The Role of Cytokines and Chemokines in Filovirus Infection

Long-term Sudan Virus Ebola Survivors Maintain Multiple Antiviral Defense Mechanisms

BACKGROUND

The critical issues of sustained memory immunity following ebolavirus disease among long-term survivors are still unclear.

METHODS

Here, we examine virus-specific immune and inflammatory responses following in vitro challengd in 12 Sudan virus (SUDV) long-term survivors from Uganda's 2000-2001 Gulu outbreak, 15 years after recovery. Total RNA from isolated SUDV-stimulated and unstimulated peripheral blood mononuclear cells was extracted and analyzed. Matched serum samples were also collected to determine SUDV IgG levels and functionality.

RESULTS

We detected persistent humoral (58%, 7 of 12) and cellular (33%, 4 of 12) immune responses in SUDV long-term survivors and identified critical molecular mechanisms of innate and adaptive immunity. Gene expression in immune pathways, the interferon signaling system, antiviral defense response, and activation and regulation of T- and B-cell responses were observed. SUDV long-term survivors also maintained robust virus-specific IgG antibodies capable of polyfunctional responses, including neutralizing and innate Fc effector functions.

CONCLUSIONS

Data integration identified significant correlations among humoral and cellular immune responses and pinpointed a specific innate and adaptive gene expression signature associated with long-lasting immunity. This could help identify natural and vaccine correlates of protection against ebolavirus disease.

Potent immunogenicity and protective efficacy of a multi-pathogen vaccination targeting Ebola, Sudan, Marburg and Lassa viruse

Viral haemorrhagic fevers (VHF) pose a significant threat to human health. In recent years, VHF outbreaks caused by Ebola, Marburg and Lassa viruses have caused substantial morbidity and mortality in West and Central Africa. In 2022, an Ebola disease outbreak in Uganda caused by Sudan virus resulted in 164 cases with 55 deaths. In 2023, a Marburg disease outbreak was confirmed in Equatorial Guinea and Tanzania resulting in over 49 confirmed or suspected cases; 41 of which were fatal. There are no clearly defined correlates of protection against these VHF, impeding targeted vaccine development. Any vaccine developed should therefore induce strong and preferably long-lasting humoral and cellular immunity against these viruses. Ideally this immunity should also cross-protect against viral variants, which are known to circulate in animal reservoirs and cause human disease. We have utilized two viral vectored vaccine platforms, an adenovirus (ChAdOx1) and Modified Vaccinia Ankara (MVA), to develop a multi-pathogen vaccine regime against three filoviruses (Ebola virus, Sudan virus, Marburg virus) and an arenavirus (Lassa virus). These platform technologies have consistently demonstrated the capability to induce robust cellular and humoral antigen-specific immunity in humans, most recently in the rollout of the licensed ChAdOx1-nCoV19/AZD1222. Here, we show that our multi-pathogen vaccines elicit strong cellular and humoral immunity, induce a diverse range of chemokines and cytokines, and most importantly, confers protection after lethal Ebola virus, Sudan virus and Marburg virus challenges in a small animal model.

Novel antiviral approaches for Marburg: a promising therapeutics in the pipeline

Marburg virus disease (MVD) presents a significant global health threat, lacking effective antivirals and with current supportive care offering limited therapeutic options. This mini review explores the emerging landscape of novel antiviral strategies against MVD, focusing on promising therapeutics currently in the development pipeline. We delve into direct-acting antiviral approaches, including small molecule inhibitors targeting viral entry, replication, and assembly, alongside nucleic acid antisense and RNA interference strategies. Host-targeting antivirals are also considered, encompassing immune modulators like interferons and cytokine/chemokine modulators, broad-spectrum antivirals, and convalescent plasma and antibody-based therapies. The paper then examines preclinical and clinical development for the novel therapeutics, highlighting in vitro and in vivo models for antiviral evaluation, safety and efficacy assessments, and the critical stages of clinical trials. Recognizing the challenges of drug resistance and viral escape, the mini review underscores the potential of combination therapy strategies and emphasizes the need for rapid diagnostic tools to optimize treatment initiation. Finally, we discuss the importance of public health preparedness and equitable access to these promising therapeutics in achieving effective MVD control and global health security. This mini review presents a comprehensive overview of the burgeoning field of MVD antivirals, highlighting the potential of these novel approaches to reshape the future of MVD treatment and prevention.

Coordinated inflammatory responses dictate Marburg virus control by reservoir bats

Bats are increasingly recognized as reservoirs of emerging zoonotic pathogens. Egyptian rousette bats (ERBs) are the known reservoir of Marburg virus (MARV), a filovirus that causes deadly Marburg virus disease (MVD) in humans. However, ERBs harbor MARV asymptomatically, likely due to a coadapted and specific host immunity-pathogen relationship. Recently, we measured transcriptional responses in MARV-infected ERB whole tissues, showing that these bats possess a disease tolerant strategy that limits pro-inflammatory gene induction, presumably averting MVD-linked immunopathology. However, the host resistant strategy by which ERBs actively limit MARV burden remains elusive, which we hypothesize requires localized inflammatory responses unresolvable at bulk-tissue scale. Here, we use dexamethasone to attenuate ERB pro-inflammatory responses and assess MARV replication, shedding and disease. We show that MARV-infected ERBs naturally mount coordinated pro-inflammatory responses at liver foci of infection, comprised of recruited mononuclear phagocytes and T cells, the latter of which proliferate with likely MARV-specificity. When pro-inflammatory responses are diminished, ERBs display heightened MARV replication, oral/rectal shedding and severe MVD-like liver pathology, demonstrating that ERBs balance immunoprotective tolerance with discreet MARV-resistant pro-inflammatory responses. These data further suggest that natural ERB immunomodulatory stressors like food scarcity and habitat disruption may potentiate viral shedding, transmission and therefore outbreak risk.

Peripheral immune responses to filoviruses in a reservoir versus spillover hosts reveal transcriptional correlates of disease

Several filoviruses, including Marburg virus (MARV), cause severe disease in humans and nonhuman primates (NHPs). However, the Egyptian rousette bat (ERB, Rousettus aegyptiacus), the only known MARV reservoir, shows no overt illness upon natural or experimental infection, which, like other bat hosts of zoonoses, is due to well-adapted, likely species-specific immune features. Despite advances in understanding reservoir immune responses to filoviruses, ERB peripheral blood responses to MARV and how they compare to those of diseased filovirus-infected spillover hosts remain ill-defined. We thus conducted a longitudinal analysis of ERB blood gene responses during acute MARV infection. These data were then contrasted with a compilation of published primate blood response studies to elucidate gene correlates of filovirus protection versus disease. Our work expands on previous findings in MARV-infected ERBs by supporting both host resistance and disease tolerance mechanisms, offers insight into the peripheral immunocellular repertoire during infection, and provides the most direct known cross-examination between reservoir and spillover hosts of the most prevalently-regulated response genes, pathways and activities associated with differences in filovirus pathogenesis and pathogenicity.

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.

Ebola Virus Uses Tunneling Nanotubes as an Alternate Route of Dissemination

Ebola virus (EBOV) disease is marked by rapid virus replication and spread. EBOV enters the cell by macropinocytosis and replicates in the cytoplasm, and nascent virions egress from the cell surface to infect neighboring cells. Here, we show that EBOV uses an alternate route to disseminate: tunneling nanotubes (TNTs). TNTs, an actin-based long-range intercellular communication system, allows for direct exchange of cytosolic constituents between cells. Using live, scanning electron, and high-resolution quantitative 3-dimensional microscopy, we show that EBOV infection of primary human cells results in the enhanced formation of TNTs containing viral nucleocapsids. TNTs promote the intercellular transfer of nucleocapsids in the absence of live virus, and virus could replicate in cells devoid of entry factors after initial stall. Our studies suggest an alternate model of EBOV dissemination within the host, laying the groundwork for further investigations into the pathogenesis of filoviruses and, importantly, stimulating new areas of antiviral design.

Development of tolerance to chemokine receptor antagonists: current paradigms and the need for further investigation

Chemokine G-protein coupled receptors are validated drug targets for many diseases, including cancer, neurological, and inflammatory disorders. Despite much time and effort spent on therapeutic development, very few chemokine receptor antagonists are approved for clinical use. Among potential reasons for the slow progress in developing chemokine receptor inhibitors, antagonist tolerance, a progressive reduction in drug efficacy after repeated administration, is likely to play a key role. The mechanisms leading to antagonist tolerance remain poorly understood. In many cases, antagonist tolerance is accompanied by increased receptor concentration on the cell surface after prolonged exposure to chemokine receptor antagonists. This points to a possible role of altered receptor internalization and presentation on the cell surface, as has been shown for agonist (primarily opioid) tolerance. In addition, examples of antagonist tolerance in the context of other G-protein coupled receptors suggest the involvement of noncanonical signal transduction in opposing the effects of the antagonists. In this review, we summarize the available progress and challenges in therapeutic development of chemokine receptor antagonists, describe the available knowledge about antagonist tolerance, and propose new avenues for future investigation of this important phenomenon. Furthermore, we highlight the modern methodologies that have the potential to reveal novel mechanisms leading to antagonist tolerance and to propel the field forward by advancing the development of potent "tolerance-free" antagonists of chemokine receptors.

Pathogenicity and virulence of Marburg virus

Marburg virus (MARV) has been a major concern since 1967, with two major outbreaks occurring in 1998 and 2004. Infection from MARV results in severe hemorrhagic fever, causing organ dysfunction and death. Exposure to fruit bats in caves and mines, and human-to-human transmission had major roles in the amplification of MARV outbreaks in African countries. The high fatality rate of up to 90% demands the broad study of MARV diseases (MVD) that correspond with MARV infection. Since large outbreaks are rare for MARV, clinical investigations are often inadequate for providing the substantial data necessary to determine the treatment of MARV disease. Therefore, an overall review may contribute to minimizing the limitations associated with future medical research and improve the clinical management of MVD. In this review, we sought to analyze and amalgamate significant information regarding MARV disease epidemics, pathophysiology, and management approaches to provide a better understanding of this deadly virus and the associated infection.

Development of a Well-Characterized Cynomolgus Macaque Model of Sudan Virus Disease for Support of Product Development

The primary objective of this study was to characterize the disease course in cynomolgus macaques exposed to Sudan virus (SUDV), to determine if infection in this species is an appropriate model for the evaluation of filovirus countermeasures under the FDA Animal Rule. Sudan virus causes Sudan virus disease (SVD), with an average case fatality rate of approximately 50%, and while research is ongoing, presently there are no approved SUDV vaccines or therapies. Well characterized animal models are crucial for further developing and evaluating countermeasures for SUDV. Twenty (20) cynomolgus macaques were exposed intramuscularly to either SUDV or sterile phosphate-buffered saline; 10 SUDV-exposed animals were euthanized on schedule to characterize pathology at defined durations post-exposure and 8 SUDV-exposed animals were not part of the scheduled euthanasia cohort. Survival was assessed, along with clinical observations, body weights, body temperatures, hematology, clinical chemistry, coagulation, viral load (serum and tissues), macroscopic observations, and histopathology. There were statistically significant differences between SUDV-exposed animals and mock-exposed animals for 26 parameters, including telemetry body temperature, clinical chemistry parameters, hematology parameters, activated partial thromboplastin time, serum viremia, and biomarkers that characterize the disease course of SUDV in cynomolgus macaques.

Development of a Well-Characterized Cynomolgus Macaque Model of Marburg Virus Disease for Support of Vaccine and Therapy Development

Marburg virus (MARV) is a filovirus that can infect humans and nonhuman primates (NHPs), causing severe disease and death. Of the filoviruses, Ebola virus (EBOV) has been the primary target for vaccine and therapeutic development. However, MARV has an average case fatality rate of approximately 50%, the infectious dose is low, and there are currently no approved vaccines or therapies targeted at infection with MARV. The purpose of this study was to characterize disease course in cynomolgus macaques intramuscularly exposed to MARV Angola variant. There were several biomarkers that reliably correlated with MARV-induced disease, including: viral load; elevated total clinical scores; temperature changes; elevated ALT, ALP, BA, TBIL, CRP and decreased ALB values; decreased lymphocytes and platelets; and prolonged PTT. A scheduled euthanasia component also provided the opportunity to study the earliest stages of the disease. This study provides evidence for the application of this model to evaluate potential vaccines and therapies against MARV and will be valuable in improving existing models.

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.

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.

Perspectives on the Use of Small Noncoding RNAs as a Therapy for Severe Virus-Induced Disease Manifestations and Late Complications

Many viruses appear each year. Some of these viruses result in severe disease and even death. The frequency of epidemics and pandemics is growing at an alarming rate. The lack of virus-specific etiopathogenic drugs necessitates the search for new tools for the complex treatment of severe viral diseases and their late complications. Small noncoding RNAs and their antagonists may be effective therapeutic tools for preventing virus-induced damage to targeted epithelial cells and surrounding tissues in the manifestation stage. Moreover, sncRNAs could interfere with the virus-interacting host genes that trigger the malignant transformation of target cells as a late complication of severe viral diseases.

Cytokines Studied in Carp (Cyprinus carpio L.) in Response to Important Diseases

Cytokines belong to the most widely studied group of intracellular molecules involved in the function of the immune system. Their secretion is induced by various infectious stimuli. Cytokine release by host cells has been extensively used as a powerful tool for studying immune reactions in the early stages of viral and bacterial infections. Recently, research attention has shifted to the investigation of cytokine responses using mRNA expression, an essential mechanism related to pathogenic and nonpathogenic-immune stimulants in fish. This review represents the current knowledge of cytokine responses to infectious diseases in the common carp (Cyprinus carpio L.). Given the paucity of literature on cytokine responses to many infections in carp, only select viral diseases, such as koi herpesvirus disease (KHVD), spring viremia of carp (SVC), and carp edema virus disease (CEVD), are discussed. Aeromonas hydrophila is one of the most studied bacterial pathogens associated with cytokine responses in common carp. Therefore, the cytokine-based immunoreactivity raised by this specific bacterial pathogen is also highlighted in this review.

A Double-Edged Sword Role of Cytokines in Prostate Cancer Immunotherapy

Prostate cancer (PC) is one of the most common malignancies among men and is the second leading cause of cancer death. PC immunotherapy has taken relatively successful steps in recent years, and these treatments are still being developed and tested. Evidence suggests that immunotherapy using cytokines as essential mediators in the immune system may help treat cancer. It has been shown that cytokines play an important role in anti-tumor defense. On the other hand, other cytokines can also favor the tumor and suppress anti-tumor responses. Moreover, the dose of cytokine in cancer cytokine-based immunotherapy, as well as the side effects of high doses, can also affect the outcomes of treatment. Cytokines can also be determinative in the outcome of other immunotherapy methods used in PC. In this review, the role of cytokines in the pathogenesis of cancer and their impacts on the main types of immunotherapies in the treatment of PC are discussed.

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.

Modulating Neurological Complications of Emerging Infectious Diseases: Mechanistic Approaches to Candidate Phytochemicals

Growing studies are revealing the critical manifestations of influenza, dengue virus (DENV) infection, Zika virus (ZIKV) disease, and Ebola virus disease (EVD) as emerging infectious diseases. However, their corresponding mechanisms of major complications headed for neuronal dysfunction are not entirely understood. From the mechanistic point of view, inflammatory/oxidative mediators are activated during emerging infectious diseases towards less cell migration, neurogenesis impairment, and neuronal death. Accordingly, the virus life cycle and associated enzymes, as well as host receptors, cytokine storm, and multiple signaling mediators, are the leading players of emerging infectious diseases. Consequently, chemokines, interleukins, interferons, carbohydrate molecules, toll-like receptors (TLRs), and tyrosine kinases are leading orchestrates of peripheral and central complications which are in near interconnections. Some of the resulting neuronal manifestations have attracted much attention, including inflammatory polyneuropathy, encephalopathy, meningitis, myelitis, stroke, Guillain-Barré syndrome (GBS), radiculomyelitis, meningoencephalitis, memory loss, headaches, cranial nerve abnormalities, tremor, and seizure. The complex pathophysiological mechanism behind the aforementioned complications urges the need for finding multi-target agents with higher efficacy and lower side effects. In recent decades, the natural kingdom has been highlighted as promising neuroprotective natural products in modulating several dysregulated signaling pathways/mediators. The present study provides neuronal manifestations of some emerging infectious diseases and underlying pathophysiological mechanisms. Besides, a mechanistic-based strategy is developed to introduce candidate natural products as promising multi-target agents in combating major dysregulated pathways towards neuroprotection in influenza, DENV infection, ZIKV disease, and EVD.

Lymphopenia Caused by Virus Infections and the Mechanisms Beyond

Viral infections can give rise to a systemic decrease in the total number of lymphocytes in the blood, referred to as lymphopenia. Lymphopenia may affect the host adaptive immune responses and impact the clinical course of acute viral infections. Detailed knowledge on how viruses induce lymphopenia would provide valuable information into the pathogenesis of viral infections and potential therapeutic targeting. In this review, the current progress of viruses-induced lymphopenia is summarized and the potential mechanisms and factors involved are discussed.

Mega doses of retinol: A possible immunomodulation in Covid-19 illness in resource-limited settings

Of all the nutrients, vitamin A has been the most extensively evaluated for its impact on immunity. There are three main forms of vitamin A, retinol, retinal and retinoic acid (RA) with the latter being most biologically active and all-trans-RA (ATRA) its main derivative. Vitamin A is a key regulator of the functions of various innate and adaptive immune cells and promotes immune-homeostasis. Importantly, it augments the interferon-based innate immune response to RNA viruses decreasing RNA virus replication. Several clinical trials report decreased mortality in measles and Ebola with vitamin A supplementation.During the Covid-19 pandemic interventions such as convalescent plasma, antivirals, monoclonal antibodies and immunomodulator drugs have been tried but most of them are difficult to implement in resource-limited settings. The current review explores the possibility of mega dose vitamin A as an affordable adjunct therapy for Covid-19 illness with minimal reversible side effects. Insight is provided into the effect of vitamin A on ACE-2 expression in the respiratory tract and its association with the prognosis of Covid-19 patients. Vitamin A supplementation may aid the generation of protective immune response to Covid-19 vaccines. An overview of the dosage and safety profile of vitamin A is presented along with recommended doses for prophylactic/therapeutic use in randomised controlled trials in Covid-19 patients.

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.

Immunocompetent mouse model for Crimean-Congo hemorrhagic fever virus

Crimean-Congo hemorrhagic fever (CCHF) is a severe tick-borne febrile illness with wide geographic distribution. CCHF is caused by infection with the Crimean-Congo hemorrhagic fever virus (CCHFV) and case fatality rates can be as high as 30%. Despite causing severe disease in humans, our understanding of the host and viral determinants of CCHFV pathogenesis are limited. A major limitation in the investigation of CCHF has been the lack of suitable small animal models. Wild-type mice are resistant to clinical isolates of CCHFV and consequently, mice must be deficient in type I interferon responses to study the more severe aspects of CCHFV. We report here a mouse-adapted variant of CCHFV that recapitulates in adult, immunocompetent mice the severe CCHF observed in humans. This mouse-adapted variant of CCHFV significantly improves our ability to study host and viral determinants of CCHFV-induced disease in a highly tractable mouse model.

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.

Quantification of Viral and Host Biomarkers in the Liver of Rhesus Macaques: A Longitudinal Study of Zaire Ebolavirus Strain Kikwit (EBOV/Kik)

Zaire ebolavirus (EBOV) causes Ebola virus disease (EVD), which carries a fatality rate between 25% and 90% in humans. Liver pathology is a hallmark of terminal EVD; however, little is known about temporal disease progression. We used multiplexed fluorescent immunohistochemistry and in situ hybridization in combination with whole slide imaging and image analysis (IA) to quantitatively characterize temporospatial signatures of viral and host factors as related to EBOV pathogenesis. Eighteen rhesus monkeys euthanized between 3 and 8 days post-infection, and 3 uninfected controls were enrolled in this study. Compared with semiquantitative histomorphologic ordinal scoring, quantitative IA detected subtle and progressive features of early and terminal EVD that was not feasible with routine approaches. Sinusoidal macrophages were the earliest cells to respond to infection, expressing proinflammatory cytokine interleukin 6 (IL6) mRNA, which was subsequently also observed in fibrovascular compartments. The mRNA of interferon-stimulated gene-15 (ISG-15), also known as ISG15 ubiquitin like modifier (ISG15), was observed early, with a progressive and ubiquitous hybridization signature involving mesenchymal and epithelial compartments. ISG-15 mRNA was prominent near infected cells, but not in infected cells, supporting the hypothesis that bystander cells produce a robust interferon gene response. This study contributes to our current understanding of early EVD progression and illustrates the value that digital pathology and quantitative IA serve in infectious disease research.

Recent Advances on Phagocytic B Cells in Teleost Fish

The momentous discovery of phagocytic activity in teleost B cells has caused a dramatic paradigm shift from the belief that phagocytosis is performed mainly by professional phagocytes derived from common myeloid progenitor cells, such as macrophages/monocytes, neutrophils, and dendritic cells. Recent advances on phagocytic B cells and their microbicidal ability in teleost fish position B cells at the crossroads, bridging innate with adaptive immunity. Most importantly, an increasing body of experimental evidence demonstrates that, in both teleosts and mammals, phagocytic B cells can recognize, take up, and destroy particulate antigens and then present those processed antigens to CD4⁺ T cells to elicit adaptive immune responses and that the phagocytosis is mediated by pattern recognition receptors and involves multiple cytokines. Thus, current findings collectively indicate that teleost phagocytic B cells, as well as their counterpart mammalian B1-B cells, can be considered one kind of professional phagocyte. The aim of this review is to summarize recent advances regarding teleost phagocytic B cells, with a particular focus on the recognizing receptors and modulating mechanisms of phagocytic B cells and the process of antigen presentation for T-cell activation. We also attempt to provide new insights into the adaptive evolution of the teleost fish phagocytic B cell on the basis of its innate and adaptive roles.

Kinetics of Soluble Mediators of the Host Response in Ebola Virus Disease

Background

The pathophysiology of Ebola virus disease (EVD) is still poorly understood. This study aimed at identifying soluble biomarkers that inform on disease mechanisms.

Methods

Fifty-four soluble mediators of the immune, coagulation, and endothelial system were measured in baseline and follow-up samples from hospitalized patients with EVD, using Luminex technology. Cross-sectional expression levels and changes over time were correlated with outcome.

Results

Levels of circulating proinflammatory cytokines and chemokines, as well as markers of endothelial dysfunction and coagulopathy, were elevated on admission to hospital in patients who died from EVD as compared to survivors. These markers further increased in patients who died and/or decreased over time in survivors. In contrast, markers of gut integrity and T-cell response were higher in survivors and increased until discharge.

Conclusions

Inflammatory response, endothelial integrity, gastric tissue protection, and T cell immunity play a role in EVD pathophysiology.

Perspectives towards antiviral drug discovery against Ebola virus

Ebola virus disease (EVD), caused by Ebola viruses, resulted in more than 11 500 deaths according to a recent 2018 WHO report. With mortality rates up to 90%, it is nowadays one of the most deadly infectious diseases. However, no Food and Drug Administration‐approved Ebola drugs or vaccines are available yet with the mainstay of therapy being supportive care. The high fatality rate and absence of effective treatment or vaccination make Ebola virus a category‐A biothreat pathogen. Fortunately, a series of investigational countermeasures have been developed to control and prevent this global threat. This review summarizes the recent therapeutic advances and ongoing research progress from research and development to clinical trials in the development of small‐molecule antiviral drugs, small‐interference RNA molecules, phosphorodiamidate morpholino oligomers, full‐length monoclonal antibodies, and vaccines. Moreover, difficulties are highlighted in the search for effective countermeasures against EVD with additional focus on the interplay between available in silico prediction methods and their evidenced potential in antiviral drug discovery.

Cytokine Effects on the Entry of Filovirus Envelope Pseudotyped Virus-Like Particles into Primary Human Macrophages

Macrophages are one of the first and also a major site of filovirus replication and, in addition, are a source of multiple cytokines, presumed to play a critical role in the pathogenesis of the viral infection. Some of these cytokines are known to induce macrophage phenotypic changes in vitro, but how macrophage polarization may affect the cell susceptibility to filovirus entry remains largely unstudied. We generated different macrophage subsets using cytokine pre-treatment and subsequently tested their ability to fuse with beta-lactamase containing virus-like particles (VLP), pseudotyped with the surface glycoprotein of Ebola virus (EBOV) or the glycoproteins of other clinically relevant filovirus species. We found that pre-incubation of primary human monocyte-derived macrophages (MDM) with interleukin-10 (IL-10) significantly enhanced filovirus entry into cells obtained from multiple healthy donors, and the IL-10 effect was preserved in the presence of pro-inflammatory cytokines found to be elevated during EBOV disease. In contrast, fusion of IL-10-treated macrophages with influenza hemagglutinin/neuraminidase pseudotyped VLPs was unchanged or slightly reduced. Importantly, our in vitro data showing enhanced virus entry are consistent with the correlation established between elevated serum IL-10 and increased mortality in filovirus infected patients and also reveal a novel mechanism that may account for the IL-10-mediated increase in filovirus pathogenicity.

Small Animal Models for Studying Filovirus Pathogenesis

Filovirus small animal disease models have so far been developed in laboratory mice, guinea pigs, and hamsters. Since immunocompetent rodents do not exhibit overt signs of disease following infection with wild-type filoviruses isolated from humans, rodent models have been established using adapted viruses produced through sequential passage in rodents. Rodent-adapted viruses target the same cells/tissues as the wild-type viruses, making rodents invaluable basic research tools for studying filovirus pathogenesis. Moreover, comparative analyses using wild-type and rodent-adapted viruses have provided beneficial insights into the molecular mechanisms of pathogenicity and acquisition of species-specific virulence. Additionally, wild-type filovirus infections in immunodeficient rodents have provided a better understanding of the host factors required for resistance to filovirus infection and of the immune response against the infection. This chapter provides comprehensive information on the filovirus rodent models and rodent-adapted filoviruses. Specifically, we summarize the clinical and pathological features of filovirus infections in all rodent models described to date, including the recently developed humanized and collaborative cross (CC) resource recombinant inbred (RI) intercrossed (CC-RIX) mouse models. We also cover the molecular determinants responsible for adaptation and virulence acquisition in a number of rodent-adapted filoviruses. This chapter clearly defines the characteristic and advantages/disadvantages of rodent models, helping to evaluate the practical use of rodent models in future filovirus studies.

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.

Inflammatory and Humoral Immune Response during Ebola Virus Infection in Survivor and Fatal Cases Occurred in Sierra Leone during the 2014⁻2016 Outbreak in West Africa

Ebola virus (EBOV) infection is characterized by an excessive inflammatory response, a loss of lymphocytes and a general paralysis of the immune system, however pathophysiological mechanisms are not fully understood. In a cohort of 23 fatal and 21 survivors of ebola virus disease (EVD) cases admitted to the Emergency Ebola-Treatment-Center in Goderich (Freetown, Sierra Leone) during the 2014 to 2016 EBOV epidemic in Western Africa, we analyzed the pathway-focused gene expression profile of secreted proteins involved in the immune response and the levels of specific anti-EBOV IgM and IgG from the time of admission till discharge or death. We observed a dysregulated inflammatory response in fatal patients as compared to survivors, mainly consisting of the upregulation of inflammatory mediators, whose extent directly correlated with viremia levels. The upregulation persisted and intensified during the late phase of infection. Relevant differences were also found in humoral immunity, as an earlier and more robust EBOV antibody response was observed in survivor patients.

Regulation of Chemokines and Cytokines by Histone Deacetylases and an Update on Histone Decetylase Inhibitors in Human Diseases

Histone acetyltransferases (HATs) and histone deacetylases (HDACs) counteract with each other to regulate gene expression by altering chromatin structure. Aberrant HDAC activity was reported in many human diseases including wide range of cancers, viral infections, cardiovascular complications, auto-immune diseases and kidney diseases. HDAC inhibitors are small molecules designed to block the malignant activity of HDACs. Chemokines and cytokines control inflammation, immunological and other key biological processes and are shown to be involved in various malignancies. Various HDACs and HDAC inhibitors were reported to regulate chemokines and cytokines. Even though HDAC inhibitors have remarkable anti-tumor activity in hematological cancers, they are not effective in treating many diseases and many patients relapse after treatment. However, the role of HDACs and cytokines in regulating these diseases still remain unclear. Therefore, understanding exact mechanisms and effector functions of HDACs are urgently needed to selectively inhibit them and to establish better a platform to combat various malignancies. In this review, we address regulation of chemokines and cytokines by HDACs and HDAC inhibitors and update on HDAC inhibitors in human diseases.

The Cytokine Response Profile of Ebola Virus Disease in a Large Cohort of Rhesus Macaques Treated With Monoclonal Antibodies

Ebola virus (EBOV) is a highly pathogenic filovirus that causes outbreaks of a severe hemorrhagic fever known as EBOV disease (EVD). Ebola virus disease is characterized in part by a dysregulated immune response and massive production of both pro- and anti-inflammatory cytokines. To better understand the immune response elicited by EVD in the context of treatment with experimental anti-EBOV antibody cocktails, we analyzed 29 cytokines in 42 EBOV-infected rhesus macaques. In comparison to the surviving treated animals, which exhibited minimal aberrations in only a few cytokine levels, nonsurviving animals exhibited a dramatically upregulated inflammatory response that was delayed by antibody treatment.

Viral infections of the central nervous system in Africa

Viral infections are a major cause of human central nervous system infection, and may be associated with significant mortality, and long-term sequelae. In Africa, the lack of effective therapies, limited diagnostic and human resource facilities are especially in dire need. Most viruses that affect the central nervous system are opportunistic or accidental pathogens. Some of these viruses were initially considered harmless, however they have now evolved to penetrate the nervous system efficiently and exploit neuronal cell biology thus resulting in severe illness. A number of potentially lethal neurotropic viruses have been discovered in Africa and over the course of time shown their ability to spread wider afield involving other continents leaving a devastating impact in their trail. In this review we discuss key viruses involved in central nervous system disease and of major public health concern with respect to Africa. These arise from the families of Flaviviridae, Filoviridae, Retroviridae, Bunyaviridae, Rhabdoviridae and Herpesviridae. In terms of the number of cases affected by these viruses, HIV (Retroviridae) tops the list for morbidity, mortality and long term disability, while the Rift Valley Fever virus (Bunyaviridae) is at the bottom of the list. The most deadly are the Ebola and Marburg viruses (Filoviridae). This review describes their epidemiology and key neurological manifestations as regards the central nervous system such as meningoencephalitis and Guillain-Barré syndrome. The potential pathogenic mechanisms adopted by these viruses are debated and research perspectives suggested.

Decoding the enigma of antiviral crisis: Does one target molecule regulate all?

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IL-6 class switching provides regulation over pro- and anti-inflammatory responses.

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Unregulated IL-6 trans-signaling promotes uncontrolled pro-inflammatory responses.

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ADAM-17 regulates class switching between IL-6 trans- and classical-signaling.

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Selective ADAM-17 blocking restricts overexpression of pro-inflammatory cytokines.

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ADAM-17 may be an antiviral drug target to reduce immunopathology disease severity.

Disease fatality associated with Ebola, SARS-CoV and dengue infections in humans is attributed to a cytokine storm that is triggered by excessive pro-inflammatory responses. Interleukin (IL)-6 acts as a mediator between pro- and anti-inflammatory reactivity by initiating trans- and classical-signaling, respectively. Hence, IL-6 is assumed to provide a target for a broad range of antiviral agents. Available immunosuppressive antivirals are directed to control an often exaggerated pro-inflammatory response that gives rise to complex clinical conditions such as lymphocytopenia. It is known that IL-6, via its soluble receptor (sIL-6R), initiates a pro-inflammatory response while an anti-inflammatory response is triggered by the membrane-bound IL-6 receptor (IL-6R). Future antivirals should thus aim to target the mechanism that regulates switching between IL-6 trans- and classical-signaling. In this review, we propose that the tumour necrosis factor-α converting enzyme ADAM-17 could be the master molecule involved in regulating IL-6 class switching and through this in controlling pro- and anti-inflammatory responses to viral antigenic stimuli. Therefore, ADAM-17 should be considered as a potential target molecule for novel antiviral drug discovery that would regulate host reactivity to infection and thereby limit or prevent fatal outcomes.

Cytokine-Mediated Tissue Injury in Non-human Primate Models of Viral Infections

Viral infections trigger robust secretion of interferons and other antiviral cytokines by infected and bystander cells, which in turn can tune the immune response and may lead to viral clearance or immune suppression. However, aberrant or unrestricted cytokine responses can damage host tissues, leading to organ dysfunction, and even death. To understand the cytokine milieu and immune responses in infected host tissues, non-human primate (NHP) models have emerged as important tools. NHP have been used for decades to study human infections and have played significant roles in the development of vaccines, drug therapies and other immune treatment modalities, aided by an ability to control disease parameters, and unrestricted tissue access. In addition to the genetic and physiological similarities with humans, NHP have conserved immunologic properties with over 90% amino acid similarity for most cytokines. For example, human-like symptomology and acute respiratory syndrome is found in cynomolgus macaques infected with highly pathogenic avian influenza virus, antibody enhanced dengue disease is common in neotropical primates, and in NHP models of viral hepatitis cytokine-induced inflammation induces severe liver damage, fibrosis, and hepatocellular carcinoma recapitulates human disease. To regulate inflammation, anti-cytokine therapy studies in NHP are underway and will provide important insights for future human interventions. This review will provide a comprehensive outline of the cytokine-mediated exacerbation of disease and tissue damage in NHP models of viral infections and therapeutic strategies that can aid in prevention/treatment of the disease syndromes.

Ebola Virus VP40 Modulates Cell Cycle and Biogenesis of Extracellular Vesicles

Background

Ebola virus (EBOV) mainly targets myeloid cells; however, extensive death of T cells is often observed in lethal infections. We have previously shown that EBOV VP40 in exosomes causes recipient immune cell death.

Methods

Using VP40-producing clones, we analyzed donor cell cycle, extracellular vesicle (EV) biogenesis, and recipient immune cell death. Transcription of cyclin D1 and nuclear localization of VP40 were examined via kinase and chromatin immunoprecipitation assays. Extracellular vesicle contents were characterized by mass spectrometry, cytokine array, and western blot. Biosafety level-4 facilities were used for wild-type Ebola virus infection studies.

Results

VP40 EVs induced apoptosis in recipient T cells and monocytes. VP40 clones were accelerated in growth due to cyclin D1 upregulation, and nuclear VP40 was found bound to the cyclin D1 promoter. Accelerated cell cycling was related to EV biogenesis, resulting in fewer but larger EVs. VP40 EV contents were enriched in ribonucleic acid-binding proteins and cytokines (interleukin-15, transforming growth factor-β1, and interferon-γ). Finally, EBOV-infected cell and animal EVs contained VP40, nucleoprotein, and glycoprotein.

Conclusions

Nuclear VP40 upregulates cyclin D1 levels, resulting in dysregulated cell cycle and EV biogenesis. Packaging of cytokines and EBOV proteins into EVs from infected cells may be responsible for the decimation of immune cells during EBOV pathogenesis.

A conserved transcriptional response to intranasal Ebola virus exposure in nonhuman primates prior to onset of fever

Ebola virus disease (EVD), caused by Ebola virus (EBOV), is a severe illness characterized by case fatality rates of up to 90%. The sporadic nature of outbreaks in resource-limited areas has hindered the ability to characterize the pathogenesis of EVD at all stages of infection but particularly early host responses. Pathogenesis is often studied in nonhuman primate (NHP) models of disease that replicate major aspects of human EVD. Typically, NHP models use a large infectious dose, are carried out through intramuscular or aerosol exposure, and have a fairly uniform disease course. By contrast, we report our analysis of the host response to EBOV after intranasal exposure. Twelve cynomolgus macaques were infected with 100 plaque-forming units of EBOV/Makona through intranasal exposure and presented with varying times to onset of EVD. We used RNA sequencing and a newly developed NanoString CodeSet to monitor the host response via changes in RNA transcripts over time. When individual animal gene expression data were phased based on the onset of sustained fever, the first clinical sign of severe disease, mathematical models indicated that interferon-stimulated genes appeared as early as 4 days before fever onset. This demonstrates that lethal EVD has a uniform and predictable response to infection regardless of time to onset. Furthermore, expression of a subset of genes could predict disease development before other host-based indications of infection such as fever.

Host Transcriptional Response to Ebola Virus Infection

Ebola virus disease (EVD) is a serious illness that causes severe disease in humans and non-human primates (NHPs) and has mortality rates up to 90%. EVD is caused by the Ebolavirus and currently there are no licensed therapeutics or vaccines to treat EVD. Due to its high mortality rates and potential as a bioterrorist weapon, a better understanding of the disease is of high priority. Multiparametric analysis techniques allow for a more complete understanding of a disease and the host response. Analysis of RNA species present in a sample can lead to a greater understanding of activation or suppression of different states of the immune response. Transcriptomic analyses such as microarrays and RNA-Sequencing (RNA-Seq) have been important tools to better understand the global gene expression response to EVD. In this review, we outline the current knowledge gained by transcriptomic analysis of EVD.

Ebola Virus Glycoprotein Induces an Innate Immune Response In vivo via TLR4

Ebola virus (EBOV), a member of the Filoviridae family, causes the most severe form of viral hemorrhagic fever. Although no FDA licensed vaccine or treatment against Ebola virus disease (EVD) is currently available, Ebola virus glycoprotein (GP) is the major antigen used in all candidate Ebola vaccines. Recent reports of protection as quickly as within 6 days of administration of the rVSV-based vaccine expressing EBOV GP before robust humoral responses were generated suggests that the innate immune responses elicited early after vaccination may contribute to the protection. However, the innate immune responses induced by EBOV GP in the absence of viral vectors or adjuvants have not been fully characterized in vivo. Our recent studies demonstrated that immunization with highly purified recombinant GP in the absence of adjuvants induced a robust IgG response and partial protection against EBOV infection suggesting that GP alone can induce protective immunity. In this study we investigated the early immune response to purified EBOV GP alone in vitro and in vivo. We show that GP was efficiently internalized by antigen presenting cells and subsequently induced production of key inflammatory cytokines. In vivo, immunization of mice with EBOV GP triggered the production of key Th1 and Th2 innate immune cytokines and chemokines, which directly governed the recruitment of CD11b⁺ macrophages and CD11c⁺ dendritic cells to the draining lymph nodes (DLNs). Pre-treatment of mice with a TLR4 antagonist inhibited GP-induced cytokine production and recruitment of immune cells to the DLN. EBOV GP also upregulated the expression of costimulatory molecules in bone marrow derived macrophages suggesting its ability to enhance APC stimulatory capacity, which is critical for the induction of effective antigen-specific adaptive immunity. Collectively, these results provide the first in vivo evidence that early innate immune responses to EBOV GP are mediated via the TLR4 pathway and are able to modulate the innate-adaptive interface. These mechanistic insights into the adjuvant-like property of EBOV GP may help to develop a better understanding of how optimal prophylactic efficacy of EBOV vaccines can be achieved as well as further explore the potential post-exposure use of vaccines to prevent filoviral disease.

Discovering Drugs for the Treatment of Ebola Virus

Purpose of review

Ebola virus, a member of the Filoviridae family, is a causative agent of severe viral hemorrhagic fever in humans. Over the past 40 years, the virus has been linked to several high mortality outbreaks in Africa with the recent West African outbreak resulting in over 11,000 deaths. This review provides a summary of the status of the drug discovery and development process for therapeutics for Ebola virus disease, with a focus on the strategies being used and the challenges facing each stage of the process.

Recent findings

Despite the wealth of in vitro efficacy data, preclinical data in animal models, and human clinical data, no therapeutics have been approved for the treatment of Ebola virus disease. However, several promising candidates, such as ZMapp and GS-5734, have advanced into ongoing clinical trials.

Summary

The gravity of the 2014-2016 outbreak spurred a heightened effort to identify and develop new treatments for Ebola virus disease, including small molecules, immunotherapeutics, host factors, and clinical disease management options.

Disclaimer

Opinions, interpretations, conclusions, and recommendations are those of the authors and are not necessarily endoresed by the U.S. Army.

A dose-dependent plasma signature of the safety and immunogenicity of the rVSV-Ebola vaccine in Europe and Africa

The 2014-2015 Ebola epidemic affected several African countries, claiming more than 11,000 lives and leaving thousands with ongoing sequelae. Safe and effective vaccines could prevent or limit future outbreaks. The recombinant vesicular stomatitis virus-vectored Zaire Ebola (rVSV-ZEBOV) vaccine has shown marked immunogenicity and efficacy in humans but is reactogenic at higher doses. To understand its effects, we examined plasma samples from 115 healthy volunteers from Geneva who received low-dose (LD) or high-dose (HD) vaccine or placebo. Fifteen plasma chemokines/cytokines were assessed at baseline and on days 1, 2 to 3, and 7 after injection. Significant increases in monocyte-mediated MCP-1/CCL2, MIP-1β/CCL4, IL-6, TNF-α, IL-1Ra, and IL-10 occurred on day 1. A signature explaining 68% of cytokine/chemokine vaccine-response variability was identified. Its score was higher in HD versus LD vaccinees and was associated positively with vaccine viremia and negatively with cytopenia. It was higher in vaccinees with injection-site pain, fever, myalgia, chills, and headache; higher scores reflected increasing severity. In contrast, HD vaccinees who subsequently developed arthritis had lower day 1 scores than other HD vaccinees. Vaccine dose did not influence the signature despite its influence on specific outcomes. The Geneva-derived signature associated strongly (ρ = 0.97) with that of a cohort of 75 vaccinees from a parallel trial in Lambaréné, Gabon. Its score in Geneva HD vaccinees with subsequent arthritis was significantly lower than that in Lambaréné HD vaccinees, none of whom experienced arthritis. This signature, which reveals monocytes' critical role in rVSV-ZEBOV immunogenicity and safety across doses and continents, should prove useful in assessments of other vaccines.

Ebolaviruses Associated with Differential Pathogenicity Induce Distinct Host Responses in Human Macrophages

Ebola virus (EBOV) and Reston virus (RESTV) are members of the Ebolavirus genus which greatly differ in their pathogenicity. While EBOV causes a severe disease in humans characterized by a dysregulated inflammatory response and elevated cytokine and chemokine production, there are no reported disease-associated human cases of RESTV infection, suggesting that RESTV is nonpathogenic for humans. The underlying mechanisms determining the pathogenicity of different ebolavirus species are not yet known. In this study, we dissected the host response to EBOV and RESTV infection in primary human monocyte-derived macrophages (MDMs). As expected, EBOV infection led to a profound proinflammatory response, including strong induction of type I and type III interferons (IFNs). In contrast, RESTV-infected macrophages remained surprisingly silent. Early activation of IFN regulatory factor 3 (IRF3) and NF-κB was observed in EBOV-infected, but not in RESTV-infected, MDMs. In concordance with previous results, MDMs treated with inactivated EBOV and Ebola virus-like particles (VLPs) induced NF-κB activation mediated by Toll-like receptor 4 (TLR4) in a glycoprotein (GP)-dependent manner. This was not the case in cells exposed to live RESTV, inactivated RESTV, or VLPs containing RESTV GP, indicating that RESTV GP does not trigger TLR4 signaling. Our results suggest that the lack of immune activation in RESTV-infected MDMs contributes to lower pathogenicity by preventing the cytokine storm observed in EBOV infection. We further demonstrate that inhibition of TLR4 signaling abolishes EBOV GP-mediated NF-κB activation. This finding indicates that limiting the excessive TLR4-mediated proinflammatory response in EBOV infection should be considered as a potential supportive treatment option for EBOV disease.IMPORTANCE Emerging infectious diseases are a major public health concern, as exemplified by the recent devastating Ebola virus (EBOV) outbreak. Different ebolavirus species are associated with widely varying pathogenicity in humans, ranging from asymptomatic infections for Reston virus (RESTV) to severe disease with fatal outcomes for EBOV. In this comparative study of EBOV- and RESTV-infected human macrophages, we identified key differences in host cell responses. Consistent with previous data, EBOV infection is associated with a proinflammatory signature triggered by the surface glycoprotein (GP), which can be inhibited by blocking TLR4 signaling. In contrast, infection with RESTV failed to stimulate a strong host response in infected macrophages due to the inability of RESTV GP to stimulate TLR4. We propose that disparate proinflammatory host signatures contribute to the differences in pathogenicity reported for ebolavirus species and suggest that proinflammatory pathways represent an intriguing target for the development of novel therapeutics.

Ebolavirus: An Overview of Molecular and Clinical Pathogenesis

Ebolaviruses cause severe, often fatal hemorrhagic fever in Central, East, and West Africa. Until recently, they have been viewed as rare but highly pathogenic infections with regional, but limited, global public health impact. This view has changed with the emergence of the first epidemic of Ebola hemorrhagic fever in West Africa. In this chapter we provide an introduction of the pathogenesis of ebolaviruses as well as a description of clinical disease features. We also describe the current animal models used in ebolavirus research, detailing each model's unique strengths and weaknesses. We focus on Ebola virus representing the type species Zaire ebolavirus of the genus Ebolavirus, as most work relates to this pathogen.