Ebola virus glycoprotein directly triggers T lymphocyte death despite of the lack of infection

Synergistic effect of Toll-like receptor 2 ligands and alendronate on proinflammatory cytokine production in mouse macrophage-like RAW-ASC cells is accompanied by upregulation of MyD88 expression

OBJECTIVES

Toll-like receptors (TLRs) recognize whole cells or components of microorganisms. Alendronate (ALN) is an anti-bone-resorptive drug that has inflammatory side effects. The aim in this study was to examine whether ALN augments TLR2 ligand-induced proinflammatory cytokine production using mouse macrophage-like RAW264.7 cells transfected with murine apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) gene (hereafter, referred to as "RAW-ASC cells").

METHODS

RAW-ASC cells were pretreated with or without ALN and then incubated with or without TLR2 ligands. The levels of secreted mouse IL-1α, IL-1β, IL-6, and tumor necrosis factor-α (TNF-α) in culture supernatants and the activation of activator protein-1 (AP-1) or nuclear factor-κB (NF-κB) were measured using enzyme-linked immunosorbent assay (ELISA). The expressions of myeloid differentiation factor 88 (MyD88), caspase-11, nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3), ASC, NF-κB p65, and actin were analyzed via Western blotting. TLR2 expression was analyzed using flow cytometry.

RESULTS

ALN substantially upregulated the Pam3CSK4-induced release of IL-1α, IL-1β, IL-6, and TNF-α and MyD88 expression in RAW-ASC cells. ST-2825, a MyD88 inhibitor, inhibited the ALN-augmented release of these cytokines. Pretreatment with ALN augmented Pam3CSK4-induced NF-κB activation in RAW-ASC cells and upregulated AP-1 activation. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) S protein and ALN synergically upregulated the release of IL-1α, IL-1β, IL-6 and TNF-α in RAW-ASC cells.

CONCLUSIONS

Our findings suggest that ALN augments TLR2 ligand-induced proinflammatory cytokine production via the upregulation of MyD88 expression, and this augmentation is accompanied by the activation of NF-κB and AP-1 in RAW-ASC cells.

Ebola virus-induced eye sequelae: a murine model for evaluating glycoprotein-targeting therapeutics

BACKGROUND

Ebola virus disease (EVD) survivors experience ocular sequelae including retinal lesions, cataracts, and vision loss. While monoclonal antibodies targeting the Ebola virus glycoprotein (EBOV-GP) have shown promise in improving prognosis, their effectiveness in mitigating ocular sequelae remains uncertain.

METHODS

We developed and characterized a BSL-2-compatible immunocompetent mouse model to evaluate therapeutics targeting EBOV-GP by inoculating neonatal mice with vesicular stomatitis virus expressing EBOV-GP (VSV-EBOV). To examine the impact of anti-EBOV-GP antibody treatment on acute retinitis and ocular sequelae, VSV-EBOV-infected mice were treated with polyclonal antibodies or monoclonal antibody preparations with antibody-dependent cellular cytotoxicity (ADCC-mAb) or neutralizing activity (NEUT-mAb).

FINDINGS

Treatment with all anti-EBOV-GP antibodies tested dramatically reduced viremia and improved survival. Further, all treatments reduced the incidence of cataracts. However, NEUT-mAb alone or in combination with ADCC-mAb reduced viral load in the eyes, downregulated the ocular immune and inflammatory responses, and minimized retinal damage more effectively.

INTERPRETATION

Anti-EBOV-GP antibodies can improve survival among EVD patients, but improved therapeutics are needed to reduce life altering sequelae. This animal model offers a new platform to examine the acute and long-term effect of the virus in the eye and the relative impact of therapeutic candidates targeting EBOV-GP. Results indicate that even antibodies that improve systemic viral clearance and survival can differ in their capacity to reduce acute ocular inflammation, and long-term retinal pathology and corneal degeneration.

FUNDING

This study was partly supported by Postgraduate Research Fellowship Awards from ORISE through an interagency agreement between the US DOE and the US FDA.

Systems immunology of transcriptional responses to viral infection identifies conserved antiviral pathways across macaques and humans

Viral pandemics and epidemics pose a significant global threat. While macaque models of viral disease are routinely used, it remains unclear how conserved antiviral responses are between macaques and humans. Therefore, we conducted a cross-species analysis of transcriptomic data from over 6,088 blood samples from macaques and humans infected with one of 31 viruses. Our findings demonstrate that irrespective of primate or viral species, there are conserved antiviral responses that are consistent across infection phase (acute, chronic, or latent) and viral genome type (DNA or RNA viruses). Leveraging longitudinal data from experimental challenges, we identify virus-specific response kinetics such as host responses to Coronaviridae and Orthomyxoviridae infections peaking 1-3 days earlier than responses to Filoviridae and Arenaviridae viral infections. Our results underscore macaque studies as a powerful tool for understanding viral pathogenesis and immune responses that translate to humans, with implications for viral therapeutic development and pandemic preparedness.

Recent Advances in Therapeutic Approaches Against Ebola Virus Infection

BACKGROUND

Ebola virus (EBOV) is a genus of negative-strand RNA viruses belonging to the family Filoviradae that was first described in 1976 in the present-day Democratic Republic of the Congo. It has intermittently affected substantial human populations in West Africa and presents itself as a global health menace due to the high mortality rate of patients, high transmission rate, difficult patient management, and the emergence of complicated autoimmune disease-like conditions post-infection.

OBJECTIVE

EBOV or other EBOV-like species as a biochemical weapon pose a significant risk; hence, the need to develop both prophylactic and therapeutic medications to combat the virus is unquestionable.

METHODS

In this review work, we have compiled the literature pertaining to transmission, pathogenesis, immune response, and diagnosis of EBOV infection. We included detailed structural details of EBOV along with all the available therapeutics against EBOV disease. We have also highlighted current developments and recent advances in therapeutic approaches against Ebola virus disease (EVD).

DISCUSSION

The development of preventive vaccines against the virus is proving to be a successful effort as of now; however, problems concerning logistics, product stability, multi- dosing, and patient tracking are prominent in West Africa. Monoclonal antibodies that target EBOV proteins have also been developed and approved in the clinic; however, no small drug molecules that target these viral proteins have cleared clinical trials. An understanding of clinically approved vaccines and their shortcomings also serves an important purpose for researchers in vaccine design in choosing the right vector, antigen, and particular physicochemical properties that are critical for the vaccine's success against the virus across the world.

CONCLUSION

Our work brings together a comprehensive review of all available prophylactic and therapeutic medications developed and under development against the EBOV, which will serve as a guide for researchers in pursuing the most promising drug discovery strategies against the EBOV and also explore novel mechanisms of fighting against EBOV infection.

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.

Interplay of Ebola Virus With Immune Cells Leading to Their Death by Diverse Mechanisms

Inflammation and cytopenia are commonly observed during Ebola virus (EBOV) infection; however, mechanisms responsible for EBOV-induced cell death remain obscure. While apoptosis and necrosis are already identified as mechanisms of cell death induced by the virus, our study demonstrates that THP-1 monocytes and SupT1 T cells exposed to EBOV undergo pyroptosis and necroptosis, respectively, through a direct contact with EBOV, and also mediate pyroptosis or necroptosis of uninfected bystander cells via indirect effects associated with secreted soluble factors. These results emphasize novel aspects of interactions between EBOV and immune cell populations and provide a better understanding of the immunopathogenesis of EBOV disease.

Ebola Virus Infection Induces HCAR2 Expression Leading to Cell Death

Ebola virus (EBOV) induces cell death not only in infected permissive cells but also in nonpermissive, bystander cells by employing different mechanisms. Hydroxycarboxylic acid receptor 2 (HCAR2) has been reported to be involved in apoptotic cell death. We previously reported an increase in the expression of HCAR2-specific mRNA in EBOV-infected individuals with fatal outcomes. Here, we report that infection with an EBOV lacking the VP30 gene (EBOVΔVP30) results in the upregulation of HCAR2 mRNA expression in human hepatocyte Huh7.0 cells stably expressing VP30. Transient overexpression of HCAR2 reduced the viability of Huh7.0 cells and human embryonic kidney cells. Phosphatidylserine externalization and cell membrane permeabilization by HCAR2 overexpression was also observed. Interestingly, coexpression of HCAR2 with EBOV VP40 further reduced cell viability in transfected cells compared to HCAR2 coexpression with other viral proteins. Our data suggest that HCAR2 may contribute to EBOV-induced cell death.

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.

Ebola virus disrupts the inner blood-retinal barrier by induction of vascular endothelial growth factor in pericytes

Ebola virus (EBOV) causes severe hemorrhagic fever in humans with high mortality. In Ebola virus disease (EVD) survivors, EBOV persistence in the eyes may break through the inner blood-retinal barrier (iBRB), leading to ocular complications and EVD recurrence. However, the mechanism by which EBOV affects the iBRB remains unclear. Here, we used the in vitro iBRB model to simulate EBOV in retinal tissue and found that Ebola virus-like particles (EBO-VLPs) could disrupt the iBRB. Cytokine screening revealed that EBO-VLPs stimulate pericytes to secrete vascular endothelial growth factor (VEGF) to cause iBRB breakdown. VEGF downregulates claudin-1 to disrupt the iBRB. Ebola glycoprotein is crucial for VEGF stimulation and iBRB breakdown. Furthermore, EBO-VLPs caused iBRB breakdown by stimulating VEGF in rats. This study provides a mechanistic insight into that EBOV disrupts the iBRB, which will assist in developing new strategies to treat EBOV persistence in EVD survivors.

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.

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.

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.

RNA Viruses, Pregnancy and Vaccination: Emerging Lessons from COVID-19 and Ebola Virus Disease

Pathogenic viruses with an RNA genome represent a challenge for global human health since they have the tremendous potential to develop into devastating pandemics/epidemics. The management of the recent COVID-19 pandemic was possible to a certain extent only because of the strong foundations laid by the research on previous viral outbreaks, especially Ebola Virus Disease (EVD). A clear understanding of the mechanisms of the host immune response generated upon viral infections is a prime requisite for the development of new therapeutic strategies. Hence, we present here a comparative study of alterations in immune response upon SARS-CoV-2 and Ebola virus infections that illustrate many common features. Vaccination and pregnancy are two important aspects that need to be studied from an immunological perspective. So, we summarize the outcomes and immune responses in vaccinated and pregnant individuals in the context of COVID-19 and EVD. Considering the significance of immunomodulatory approaches in combating both these diseases, we have also presented the state of the art of such therapeutics and prophylactics. Currently, several vaccines against these viruses have been approved or are under clinical trials in various parts of the world. Therefore, we also recapitulate the latest developments in these which would inspire researchers to look for possibilities of developing vaccines against many other RNA viruses. We hope that the similar aspects in COVID-19 and EVD open up new avenues for the development of pan-viral therapies.

Hyperinflammation, apoptosis, and organ damage

The cytokine storm (CS) in hyperinflammation is characterized by high levels of cytokines, extreme activation of innate as well as adaptive immune cells and initiation of apoptosis. High levels of apoptotic cells overwhelm the proper recognition and removal system of these cells. Phosphatidylserine on the apoptotic cell surface, which normally provides a recognition signal for removal, becomes a target for hemostatic proteins and secretory phospholipase A2. The dysregulation of these normal pathways in hemostasis and the inflammasome result in a prothrombotic state, cellular death, and end-organ damage. In this review, we provide the argument that this imbalance in recognition and removal is a common denominator regardless of the inflammatory trigger. The complex reaction of the immune defense system in hyperinflammation leads to self-inflicted damage. This common endpoint may provide additional options to monitor the progression of the inflammatory syndrome, predict severity, and may add to possible treatment strategies.

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.

Transient Liver Damage and Hemolysis Are Associated With an Inhibition of Ebola Virus Glycoprotein-Specific Antibody Response and Lymphopenia

Numerous studies have demonstrated the importance of the adaptive immunity for survival following Ebola virus (EBOV) infection. To evaluate the contribution of tissue damage to EBOV-induced immune suppression, acute liver damage or hemolysis, 2 symptoms associated with lethal EBOV infection, were chemically induced in vaccinated mice. Results show that either liver damage or hemolysis was sufficient to inhibit the host humoral response against EBOV glycoprotein and to drastically reduce the level of circulating T cells. This study thus provides a possible mechanism for the limited specific antibody production and lymphopenia in individuals with lethal hemorrhagic fever infections.

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.

On the possibility of oscillating in the Ebola virus dynamics and investigating the effect of the lifetime of T lymphocytes

Ebola virus (EBOV) targets immune cells and tries to inactivate dendritic cells and interferon molecules to continue its replication process. Since EBOV detailed mechanism has not been identified so far, it would be useful to understand the growth and spread of EBOV dynamics based on mathematical methods and simulation approaches. Computational approaches such as Cellular Automata (CA) have the advantage of simplicity over solving complicated differential equations. The spread of Ebola virus in lymph nodes is studied using a simplified Cellular Automata model with only four parameters. In addition to considering healthy and infected cells, this paper also considers T lymphocytes as well as cell movement ability during the simulation in order to investigate different scenarios in the dynamics of an EBOV system. It is shown that the value of the probability of death of T cells affects the number of infected cells significantly in the steady-state. For a special case of parameters set, the system shows oscillating dynamics. The results were in good agreement with an ordinary differential equation-based model which indicated CA method in combination with experimental discoveries could help biologists find out more about the EBOV mechanism and hopefully to control the disease.

NLRP3 Inflammasome Activation is a Prognostic Marker of Recovery in HEV-Infected Patients

Hepatitis E contributes to 3.3 million acute hepatitis cases worldwide with 30% mortality in pregnant women. Pathogenesis of Hepatitis E is complex; thus, the present study was aimed at inflammasomes and associated cytokines in the immunopathogenesis of viral hepatitis E. PBMCs were isolated from 45 HEV IgM/HEV RNA-positive AVH/ALF and 19 healthy individuals and processed for mRNA expressions of NLRs, RLRs, and cytokines. PBMCs were cultured and stimulated with HEV-pORF-2 peptide in vitro for mRNA expression by RT-PCR and cytokines levels in serum/culture supernatant by ELISA. siRNA transfection and post-silencing effect in AVH PBMCs were also assessed by NLRP3 gene expression and IL-1β and IL-18 levels by ELISA. The results demonstrated high viral load in ALF than AVH cases. mRNA expression of NLRP3 in AVH patients was found to be positively correlated with IL-18 (r = 0.74) and IL-1β (r = 0.68); P < 0.0001***. Significant levels of serum IL-1β and IL-18 cytokines were observed in AVH as compared to ALF patients. The levels of IL-1β in the culture supernatant in mock and stimulated conditions were significantly higher in AVH than in ALF patients. Significant downregulation in NLRP3 gene expression was correlated with the reduced levels of IL-1β and IL-18 cytokines in NLRP3-siRNA-transfected PBMCs. This study highlighted the significance of upregulated NLRP3 inflammasome leading to increased production of IL-18 and IL-1β cytokines in sera of AVH patients. Thus, it indicated the role of Th1 response acting through the NLRP3 pathway which might have been helpful in the recovery of AVH patients. These promising results open multiple treatment avenues where specific inhibitors can be designed to modulate the progress of disease and its pathogenicity.

Categorizing sequences of concern by function to better assess mechanisms of microbial pathogenesis

To identify sequences with a role in microbial pathogenesis, we assessed the adequacy of their annotation by existing controlled vocabularies and sequence databases. Our goal was to regularize descriptions of microbial pathogenesis for improved integration with bioinformatic applications. Here, we review the challenges of annotating sequences for pathogenic activity. We relate the categorization of more than 2,750 sequences of pathogenic microbes through a controlled vocabulary called Functions of Sequences of Concern (FunSoCs). These allow for an ease of description by both humans and machines. We provide a subset of 220 fully annotated sequences in the supplemental material as examples. The use of this compact (∼30 terms), controlled vocabulary has potential benefits for research in microbial genomics, public health, biosecurity, biosurveillance, and the characterization of new and emerging pathogens.

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.

Interferon-Induced HERC5 Inhibits Ebola Virus Particle Production and Is Antagonized by Ebola Glycoprotein

Survival following Ebola virus (EBOV) infection correlates with the ability to mount an early and robust interferon (IFN) response. The host IFN-induced proteins that contribute to controlling EBOV replication are not fully known. Among the top genes with the strongest early increases in expression after infection in vivo is IFN-induced HERC5. Using a transcription- and replication-competent VLP system, we showed that HERC5 inhibits EBOV virus-like particle (VLP) replication by depleting EBOV mRNAs. The HERC5 RCC1-like domain was necessary and sufficient for this inhibition and did not require zinc finger antiviral protein (ZAP). Moreover, we showed that EBOV (Zaire) glycoprotein (GP) but not Marburg virus GP antagonized HERC5 early during infection. Our data identify a novel ‘protagonist–antagonistic’ relationship between HERC5 and GP in the early stages of EBOV infection that could be exploited for the development of novel antiviral therapeutics.

Transcriptional Analysis of Infection With Early or Late Isolates From the 2013-2016 West Africa Ebola Virus Epidemic Does Not Suggest Attenuated Pathogenicity as a Result of Genetic Variation

The 2013-2016 West Africa Ebola virus (EBOV) epidemic caused by the EBOV-Makona isolate is the largest and longest recorded to date. It incurred over 28,000 infections and ∼11,000 deaths. Early in this epidemic, several mutations in viral glycoprotein (A82V), nucleoprotein (R111C), and polymerase L (D759G) emerged and stabilized. In vitro studies of these new EBOV-Makona isolates showed enhanced fitness and viral replication capacity. However, in vivo studies in mice and rhesus macaques did not provide any evidence of enhanced viral fitness or shedding. Infection with late isolates carrying or early isolates lacking (early) these mutations resulted in uniformly lethal disease in nonhuman primates (NHPs), albeit with slightly delayed kinetics with late isolates. The recent report of a possible reemergence of EBOV from a persistent infection in a survivor of the epidemic highlights the urgency for understanding the impact of genetic variation on EBOV pathogenesis. However, potential molecular differences in host responses remain unknown. To address this gap in knowledge, we conducted the first comparative analysis of the host responses to lethal infection with EBOV-Mayinga and EBOV-Makona isolates using bivariate, longitudinal, regression, and discrimination transcriptomic analyses. Our analysis shows a conserved core of differentially expressed genes (DEGs) involved in antiviral defense, immune cell activation, and inflammatory processes in response to EBOV-Makona and EBOV-Mayinga infections. Additionally, EBOV-Makona and EBOV-Mayinga infections could be discriminated based on the expression pattern of a small subset of genes. Transcriptional responses to EBOV-Makona isolates that emerged later during the epidemic, specifically those from Mali and Liberia, lacked signatures of profound lymphopenia and excessive inflammation seen following infection with EBOV-Mayinga and early EBOV-Makona isolate C07. Overall, these findings provide novel insight into the mechanisms underlying the lower case fatality rate (CFR) observed with EBOV-Makona compared to EBOV-Mayinga.

Distinct transcriptional responses to fatal Ebola virus infection in cynomolgus and rhesus macaques suggest species-specific immune responses

Ebola virus (EBOV) is a negative single-stranded RNA virus within the Filoviridae family and the causative agent of Ebola virus disease (EVD). Nonhuman primates (NHPs), including cynomolgus and rhesus macaques, are considered the gold standard animal model to interrogate mechanisms of EBOV pathogenesis. However, despite significant genetic similarity (>90%), NHP species display different clinical presentation following EBOV infection, notably a ∼1-2 days delay in disease progression. Consequently, evaluation of therapeutics is generally conducted in rhesus macaques, whereas cynomolgus macaques are utilized to determine efficacy of preventative treatments, notably vaccines. This observation is in line with reported differences in disease severity and host responses between these two NHP following infection with simian varicella virus, influenza A and SARS-CoV-2. However, the molecular underpinnings of these differential outcomes following viral infections remain poorly defined. In this study, we compared published transcriptional profiles obtained from cynomolgus and rhesus macaques infected with the EBOV-Makona Guinea C07 using bivariate and regression analyses to elucidate differences in host responses. We report the presence of a shared core of differentially expressed genes (DEGs) reflecting EVD pathology, including aberrant inflammation, lymphopenia, and coagulopathy. However, the magnitudes of change differed between the two macaque species. These findings suggest that the differential clinical presentation of EVD in these two species is mediated by altered transcriptional responses.

Antibody responses to filovirus infections in humans: protective or not?

Disease outbreaks caused by Ebola virus and other filoviruses highlight the urgent need for an in-depth understanding of the role of antibody responses in recovery. In this Personal View we aim to discuss the controversial biological role of antibodies during natural filovirus infections in humans. Survival during natural human filovirus infections correlates with the magnitude of the process of antibodies binding to the filovirus glycoprotein and neutralising the virus. Despite the severity of the disease, highly potent monoclonal antibodies have been isolated from survivors of natural filovirus infections, suggesting that the magnitude of the antibody response is insufficient for prevention of severe disease. Unlike natural infections, filovirus vaccines, which express the viral glycoprotein, do induce protective concentrations of antibodies, albeit only when administered at very high doses. Multiple mechanisms by which filoviruses can delay and reduce the antibody response have been identified in the past decade. Furthermore, subneutralising antibody concentrations have been shown to enhance filovirus infections of immune cells bearing Fc receptors. Understanding the role of antibody responses during natural filovirus infections is important for the development of safe and potent vaccines and antibody-based treatments.

Longitudinal in vivo imaging of acute neuropathology in a monkey model of Ebola virus infection

Ebola virus (EBOV) causes neurological symptoms yet its effects on the central nervous system (CNS) are not well-described. Here, we longitudinally assess the acute effects of EBOV on the brain, using quantitative MR-relaxometry, 18F-Fluorodeoxyglucose PET and immunohistochemistry in a monkey model. We report blood-brain barrier disruption, likely related to high cytokine levels and endothelial viral infection, with extravasation of fluid, Gadolinium-based contrast material and albumin into the extracellular space. Increased glucose metabolism is also present compared to the baseline, especially in the deep gray matter and brainstem. This regional hypermetabolism corresponds with mild neuroinflammation, sporadic neuronal infection and apoptosis, as well as increased GLUT3 expression, consistent with increased neuronal metabolic demands. Neuroimaging changes are associated with markers of disease progression including viral load and cytokine/chemokine levels. Our results provide insight into the pathophysiology of CNS involvement with EBOV and may help assess vaccine/treatment efficacy in real time.

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.

Investigating the Interaction between Negative Strand RNA Viruses and Their Hosts for Enhanced Vaccine Development and Production

The current pandemic has highlighted the ever-increasing risk of human to human spread of zoonotic pathogens. A number of medically-relevant zoonotic pathogens are negative-strand RNA viruses (NSVs). NSVs are derived from different virus families. Examples like Ebola are known for causing severe symptoms and high mortality rates. Some, like influenza, are known for their ease of person-to-person transmission and lack of pre-existing immunity, enabling rapid spread across many countries around the globe. Containment of outbreaks of NSVs can be difficult owing to their unpredictability and the absence of effective control measures, such as vaccines and antiviral therapeutics. In addition, there remains a lack of essential knowledge of the host–pathogen response that are induced by NSVs, particularly of the immune responses that provide protection. Vaccines are the most effective method for preventing infectious diseases. In fact, in the event of a pandemic, appropriate vaccine design and speed of vaccine supply is the most critical factor in protecting the population, as vaccination is the only sustainable defense. Vaccines need to be safe, efficient, and cost-effective, which is influenced by our understanding of the host–pathogen interface. Additionally, some of the major challenges of vaccines are the establishment of a long-lasting immunity offering cross protection to emerging strains. Although many NSVs are controlled through immunisations, for some, vaccine design has failed or efficacy has proven unreliable. The key behind designing a successful vaccine is understanding the host–pathogen interaction and the host immune response towards NSVs. In this paper, we review the recent research in vaccine design against NSVs and explore the immune responses induced by these viruses. The generation of a robust and integrated approach to development capability and vaccine manufacture can collaboratively support the management of outbreaking NSV disease health risks.

COVID-19 and Toll-Like Receptor 4 (TLR4): SARS-CoV-2 May Bind and Activate TLR4 to Increase ACE2 Expression, Facilitating Entry and Causing Hyperinflammation

Causes of mortality from COVID-19 include respiratory failure, heart failure, and sepsis/multiorgan failure. TLR4 is an innate immune receptor on the cell surface that recognizes pathogen-associated molecular patterns (PAMPs) including viral proteins and triggers the production of type I interferons and proinflammatory cytokines to combat infection. It is expressed on both immune cells and tissue-resident cells. ACE2, the reported entry receptor for SARS-CoV-2, is only present on ~1-2% of the cells in the lungs or has a low pulmonary expression, and recently, the spike protein has been proposed to have the strongest protein-protein interaction with TLR4. Here, we review and connect evidence for SARS-CoV-1 and SARS-CoV-2 having direct and indirect binding to TLR4, together with other viral precedents, which when combined shed light on the COVID-19 pathophysiological puzzle. We propose a model in which the SARS-CoV-2 spike glycoprotein binds TLR4 and activates TLR4 signalling to increase cell surface expression of ACE2 facilitating entry. SARS-CoV-2 also destroys the type II alveolar cells that secrete pulmonary surfactants, which normally decrease the air/tissue surface tension and block TLR4 in the lungs thus promoting ARDS and inflammation. Furthermore, SARS-CoV-2-induced myocarditis and multiple-organ injury may be due to TLR4 activation, aberrant TLR4 signalling, and hyperinflammation in COVID-19 patients. Therefore, TLR4 contributes significantly to the pathogenesis of SARS-CoV-2, and its overactivation causes a prolonged or excessive innate immune response. TLR4 appears to be a promising therapeutic target in COVID-19, and since TLR4 antagonists have been previously trialled in sepsis and in other antiviral contexts, we propose the clinical trial testing of TLR4 antagonists in the treatment of severe COVID-19. Also, ongoing clinical trials of pulmonary surfactants in COVID-19 hold promise since they also block TLR4.

Single-Cell Profiling of Ebola Virus Disease In Vivo Reveals Viral and Host Dynamics

Ebola virus (EBOV) causes epidemics with high mortality yet remains understudied due to the challenge of experimentation in high-containment and outbreak settings. Here, we used single-cell transcriptomics and CyTOF-based single-cell protein quantification to characterize peripheral immune cells during EBOV infection in rhesus monkeys. We obtained 100,000 transcriptomes and 15,000,000 protein profiles, finding that immature, proliferative monocyte-lineage cells with reduced antigen-presentation capacity replace conventional monocyte subsets, while lymphocytes upregulate apoptosis genes and decline in abundance. By quantifying intracellular viral RNA, we identify molecular determinants of tropism among circulating immune cells and examine temporal dynamics in viral and host gene expression. Within infected cells, EBOV downregulates STAT1 mRNA and interferon signaling, and it upregulates putative pro-viral genes (e.g., DYNLL1 and HSPA5), nominating pathways the virus manipulates for its replication. This study sheds light on EBOV tropism, replication dynamics, and elicited immune response and provides a framework for characterizing host-virus interactions under maximum containment.

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.

HER2-mediated enhancement of Ebola virus entry

Multiple cell surface molecules including TAM receptors (TYRO3, AXL, and MERTK), a family of tyrosine kinase receptors, can serve as attachment receptors for Ebola virus (EBOV) entry into cells. The interaction of these receptors with EBOV particles is believed to trigger the initial internalization events that lead to macropinocytosis. However, the details of how these interactions lead to EBOV internalization have yet to be elucidated. Here, we screened receptor tyrosine kinase (RTK) inhibitors for anti-EBOV activity by using our previously established biologically contained Ebola virus that lacks the VP30 gene (EBOVΔVP30) and identified several RTKs, including human epidermal growth factor receptor 2 (HER2), as potential targets of anti-EBOV inhibitors and as novel host factors that have a role in EBOV infection. Of these identified RTKs, it was only HER2 whose knockdown by siRNAs impaired EBOVΔVP30-induced AKT1 phosphorylation, an event that is required for AKT1 activation and subsequent macropinocytosis. Stable expression of HER2 resulted in constitutive activation of AKT1, resulting in the enhancement of EBOVΔVP30 growth, EBOV GP-mediated entry, and macropinocytosis. Moreover, we found that HER2 interacts with the TAM receptors, and in particular forms a complex with TYRO3 and EBOVΔVP30 particles on the cell surface. Interestingly, HER2 was required for EBOVΔVP30-induced TYRO3 and AKT1 activation, but the other TAM receptors (TYRO3 and MERTK) were not essential for EBOVΔVP30-induced HER2 and AKT1 activation. Our findings demonstrate that HER2 plays an important role in EBOV entry and provide novel insights for the development of therapeutics against the virus.

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.

Hematological manifestations of COVID-19

The emergence of the Coronavirus Disease -19 (COVID-19) pandemic, has had a tremendous global impact, resulting in substantial morbidity and mortality worldwide and especially in the United States, where nearly one third of the cases are located. Although involvement of the lower respiratory track accounts for most of the morbidity and mortality seen, the virus involves several organ systems and the syndrome exhibits clinical diversity with a wide range of symptoms and manifestations. The involvement of elements of the hematopoietic system is prominent in severe cases and associated with poor outcomes and mortality. Lymphopenia, leukopenia, thrombocytopenia, disseminated intravascular coagulation, and a prothrombotic state are common manifestations of COVID-19 and have important treatment and prognostic implications. Better understanding of the mechanisms of the pathophysiology of COVID-19-induced hematological abnormalities may ultimately result in better ways to treat them and decrease the associated morbidity and mortality.

Immunologic timeline of Ebola virus disease and recovery in humans

A complete understanding of human immune responses to Ebola virus infection is limited by the availability of specimens and the requirement for biosafety level 4 (BSL-4) containment. In an effort to bridge this gap, we evaluated cryopreserved PBMCs from 4 patients who survived Ebola virus disease (EVD) using an established mass cytometry antibody panel to characterize various cell populations during both the acute and convalescent phases. Acute loss of nonclassical monocytes and myeloid DCs, especially CD1c+ DCs, was noted. Classical monocyte proliferation and CD38 upregulation on plasmacytoid DCs coincided with declining viral load. Unsupervised analysis of cell abundance demonstrated acute declines in monocytic, NK, and T cell populations, but some populations, many of myeloid origin, increased in abundance during the acute phase, suggesting emergency hematopoiesis. Despite cell losses during the acute phase, upregulation of Ki-67 correlated with recovery of cell populations over time. These data provide insights into the human immune response during EVD.

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.

N-Glycans Mediate the Ebola Virus-GP1 Shielding of Ligands to Immune Receptors and Immune Evasion

The Ebola Virus (EBOV) glycoprotein (GP) sterically shields cell-membrane ligands to immune receptors such as human leukocyte antigen class-1 (HLA-I) and MHC class I polypeptide-related sequence A (MICA), thus mediating immunity evasion. It was suggested that the abundant N-glycosylation of the EBOV-GP is involved in this steric shielding. We aimed to characterize (i) the GP N-glycosylation sites contributing to the shielding, and (ii) the effect of mutating these sites on immune subversion by the EBOV-GP. The two highly glycosylated domains of GP are the mucin-like domain (MLD) and the glycan cap domain (GCD) with three and six N-glycosylation sites, respectively. We mutated the N-glycosylation sites either in MLD or in GCD or in both domains. We showed that the glycosylation sites in both the MLD and GCD domains contribute to the steric shielding. This was shown for the steric shielding of either HLA-I or MICA. We then employed the fluorescence resonance energy transfer (FRET) method to measure the effect of N-glycosylation site removal on the distance in the cell membrane between the EBOV-GP and HLA-I (HLA.A^*0201 allele). We recorded high FRET values for the interaction of CFP-fused HLA.A^*0201 and YFP-fused EBOV-GP, demonstrating the very close distance (<10 nm) between these two proteins on the cell membrane of GP-expressing cells. The co-localization of HLA-I and Ebola GP was unaffected by the disruption of steric shielding, as the removal of N-glycosylation sites on Ebola GP revealed similar FRET values with HLA-I. However, these mutations directed to N-glycosylation sites had restored immune cell function otherwise impaired due to steric shielding over immune cell ligands by WT Ebola GP. Overall, we showed that the GP-mediated steric shielding aimed to impair immune function is facilitated by the N-glycans protruding from its MLD and GCD domains, but these N-glycans are not controlling the close distance between GP and its shielded proteins.

Utility of primary cells to examine NPC1 receptor expression in Mops condylurus, a potential Ebola virus reservoir

The significance of the integral membrane protein Niemann-Pick C1 (NPC1) in the ebolavirus entry process has been determined using various cell lines derived from humans, non-human primates and fruit bats. Fruit bats have long been purported as the potential reservoir host for ebolaviruses, however several studies provide evidence that Mops condylurus, an insectivorous microbat, is also an ebolavirus reservoir. NPC1 receptor expression in the context of ebolavirus replication in microbat cells remains unstudied.

In order to study Ebola virus (EBOV) cellular entry and replication in M. condylurus, we derived primary and immortalized cell cultures from 12 different organs. The NPC1 receptor expression was characterized by confocal microscopy and flow cytometry comparing the expression levels of M. condylurus primary and immortalized cells, HeLa cells, human embryonic kidney cells and cells from a European microbat species. EBOV replication kinetics was studied for four representative cell cultures using qRT-PCR. The aim was to elucidate the suitability of primary and immortalized cells from different tissues for studying NPC1 receptor expression levels and their potential influence on EBOV replication.

The NPC1 receptor expression level in M. condylurus primary cells differed depending on the organ they were derived from and was for most cell types significantly lower than in human cell lines. Immortalized cells showed for most cell types higher expression levels than their corresponding primary cells. Concluding from our infection experiments with EBOV we suggest a potential correlation between NPC1 receptor expression level and virus replication rate in vitro.

Although there have been Ebola virus (EBOV) outbreaks for more than 40 years, the animal natural reservoir that maintains this virus in nature has not been identified. Viruses and their respective reservoirs coevolve over millions of years, often without causing diseases in the reservoir itself. Upon entering a new host, infection can have devastating consequences, as in the case of EBOV. To gain entry into cells prior to replication, all ebolaviruses utilize the cellular receptor Niemann-Pick C1 (NPC1). In this study the authors focus their work on the Angolan free-tailed bat (Mops condylurus) as a potential reservoir for EBOV. Cells from various organs of this bat were isolated in culture and tested for the presence of NPC1. Most bat cell types had a lower amount of NPC1 compared to the tested human cells. These bat cells were also less efficiently infected by EBOV, indicating adaptation to EBOV. These results suggest low levels of virus replication in the respective tissues of M. condylurus and might be indicative of a virus-natural reservoir relationship.

IL-4/IL-13 polarization of macrophages enhances Ebola virus glycoprotein-dependent infection

BACKGROUND

Ebolavirus (EBOV) outbreaks, while sporadic, cause tremendous morbidity and mortality. No therapeutics or vaccines are currently licensed; however, a vaccine has shown promise in clinical trials. A critical step towards development of effective therapeutics is a better understanding of factors that govern host susceptibility to this pathogen. As macrophages are an important cell population targeted during virus replication, we explore the effect of cytokine polarization on macrophage infection.

METHODS/MAIN FINDINGS

We utilized a BSL2 EBOV model virus, infectious, recombinant vesicular stomatitis virus encoding EBOV glycoprotein (GP) (rVSV/EBOV GP) in place of its native glycoprotein. Macrophages polarized towards a M2-like anti-inflammatory state by combined IL-4 and IL-13 treatment were more susceptible to rVSV/EBOV GP, but not to wild-type VSV (rVSV/G), suggesting that EBOV GP-dependent entry events were enhanced by these cytokines. Examination of RNA expression of known surface receptors that bind and internalize filoviruses demonstrated that IL-4/IL-13 stimulated expression of the C-type lectin receptor DC-SIGN in human macrophages and addition of the competitive inhibitor mannan abrogated IL-4/IL-13 enhanced infection. Two murine DC-SIGN-like family members, SIGNR3 and SIGNR5, were upregulated by IL-4/IL-13 in murine macrophages, but only SIGNR3 enhanced virus infection in a mannan-inhibited manner, suggesting that murine SIGNR3 plays a similar role to human DC-SIGN. In vivo IL-4/IL-13 administration significantly increased virus-mediated mortality in a mouse model and transfer of ex vivo IL-4/IL-13-treated murine peritoneal macrophages into the peritoneal cavity of mice enhanced pathogenesis.

SIGNIFICANCE

These studies highlight the ability of macrophage polarization to influence EBOV GP-dependent virus replication in vivo and ex vivo, with M2a polarization upregulating cell surface receptor expression and thereby enhancing virus replication. Our findings provide an increased understanding of the host factors in macrophages governing susceptibility to filoviruses and identify novel murine receptors mediating EBOV entry.

Human labour is associated with altered regulatory T cell function and maternal immune activation

During human pregnancy, regulatory T cell (T_reg ) function is enhanced and immune activation is repressed allowing the growth and development of the feto-placental unit. Here, we have investigated whether human labour is associated with a reversal of the pregnancy-induced changes in the maternal immune system. We tested the hypothesis that human labour is associated with a decline in T_reg function, specifically their ability to modulate Toll-like receptor (TLR)-induced immune responses. We studied the changes in cell number, activation status and functional behaviour of peripheral blood, myometrial (myoMC) and cord blood mononuclear cells (CBMC) with the onset of labour. We found that T_reg function declines and that T_reg cellular targets change with labour onset. The changes in T_reg function were associated with increased activation of myoMC, assessed by their expression of major histocompatibility complex (MHC) class II molecules and CBMC inflammatory cells. The innate immune system showed increased activation, as shown by altered monocyte and neutrophil cell phenotypes, possibly to be ready to respond to microbial invasion after birth or to contribute to tissue remodelling. Our results highlight changes in the function of the adaptive and innate immune systems that may have important roles in the onset of human labour.

Ebola virus-mediated T-lymphocyte depletion is the result of an abortive infection

Ebola virus (EBOV) infections are characterized by a pronounced lymphopenia that is highly correlative with fatalities. However, the mechanisms leading to T-cell depletion remain largely unknown. Here, we demonstrate that both viral mRNAs and antigens are detectable in CD4⁺ T cells despite the absence of productive infection. A protein phosphatase 1 inhibitor, 1E7-03, and siRNA-mediated suppression of viral antigens were used to demonstrate de novo synthesis of viral RNAs and antigens in CD4⁺ T cells, respectively. Cell-to-cell fusion of permissive Huh7 cells with non-permissive Jurkat T cells impaired productive EBOV infection suggesting the presence of a cellular restriction factor. We determined that viral transcription is partially impaired in the fusion T cells. Lastly, we demonstrate that exposure of T cells to EBOV resulted in autophagy through activation of ER-stress related pathways. These data indicate that exposure of T cells to EBOV results in an abortive infection, which likely contributes to the lymphopenia observed during EBOV infections.

Lymphopenia is a common characteristic of the disease caused by EBOV. We determined that despite the apparent lack of productive infection, EBOV is capable of entering T cells and producing both viral RNAs and proteins. Furthermore, we demonstrate that EBOV causes an abortive infection in T cells due to the presence of a cellular restriction factor. The abortive infection was associated with cell death following ER-stress induced autophagy. Collectively, these findings suggest that abortive infection in T cells is likely to contribute to lymphopenia during Ebola virus disease, which is uniformly linked with the severity of the disease. All EBOV vaccine candidates utilize GP as the sole antigen inducing a protective antibody response and in some clinical trials were shown to induce adverse side effects. The present study suggests that these effects can be associated with GP, which may lead to abortive infection of the vaccine construct in T cells contributing to the inflammatory response to the vaccines.

The Induction of IL-1β Secretion Through the NLRP3 Inflammasome During Ebola Virus Infection

The inflammasome is part of the innate immune system that regulates the secretion of proinflammatory cytokines such as interleukin-1β (IL-1β). Ebola virus (EBOV) infection of monocytes and macrophages (primary target cells early during infection) leads to the production of proinflammatory cytokines; however, the mechanism behind the activation and release of these cytokines is not fully understood. Here, we demonstrate that EBOV infection leads to the activation of the NLRP3 inflammasome and the subsequent secretion of IL-1β and IL-18. This process is dependent on protease caspase-1, a component of the NLRP3 inflammasome complex, but is independent of virus replication. These findings may lead to the development of novel drugs that impede the pathogenesis of EBOV infection.

Ebola Virus Shed Glycoprotein Triggers Differentiation, Infection, and Death of Monocytes Through Toll-Like Receptor 4 Activation

A better understanding of the mechanisms used by Ebola virus to disable the host immune system and spread the infection are of great importance for development of new therapeutic strategies. We demonstrate that treatment of monocytic cells with Ebola virus shed glycoprotein (GP) promotes their differentiation resulting in increased infection and cell death. The effects were inhibited by blocking Toll-like receptor 4 pathway. In addition, high levels of shed GP were detected in supernatants of cells treated with Ebola vaccines. This study highlights the role of shed GP in Ebola pathogenesis and also in adverse effects associated with Ebola vaccines.

Role of Transmembrane Protein 16F in the Incorporation of Phosphatidylserine Into Budding Ebola Virus Virions

Viral apoptotic mimicry, which is defined by exposure of phosphatidylserine (PtdSer) into the outer leaflet of budding enveloped viruses, increases viral tropism, infectivity and promotes immune evasion. Here, we report that the calcium (Ca2+)-dependent scramblase, transmembrane protein 16F (TMEM16F), is responsible for the incorporation of PtdSer into virion membranes during Ebola virus infection. Infection of Huh7 cells with Ebola virus resulted in a pronounced increase in plasma membrane-associated PtdSer, which was demonstrated to be dependent on TMEM16F function. Analysis of virions using imaging flow cytometry revealed that short hairpin RNA-mediated down-regulation of TMEM16F function directly reduced virion-associated PtdSer. Taken together, these studies demonstrate that TMEM16F is a central cellular factor in the exposure of PtdSer in the outer leaflet of viral membranes.

Dynamic changes of lymphocyte counts in adult patients with severe pandemic H1N1 influenza A

Background

Lymphopenia has been observed in severe pandemic influenza A/H1N1 in developed countries. However, data from developing countries are rare and dynamic change of lymphocyte counts in severe pandemic influenza A/H1N1 is scarcely reported. This study aimed to observe change of lymphocyte counts in patients with severe pandemic influenza A/H1N1 and to investigate the correlation of lymphopenia and severe pandemic influenza A/H1N1.

Methods

We retrospectively analyzed the white blood cell counts and differentials and other clinical data in 21 hospitalized patients with severe pandemic influenza A/H1N1 confirmed by reverse-transcription PCR during 2009 and 2010.

Results

All patients, except two cases with bacterial co-infections, had normal or reduced white blood cell counts. Seventeen (81.0%) patients had decreased lymphocyte proportions (<20%) and counts (<0.8 × 10⁹/L), with the lowest value of 1.2% and 0.1 × 10⁹/L respectively. A patient with nosocomial infection of influenza A/H1N1 showed that lymphopenia occurred on the first day of illness. Lymphocyte proportions and absolute counts returned to normal or slightly higher than normal in 16 of the 17 patients within 2–3 weeks after the disease onset.

Conclusions

Lymphopenia along with other clinical parameters may be helpful in early differential diagnosis of severe pandemic influenza A/H1N1.

Extracellular Vesicles and Ebola Virus: A New Mechanism of Immune Evasion

Ebola virus (EBOV) disease can result in a range of symptoms anywhere from virtually asymptomatic to severe hemorrhagic fever during acute infection. Additionally, spans of asymptomatic persistence in recovering survivors is possible, during which transmission of the virus may occur. In acute infection, substantial cytokine storm and bystander lymphocyte apoptosis take place, resulting in uncontrolled, systemic inflammation in affected individuals. Recently, studies have demonstrated the presence of EBOV proteins VP40, glycoprotein (GP), and nucleoprotein (NP) packaged into extracellular vesicles (EVs) during infection. EVs containing EBOV proteins have been shown to induce apoptosis in recipient immune cells, as well as contain pro-inflammatory cytokines. In this manuscript, we review the current field of knowledge on EBOV EVs including the mechanisms of their biogenesis, their cargo and their effects in recipient cells. Furthermore, we discuss some of the effects that may be induced by EBOV EVs that have not yet been characterized and highlight the remaining questions and future directions.

T-Cell Response to Viral Hemorrhagic Fevers

Viral hemorrhagic fevers (VHF) are a group of clinically similar diseases that can be caused by enveloped RNA viruses primarily from the families Arenaviridae, Filoviridae, Hantaviridae, and Flaviviridae. Clinically, this group of diseases has in common fever, fatigue, dizziness, muscle aches, and other associated symptoms that can progress to vascular leakage, bleeding and multi-organ failure. Most of these viruses are zoonotic causing asymptomatic infections in the primary host, but in human beings, the infection can be lethal. Clinical and experimental evidence suggest that the T-cell response is needed for protection against VHF, but can also cause damage to the host, and play an important role in disease pathogenesis. Here, we present a review of the T-cell immune responses to VHF and insights into the possible ways to improve counter-measures for these viral agents.

The role of mononuclear phagocytes in Ebola virus infection

The filovirus, Zaire Ebolavirus (EBOV), infects tissue macrophages (Mϕs) and dendritic cells (DCs) early during infection. Viral infection of both cells types is highly productive, leading to increased viral load. However, virus infection of these two cell types results in different consequences for cellular function. Infection of Mϕs stimulates the production of proinflammatory and immunomodulatory cytokines and chemokines, leading to the production of a cytokine storm, while simultaneously increasing tissue factor production and thus facilitating disseminated intravascular coagulation. In contrast, EBOV infection of DCs blocks DC maturation and antigen presentation rendering these cells unable to communicate with adaptive immune response elements. Details of the known interactions of these cells with EBOV are reviewed here. We also identify a number of unanswered questions that remain about interactions of filoviruses with these cells.