Cutting edge: impairment of dendritic cells and adaptive immunity by Ebola and Lassa viruses

Improving the Breadth of the Host's Immune Response to Lassa Virus

In 2017, the global Coalition for Epidemic Preparedness (CEPI) declared Lassa virus disease to be one of the world's foremost biothreats. In January 2018, World Health Organization experts met to address the Lassa biothreat. It was commonly recognized that the diversity of Lassa virus (LASV) isolated from West African patient samples was far greater than that of the Ebola isolates from the West African epidemic of 2013⁻2016. Thus, vaccines produced against Lassa virus disease face the added challenge that they must be broadly-protective against a wide variety of LASV. In this review, we discuss what is known about the immune response to Lassa infection. We also discuss the approaches used to make broadly-protective influenza vaccines and how they could be applied to developing broad vaccine coverage against LASV disease. Recent advances in AIDS research are also potentially applicable to the design of broadly-protective medical countermeasures against LASV disease.

Porcine monocyte-derived dendritic cells can be differentially activated by vesicular stomatitis virus and its matrix protein mutants

Vesicular stomatitis virus (VSV) can cause serious vesicular lesions in pigs, and the matrix (M) protein is its predominant virulence factor. Dendritic cells (DCs) act as the bridge between innate and adaptive immune responses. However, the susceptibility of porcine DCs to VSV infection and the role of M protein in modulating the function of infected DCs are still poorly defined. Thus, this study aimed to determine the ability of virulent wild-type VSV(wtVSV) and two attenuated M protein variants (VSV_ΔM51 and VSV_MT) to induce maturation of porcine monocyte-derived DCs (MoDCs) in vitro. It was found that both wtVSV and the M protein mutant VSVs could productively replicate in porcine MoDCs. Infection with wtVSV resulted in weak proinflammatory cytokine responses and interfered with DC maturation via downregulation of the costimulatory molecule complex CD80/86. Whilst VSV_ΔM51 could activate porcine MoDCs, VSV_MT, a highly attenuated recombinant VSV with triple mutations in the M protein, induced a potent maturation of MoDCs, as evidenced by efficient cytokine induction, and upregulation of CD80/86 and MHC class II. Overall, our findings reveal that porcine MoDCs are differentially activated by VSV, dependent on the presence of a functional M protein. M protein plays a crucial role in modulating porcine DC-VSV interactions. The data further support the potential use of VSV_MT as a vaccine vector for pigs.

Epidemiology, Pathogenesis, and Control of a Tick-Borne Disease- Kyasanur Forest Disease: Current Status and Future Directions

In South Asia, Haemaphysalis spinigera tick transmits Kyasanur Forest Disease Virus (KFDV), a flavivirus that causes severe hemorrhagic fever with neurological manifestations such as mental disturbances, severe headache, tremors, and vision deficits in infected human beings with a fatality rate of 3-10%. The disease was first reported in March 1957 from Kyasanur forest of Karnataka (India) from sick and dying monkeys. Since then, between 400 and 500 humans cases per year have been recorded; monkeys and small mammals are common hosts of this virus. KFDV can cause epizootics with high fatality in primates and is a level-4 virus according to the international biosafety rules. The density of tick vectors in a given year correlates with the incidence of human disease. The virus is a positive strand RNA virus and its genome was discovered to code for one polyprotein that is cleaved post-translationally into 3 structural proteins (Capsid protein, Envelope Glycoprotein M and Envelope Glycoprotein E) and 7 non-structural proteins (NS1, NS2A, NS2B, NS3, NS4A, NS4B, and NS5). KFDV has a high degree of sequence homology with most members of the TBEV serocomplex. Alkhurma virus is a KFDV variant sharing a sequence similarity of 97%. KFDV is classified as a NIAID Category C priority pathogen due to its extreme pathogenicity and lack of US FDA approved vaccines and therapeutics; also, the infectious dose is currently unknown for KFD. In India, formalin-inactivated KFDV vaccine produced in chick embryo fibroblast is being used. Nevertheless, further efforts are required to enhance its long-term efficacy. KFDV remains an understudied virus and there remains a lack of insight into its pathogenesis; moreover, specific treatment to the disease is not available to date. Environmental and climatic factors involved in disseminating Kyasanur Forest Disease are required to be fully explored. There should be a mapping of endemic areas and cross-border veterinary surveillance needs to be developed in high-risk regions. The involvement of both animal and health sector is pivotal for circumscribing the spread of this disease to new areas.

DNA vaccines elicit durable protective immunity against individual or simultaneous infections with Lassa and Ebola viruses in guinea pigs

We previously developed optimized DNA vaccines against both Lassa fever and Ebola hemorrhagic fever viruses and demonstrated that they were protective individually in guinea pig and nonhuman primate models. In this study, we vaccinated groups of strain 13 guinea pigs two times, four weeks apart with 50 µg of each DNA vaccine or a mock vaccine at discrete sites by intradermal electroporation. Five weeks following the second vaccinations, guinea pigs were exposed to lethal doses of Lassa virus, Ebola virus, or a combination of both viruses simultaneously. None of the vaccinated guinea pigs, regardless of challenge virus and including the coinfected group, displayed weight loss, fever or other disease signs, and all survived to the study endpoint. All of the mock-vaccinated guinea pigs that were infected with Lassa virus, and all but one of the EBOV-infected mock-vaccinated guinea pigs succumbed. In order to determine if the dual-agent vaccination strategy could protect against both viruses if exposures were temporally separated, we held the surviving vaccinates in BSL-4 for approximately 120 days to perform a cross-challenge experiment in which guinea pigs originally infected with Lassa virus received a lethal dose of Ebola virus and those originally infected with Ebola virus were infected with a lethal dose of Lassa virus. All guinea pigs remained healthy and survived to the study endpoint. This study clearly demonstrates that DNA vaccines against Lassa and Ebola viruses can elicit protective immunity against both individual virus exposures as well as in a mixed-infection environment.

Defining a standard and weighted mathematical index for maturation of dendritic cells

The concept of dendritic cell (DC) maturation generally refers to the changes in morphology and function of DCs. Conventionally, DC maturity is based on three criteria: loss of endocytic ability, gain of high-level capacity to present antigens and induce proliferation of T cells, and mobility of DCs toward high concentrations of CCL19. Impairment of DC maturation has been suggested as the main reason for infectivity or chronicity of several infectious agents. In the case of hepatitis C virus, this has been a matter of controversy for the last two decades. However, insufficient attention has been paid to the method of ex vivo maturation as the possible source of such controversies. We previously reported striking differences between DCs matured with different methods, so we propose the use of a standard quantitative index to determine the level of maturity in DCs as an approach to compare results from different studies. We designed and formulated a mathematically calculated index to numerically define the level of maturity based on experimental data from ex vivo assays. This introduces a standard maturation index (SMI) and weighted maturation index (WMI) based on strictly standardized mean differences between different methods of generating mature DCs. By calculating an SMI and a WMI, numerical values were assigned to the level of maturity achieved by DCs matured with different methods. SMI and WMI could be used as a standard tool to compare diversely generated mature DCs and so better interpret outcomes of ex vivo and in vivo studies with mature DCs.

Exploring the Immunopathogenesis of Viral Hemorrhagic Fever in Mice with a Humanized Immune System

Viral hemorrhagic fever (VHF) as a disease entity was first codified in the 1930s by soviet scientists investigating patients suffering from hantavirus infection. The group of hemorrhagic fever viruses (HFVs) has since expanded to include members from at least four different virus families: Arenaviridae, Bunyaviridae, Filoviridae, and Flaviviridae, all enveloped single-stranded RNA viruses. After infection, the natural hosts of HFVs do not develop symptoms, whereas humans can be severely affected. This observation and other evidence from experimental data suggest that the human immune system plays a crucial role in VHF pathogenesis. For this reason mice with a human immune system, referred to here as humanized mice (humice), are valuable tools that provide insight into disease mechanisms and allow for preclinical testing of novel vaccinations approaches as well as antiviral agents. In this article, we review the impact of humice in VHF research.

Ebola Virus Binding to Tim-1 on T Lymphocytes Induces a Cytokine Storm

Ebola virus (EBOV) disease (EVD) results from an exacerbated immunological response that is highlighted by a burst in the production of inflammatory mediators known as a "cytokine storm." Previous reports have suggested that nonspecific activation of T lymphocytes may play a central role in this phenomenon. T-cell immunoglobulin and mucin domain-containing protein 1 (Tim-1) has recently been shown to interact with virion-associated phosphatidylserine to promote infection. Here, we demonstrate the central role of Tim-1 in EBOV pathogenesis, as Tim-1^-/- mice exhibited increased survival rates and reduced disease severity; surprisingly, only a limited decrease in viremia was detected. Tim-1^-/- mice exhibited a modified inflammatory response as evidenced by changes in serum cytokines and activation of T helper subsets. A series of in vitro assays based on the Tim-1 expression profile on T cells demonstrated that despite the apparent absence of detectable viral replication in T lymphocytes, EBOV directly binds to isolated T lymphocytes in a phosphatidylserine-Tim-1-dependent manner. Exposure to EBOV resulted in the rapid development of a CD4^Hi CD3^Low population, non-antigen-specific activation, and cytokine production. Transcriptome and Western blot analysis of EBOV-stimulated CD4⁺ T cells confirmed the induction of the Tim-1 signaling pathway. Furthermore, comparative analysis of transcriptome data and cytokine/chemokine analysis of supernatants highlight the similarities associated with EBOV-stimulated T cells and the onset of a cytokine storm. Flow cytometry revealed virtually exclusive binding and activation of central memory CD4⁺ T cells. These findings provide evidence for the role of Tim-1 in the induction of a cytokine storm phenomenon and the pathogenesis of EVD.IMPORTANCE Ebola virus infection is characterized by a massive release of inflammatory mediators, which has come to be known as a cytokine storm. The severity of the cytokine storm is consistently linked with fatal disease outcome. Previous findings have demonstrated that specific T-cell subsets are key contributors to the onset of a cytokine storm. In this study, we investigated the role of Tim-1, a T-cell-receptor-independent trigger of T-cell activation. We first demonstrated that Tim-1-knockout (KO) mice survive lethal Ebola virus challenge. We then used a series of in vitro assays to demonstrate that Ebola virus directly binds primary T cells in a Tim-1-phosphatidylserine-dependent manner. We noted that binding induces a cytokine storm-like phenomenon and that blocking Tim-1-phosphatidylserine interactions reduces viral binding, T-cell activation, and cytokine production. These findings highlight a previously unknown role of Tim-1 in the development of a cytokine storm and "immune paralysis."

Ebola Virus Binding to Tim-1 on T Lymphocytes Induces a Cytokine Storm

Ebola virus (EBOV) disease (EVD) results from an exacerbated immunological response that is highlighted by a burst in the production of inflammatory mediators known as a "cytokine storm." Previous reports have suggested that nonspecific activation of T lymphocytes may play a central role in this phenomenon. T-cell immunoglobulin and mucin domain-containing protein 1 (Tim-1) has recently been shown to interact with virion-associated phosphatidylserine to promote infection. Here, we demonstrate the central role of Tim-1 in EBOV pathogenesis, as Tim-1^-/- mice exhibited increased survival rates and reduced disease severity; surprisingly, only a limited decrease in viremia was detected. Tim-1^-/- mice exhibited a modified inflammatory response as evidenced by changes in serum cytokines and activation of T helper subsets. A series of in vitro assays based on the Tim-1 expression profile on T cells demonstrated that despite the apparent absence of detectable viral replication in T lymphocytes, EBOV directly binds to isolated T lymphocytes in a phosphatidylserine-Tim-1-dependent manner. Exposure to EBOV resulted in the rapid development of a CD4^Hi CD3^Low population, non-antigen-specific activation, and cytokine production. Transcriptome and Western blot analysis of EBOV-stimulated CD4⁺ T cells confirmed the induction of the Tim-1 signaling pathway. Furthermore, comparative analysis of transcriptome data and cytokine/chemokine analysis of supernatants highlight the similarities associated with EBOV-stimulated T cells and the onset of a cytokine storm. Flow cytometry revealed virtually exclusive binding and activation of central memory CD4⁺ T cells. These findings provide evidence for the role of Tim-1 in the induction of a cytokine storm phenomenon and the pathogenesis of EVD.IMPORTANCE Ebola virus infection is characterized by a massive release of inflammatory mediators, which has come to be known as a cytokine storm. The severity of the cytokine storm is consistently linked with fatal disease outcome. Previous findings have demonstrated that specific T-cell subsets are key contributors to the onset of a cytokine storm. In this study, we investigated the role of Tim-1, a T-cell-receptor-independent trigger of T-cell activation. We first demonstrated that Tim-1-knockout (KO) mice survive lethal Ebola virus challenge. We then used a series of in vitro assays to demonstrate that Ebola virus directly binds primary T cells in a Tim-1-phosphatidylserine-dependent manner. We noted that binding induces a cytokine storm-like phenomenon and that blocking Tim-1-phosphatidylserine interactions reduces viral binding, T-cell activation, and cytokine production. These findings highlight a previously unknown role of Tim-1 in the development of a cytokine storm and "immune paralysis."

Metabolomics analyses identify platelet activating factors and heme breakdown products as Lassa fever biomarkers

Lassa fever afflicts tens of thousands of people in West Africa annually. The rapid progression of patients from febrile illness to fulminant syndrome and death provides incentive for development of clinical prognostic markers that can guide case management. The small molecule profile of serum from febrile patients triaged to the Viral Hemorrhagic Fever Ward at Kenema Government Hospital in Sierra Leone was assessed using untargeted Ultra High Performance Liquid Chromatography Mass Spectrometry. Physiological dysregulation resulting from Lassa virus (LASV) infection occurs at the small molecule level. Effects of LASV infection on pathways mediating blood coagulation, and lipid, amino acid, nucleic acid metabolism are manifest in changes in the levels of numerous metabolites in the circulation. Several compounds, including platelet activating factor (PAF), PAF-like molecules and products of heme breakdown emerged as candidates that may prove useful in diagnostic assays to inform better care of Lassa fever patients.

Lassa fever afflicts tens of thousands of people in West Africa each year. The disease progresses rapidly, but there are no tests available to determine which patients are at high risk for dying. We measured the levels of small molecules in the blood of febrile patients with and without infection by LASV that presented to Kenema Government Hospital in Sierra Leone using Ultra High Performance Liquid Chromatography Mass Spectrometry (LCMS), which identifies compounds based on their precise mass. Computational analyses were used to identify compounds that differed in patients with an acute LASV infection, patients with evidence of prior exposure to LASV and patients with fever, but who did not have evidence of exposure to LASV. Several serum metabolites, including factors that are involved in blood clotting and breakdown products of heme, were identified that may prove useful in diagnostic assays that will inform better care of Lassa fever patients or development of therapeutic interventions.

A Case of Human Lassa Virus Infection With Robust Acute T-Cell Activation and Long-Term Virus-Specific T-Cell Responses

A nurse who acquired Lassa virus infection in Togo in the spring of 2016 was repatriated to the United States for care at Emory University Hospital. Serial sampling from this patient permitted the characterization of several aspects of the innate and cellular immune responses to Lassa virus. Although most of the immune responses correlated with the kinetics of viremia resolution, the CD8 T-cell response was of surprisingly high magnitude and prolonged duration, implying prolonged presentation of viral antigens. Indeed, long after viremia resolution, there was persistent viral RNA detected in the semen of the patient, accompanied by epididymitis, suggesting the male reproductive tract as 1 site of antigen persistence. Consistent with the magnitude of acute T-cell responses, the patient ultimately developed long-term, polyfunctional memory T-cell responses to Lassa virus.

Infection with the Makona variant results in a delayed and distinct host immune response compared to previous Ebola virus variants

Zaire Ebolavirus (ZEBOV) continues to pose a significant threat to human health as highlighted by the recent epidemic that originated in West Africa and the ongoing outbreak in the Democratic Republic of the Congo. Although the ZEBOV variant responsible for this epidemic (Makona) shares significant genetic similarity with previously identified variants (Kikwit and Mayinga), recent reports suggest slower disease progression in nonhuman primates. However, the pathogenesis caused by the new variant is not fully understood. We present the first comprehensive approach in understanding ZEBOV-Makona pathogenesis in cynomolgus macaques by measuring changes in immune cell frequencies, plasma levels of immune mediators, and differentially expressed genes (DEGs) within whole blood (WB) and peripheral blood mononuclear cells (PBMC). Our combined approach revealed a link between: 1) increased interferon-stimulated gene expression, IFNα levels, and activated plasmacytoid dendritic cells; 2) higher proinflammatory gene expression, cytokine and chemokine levels, and non-classical monocytes; 3) gene signature of leukocyte activation and increased granulocytes; and 4) decreased expression of lymphocyte related genes and lymphopenia. In addition, our data strongly indicate delayed disease progression as well as limited overlap (~30%) in host transcriptome changes following ZEBOV-Makona infection compared to ZEBOV-Kikwit. These observations provide novel insight into the molecular mechanisms of ZEBOV-Makona pathogenesis.

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.

Clinical Evaluation of Ebola Virus Disease Therapeutics

Ebola virus disease (EVD) was first described over 40 years ago, but no treatment has been approved for humans. The 2013-2016 EVD outbreak in West Africa has expedited the clinical evaluation of several candidate therapeutics that act through different mechanisms, but with mixed results. Nevertheless, these studies are important because the accumulation of clinical data and valuable experience in conducting efficacy trials under emergency circumstances will lead to better implementation of similar studies in the future. Here, we summarize the results of EVD clinical trials, focus on the discussion of factors that may have potentially impeded the effectiveness of existing candidate therapeutics, and highlight considerations that may help meet the challenges ahead in the quest to develop clinically approved drugs.

Molecular pathogenesis of viral hemorrhagic fever

The clinical syndrome referred to as viral hemorrhagic fever (VHF) can be caused by several different families of RNA viruses, including select members of the arenaviruses, bunyaviruses, filoviruses, and flaviviruses. VHF is characterized by malaise, fever, vascular permeability, decreased plasma volume, coagulation abnormalities, and varying degrees of hemorrhage. Study of the filovirus Ebola virus has demonstrated a critical role for suppression of innate antiviral defenses in viral pathogenesis. Additionally, antigen-presenting cells are targets of productive infection and immune dysregulation. Among these cell populations, monocytes and macrophages are proposed to produce damaging inflammatory cytokines, while infected dendritic cells fail to undergo proper maturation, potentially impairing adaptive immunity. Uncontrolled virus replication and accompanying inflammatory responses are thought to promote vascular leakage and coagulopathy. However, the specific molecular pathways that underlie these features of VHF remain poorly understood. The arenavirus Lassa virus and the flavivirus yellow fever virus exhibit similar molecular pathogenesis suggesting common underlying mechanisms. Because non-human primate models that closely mimic VHF are available for Ebola, Lassa, and yellow fever viruses, we propose that comparative molecular studies using these models will yield new insights into the molecular underpinnings of VHF and suggest new therapeutic approaches.

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

Fatal outcomes of Ebola virus (EBOV) infections are typically preceded by a 'sepsis-like' syndrome and lymphopenia despite T cells being resistant to Ebola infection. The mechanisms that lead to T lymphocytes death remain largely unknown; however, the degree of lymphopenia is highly correlative with fatalities. Here we investigated whether the addition of EBOV or its envelope glycoprotein (GP) to isolated primary human CD4+ T cells induced cell death. We observed a significant decrease in cell viability in a GP-dependent manner, which is suggestive of a direct role of GP in T cell death. Using immunoprecipitation assays and flow cytometry, we demonstrate that EBOV directly binds to CD4+ T cells through interaction of GP with TLR4. Transcriptome analysis revealed that the addition of EBOV to CD4+ T cells results in the significant upregulation of pathways associated with interferon signaling, pattern recognition receptors and intracellular activation of NFκB signaling pathway. Both transcriptome analysis and specific inhibitors allowed identification of apoptosis and necrosis as mechanisms associated with the observed T cell death following exposure to EBOV. The addition of the TLR4 inhibitor CLI-095 significantly reduced CD4+ T cell death induced by GP. EBOV stimulation of primary CD4+ T cells resulted in a significant increase in secreted TNFα; inhibition of TNFα-mediated signaling events significantly reduced T cell death while inhibitors of both necrosis and apoptosis similarly reduced EBOV-induced T cell death. Lastly, we show that stimulation with EBOV or GP augments monocyte maturation as determined by an overall increase in expression levels of markers of differentiation. Subsequently, the increased rates of cellular differentiation resulted in higher rates of infection further contributing to T cell death. These results demonstrate that GP directly subverts the host's immune response by increasing the susceptibility of monocytes to EBOV infection and triggering lymphopenia through direct and indirect mechanisms.

Ebola virus infection kinetics in chimeric mice reveal a key role of T cells as barriers for virus dissemination

Ebola virus (EBOV) causes severe systemic disease in humans and non-human primates characterized by high levels of viremia and virus titers in peripheral organs. The natural portals of virus entry are the mucosal surfaces and the skin where macrophages and dendritic cells (DCs) are primary EBOV targets. Due to the migratory properties of DCs, EBOV infection of these cells has been proposed as a necessary step for virus dissemination via draining lymph nodes and blood. Here we utilize chimeric mice with competent hematopoietic-driven immunity, to show that EBOV primarily infects CD11b⁺ DCs in non-lymphoid and lymphoid tissues, but spares the main cross-presenting CD103⁺ DC subset. Furthermore, depletion of CD8 and CD4 T cells resulted in loss of early control of virus replication, viremia and fatal Ebola virus disease (EVD). Thus, our findings point out at T cell function as a key determinant of EVD progress and outcome.

Immunobiology of Ebola and Lassa virus infections

Two of the most important contemporary emerging viruses that affect human health in Africa are Ebola virus (EBOV) and Lassa virus (LASV). The 2013-2016 West African outbreak of EBOV was responsible for more than 11,000 deaths, primarily in Guinea, Sierra Leone and Liberia. LASV is constantly emerging in these and surrounding West African countries, with an estimate of more than 500,000 cases of Lassa fever, and approximately 5,000 deaths, annually. Both EBOV and LASV are zoonotic, and human infection often results in a severe haemorrhagic fever in both cases. However, the contribution of specific immune responses to disease differs between EBOV and LASV. This Review examines innate and adaptive immune responses to these viruses with the goal of delineating responses that are associated with protective versus pathogenic outcomes.

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.

The Ebola Interferon Inhibiting Domains Attenuate and Dysregulate Cell-Mediated Immune Responses

Ebola virus (EBOV) infections are characterized by deficient T-lymphocyte responses, T-lymphocyte apoptosis and lymphopenia. We previously showed that disabling of interferon-inhibiting domains (IIDs) in the VP24 and VP35 proteins effectively unblocks maturation of dendritic cells (DCs) and increases the secretion of cytokines and chemokines. Here, we investigated the role of IIDs in adaptive and innate cell-mediated responses using recombinant viruses carrying point mutations, which disabled IIDs in VP24 (EBOV/VP24m), VP35 (EBOV/VP35m) or both (EBOV/VP35m/VP24m). Peripheral blood mononuclear cells (PBMCs) from cytomegalovirus (CMV)-seropositive donors were inoculated with the panel of viruses and stimulated with CMV pp65 peptides. Disabling of the VP35 IID resulted in increased proliferation and higher percentages of CD4+ T cells secreting IFNγ and/or TNFα. To address the role of aberrant DC maturation in the IID-mediated suppression of T cell responses, CMV-stimulated DCs were infected with the panel of viruses and co-cultured with autologous T-lymphocytes. Infection with EBOV/VP35m infection resulted in a significant increase, as compared to wt EBOV, in proliferating CD4+ cells secreting IFNγ, TNFα and IL-2. Experiments with expanded CMV-specific T cells demonstrated their increased activation following co-cultivation with CMV-pulsed DCs pre-infected with EBOV/VP24m, EBOV/VP35m and EBOV/VP35m/VP24m, as compared to wt EBOV. Both IIDs were found to block phosphorylation of TCR complex-associated adaptors and downstream signaling molecules. Next, we examined the effects of IIDs on the function of B cells in infected PBMC. Infection with EBOV/VP35m and EBOV/VP35m/VP24m resulted in significant increases in the percentages of phenotypically distinct B-cell subsets and plasma cells, as compared to wt EBOV, suggesting inhibition of B cell function and differentiation by VP35 IID. Finally, infection with EBOV/VP35m increased activation of NK cells, as compared to wt EBOV. These results demonstrate a global suppression of cell-mediated responses by EBOV IIDs and identify the role of DCs in suppression of T-cell responses.

Identification of genetic pathways driving Ebola virus disease in humans and targets for therapeutic intervention

Introduction: LCK gene, also known as lymphocyte-specific proto-oncogene, is expressed in lymphocytes, and associated with coordinated expression of MHC class I and II in response to physiological stimuli, mediated through a combined interaction of promoters, suppressors, and enhancers. Differential usage of LCK promoters, transcribes dysfunctional transcript variants leading to leukemogenesis and non-induction of MHC class I gene variants. Viruses use C-type lectins, like CD209, to penetrate the cell, and inhibit Pattern Recognition Receptors (PRR), hence evading immune destruction. Given that Ebolavirus (EBOV) disease burden could result from a dysfunctional LCK pathway, identification of the genetic pathway leading to proper immune induction is a major priority. Methods: Data for EBOV related virus samples were obtained from Gene Expression Omnibus database and RMEAN information per gene per sample were entered into a table of values. R software v.3.3.1 was used to process differential expression patterns across samples for LCK, CD209 and immune-related genes. Principal component analysis (PCA) using ggbiplot v.0.55 was used to explain the variance across samples. Results: Data analyses identified three viral clusters based on transmission patterns as follows: LCK-CD209 dependent, LCK-dependent specific to EBOV, and CD209 dependent. Compared to HLA class II gene variants, HLA class I (A, B and C) variants were <2 fold expressed, especially for EBOV samples. PCA analyses classified TYRO3, TBK1 and LCK genes independent of the data, leading to identification of a possible pathway involving LCK, IL2, PI3k, TBK1, TYRO3 and MYB genes with downstream induction of immune T-cells. Discussion: This is the first study undertaken to understand the non-functional immune pathway, leading to EBOV disease pathogenesis and high fatality rates. Our lab currently exploits, through cutting edge genetic technology to understand the interplay of identified genes required for proper immune induction. This will guide antiviral therapy and possible markers for viral disease identification during outbreaks.

Molecular mechanisms of Ebola pathogenesis

Ebola viruses (EBOVs) and Marburg viruses (MARVs) are among the deadliest human viruses, as highlighted by the recent and widespread Ebola virus outbreak in West Africa, which was the largest and longest epidemic of Ebola virus disease (EVD) in history, resulting in significant loss of life and disruptions across multiple continents. Although the number of cases has nearly reached its nadir, a recent cluster of 5 cases in Guinea on March 17, 2016, has extended the enhanced surveillance period to June 15, 2016. New, enhanced 90-d surveillance windows replaced the 42-d surveillance window to ensure the rapid detection of new cases that may arise from a missed transmission chain, reintroduction from an animal reservoir, or more important, reemergence of the virus that has persisted in an EVD survivor. In this review, we summarize our current understanding of EBOV pathogenesis, describe vaccine and therapeutic candidates in clinical trials, and discuss mechanisms of viral persistence and long-term health sequelae for EVD survivors.

Ebola Virus Disease Is Characterized by Poor Activation and Reduced Levels of Circulating CD16+ Monocytes

A number of previous studies have identified antigen-presenting cells (APCs) as key targets of Ebola virus (EBOV), but the role of APCs in human Ebola virus disease (EVD) is not known. We have evaluated the phenotype and kinetics of monocytes, neutrophils, and dendritic cells (DCs) in peripheral blood of patients for whom EVD was diagnosed by the European Mobile Laboratory in Guinea. Acute EVD was characterized by reduced levels of circulating nonclassical CD16⁺ monocytes with a poor activation profile. In survivors, CD16⁺ monocytes were activated during recovery, coincident with viral clearance, suggesting an important role of this cell subset in EVD pathophysiology.

Vaccine platforms to control Lassa fever

INTRODUCTION

Lassa virus (LASV), the most prominent human pathogen of the Arenaviridae, is transmitted to humans from infected rodents and can cause Lassa Fever (LF). The sizeable disease burden in West Africa, numerous imported LF cases worldwide, and the possibility that LASV can be used as an agent of biological warfare make a strong case for vaccine development. There are no licensed LASV vaccines and the antiviral treatment is limited to an off-label use of ribavirin that is only partially effective.

AREAS COVERED

LASV vaccine development is hampered by high cost of biocontainment requirement, the absence of appropriate small animal models, genetic diversity of LASV species, and by high HIV-1 prevalence in LASV endemic areas. Over the past 15 years several vaccine platforms have been developed. Natural history of LASV and pathogenesis of the disease provide strong justification for replication-competent (RC) vaccine as one of the most feasible approaches to control LF. Development of LASV vaccine candidates based on reassortant, recombinant, and alphavirus replicon technologies is covered in this review. Expert commentary: Two lead RC vaccine candidates, reassortant ML29 and recombinant VSV/LASV, have been successfully tested in non-human primates and have been recommended by international vaccine experts for rapid clinical development. Both platforms have powerful molecular tools to further secure safety, improve immunogenicity, and cross-protection. These platforms are well positioned to design multivalent vaccines to protect against all LASV strains citculatrd in West Africa. The regulatory pathway of Candid #1, the first live-attenuated arenaviral vaccine against Argentine hemorrhagic, will be a reasonable guideline for LASV vaccine efficacy trials.

Chimeric Mice with Competent Hematopoietic Immunity Reproduce Key Features of Severe Lassa Fever

Lassa fever (LASF) is a highly severe viral syndrome endemic to West African countries. Despite the annual high morbidity and mortality caused by LASF, very little is known about the pathophysiology of the disease. Basic research on LASF has been precluded due to the lack of relevant small animal models that reproduce the human disease. Immunocompetent laboratory mice are resistant to infection with Lassa virus (LASV) and, to date, only immunodeficient mice, or mice expressing human HLA, have shown some degree of susceptibility to experimental infection. Here, transplantation of wild-type bone marrow cells into irradiated type I interferon receptor knockout mice (IFNAR-/-) was used to generate chimeric mice that reproduced important features of severe LASF in humans. This included high lethality, liver damage, vascular leakage and systemic virus dissemination. In addition, this model indicated that T cell-mediated immunopathology was an important component of LASF pathogenesis that was directly correlated with vascular leakage. Our strategy allows easy generation of a suitable small animal model to test new vaccines and antivirals and to dissect the basic components of LASF pathophysiology.

Effects of Filovirus Interferon Antagonists on Responses of Human Monocyte-Derived Dendritic Cells to RNA Virus Infection

Dendritic cells (DCs) are major targets of filovirus infection in vivo Previous studies have shown that the filoviruses Ebola virus (EBOV) and Marburg virus (MARV) suppress DC maturation in vitro Both viruses also encode innate immune evasion functions. The EBOV VP35 (eVP35) and the MARV VP35 (mVP35) proteins each can block RIG-I-like receptor signaling and alpha/beta interferon (IFN-α/β) production. The EBOV VP24 (eVP24) and MARV VP40 (mVP40) proteins each inhibit the production of IFN-stimulated genes (ISGs) by blocking Jak-STAT signaling; however, this occurs by different mechanisms, with eVP24 blocking nuclear import of tyrosine-phosphorylated STAT1 and mVP40 blocking Jak1 function. MARV VP24 (mVP24) has been demonstrated to modulate host cell antioxidant responses. Previous studies demonstrated that eVP35 is sufficient to strongly impair primary human monocyte-derived DC (MDDC) responses upon stimulation induced through the RIG-I-like receptor pathways. We demonstrate that mVP35, like eVP35, suppresses not only IFN-α/β production but also proinflammatory responses after stimulation of MDDCs with RIG-I activators. In contrast, eVP24 and mVP40, despite suppressing ISG production upon RIG-I activation, failed to block upregulation of maturation markers or T cell activation. mVP24, although able to stimulate expression of antioxidant response genes, had no measurable impact of DC function. These data are consistent with a model where filoviral VP35 proteins are the major suppressors of DC maturation during filovirus infection, whereas the filoviral VP24 proteins and mVP40 are insufficient to prevent DC maturation.

IMPORTANCE

The ability to suppress the function of dendritic cells (DCs) likely contributes to the pathogenesis of disease caused by the filoviruses Ebola virus and Marburg virus. To clarify the basis for this DC suppression, we assessed the effect of filovirus proteins known to antagonize innate immune signaling pathways, including Ebola virus VP35 and VP24 and Marburg virus VP35, VP40, and VP24, on DC maturation and function. The data demonstrate that the VP35s from Ebola virus and Marburg virus are the major suppressors of DC maturation and that the effects on DCs of the remaining innate immune inhibitors are minor.

Inhibition of Innate Immune Responses Is Key to Pathogenesis by Arenaviruses

Mammalian arenaviruses are zoonotic viruses that cause asymptomatic, persistent infections in their rodent hosts but can lead to severe and lethal hemorrhagic fever with bleeding and multiorgan failure in human patients. Lassa virus (LASV), for example, is endemic in several West African countries, where it is responsible for an estimated 500,000 infections and 5,000 deaths annually. There are currently no FDA-licensed therapeutics or vaccines available to combat arenavirus infection. A hallmark of arenavirus infection (e.g., LASV) is general immunosuppression that contributes to high viremia. Here, we discuss the early host immune responses to arenavirus infection and the recently discovered molecular mechanisms that enable pathogenic viruses to suppress host immune recognition and to contribute to the high degree of virulence. We also directly compare the innate immune evasion mechanisms between arenaviruses and other hemorrhagic fever-causing viruses, such as Ebola, Marburg, Dengue, and hantaviruses. A better understanding of the immunosuppression and immune evasion strategies of these deadly viruses may guide the development of novel preventative and therapeutic options.

Temporal Progression of Lesions in Guinea Pigs Infected With Lassa Virus

Lassa virus (LASV) infection causes an acute, multisystemic viral hemorrhagic fever that annually infects an estimated 100 000 to 300 000 persons in West Africa. This pathogenesis study evaluated the temporal progression of disease in guinea pigs following aerosol and subcutaneous inoculation of the Josiah strain of LASV as well as the usefulness of Strain 13 guinea pigs as an animal model for Lassa fever. After experimental infection, guinea pigs ( Cavia porcellus; n = 67) were serially sampled to evaluate the temporal progression of infection, gross and histologic lesions, and serum chemistry and hematologic changes. Guinea pigs developed viremia on day 5 to 6 postexposure (PE), with clinical signs appearing by day 7 to 8 PE. Complete blood counts revealed lymphopenia and thrombocytopenia. Gross pathologic findings included skin lesions and congested lungs. Histologic lesions consisted of cortical lymphoid depletion by day 6 to 7 PE with lymphohistiocytic interstitial pneumonia at 7 to 8 days PE. Scattered hepatocellular degeneration and cell death were also noted in the liver and, to a lesser extent, in other tissues including the haired skin, lung, heart, adrenal gland, lymph nodes, thymus, and spleen. The first cell types to demonstrate staining for viral antigen were fibroblastic reticular cells and macrophages/dendritic cells in the lymph nodes on day 5 to 6 PE. This study demonstrates similarities between Lassa viral disease in human infections and experimental guinea pig infection. These shared pathologic characteristics support the utility of guinea pigs as an additional animal model for vaccine and therapeutic development under the Food and Drug Administration's Animal Rule.

Ebola Virus Disease: A Review of Its Past and Present

Ebola virus, the virus responsible for Ebola virus disease, has spawned several epidemics during the past 38 years. In 2014, an Ebola epidemic spread from Africa to other continents, becoming a pandemic. The virus's relatively unique structure, its infectivity and lethality, the difficulty in stopping its spread, and the lack of an effective treatment captured the world's attention. This article provides a brief review of the known history of Ebola virus disease, its etiology, epidemiology, and pathophysiology and a review of the limited information on managing patients with Ebola virus disease.

Interferon-γ Inhibits Ebola Virus Infection

Ebola virus outbreaks, such as the 2014 Makona epidemic in West Africa, are episodic and deadly. Filovirus antivirals are currently not clinically available. Our findings suggest interferon gamma, an FDA-approved drug, may serve as a novel and effective prophylactic or treatment option. Using mouse-adapted Ebola virus, we found that murine interferon gamma administered 24 hours before or after infection robustly protects lethally-challenged mice and reduces morbidity and serum viral titers. Furthermore, we demonstrated that interferon gamma profoundly inhibits Ebola virus infection of macrophages, an early cellular target of infection. As early as six hours following in vitro infection, Ebola virus RNA levels in interferon gamma-treated macrophages were lower than in infected, untreated cells. Addition of the protein synthesis inhibitor, cycloheximide, to interferon gamma-treated macrophages did not further reduce viral RNA levels, suggesting that interferon gamma blocks life cycle events that require protein synthesis such as virus replication. Microarray studies with interferon gamma-treated human macrophages identified more than 160 interferon-stimulated genes. Ectopic expression of a select group of these genes inhibited Ebola virus infection. These studies provide new potential avenues for antiviral targeting as these genes that have not previously appreciated to inhibit negative strand RNA viruses and specifically Ebola virus infection. As treatment of interferon gamma robustly protects mice from lethal Ebola virus infection, we propose that interferon gamma should be further evaluated for its efficacy as a prophylactic and/or therapeutic strategy against filoviruses. Use of this FDA-approved drug could rapidly be deployed during future outbreaks.

Filovirus outbreaks occur sporadically, but with increasing frequency. With no current approved filovirus therapeutics, the 2014 Makona Ebola virus epidemic in Guinea, Sierra Leone and Liberia emphasizes the need for effective treatments against this highly pathogenic family of viruses. The use of this FDA-approved drug to inhibit Ebola virus infection would allow rapid implementation of a novel antiviral therapy for future crises. Interferon gamma elicits an antiviral state in antigen-presenting cells and stimulates cellular immune responses. We demonstrate that interferon gamma profoundly inhibits Ebola virus infection of macrophages, which are early cellular targets of Ebola virus. We also identify novel interferon gamma-stimulated genes in human macrophage populations that have not been previously appreciated to inhibit filoviruses or other negative strand RNA viruses. Finally and most importantly, we show that interferon gamma given 24 hours prior to or after virus infection protects mice from lethal Ebola virus challenge, suggesting that this drug may serve as an effective prophylactic and/or therapeutic strategy against this deadly virus.

The Role of Cytokines and Chemokines in Filovirus Infection

Ebola- and marburgviruses are highly pathogenic filoviruses and causative agents of viral hemorrhagic fever. Filovirus disease is characterized by a dysregulated immune response, severe organ damage, and coagulation abnormalities. This includes modulation of cytokines, signaling mediators that regulate various components of the immune system as well as other biological processes. Here we examine the role of cytokines in filovirus infection, with an emphasis on understanding how these molecules affect development of the antiviral immune response and influence pathology. These proteins may present targets for immune modulation by therapeutic agents and vaccines in an effort to boost the natural immune response to infection and/or reduce immunopathology.

Filovirus pathogenesis and immune evasion: insights from Ebola virus and Marburg virus

Ebola viruses and Marburg viruses, members of the filovirus family, are zoonotic pathogens that cause severe disease in people, as highlighted by the latest Ebola virus epidemic in West Africa. Filovirus disease is characterized by uncontrolled virus replication and the activation of host responses that contribute to pathogenesis. Underlying these phenomena is the potent suppression of host innate antiviral responses, particularly the type I interferon response, by viral proteins, which allows high levels of viral replication. In this Review, we describe the mechanisms used by filoviruses to block host innate immunity and discuss the links between immune evasion and filovirus pathogenesis.

Ebola virus infection induces irregular dendritic cell gene expression

Filoviruses subvert the human immune system in part by infecting and replicating in dendritic cells (DCs). Using gene arrays, a phenotypic profile of filovirus infection in human monocyte-derived DCs was assessed. Monocytes from human donors were cultured in GM-CSF and IL-4 and were infected with Ebola virus Kikwit variant for up to 48 h. Extracted DC RNA was analyzed on SuperArray's Dendritic and Antigen Presenting Cell Oligo GEArray and compared to uninfected controls. Infected DCs exhibited increased expression of cytokine, chemokine, antiviral, and anti-apoptotic genes not seen in uninfected controls. Significant increases of intracellular antiviral and MHC I and II genes were also noted in EBOV-infected DCs. However, infected DCs failed to show any significant difference in co-stimulatory T-cell gene expression from uninfected DCs. Moreover, several chemokine genes were activated, but there was sparse expression of chemokine receptors that enabled activated DCs to home to lymph nodes. Overall, statistically significant expression of several intracellular antiviral genes was noted, which may limit viral load but fails to stop replication. EBOV gene expression profiling is of vital importance in understanding pathogenesis and devising novel therapeutic treatments such as small-molecule inhibitors.

Immunological features underlying viral hemorrhagic fevers

Several enveloped RNA viruses of the arenavirus, bunyavirus, filovirus and flavivirus families are associated with a syndrome known as viral hemorrhagic fever (VHF). VHF is characterized by fever, vascular leakage, coagulation defects and multi organ system failure. VHF is currently viewed as a disease precipitated by viral suppression of innate immunity, which promotes systemic virus replication and excessive proinflammatory cytokine responses that trigger the manifestations of severe disease. However, the mechanisms by which immune dysregulation contributes to disease remain poorly understood. Infection of nonhuman primates closely recapitulates human VHF, notably Ebola and yellow fever, thereby providing excellent models to better define the immunological basis for this syndrome. Here we review the current state of our knowledge and suggest future directions that will better define the immunological mechanisms underlying VHF.

Molecular mechanisms of Ebola virus pathogenesis: focus on cell death

Ebola virus (EBOV) belongs to the Filoviridae family and is responsible for a severe disease characterized by the sudden onset of fever and malaise accompanied by other non-specific signs and symptoms; in 30–50% of cases hemorrhagic symptoms are present. Multiorgan dysfunction occurs in severe forms with a mortality up to 90%. The EBOV first attacks macrophages and dendritic immune cells. The innate immune reaction is characterized by a cytokine storm, with secretion of numerous pro-inflammatory cytokines, which induces a huge number of contradictory signals and hurts the immune cells, as well as other tissues. Other highly pathogenic viruses also trigger cytokine storms, but Filoviruses are thought to be particularly lethal because they affect a wide array of tissues. In addition to the immune system, EBOV attacks the spleen and kidneys, where it kills cells that help the body to regulate its fluid and chemical balance and that make proteins that help the blood to clot. In addition, EBOV causes liver, lungs and kidneys to shut down their functions and the blood vessels to leak fluid into surrounding tissues. In this review, we analyze the molecular mechanisms at the basis of Ebola pathogenesis with a particular focus on the cell death pathways induced by the virus. We also discuss how the treatment of the infection can benefit from the recent experience of blocking/modulating cell death in human degenerative diseases.

Human hemorrhagic Fever causing arenaviruses: molecular mechanisms contributing to virus virulence and disease pathogenesis

Arenaviruses include multiple human pathogens ranging from the low-risk lymphocytic choriomeningitis virus (LCMV) to highly virulent hemorrhagic fever (HF) causing viruses such as Lassa (LASV), Junin (JUNV), Machupo (MACV), Lujo (LUJV), Sabia (SABV), Guanarito (GTOV), and Chapare (CHPV), for which there are limited preventative and therapeutic measures. Why some arenaviruses can cause virulent human infections while others cannot, even though they are isolated from the same rodent hosts, is an enigma. Recent studies have revealed several potential pathogenic mechanisms of arenaviruses, including factors that increase viral replication capacity and suppress host innate immunity, which leads to high viremia and generalized immune suppression as the hallmarks of severe and lethal arenaviral HF diseases. This review summarizes current knowledge of the roles of each of the four viral proteins and some known cellular factors in the pathogenesis of arenaviral HF as well as of some human primary cell-culture and animal models that lend themselves to studying arenavirus-induced HF disease pathogenesis. Knowledge gained from these studies can be applied towards the development of novel therapeutics and vaccines against these deadly human pathogens.

Different Temporal Effects of Ebola Virus VP35 and VP24 Proteins on Global Gene Expression in Human Dendritic Cells

Ebola virus (EBOV) causes a severe hemorrhagic fever with a deficient immune response, lymphopenia, and lymphocyte apoptosis. Dendritic cells (DC), which trigger the adaptive response, do not mature despite EBOV infection. We recently demonstrated that DC maturation is unblocked by disabling the innate response antagonizing domains (IRADs) in EBOV VP35 and VP24 by the mutations R312A and K142A, respectively. Here we analyzed the effects of VP35 and VP24 with the IRADs disabled on global gene expression in human DC. Human monocyte-derived DC were infected by wild-type (wt) EBOV or EBOVs carrying the mutation in VP35 (EBOV/VP35m), VP24 (EBOV/VP24m), or both (EBOV/VP35m/VP24m). Global gene expression at 8 and 24 h was analyzed by deep sequencing, and the expression of interferon (IFN) subtypes up to 5 days postinfection was analyzed by quantitative reverse transcription-PCR (qRT-PCR). wt EBOV induced a weak global gene expression response, including markers of DC maturation, cytokines, chemokines, chemokine receptors, and multiple IFNs. The VP35 mutation unblocked the expression, resulting in a dramatic increase in expression of these transcripts at 8 and 24 h. Surprisingly, DC infected with EBOV/VP24m expressed lower levels of many of these transcripts at 8 h after infection, compared to wt EBOV. In contrast, at 24 h, expression of the transcripts increased in DC infected with any of the three mutants, compared to wt EBOV. Moreover, sets of genes affected by the two mutations only partially overlapped. Pathway analysis demonstrated that the VP35 mutation unblocked pathways involved in antigen processing and presentation and IFN signaling. These data suggest that EBOV IRADs have profound effects on the host adaptive immune response through massive transcriptional downregulation of DC.

IMPORTANCE

This study shows that infection of DC with EBOV, but not its mutant forms with the VP35 IRAD and/or VP24 IRAD disabled, causes a global block in expression of host genes. The temporal effects of mutations disrupting the two IRADs differ, and the lists of affected genes only partially overlap such that VP35 and VP24 IRADs each have profound effects on antigen presentation by exposed DC. The global modulation of DC gene expression and the resulting lack of their maturation represent a major mechanism by which EBOV disables the T cell response and suggests that these suppressive pathways are a therapeutic target that may unleash the T cell responses during EBOV infection.

Pathophysiology of Ebola Virus Infection: Current Challenges and Future Hopes

The filoviruses, Ebola virus (EBOV) and Marburg virus (MARV), are among the deadliest viruses that cause disease in humans, with reported case fatality rates of up to 90% in some outbreaks. The high virulence of EBOV and MARV is largely attributed to the ability of these viruses to interfere with the host immune response. Currently, there are no approved vaccines or postexposure therapeutics, and treatment options for patients infected with EBOV are limited to supportive care. In this review, we discuss mechanisms of EBOV pathogenesis and its ability to subvert host immunity as well as several vaccines and therapeutics with respect to their evaluation in small animal models, nonhuman primates, and human clinical trials.

Hegemonic structure of basic, clinical and patented knowledge on Ebola research: a US army reductionist initiative

Background

Ebola hemorrhagic fever (Ebola) is still a highly lethal infectious disease long affecting mainly neglected populations in sub-Saharan Africa. Moreover, this disease is now considered a potential worldwide threat. In this paper, we present an approach to understand how the basic, clinical and patent knowledge on Ebola is organized and intercommunicated and what leading factor could be shaping the evolution of the knowledge translation process for this disease.

Methodology

A combination of citation network analysis; analysis of Medical heading Subject (MeSH) and Gene Ontology (GO) terms, and quantitative content analysis for patents and scientific literature, aimed to map the organization of Ebola research was carried out.

Results

We found six putative research fronts (i.e. clusters of high interconnected papers). Three research fronts are basic research on Ebola virus structural proteins: glycoprotein, VP40 and VP35, respectively. There is a fourth research front of basic research papers on pathogenesis, which is the organizing hub of Ebola research. A fifth research front is pre-clinical research focused on vaccines and glycoproteins. Finally, a clinical-epidemiology research front related to the disease outbreaks was identified. The network structure of patent families shows that the dominant design is the use of Ebola virus proteins as targets of vaccines and other immunological treatments. Therefore, patents network organization resembles the organization of the scientific literature. Specifically, the knowledge on Ebola would flow from higher (clinical-epidemiology) to intermediated (cellular-tissular pathogenesis) to lower (molecular interactions) levels of organization.

Conclusion

Our results suggest a strong reductionist approach for Ebola research probably influenced by the lethality of the disease. On the other hand, the ownership profile of the patent families network and the main researches relationship with the United State Army suggest a strong involvement of this military institution in Ebola research.

L’Émergence du virus EBOLA chez l’homme: un long processus pas totalement élucidé

Le virus Ébola cause régulièrement depuis 1976 des petites épidémies meurtrières généralement maitrisées en quelques mois. Alors que seule l’Afrique Centrale en avait été victime jusqu’alors, une épidémie à virus Ébola d’une ampleur extraordinaire embrase dramatiquement plusieurs pays d’Afrique de l’Ouest depuis le mois de décembre 2013 principalement en raison des défaillances majeures dans la mise en œuvre des mesures visant à empêcher les transmissions interhumaines du virus. Après une période d’incubation d’environ une semaine, la maladie se manifeste par l’apparition soudaine d’une forte fièvre aboutissant in fine à des hémorragies multiples puis à la défaillance généralisée des organes. Plusieurs espèces de chauves-souris seraient les principaux réservoirs du virus Ébola. La contamination de l’homme se produirait soit directement auprès des chauves-souris, largement consommées par les populations locales, soit par l’intermédiaire d’espèces animales sensibles au virus, telles que les chimpanzés et les gorilles. À côté de ce « cycle naturel », l’hypothèse d’un « cycle épidémique » impliquant des espèces animales domestiques vivant dans les villages tels que les chiens ou les porcs, tend désormais à être sérieusement avancée. Ainsi, en fonction des animaux impliqués et de la forme clinique des infections développées, les modalités de la contamination de l’homme peuvent être multiples et sont donc encore largement méconnues. Dans un tel contexte, tous les efforts qui pourront être déployés pour percer le mystère de l’émergence du virus Ébola chez l’homme et clarifier les modalités de la transmission du virus, permettront peut-être de prédire voire d’anticiper l’apparition des épidémies. L’objectif de cette revue est de dresser un état des lieux exhaustif de l’écologie du virus Ébola et de mettre en lumière les évènements qui gouvernent la transmission du virus à l’homme tout en précisant les points encore nombreux qui demeurent non élucidés.

Human Ebola virus infection results in substantial immune activation

Four Ebola patients received care at Emory University Hospital, presenting a unique opportunity to examine the cellular immune responses during acute Ebola virus infection. We found striking activation of both B and T cells in all four patients. Plasmablast frequencies were 10-50% of B cells, compared with less than 1% in healthy individuals. Many of these proliferating plasmablasts were IgG-positive, and this finding coincided with the presence of Ebola virus-specific IgG in the serum. Activated CD4 T cells ranged from 5 to 30%, compared with 1-2% in healthy controls. The most pronounced responses were seen in CD8 T cells, with over 50% of the CD8 T cells expressing markers of activation and proliferation. Taken together, these results suggest that all four patients developed robust immune responses during the acute phase of Ebola virus infection, a finding that would not have been predicted based on our current assumptions about the highly immunosuppressive nature of Ebola virus. Also, quite surprisingly, we found sustained immune activation after the virus was cleared from the plasma, observed most strikingly in the persistence of activated CD8 T cells, even 1 mo after the patients' discharge from the hospital. These results suggest continued antigen stimulation after resolution of the disease. From these convalescent time points, we identified CD4 and CD8 T-cell responses to several Ebola virus proteins, most notably the viral nucleoprotein. Knowledge of the viral proteins targeted by T cells during natural infection should be useful in designing vaccines against Ebola virus.

Genomic profiling of host responses to Lassa virus: therapeutic potential from primate to man

Lassa virus infection elicits distinctive changes in host gene expression and metabolism. We focus on changes in host gene expression that may be biomarkers that discriminate individual pathogens or may help to provide a prognosis for disease. In addition to assessing mRNA changes, functional studies are also needed to discriminate causes of disease from mechanisms of host resistance. Host responses that drive pathogenesis are likely to be targets for prevention or therapy. Host responses to Lassa or its related arenaviruses have been monitored in cell culture, in animal models of hemorrhagic fever, in Lassa-infected nonhuman primates and, to a limited extent, in infected human beings. Here, we describe results from those studies and discuss potential targets for reducing virus replication and mitigating disease.

Tissue and cellular tropism, pathology and pathogenesis of Ebola and Marburg viruses

Ebola viruses and Marburg viruses include some of the most virulent and fatal pathogens known to humans. These viruses cause severe haemorrhagic fevers, with case fatality rates in the range 25-90%. The diagnosis of filovirus using formalin-fixed tissues from fatal cases poses a significant challenge. The most characteristic histopathological findings are seen in the liver; however, the findings overlap with many other viral and non-viral haemorrhagic diseases. The need to distinguish filovirus infections from other haemorrhagic fevers, particularly in areas with multiple endemic viral haemorrhagic agents, is of paramount importance. In this review we discuss the current state of knowledge of filovirus infections and their pathogenesis, including histopathological findings, epidemiology, modes of transmission and filovirus entry and spread within host organisms. The pathogenesis of filovirus infections is complex and involves activation of the mononuclear phagocytic system, with release of pro-inflammatory cytokines, chemokines and growth factors, endothelial dysfunction, alterations of the innate and adaptive immune systems, direct organ and endothelial damage from unrestricted viral replication late in infection, and coagulopathy. Although our understanding of the pathogenesis of filovirus infections has rapidly increased in the past few years, many questions remain unanswered.

Ebola: translational science considerations

We are currently in the midst of the most aggressive and fulminating outbreak of Ebola-related disease, commonly referred to as "Ebola", ever recorded. In less than a year, the Ebola virus (EBOV, Zaire ebolavirus species) has infected over 10,000 people, indiscriminately of gender or age, with a fatality rate of about 50%. Whereas at its onset this Ebola outbreak was limited to three countries in West Africa (Guinea, where it was first reported in late March 2014, Liberia, where it has been most rampant in its capital city, Monrovia and other metropolitan cities, and Sierra Leone), cases were later reported in Nigeria, Mali and Senegal, as well as in Western Europe (i.e., Madrid, Spain) and the US (i.e., Dallas, Texas; New York City) by late October 2014. World and US health agencies declared that the current Ebola virus disease (EVD) outbreak has a strong likelihood of growing exponentially across the world before an effective vaccine, treatment or cure can be developed, tested, validated and distributed widely. In the meantime, the spread of the disease may rapidly evolve from an epidemics to a full-blown pandemic. The scientific and healthcare communities actively research and define an emerging kaleidoscope of knowledge about critical translational research parameters, including the virology of EBOV, the molecular biomarkers of the pathological manifestations of EVD, putative central nervous system involvement in EVD, and the cellular immune surveillance to EBOV, patient-centered anthropological and societal parameters of EVD, as well as translational effectiveness about novel putative patient-targeted vaccine and pharmaceutical interventions, which hold strong promise, if not hope, to curb this and future Ebola outbreaks. This work reviews and discusses the principal known facts about EBOV and EVD, and certain among the most interesting ongoing or future avenues of research in the field, including vaccination programs for the wild animal vectors of the virus and the disease from global translational science perspective.