild-type virus correlating with significantly lower TMPRSS2-dependent replication in the lungs, and lower cellular syncytium formation. In contrast, the Omicron variant shows high TMPRSS2-independent replication in the upper airway organs, but lower pathogenicity in animal studies and clinics. Based on recent data, we present here a hypothesis proposing that the changed charge distribution in the Omicron’s spike protein could lead to lower activation of Toll-like receptors (TLRs) in innate immune cells, resulting in lower NF-κB activation, furin expression, and viral replication in the lungs, and lower immune hyper-activation.

PET imaging of TSPO expression in immune cells can assess organ-level pathophysiology in high-consequence viral infections

Ebola virus (EBOV) disease is characterized by lymphopenia, breach in vascular integrity, cytokine storm, and multiorgan failure. The pathophysiology of organ involvement, however, is incompletely understood. Using [18F]-DPA-714 positron emission tomography (PET) imaging targeting the translocator protein (TSPO), an immune cell marker, we sought to characterize the progression of EBOV-associated organ-level pathophysiology in the EBOV Rhesus macaque model. Dynamic [18F]-DPA-714 PET/computed tomography imaging was performed longitudinally at baseline and at multiple time points after EBOV inoculation, and distribution volumes (Vt) were calculated as a measure of peripheral TSPO binding. Using a mixed-effect linear regression model, spleen and lung Vt decreased, while the bone marrow Vt increased over time after infection. No clear trend was found for liver Vt. Multiple plasma cytokines correlated negatively with lung/spleen Vt and positively with bone marrow Vt. Multiplex immunofluorescence staining in spleen and lung sections confirmed organ-level lymphoid and monocytic loss/apoptosis, thus validating the imaging results. Our findings are consistent with EBOV-induced progressive monocytic and lymphocytic depletion in the spleen, rather than immune activation, as well as depletion of alveolar macrophages in the lungs, with inefficient reactive neutrophilic activation. Increased bone marrow Vt, on the other hand, suggests hematopoietic activation in response to systemic immune cell depletion and leukocytosis and could have prognostic relevance. In vivo PET imaging provided better understanding of organ-level pathophysiology during EBOV infection. A similar approach can be used to delineate the pathophysiology of other systemic infections and to evaluate the effectiveness of newly developed treatment and vaccine strategies.

Synthetic nanobody-functionalized nanoparticles for accelerated development of rapid, accessible detection of viral antigens

Successful control of emerging infectious diseases requires accelerated development of fast, affordable, and accessible assays for wide implementation at a high frequency. This paper presents a design for an in-solution assay pipeline, featuring nanobody-functionalized nanoparticles for rapid, electronic detection (Nano2RED) of Ebola and COVID-19 antigens. Synthetic nanobody binders with high affinity, specificity, and stability are selected from a combinatorial library and site-specifically conjugated to gold nanoparticles (AuNPs). Without requiring any fluorescent labelling, washing, or enzymatic amplification, these multivalent AuNP sensors reliably transduce antigen binding signals upon mixing into physical AuNP aggregation and sedimentation processes, displaying antigen-dependent optical extinction readily detectable by spectrometry or portable electronic circuitry. With Ebola virus secreted glycoprotein (sGP) and a SARS-CoV-2 spike protein receptor binding domain (RBD) as targets, Nano2RED showed a high sensitivity (the limit of detection of ∼10 pg /mL, or 0.13 pM for sGP and ∼40 pg/mL, or ∼1.3 pM for RBD in diluted human serum), a high specificity, a large dynamic range (∼7 logs),and fast readout within minutes. The rapid detection, low material cost (estimated <$0.01 per test), inexpensive and portable readout system (estimated <$5), and digital data output, make Nano2RED a particularly accessible assay in screening of patient samples towards successful control of infectious diseases.

Ebola Virus GP Activates Endothelial Cells via Host Cytoskeletal Signaling Factors

Ebola virus disease (EVD) is a lethal disease caused by the highly pathogenic Ebola virus (EBOV), and its major symptoms in severe cases include vascular leakage and hemorrhage. These symptoms are caused by abnormal activation and disruption of endothelial cells (ECs) whose mediators include EBOV glycoprotein (GP) without the need for viral replication. However, the detailed molecular mechanisms underlying virus-host interactions remain largely unknown. Here, we show that EBOV-like particles (VLPs) formed by GP, VP40, and NP activate ECs in a GP-dependent manner, as demonstrated by the upregulation of intercellular adhesion molecules-1 (ICAM-1) expression. VLPs-mediated ECs activation showed a different kinetic pattern from that of TNF-α-mediated activation and was associated with apoptotic ECs disruption. In contrast to TNF-α, VLPs induced ICAM-1 overexpression at late time points. Furthermore, screening of host cytoskeletal signaling inhibitors revealed that focal adhesion kinase inhibitors were found to be potent inhibitors of ICAM-1 expression mediated by both TNF-α and VLPs. Our results suggest that EBOV GP stimulates ECs to induce endothelial activation and dysfunction with the involvement of host cytoskeletal signaling factors, which represent potential therapeutic targets for EVD.

Ebola virus delta peptide is an enterotoxin

During the 2013-2016 West African (WA) Ebola virus (EBOV) outbreak, severe gastrointestinal symptoms were common in patients and associated with poor outcome. Delta peptide is a conserved product of post-translational processing of the abundant EBOV soluble glycoprotein (sGP). The murine ligated ileal loop model was used to demonstrate that delta peptide is a potent enterotoxin. Dramatic intestinal fluid accumulation follows injection of biologically relevant amounts of delta peptide into ileal loops, along with gross alteration of villous architecture and loss of goblet cells. Transcriptomic analyses show that delta peptide triggers damage response and cell survival pathways and downregulates expression of transporters and exchangers. Induction of diarrhea by delta peptide occurs via cellular damage and regulation of genes that encode proteins involved in fluid secretion. While distinct differences exist between the ileal loop murine model and EBOV infection in humans, these results suggest that delta peptide may contribute to EBOV-induced gastrointestinal pathology.

CD47 expression attenuates Ebola virus-induced immunopathology in mice

It has been shown that a very early cell-intrinsic response to infection is the upregulation of CD47 cell surface expression, a molecule known for delivering a "don't eat me signal" that inhibits macrophage-mediated phagocytosis and antigen presentation. Thus, blockade of CD47 signaling during lymphocytic choriomenigitis virus infections of mice has been shown to enhance the kinetics and potency of immune responses, thereby producing faster recovery. It seems counterintuitive that one of the earliest responses to infection would be immunoinhibitory, but it has been hypothesized that CD47 induction acts as an innate immune system checkpoint to prevent immune overactivation and immunopathogenic responses during certain infections. In the current study we examined the effect of CD47 blockade on lethal Ebola virus infection of mice. At 6 days post-infection, CD47 blockade was associated with significantly increased activation of B cells along with increases in recently cytolytic CD8+ T cells. However, the anti-CD47-treated mice exhibited increased weight loss, higher virus titers, and succumbed more rapidly. The anti-CD47-treated mice also had increased inflammatory cytokines in the plasma indicative of a "cytokine storm". Thus, in the context of this rapid hemorrhagic disease, CD47 blockade indeed exacerbated immunopathology and disease severity.

Pathogenicity and Virulence of Ebolaviruses with Species- and Variant-specificity

Ebola virus (EBOV), belonging to the species Zaire ebolavirus in the genus Ebolavirus, causes a severe febrile illness in humans with case fatality rates (CFRs) up to 90%. While there have been six virus species classified, which each have a single type virus in the genus Ebolavirus, CFRs of ebolavirus infections vary among viruses belonging to each distinct species. In this review, we aim to define the ebolavirus species-specific virulence on the basis of currently available laboratory and experimental findings. In addition, this review will also cover the variant-specific virulence of EBOV by referring to the unique biological and pathogenic characteristics of EBOV variant Makona, a new EBOV variant isolated from the 2013-2016 EBOV disease outbreak in West Africa. A better definition of species-specific and variant-specific virulence of ebolaviruses will facilitate our comprehensive knowledge on genus Ebolavirus biology, leading to the development of therapeutics against well-focused pathogenic mechanisms of each Ebola disease.

Therapeutic vaccination strategies against EBOV by rVSV-EBOV-GP: the role of innate immunity

Zaire Ebola virus (EBOV) is a member of the Filoviridae family. Infection with EBOV causes Ebola virus disease (EVD) characterized by excessive inflammation, lymphocyte death, coagulopathy, and multi-organ failure. In 2019, the FDA-approved the first anti-EBOV vaccine, rVSV-EBOV-GP (Ervebo® by Merck). This live-recombinant vaccine confers both prophylactic and therapeutic protection to nonhuman primates and humans. While mechanisms conferring prophylactic protection are well-investigated, those underlying protection conferred shortly before and after exposure to EBOV remain poorly understood. In this review, we review data from in vitro and in vivo studies analyzing early immune responses to rVSV-EBOV-GP and discuss the role of innate immune activation in therapeutic protection.

Structural and Functional Aspects of Ebola Virus Proteins

Ebola virus (EBOV), member of genus Ebolavirus, family Filoviridae, have a non-segmented, single-stranded RNA that contains seven genes: (a) nucleoprotein (NP), (b) viral protein 35 (VP35), (c) VP40, (d) glycoprotein (GP), (e) VP30, (f) VP24, and (g) RNA polymerase (L). All genes encode for one protein each except GP, producing three pre-proteins due to the transcriptional editing. These pre-proteins are translated into four products, namely: (a) soluble secreted glycoprotein (sGP), (b) Δ-peptide, (c) full-length transmembrane spike glycoprotein (GP), and (d) soluble small secreted glycoprotein (ssGP). Further, shed GP is released from infected cells due to cleavage of GP by tumor necrosis factor α-converting enzyme (TACE). This review presents a detailed discussion on various functional aspects of all EBOV proteins and their residues. An introduction to ebolaviruses and their life cycle is also provided for clarity of the available analysis. We believe that this review will help understand the roles played by different EBOV proteins in the pathogenesis of the disease. It will help in targeting significant protein residues for therapeutic and multi-protein/peptide vaccine development.

Filovirus Neutralising Antibodies: Mechanisms of Action and Therapeutic Application

Filoviruses, especially Ebola virus, cause sporadic outbreaks of viral haemorrhagic fever with very high case fatality rates in Africa. The 2013–2016 Ebola epidemic in West Africa provided large survivor cohorts spurring a large number of human studies which showed that specific neutralising antibodies played a key role in protection following a natural Ebola virus infection, as part of the overall humoral response and in conjunction with the cellular adaptive response. This review will discuss the studies in survivors and animal models which described protective neutralising antibody response. Their mechanisms of action will be detailed. Furthermore, the importance of neutralising antibodies in antibody-based therapeutics and in vaccine-induced responses will be explained, as well as the strategies to avoid immune escape from neutralising antibodies. Understanding the neutralising antibody response in the context of filoviruses is crucial to furthering our understanding of virus structure and function, in addition to improving current vaccines & antibody-based therapeutics.

Brilliant glycans and glycosylation: Seq and ye shall find

Proteoglycosylation is the addition of monosaccharides or glycans to the protein peptide chain. This is a common post-translational modification of proteins with a variety of biological functions. At present, more than half of all biopharmaceuticals in clinic are modified by glycosylation. Most glycoproteins are potential drug targets and biomarkers for disease diagnosis. Therefore, in-depth study of glycan structure of glycoproteins will ultimately improve the sensitivity and specificity of glycoproteins for clinical disease detection. With the deepening of research, the function and application value of glycans and glycosylation has gradually emerged. This review systematically introduces the latest research progress of glycans and glycosylation. It encompasses six cancers, four viruses, and their latest discoveries in Alzheimer's disease, allergic diseases, congenital diseases, gastrointestinal diseases, inflammation, and aging.

Long-lived macrophage reprogramming drives spike protein-mediated inflammasome activation in COVID-19

Innate immunity triggers responsible for viral control or hyperinflammation in COVID-19 are largely unknown. Here we show that the SARS-CoV-2 spike protein (S-protein) primes inflammasome formation and release of mature interleukin-1β (IL-1β) in macrophages derived from COVID-19 patients but not in macrophages from healthy SARS-CoV-2 naïve individuals. Furthermore, longitudinal analyses reveal robust S-protein-driven inflammasome activation in macrophages isolated from convalescent COVID-19 patients, which correlates with distinct epigenetic and gene expression signatures suggesting innate immune memory after recovery from COVID-19. Importantly, we show that S-protein-driven IL-1β secretion from patient-derived macrophages requires non-specific monocyte pre-activation in vivo to trigger NLRP3-inflammasome signaling. Our findings reveal that SARS-CoV-2 infection causes profound and long-lived reprogramming of macrophages resulting in augmented immunogenicity of the SARS-CoV-2 S-protein, a major vaccine antigen and potent driver of adaptive and innate immune signaling.

Development and Evaluation of an Ebola Virus Glycoprotein Mucin-Like Domain Replacement System as a New Dendritic Cell-Targeting Vaccine Approach against HIV-1

The development of efficient vaccine approaches against HIV infection remains challenging in the vaccine field. Here, we developed an Ebola virus envelope glycoprotein (EboGP)-based chimeric fusion protein system and demonstrated that replacement of the mucin-like domain (MLD) of EboGP with HIV C2-V3-C3 (134 amino acids [aa]) or C2-V3-C3-V4-C4-V5-C5 (243 aa) polypeptides (EbGPΔM-V3 and EbGPΔM-V3-V5, respectively) still maintained the efficiency of EboGP-mediated viral entry into human macrophages and dendritic cells (DCs). Animal studies using mice revealed that immunization with virus-like particles (VLPs) containing the above chimeric proteins, especially EbGPΔM-V3, induced significantly more potent anti-HIV antibodies than HIV gp120 alone in mouse serum and vaginal fluid. Moreover, the splenocytes isolated from mice immunized with VLPs containing EbGPΔM-V3 produced significantly higher levels of gamma interferon (IFN-γ), interleukin 2 (IL-2), IL-4, IL-5, and macrophage inflammatory protein 1α (MIP-1α). Additionally, we demonstrated that coexpression of EbGPΔM-V3 and the HIV Env glycoprotein in a recombinant vesicular stomatitis virus (rVSV) vector elicited robust anti-HIV antibodies that may have specifically recognized epitopes outside or inside the C2-V3-C3 region of HIV-1 gp120 and cross-reacted with the gp120 from different HIV strains. Thus, this study has demonstrated the great potential of this DC-targeting vaccine platform as a new vaccine approach for improving immunogen delivery and increasing vaccine efficacy.

IMPORTANCE Currently, there are more than 38.5 million reported cases of HIV globally. To date, there is no approved vaccine for HIV-1 infection. Thus, the development of an effective vaccine against HIV infection remains a global priority. This study revealed the efficacy of a novel dendritic cell (DC)-targeting vaccination approach against HIV-1. The results clearly show that the immunization of mice with virus-like particles (VLPs) and VSVs containing HIV Env and a fusion protein composed of a DC-targeting domain of Ebola virus GP with HIV C2-V3-C3 polypeptides (EbGPΔM-V3) could induce robust immune responses against HIV-1 Env and/or Gag in serum and vaginal mucosa. These findings provide a proof of concept of this novel and efficient DC-targeting vaccine approach in delivering various antigenic polypeptides of HIV-1 and/or other emergent infections to the host antigen-presenting cells to prevent HIV and other viral infections.

Complement Proteins as Soluble Pattern Recognition Receptors for Pathogenic Viruses

The complement system represents a crucial part of innate immunity. It contains a diverse range of soluble activators, membrane-bound receptors, and regulators. Its principal function is to eliminate pathogens via activation of three distinct pathways: classical, alternative, and lectin. In the case of viruses, the complement activation results in effector functions such as virion opsonisation by complement components, phagocytosis induction, virolysis by the membrane attack complex, and promotion of immune responses through anaphylatoxins and chemotactic factors. Recent studies have shown that the addition of individual complement components can neutralise viruses without requiring the activation of the complement cascade. While the complement-mediated effector functions can neutralise a diverse range of viruses, numerous viruses have evolved mechanisms to subvert complement recognition/activation by encoding several proteins that inhibit the complement system, contributing to viral survival and pathogenesis. This review focuses on these complement-dependent and -independent interactions of complement components (especially C1q, C4b-binding protein, properdin, factor H, Mannose-binding lectin, and Ficolins) with several viruses and their consequences.

Renal Manifestations of Covid-19: Physiology and Pathophysiology

Corona virus disease 2019 (COVID-19) imposes a serious public health pandemic affecting the whole world, as it is spreading exponentially. Besides its high infectivity, SARS-CoV-2 causes multiple serious derangements, where the most prominent is severe acute respiratory syndrome as well as multiple organ dysfunction including heart and kidney injury. While the deleterious impact of SARS-CoV-2 on pulmonary and cardiac systems have attracted remarkable attention, the adverse effects of this virus on the renal system is still underestimated. Kidney susceptibility to SARS-CoV-2 infection is determined by the presence of angiotensin-converting enzyme 2 (ACE2) receptor which is used as port of the viral entry into targeted cells, tissue tropism, pathogenicity and subsequent viral replication. The SARS-CoV-2 cellular entry receptor, ACE2, is widely expressed in proximal epithelial cells, vascular endothelial and smooth muscle cells and podocytes, where it supports kidney integrity and function via the enzymatic production of Angiotensin 1-7 (Ang 1-7), which exerts vasodilatory, anti-inflammatory, antifibrotic and diuretic/natriuretic actions via activation of the Mas receptor axis. Loss of this activity constitutes the potential basis for the renal damage that occurs in COVID-19 patients. Indeed, several studies in a small sample of COVID-19 patients revealed relatively high incidence of acute kidney injury (AKI) among them. Although SARS-CoV-1 -induced AKI was attributed to multiorgan failure and cytokine release syndrome, as the virus was not detectable in the renal tissue of infected patients, SARS-CoV-2 antigens were detected in kidney tubules, suggesting that SARS-CoV-2 infects the human kidney directly, and eventually induces AKI characterized with high morbidity and mortality. The mechanisms underlying this phenomenon are largely unknown. However, the fact that ACE2 plays a crucial role against renal injury, the deprivation of the kidney of this advantageous enzyme, along with local viral replication, probably plays a central role. The current review focuses on the critical role of ACE2 in renal physiology, its involvement in the development of kidney injury during SARS-CoV-2 infection, renal manifestations and therapeutic options. The latter includes exogenous administration of Ang (1-7) as an appealing option, given the high incidence of AKI in this ACE2-depleted disorder, and the benefits of ACE2/Ang1-7 including vasodilation, diuresis, natriuresis, attenuation of inflammation, oxidative stress, cell proliferation, apoptosis and coagulation.

The sphingosine kinase 1 activator, K6PC-5, attenuates Ebola virus infection

Ebola virus (EBOV) is responsible for outbreaks with case fatality rates of up to 90% and for an epidemic in West Africa with more than ten thousand deaths. EBOV glycoprotein (EBOV-GP) is the only viral surface protein and is responsible for viral entry into cells. Here, by employing pseudotyped EBOV-GP viral particles, we uncover a critical role for sphingolipids in inhibiting viral entry. Sphingosine kinase 1 (SphK1) catalyzes the phosphorylation of sphingosine to sphingosine 1-phosphate (S1P). The administration of the SphK1 activator, K6PC-5, or S1P, or the overexpression of SphK1 consistently exhibited striking inhibitory effects in EBOV-GP-driven entry in diverse cell lines. Finally, K6PC-5 markedly reduced the EBOV titer in infected cells and the de novo production of viral proteins. These data present K6PC-5 as an efficient tool to inhibit EBOV infection in endothelial cells and suggest further studies to evaluate its systemic effects.

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K6PC-5, a sphingosine kinase 1 activator, inhibits Ebola virus infection

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Sphingosine 1-phosphate, the product of SphK1, attenuates the viral entry

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Inhibiton/activation of S1P receptors has no influence on Ebola virus entry

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These data support the endogen effect of S1P in Ebola virus infection

Transcriptional Analysis of Lymphoid Tissues from Infected Nonhuman Primates Reveals the Basis for Attenuation and Immunogenicity of an Ebola Virus Encoding a Mutant VP35 Protein

Infection with Zaire ebolavirus (EBOV), a member of the Filoviridae family, causes a disease characterized by high levels of viremia, aberrant inflammation, coagulopathy, and lymphopenia. EBOV initially replicates in lymphoid tissues and disseminates via dendritic cells (DCs) and monocytes to liver, spleen, adrenal gland, and other secondary organs. EBOV protein VP35 is a critical immune evasion factor that inhibits type I interferon signaling and DC maturation. Nonhuman primates (NHPs) immunized with a high dose (5 × 10⁵ PFU) of recombinant EBOV containing a mutated VP35 (VP35m) are protected from challenge with wild-type EBOV (wtEBOV). This protection is accompanied by a transcriptional response in the peripheral blood reflecting a regulated innate immune response and a robust induction of adaptive immune genes. However, the host transcriptional response to VP35m in lymphoid tissues has not been evaluated. Therefore, we conducted a transcriptional analysis of axillary and inguinal lymph nodes and spleen tissues of NHPs infected with a low dose (2 × 10⁴ PFU) of VP35m and then back-challenged with a lethal dose of wtEBOV. VP35m induced early transcriptional responses in lymphoid tissues that are distinct from those observed in wtEBOV challenge. Specifically, we detected robust antiviral innate and adaptive responses and fewer transcriptional changes in genes with roles in angiogenesis, apoptosis, and inflammation. Two of three macaques survived wtEBOV back-challenge, with only the nonsurvivor displaying a transcriptional response reflecting Ebola virus disease. These data suggest that VP35 is a key modulator of early host responses in lymphoid tissues, thereby regulating disease progression and severity following EBOV challenge.IMPORTANCE Zaire Ebola virus (EBOV) infection causes a severe and often fatal disease characterized by inflammation, coagulation defects, and organ failure driven by a defective host immune response. Lymphoid tissues are key sites of EBOV pathogenesis and the generation of an effective immune response to infection. A recent study demonstrated that infection with an EBOV encoding a mutant VP35, a viral protein that antagonizes host immunity, can protect nonhuman primates (NHPs) against lethal EBOV challenge. However, no studies have examined the response to this mutant EBOV in lymphoid tissues. Here, we characterize gene expression in lymphoid tissues from NHPs challenged with the mutant EBOV and subsequently with wild-type EBOV to identify signatures of a protective host response. Our findings are critical for elucidating viral pathogenesis, mechanisms of host antagonism, and the role of lymphoid organs in protective responses to EBOV to improve the development of antivirals and vaccines against EBOV.

Endothelial Cells in Emerging Viral Infections

There are several reasons to consider the role of endothelial cells in COVID-19 and other emerging viral infections. First, severe cases of COVID-19 show a common breakdown of central vascular functions. Second, SARS-CoV-2 replicates in endothelial cells. Third, prior deterioration of vascular function exacerbates disease, as the most common comorbidities of COVID-19 (obesity, hypertension, and diabetes) are all associated with endothelial dysfunction. Importantly, SARS-CoV-2's ability to infect endothelium is shared by many emerging viruses, including henipaviruses, hantavirus, and highly pathogenic avian influenza virus, all specifically targeting endothelial cells. The ability to infect endothelium appears to support generalised dissemination of infection and facilitate the access to certain tissues. The disturbed vascular function observed in severe COVID-19 is also a prominent feature of many other life-threatening viral diseases, underscoring the need to understand how viruses modulate endothelial function. We here review the role of vascular endothelial cells in emerging viral infections, starting with a summary of endothelial cells as key mediators and regulators of vascular and immune responses in health and infection. Next, we discuss endotheliotropism as a possible virulence factor and detail features that regulate viruses' ability to attach to and enter endothelial cells. We move on to review how endothelial cells detect invading viruses and respond to infection, with particular focus on pathways that may influence vascular function and the host immune system. Finally, we discuss how endothelial cell function can be dysregulated in viral disease, either by viral components or as bystander victims of overshooting or detrimental inflammatory and immune responses. Many aspects of how viruses interact with the endothelium remain poorly understood. Considering the diversity of such mechanisms among different emerging viruses allows us to highlight common features that may be of general validity and point out important challenges.

Ebola virus glycoprotein stimulates IL-18-dependent natural killer cell responses

BACKGROUND

NK cells are activated by innate cytokines and viral ligands to kill virus-infected cells. These functions are enhanced during secondary immune responses and after vaccination by synergy with effector T cells and virus-specific antibodies. In human Ebola virus infection, clinical outcome is strongly associated with the initial innate cytokine response, but the role of NK cells has not been thoroughly examined.

METHODS

The novel 2-dose heterologous Adenovirus type 26.ZEBOV (Ad26.ZEBOV) and modified vaccinia Ankara-BN-Filo (MVA-BN-Filo) vaccine regimen is safe and provides specific immunity against Ebola glycoprotein, and is currently in phase 2 and 3 studies. Here, we analyzed NK cell phenotype and function in response to Ad26.ZEBOV, MVA-BN-Filo vaccination regimen and in response to in vitro Ebola glycoprotein stimulation of PBMCs isolated before and after vaccination.

RESULTS

We show enhanced NK cell proliferation and activation after vaccination compared with baseline. Ebola glycoprotein–induced activation of NK cells was dependent on accessory cells and TLR-4–dependent innate cytokine secretion (predominantly from CD14⁺ monocytes) and enriched within less differentiated NK cell subsets. Optimal NK cell responses were dependent on IL-18 and IL-12, whereas IFN-γ secretion was restricted by high concentrations of IL-10.

CONCLUSION

This study demonstrates the induction of NK cell effector functions early after Ad26.ZEBOV, MVA-BN-Filo vaccination and provides a mechanism for the activation and regulation of NK cells by Ebola glycoprotein.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02313077.

FUNDING

United Kingdom Medical Research Council Studentship in Vaccine Research, Innovative Medicines Initiative 2 Joint Undertaking, EBOVAC (grant 115861) and Crucell Holland (now Janssen Vaccines and Prevention B.V.), European Union’s Horizon 2020 research and innovation programme and European Federation of Pharmaceutical Industries and Associations (EFPIA).

Durable natural killer cell responses after heterologous two-dose Ebola vaccination

Natural killer (NK) cells are implicated among immune effectors after vaccination against viral pathogens, including Ebola virus. The two-dose heterologous Ebola virus vaccine regimen, adenovirus type 26.ZEBOV followed by modified vaccinia Ankara-BN-Filo (EBOVAC2 consortium, EU Innovative Medicines Initiative), induces NK cell activation and anti-Ebola glycoprotein (GP) antibody-dependent NK cell activation post-dose 1, which is further elevated post-dose 2. Here, in a multicentre, phase 2 clinical trial (EBL2001), we demonstrate durable ex vivo NK cell activation 180 days after dose 2, with responses enriched in CD56^bright NK cells. In vitro antibody-dependent responses to immobilised Ebola GP increased after dose 1, and remained elevated compared to pre-vaccination levels in serum collected 180 days later. Peak NK cell responses were observed post-dose 2 and NK cell IFN-γ responses remained significantly elevated at 180 days post-dose 2. Individual variation in NK cell responses were influenced by both anti-Ebola GP antibody concentrations and intrinsic interindividual differences in NK cell functional capacity. In summary, this study demonstrates durable NK cell responses after Ad26.ZEBOV, MVA-BN-Filo Ebola virus vaccination and could inform the immunological evaluation of future iterations of the vaccine regimen and vaccination schedules.

Toll-like receptor 4 mediates blood-brain barrier permeability and disease in C3H mice during Venezuelan equine encephalitis virus infection

Venezuelan equine encephalitis virus (VEEV) is an encephalitic alphavirus that can cause debilitating, acute febrile illness and potentially result in encephalitis. Currently, there are no FDA-licensed vaccines or specific therapeutics for VEEV. Previous studies have demonstrated that VEEV infection results in increased blood-brain barrier (BBB) permeability that is mediated by matrix metalloproteinases (MMPs). Furthermore, after subarachnoid hemorrhage in mice, MMP-9 is upregulated in the brain and mediates BBB permeability in a toll-like receptor 4 (TLR4)-dependent manner. Here, we demonstrate that disease in C3H mice during VEEV TC-83 infection is dependent on TLR4 because intranasal infection of C3H/HeN (TLR4^WT) mice with VEEV TC-83 resulted in mortality as opposed to survival of TLR4-defective C3H/HeJ (TLR4^mut) mice. In addition, BBB permeability was induced to a lesser extent in TLR4^mut mice compared with TLR4^WT mice during VEEV TC-83 infection as determined by sodium fluorescein and fluorescently-conjugated dextran extravasation. Moreover, MMP-9, MMP-2, ICAM-1, CCL2 and IFN-γ were all induced to significantly lower levels in the brains of infected TLR4^mut mice compared with infected TLR4^WT mice despite the absence of significantly different viral titers or immune cell populations in the brains of infected TLR4^WT and TLR4^mut mice. These data demonstrate the critical role of TLR4 in mediating BBB permeability and disease in C3H mice during VEEV TC-83 infection, which suggests that TLR4 is a potential target for the development of therapeutics for VEEV.

[The latest research findings on Ebola virus]

013-2016 Ebola virus disease (EVD) outbreak was the largest EVD outbreak ever documented that started earlier in Guinea and later widely spread throughout West Africa, ending up a total of > 28,000 human infections. In this review, we outline research findings on Ebola virus (EBOV) variant Makona, a new EBOV variant isolated from the 2013-2016 EVD outbreak, and introduce the unique biological and pathogenic characteristics of Makona variant. We also discuss about the relevance of persistent infection of EBOV in EVD survivors with resurgence of EVD outbreak in Guinea in 2021. Moreover, this review covers a recent case report of EVD relapse and deliberates new interpretations of EBOV biology and EVD outbreak.

Antiviral and Immunomodulatory Effects of Phytochemicals from Honey against COVID-19: Potential Mechanisms of Action and Future Directions

The new coronavirus disease (COVID-19), caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), has recently put the world under stress, resulting in a global pandemic. Currently, there are no approved treatments or vaccines, and this severe respiratory illness has cost many lives. Despite the established antimicrobial and immune-boosting potency described for honey, to date there is still a lack of evidence about its potential role amid COVID-19 outbreak. Based on the previously explored antiviral effects and phytochemical components of honey, we review here evidence for its role as a potentially effective natural product against COVID-19. Although some bioactive compounds in honey have shown potential antiviral effects (i.e., methylglyoxal, chrysin, caffeic acid, galangin and hesperidinin) or enhancing antiviral immune responses (i.e., levan and ascorbic acid), the mechanisms of action for these compounds are still ambiguous. To the best of our knowledge, this is the first work exclusively summarizing all these bioactive compounds with their probable mechanisms of action as antiviral agents, specifically against SARS-CoV-2.

Immunological Perspective for Ebola Virus Infection and Various Treatment Measures Taken to Fight the Disease

Ebolaviruses, discovered in 1976, belongs to the Filoviridae family, which also includes Marburg and Lloviu viruses. They are negative-stranded RNA viruses with six known species identified to date. Ebola virus (EBOV) is a member of Zaire ebolavirus species and can cause the Ebola virus disease (EVD), an emerging zoonotic disease that results in homeostatic imbalance and multi-organ failure. There are three EBOV outbreaks documented in the last six years resulting in significant morbidity (> 32,000 cases) and mortality (> 13,500 deaths). The potential factors contributing to the high infectivity of this virus include multiple entry mechanisms, susceptibility of the host cells, employment of multiple immune evasion mechanisms and rapid person-to-person transmission. EBOV infection leads to cytokine storm, disseminated intravascular coagulation, host T cell apoptosis as well as cell mediated and humoral immune response. In this review, a concise recap of cell types targeted by EBOV and EVD symptoms followed by detailed run-through of host innate and adaptive immune responses, virus-driven regulation and their combined effects contributing to the disease pathogenesis has been presented. At last, the vaccine and drug development initiatives as well as challenges related to the management of infection have been discussed.

To B or Not to B: Mechanisms of Protection Conferred by rVSV-EBOV-GP and the Roles of Innate and Adaptive Immunity

Zaire Ebola virus (EBOV) is a member of the Filoviridae family of negative sense, single-stranded RNA viruses. EBOV infection causes Ebola virus disease (EVD), characterized by coagulopathy, lymphopenia, and multi-organ failure, which can culminate in death. In 2019, the FDA approved the first vaccine against EBOV, a recombinant live-attenuated viral vector wherein the G protein of vesicular stomatitis virus is replaced with the glycoprotein (GP) of EBOV (rVSV-EBOV-GP, Ervebo^® by Merck). This vaccine demonstrates high efficacy in nonhuman primates by providing prophylactic, rapid, and post-exposure protection. In humans, rVSV-EBOV-GP demonstrated 100% protection in several phase III clinical trials in over 10,000 individuals during the 2013–2016 West Africa epidemic. As of 2020, over 218,000 doses of rVSV-EBOV-GP have been administered to individuals with high risk of EBOV exposure. Despite licensure and robust preclinical studies, the mechanisms of rVSV-EBOV-GP-mediated protection are not fully understood. Such knowledge is crucial for understanding vaccine-mediated correlates of protection from EVD and to aid the further design and development of therapeutics against filoviruses. Here, we summarize the current literature regarding the host response to vaccination and EBOV exposure, and evidence regarding innate and adaptive immune mechanisms involved in rVSV-EBOV-GP-mediated protection, with a focus on the host transcriptional response. Current data strongly suggest a protective synergy between rapid innate and humoral immunity.

Human Organs-on-Chips for Virology

While conventional in vitro culture systems and animal models have been used to study the pathogenesis of viral infections and to facilitate development of vaccines and therapeutics for viral diseases, models that can accurately recapitulate human responses to infection are still lacking. Human organ-on-a-chip (Organ Chip) microfluidic culture devices that recapitulate tissue–tissue interfaces, fluid flows, mechanical cues, and organ-level physiology have been developed to narrow the gap between in vitro experimental models and human pathophysiology. Here, we describe how recent developments in Organ Chips have enabled re-creation of complex pathophysiological features of human viral infections in vitro.

Microfluidic Organ Chip culture devices are emerging alternatives to conventional in vitro and animal models due to their ability to replicate many structural and functional features of human physiology and disease states.

Recent innovations demonstrate that Organ Chip technology is a promising strategy for virology studies where there have been successes in reproducing various viral disease phenotypes.

Organ Chips have enabled investigation of many aspects of viral infection, including virus–host interactions, viral therapy-resistance evolution, and development of new antiviral therapeutics, as well as underlying pathogenesis.

As Organ Chip-based assays provide accessibility to study virus-induced diseases in real time and at high resolution, they can open new avenues to uncover viral pathogenesis in a human-relevant environment and may eventually enable development of novel therapeutics and vaccines.

Ebola Virus: Pathogenesis and Countermeasure Development

Since its discovery in 1976, Ebola virus (EBOV) has caused numerous outbreaks of fatal hemorrhagic disease in Africa. The biggest outbreak on record is the 2013-2016 epidemic in west Africa with almost 30,000 cases and over 11,000 fatalities, devastatingly affecting Guinea, Liberia, and Sierra Leone. The epidemic highlighted the need for licensed drugs or vaccines to quickly combat the disease. While at the beginning of the epidemic no licensed countermeasures were available, several experimental drugs with preclinical efficacy were accelerated into human clinical trials and used to treat patients with Ebola virus disease (EVD) toward the end of the epidemic. In the same manner, vaccines with preclinical efficacy were administered primarily to known contacts of EVD patients on clinical trial protocols using a ring-vaccination strategy. In this review, we describe the pathogenesis of EBOV and summarize the current status of EBOV vaccine development and treatment of EVD.

Release of Immunomodulatory Ebola Virus Glycoprotein-Containing Microvesicles Is Suppressed by Tetherin in a Species-Specific Manner

The Ebola virus glycoprotein (EBOV-GP) forms GP-containing microvesicles, so-called virosomes, which are secreted from GP-expressing cells. However, determinants of GP-virosome release and their functionality are poorly understood. We characterized GP-mediated virosome formation and delineated the role of the antiviral factor tetherin (BST2, CD317) in this process. Residues in the EBOV-GP receptor-binding domain (RBD) promote GP-virosome secretion, while tetherin suppresses GP-virosomes by interactions involving the GP-transmembrane domain. Tetherin from multiple species interfered with GP-virosome release, and tetherin from the natural fruit bat reservoir showed the highest inhibitory activity. Moreover, analyses of GP from various ebolavirus strains, including the EBOV responsible for the West African epidemic, revealed the most efficient GP-virosome formation by highly pathogenic ebolaviruses. Finally, EBOV-GP-virosomes were immunomodulatory and acted as decoys for EBOV-neutralizing antibodies. Our results indicate that GP-virosome formation might be a determinant of EBOV immune evasion and pathogenicity, which is suppressed by tetherin.

Sex differences in inflammation, redox biology, mitochondria and autoimmunity

Autoimmune diseases are characterized by circulating antibodies and immune complexes directed against self-tissues that result in both systemic and organ-specific inflammation and pathology. Most autoimmune diseases occur more often in women than men. One exception is myocarditis, which is an inflammation of the myocardium that is typically caused by viral infections. Sex differences in the immune response and the role of the sex hormones estrogen and testosterone are well established based on animal models of autoimmune viral myocarditis as well as in mitochondrial function leading to reactive oxygen species production. RNA viruses like coxsackievirus B3, the primary cause of myocarditis in the US, activate the inflammasome through mitochondrial antiviral signaling protein located on the mitochondrial outer membrane. Toll-like receptor 4 and the inflammasome are the primary signaling pathways that increase inflammation during myocarditis, which is increased by testosterone. This review describes what is known about sex differences in inflammation, redox biology and mitochondrial function in the male-dominant autoimmune disease myocarditis and highlights gaps in the literature and future directions.

Collectins: Innate Immune Pattern Recognition Molecules

Collectins are collagen-containing C-type (calcium-dependent) lectins which are important pathogen pattern recognising innate immune molecules. Their primary structure is characterised by an N-terminal, triple-helical collagenous region made up of Gly-X-Y repeats, an a-helical coiled-coil trimerising neck region, and a C-terminal C-type lectin or carbohydrate recognition domain (CRD). Further oligomerisation of this primary structure can give rise to more complex and multimeric structures that can be seen under electron microscope. Collectins can be found in serum as well as in a range of tissues at the mucosal surfaces. Mannanbinding lectin can activate the complement system while other members of the collectin family are extremely versatile in recognising a diverse range of pathogens via their CRDs and bring about effector functions designed at the clearance of invading pathogens. These mechanisms include opsonisation, enhancement of phagocytosis, triggering superoxidative burst and nitric oxide production. Collectins can also potentiate the adaptive immune response via antigen presenting cells such as macrophages and dendritic cells through modulation of cytokines and chemokines, thus they can act as a link between innate and adaptive immunity. This chapter describes the structure-function relationships of collectins, their diverse functions, and their interaction with viruses, bacteria, fungi and parasites.

Dengue virus non-structural protein 1 activates the p38 MAPK pathway to decrease barrier integrity in primary human endothelial cells

Dengue virus (DENV) causes an estimated 390 million infections worldwide annually, with severe forms of disease marked by vascular leakage. Endothelial cells (EC) are directly responsible for vascular homeostasis and are highly responsive to circulating mediators but are not commonly infected. DENV encodes seven non-structural (NS) proteins; with only one of those, NS1, secreted from infected cells and accumulating in the blood of patients. NS1 has been implicated in the pathogenesis of vascular permeability, but the mechanism is not completely understood. Here we used primary endothelial cells and an array of in vitro approaches to study the effect of NS1 in disease-relevant human ECs. Confocal microscopy demonstrated rapid NS1 internalization by ECs into endosomes with accumulation over time. Transcriptomic and pathway analysis showed significant changes in functions associated with EC homeostasis and vascular permeability. Functional significance of this activation was assessed by trans-endothelial electrical resistance and showed that NS1 induced rapid and transient loss in EC barrier function within 3 h post-treatment. To understand the molecular mechanism by which NS1 induced EC activation, we evaluated the stress-sensing p38 MAPK pathway known to be directly involved in EC permeability and inflammation. WB analysis of NS1-stimulated ECs showed clear activation of p38 MAPK and downstream effectors MAPKAPK-2 and HSP27 with chemical inhibition of the p38 MAP kinase pathway restoring barrier function. Our results suggest that DENV NS1 may be involved in the pathogenesis of severe dengue by activating the p38 MAPK in ECs, promoting increased permeability that characterizes severe disease.

When Dendritic Cells Go Viral: The Role of Siglec-1 in Host Defense and Dissemination of Enveloped Viruses

Dendritic cells (DCs) are among the first cells that recognize incoming viruses at the mucosal portals of entry. Initial interaction between DCs and viruses facilitates cell activation and migration to secondary lymphoid tissues, where these antigen presenting cells (APCs) prime specific adaptive immune responses. Some viruses, however, have evolved strategies to subvert the migratory capacity of DCs as a way to disseminate infection systemically. Here we focus on the role of Siglec-1, a sialic acid-binding type I lectin receptor potently upregulated by type I interferons on DCs, that acts as a double edge sword, containing viral replication through the induction of antiviral immunity, but also favoring viral spread within tissues. Such is the case for distant enveloped viruses like human immunodeficiency virus (HIV)-1 or Ebola virus (EBOV), which incorporate sialic acid-containing gangliosides on their viral membrane and are effectively recognized by Siglec-1. Here we review how Siglec-1 is highly induced on the surface of human DCs upon viral infection, the way this impacts different antigen presentation pathways, and how enveloped viruses have evolved to exploit these APC functions as a potent dissemination strategy in different anatomical compartments.

Ebola Hemorrhagic Shock Syndrome-on-a-Chip

Ebola virus, for which we lack effective countermeasures, causes hemorrhagic fever in humans, with significant case fatality rates. Lack of experimental human models for Ebola hemorrhagic fever is a major obstacle that hinders the development of treatment strategies. Here, we model the Ebola hemorrhagic syndrome in a microvessel-on-a-chip system and demonstrate its applicability to drug studies. Luminal infusion of Ebola virus-like particles leads to albumin leakage from the engineered vessels. The process is mediated by the Rho/ROCK pathway and is associated with cytoskeleton remodeling. Infusion of Ebola glycoprotein (GP_1,2) generates a similar phenotype, indicating the key role of GP_1,2 in this process. Finally, we measured the potency of a recently developed experimental drug FX06 and a novel drug candidate, melatonin, in phenotypic rescue. Our study confirms the effects of FX06 and identifies melatonin as an effective, safe, inexpensive therapeutic option that is worth investigating in animal models and human trials.

The Roles of Ebola Virus Soluble Glycoprotein in Replication, Pathogenesis, and Countermeasure Development

Ebola virus (EBOV) is a highly lethal pathogen that has caused several outbreaks of severe hemorrhagic fever in humans since its emergence in 1976. The EBOV glycoprotein (GP_1,2) is the sole viral envelope protein and a major component of immunogenicity; it is encoded by the GP gene along with two truncated versions: soluble GP (sGP) and small soluble GP (ssGP). sGP is, in fact, the primary product of the GP gene, and it is secreted in abundance during EBOV infection. Since sGP shares large portions of its sequence with GP_1,2, it has been hypothesized that sGP may subvert the host immune response by inducing antibodies against sGP rather than GP_1,2. Several reports have shown that sGP plays multiple roles that contribute to the complex pathogenesis of EBOV. In this review, we focus on sGP and discuss its possible roles with regards to the pathogenesis of EBOV and the development of specific antiviral drugs.