Human macrophage C-type lectin specific for galactose and N-acetylgalactosamine promotes filovirus entry

Ebola virus secreted glycoprotein decreases the anti-viral immunity of macrophages in early inflammatory responses

During Ebola virus (EBOV) infection, secreted glycoprotein (sGP) is found in large quantities in the serum of both patients and infected animal models. It is thought to serve as a decoy for anti-EBOV antibodies. Using an in vitro model incorporating treatment of non-infected human THP-1 macrophages with recombinant EBOV sGP, this study sought to examine the impact of sGP upon key macrophage functions. Macrophage polarization and phagocytic capacity of activated macrophages were found to be unaltered by sGP treatment. However, treatment with sGP inhibited macrophage production of the pro-inflammatory cytokines TNFα and IL-6 while the yield of anti-inflammatory cytokine, IL-10, remained intact. Interestingly, the migratory ability of macrophages was also diminished by sGP, potentially due to a decrease in expression of CD11b, a vital macrophage integrin. Thus, EBOV sGP may operate to diminish functional contributions of non-infected macrophages to increase the potential viral dissemination.

Retro-2 and its dihydroquinazolinone derivatives inhibit filovirus infection

Members of the family Filoviridae cause severe, often fatal disease in humans, for which there are no approved vaccines and only a few experimental drugs tested in animal models. Retro-2, a small molecule that inhibits retrograde trafficking of bacterial and plant toxins inside host cells, has been demonstrated to be effective against a range of bacterial and virus pathogens, both in vitro and in animal models. Here, we demonstrated that Retro-2 and its derivatives, Retro-2.1 and compound 25, blocked infection by Ebola virus and Marburg virus in vitro. We show that the derivatives were more potent inhibitors of infection as compared to the parent compound. Pseudotyped virus assays indicated that the compounds affected virus entry into cells while virus particle localization to Niemann-Pick C1-positive compartments showed that they acted at a late step in virus entry. Our work demonstrates a potential for Retro-type drugs to be developed into anti-filoviral therapeutics.

Identification of a coumarin-based antihistamine-like small molecule as an anti-filoviral entry inhibitor

Filoviruses, consisting of Ebola virus, Marburg virus and Cuevavirus, cause severe hemorrhagic fevers in humans with high mortality rates up to 90%. Currently, there is no approved vaccine or therapy available for the prevention and treatment of filovirus infection in humans. The recent 2013-2015 West African Ebola epidemic underscores the urgency to develop antiviral therapeutics against these infectious diseases. Our previous study showed that GPCR antagonists, particularly histamine receptor antagonists (antihistamines) inhibit Ebola and Marburg virus entry. In this study, we screened a library of 1220 small molecules with predicted antihistamine activity, identified multiple compounds with potent inhibitory activity against entry of both Ebola and Marburg viruses in human cancer cell lines, and confirmed their anti-Ebola activity in human primary cells. These small molecules target a late-stage of Ebola virus entry. Further structure-activity relationship studies around one compound (cp19) reveal the importance of the coumarin fused ring structure, especially the hydrophobic substituents at positions 3 and/or 4, for its antiviral activity, and this identified scaffold represents a favorable starting point for the rapid development of anti-filovirus therapeutic agents.

Myeloid C-Type Lectin Receptors in Viral Recognition and Antiviral Immunity

Recognition of viral glycans by pattern recognition receptors (PRRs) in innate immunity contributes to antiviral immune responses. C-type lectin receptors (CLRs) are PRRs capable of sensing glycans present in viral pathogens to activate antiviral immune responses such as phagocytosis, antigen processing and presentation, and subsequent T cell activation. The ability of CLRs to elicit and shape adaptive immunity plays a critical role in the inhibition of viral spread within the host. However, certain viruses exploit CLRs for viral entry into host cells to avoid immune recognition. To block CLR interactions with viral glycoproteins, antiviral strategies may involve the use of multivalent glycan carrier systems. In this review, we describe the role of CLRs in antiviral immunity and we highlight their dual function in viral clearance and exploitation by viral pathogens.

Fasciola hepatica Immune Regulates CD11c+ Cells by Interacting with the Macrophage Gal/GalNAc Lectin

Fasciolosis, caused by Fasciola hepatica and Fasciola gigantica, is a trematode zoonosis of interest in public health and livestock production. Like other helminths, F. hepatica modulates the host immune response by inducing potent polarized Th2 and regulatory T cell immune responses and by downregulating the production of Th1 cytokines. In this work, we show that F. hepatica glycans increase Th2 immune responses by immunomodulating TLR-induced maturation and function of dendritic cells (DCs). This process was mediated by the macrophage Gal/GalNAc lectin (MGL) expressed on DCs, which recognizes the Tn antigen (GalNAc-Ser/Thr) on parasite components. More interestingly, we identified MGL-expressing CD11c⁺ cells in infected animals and showed that these cells are recruited both to the peritoneum and the liver upon F. hepatica infection. These cells express the regulatory cytokines IL-10, TNFα and TGFβ and a variety of regulatory markers. Furthermore, MGL⁺ CD11c⁺ cells expand parasite-specific Th2/regulatory cells and suppress Th1 polarization. The results presented here suggest a potential role of MGL in the immunomodulation of DCs induced by F. hepatica and contribute to a better understanding of the molecular and immunoregulatory mechanisms induced by this parasite.

Forty Years of Ebolavirus Molecular Biology: Understanding a Novel Disease Agent Through the Development and Application of New Technologies

Molecular biology is a broad discipline that seeks to understand biological phenomena at a molecular level, and achieves this through the study of DNA, RNA, proteins, and/or other macromolecules (e.g., those involved in the modification of these substrates). Consequently, it relies on the availability of a wide variety of methods that deal with the collection, preservation, inactivation, separation, manipulation, imaging, and analysis of these molecules. As such the state of the art in the field of ebolavirus molecular biology research (and that of all other viruses) is largely intertwined with, if not driven by, advancements in the technical methodologies available for these kinds of studies. Here we review of the current state of our knowledge regarding ebolavirus biology and emphasize the associated methods that made these discoveries possible.

Mechanisms of Filovirus Entry

Filovirus entry into cells is complex, perhaps as complex as any viral entry mechanism identified to date. However, over the past 10 years, the important events required for filoviruses to enter into the endosomal compartment and fuse with vesicular membranes have been elucidated (Fig. 1). Here, we highlight the important steps that are required for productive entry of filoviruses into mammalian cells.

[Molecular basis for negative-strand RNA virus entry and neutralization by antibodies]

Mononegaviruses are non-segmented negative-strand RNA viruses, and include measles, mumps, Marburg, and Ebola viruses. Measles virus and mumps virus, members of the family Paramyxoviridae, are immunotropic and neurotropic, respectively. Marburg virus and Ebola virus, members of the family Filoviridae, cause highly lethal hemorrhagic fever. In this paper, I summarize the recent structural and functional studies on the viral glycoproteins (GPs) of these viruses, which have shed light on virus entry and the humoral response. The structural and functional analyses of the interaction between viral GPs and receptors/antibodies also illuminate directions toward therapeutics against the viruses.

Fcγ-receptor IIa-mediated Src Signaling Pathway Is Essential for the Antibody-Dependent Enhancement of Ebola Virus Infection

Antibody-dependent enhancement (ADE) of Ebola virus (EBOV) infection has been demonstrated in vitro, raising concerns about the detrimental potential of some anti-EBOV antibodies. ADE has been described for many viruses and mostly depends on the cross-linking of virus-antibody complexes to cell surface Fc receptors, leading to enhanced infection. However, little is known about the molecular mechanisms underlying this phenomenon. Here we show that Fcγ-receptor IIa (FcγRIIa)-mediated intracellular signaling through Src family protein tyrosine kinases (PTKs) is required for ADE of EBOV infection. We found that deletion of the FcγRIIa cytoplasmic tail abolished EBOV ADE due to decreased virus uptake into cellular endosomes. Furthermore, EBOV ADE, but not non-ADE infection, was significantly reduced by inhibition of the Src family protein PTK pathway, which was also found to be important to promote phagocytosis/macropinocytosis for viral uptake into endosomes. We further confirmed a significant increase of the Src phosphorylation mediated by ADE. These data suggest that antibody-EBOV complexes bound to the cell surface FcγRIIa activate the Src signaling pathway that leads to enhanced viral entry into cells, providing a novel perspective for the general understanding of ADE of virus infection.

Filovirus proteins for antiviral drug discovery: A structure/function analysis of surface glycoproteins and virus entry

This review focuses on the recent progress in our understanding of filovirus protein structure/function and its impact on antiviral research. Here we focus on the surface glycoprotein GP_1,2 and its different roles in filovirus entry. We first describe the latest advances on the characterization of GP gene-overlapping proteins sGP, ssGP and Δ-peptide. Then, we compare filovirus surface GP_1,2 proteins in terms of structure, synthesis and function. As they bear potential in drug-design, the discovery of small organic compounds inhibiting filovirus entry is a currently very active field. Although it is at an early stage, the development of antiviral drugs against Ebola and Marburg virus entry might prove essential to reduce outbreak-associated fatality rates through post-exposure treatment of both suspected and confirmed cases.

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The filovirus surface glycoprotein is the key player protein responsible for viral entry.

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Secreted forms of the glycoprotein have been suggested to participate to filovirus virus pathogenicity.

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Recent structural insights of the filovirus surface glycoprotein highlight new antiviral perspectives.

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Interesting compounds and innovative antiviral strategies emerge from research and development to inhibit filovirus entry.

Characterization of Human and Murine T-Cell Immunoglobulin Mucin Domain 4 (TIM-4) IgV Domain Residues Critical for Ebola Virus Entry

Phosphatidylserine (PtdSer) receptors that are responsible for the clearance of dying cells have recently been found to mediate enveloped virus entry. Ebola virus (EBOV), a member of the Filoviridae family of viruses, utilizes PtdSer receptors for entry into target cells. The PtdSer receptors human and murine T-cell immunoglobulin mucin (TIM) domain proteins TIM-1 and TIM-4 mediate filovirus entry by binding to PtdSer on the virion surface via a conserved PtdSer binding pocket within the amino-terminal IgV domain. While the residues within the TIM-1 IgV domain that are important for EBOV entry are characterized, the molecular details of virion-TIM-4 interactions have yet to be investigated. As sequences and structural alignments of the TIM proteins suggest distinct differences in the TIM-1 and TIM-4 IgV domain structures, we sought to characterize TIM-4 IgV domain residues required for EBOV entry. Using vesicular stomatitis virus pseudovirions bearing EBOV glycoprotein (EBOV GP/VSVΔG), we evaluated virus binding and entry into cells expressing TIM-4 molecules mutated within the IgV domain, allowing us to identify residues important for entry. Similar to TIM-1, residues in the PtdSer binding pocket of murine and human TIM-4 (mTIM-4 and hTIM-4) were found to be important for EBOV entry. However, additional TIM-4-specific residues were also found to impact EBOV entry, with a total of 8 mTIM-4 and 14 hTIM-4 IgV domain residues being critical for virion binding and internalization. Together, these findings provide a greater understanding of the interaction of TIM-4 with EBOV virions.

IMPORTANCE

With more than 28,000 cases and over 11,000 deaths during the largest and most recent Ebola virus (EBOV) outbreak, there has been increased emphasis on the development of therapeutics against filoviruses. Many therapies under investigation target EBOV cell entry. T-cell immunoglobulin mucin (TIM) domain proteins are cell surface factors important for the entry of many enveloped viruses, including EBOV. TIM family member TIM-4 is expressed on macrophages and dendritic cells, which are early cellular targets during EBOV infection. Here, we performed a mutagenesis screening of the IgV domain of murine and human TIM-4 to identify residues that are critical for EBOV entry. Surprisingly, we identified more human than murine TIM-4 IgV domain residues that are required for EBOV entry. Defining the TIM IgV residues needed for EBOV entry clarifies the virus-receptor interactions and paves the way for the development of novel therapeutics targeting virus binding to this cell surface receptor.

Enhancement of Ebola Virus Infection via Ficolin-1 Interaction with the Mucin Domain of GP Glycoprotein

Ebola virus infection requires the surface viral glycoprotein to initiate entry into the target cells. The trimeric glycoprotein is a highly glycosylated viral protein which has been shown to interact with host C-type lectin receptors and the soluble complement recognition protein mannose-binding lectin, thereby enhancing viral infection. Similarly to mannose-binding lectin, ficolins are soluble effectors of the innate immune system that recognize particular glycans at the pathogen surface. In this study, we demonstrate that ficolin-1 interacts with the Zaire Ebola virus (EBOV) glycoprotein, and we characterized this interaction by surface plasmon resonance spectroscopy. Ficolin-1 was shown to bind to the viral glycoprotein with a high affinity. This interaction was mediated by the fibrinogen-like recognition domain of ficolin-1 and the mucin-like domain of the viral glycoprotein. Using a ficolin-1 control mutant devoid of sialic acid-binding capacity, we identified sialylated moieties of the mucin domain to be potential ligands on the glycoprotein. In cell culture, using both pseudotyped viruses and EBOV, ficolin-1 was shown to enhance EBOV infection independently of the serum complement. We also observed that ficolin-1 enhanced EBOV infection on human monocyte-derived macrophages, described to be major viral target cells,. Competition experiments suggested that although ficolin-1 and mannose-binding lectin recognized different carbohydrate moieties on the EBOV glycoprotein, the observed enhancement of the infection likely depended on a common cellular receptor/partner. In conclusion, ficolin-1 could provide an alternative receptor-mediated mechanism for enhancing EBOV infection, thereby contributing to viral subversion of the host innate immune system.

IMPORTANCE

A specific interaction involving ficolin-1 (M-ficolin), a soluble effector of the innate immune response, and the glycoprotein (GP) of EBOV was identified. Ficolin-1 enhanced virus infection instead of tipping the balance toward its elimination. An interaction between the fibrinogen-like recognition domain of ficolin-1 and the mucin-like domain of Ebola virus GP occurred. In this model, the enhancement of infection was shown to be independent of the serum complement. The facilitation of EBOV entry into target host cells by the interaction with ficolin-1 and other host lectins shunts virus elimination, which likely facilitates the survival of the virus in infected host cells and contributes to the virus strategy to subvert the innate immune response.

Ebola Viral Glycoprotein Bound to Its Endosomal Receptor Niemann-Pick C1

Filoviruses, including Ebola and Marburg, cause fatal hemorrhagic fever in humans and primates. Understanding how these viruses enter host cells could help to develop effective therapeutics. An endosomal protein, Niemann-Pick C1 (NPC1), has been identified as a necessary entry receptor for this process, and priming of the viral glycoprotein (GP) to a fusion-competent state is a prerequisite for NPC1 binding. Here, we have determined the crystal structure of the primed GP (GPcl) of Ebola virus bound to domain C of NPC1 (NPC1-C) at a resolution of 2.3 Å. NPC1-C utilizes two protruding loops to engage a hydrophobic cavity on head of GPcl. Upon enzymatic cleavage and NPC1-C binding, conformational change in the GPcl further affects the state of the internal fusion loop, triggering membrane fusion. Our data therefore provide structural insights into filovirus entry in the late endosome and the molecular basis for design of therapeutic inhibitors of viral entry.

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Structural basis of Ebola virus endosomal-receptor binding

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NPC1 domain C (NPC1-C) displays a helical core structure with two protruding loops

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NPC1-C binds to the primed Ebola virus GP (GPcl) protein with a low affinity

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NPC1-C utilizes two protruding loops to engage a hydrophobic cavity on head of GPcl

THE STRENGTHS, WEAKNESSES, OPPORTUNITIES, AND THREATS (SWOTs) ANALYSES OF THE EBOLA VIRUS - PAPER RETRACTED

Background:

Owing to the extreme virulence and case fatality rate of ebola virus disease (EVD), there had been so much furore, panic and public health emergency about the possible pandemic from the recent West African outbreak of the disease, with attendant handful research, both in the past and most recently. The magnitude of the epidemic of ebola virus disease has prompted global interest and urgency in the discovery of measures to mitigate the impact of the disease. Researchers in the academia and the industry were pressured to only focus on the development of effective and safe ebola virus vaccines, without consideration of the other aspects to this virus, which may influence the success or otherwise of a potential vaccine. The objective of this review was to adopt the SWOT concept to elucidate the biological Strengths, Weaknesses, Opportunities, and Threats to Ebola virus as a pathogen, with a view to understanding and devising holistic strategies at combating and overcoming the scourge of EVD.

Method:

This systematic review and narrative synthesis utilized Medline, PubMed, Google and other databases to select about 150 publications on ebola and ebola virus disease using text word searches to generate the specific terms. Relevant publications were reviewed and compared, findings were synthesized using a narrative method and summarized qualitatively.

Results:

Some of the identified strengths of ebola virus include: Ebola virus is an RNA virus with inherent capability to mutate, reassort and recombine to generate mutant or reassortant virulent strains; Ebola virus has a broad cellular tropism; Natural Reservoir of ebola virus is unconfirmed but fruit bats, arthropods, and plants are hypothesized; Ebola virus primarily targets and selectively destroys the immune system; Ebola viruses possess accessory proteins that inhibits the host’ immune responses; Secreted glycoprotein (sGP), a truncated soluble protein that triggers immune activation and increased vascular permeability is uniquely associated with Ebola virus only; Ability to effectively cross the species barrier and establish productive infection in humans, non human primates, and other mammals; Ebola virus attacks every part of the human body; The Weaknesses include: Ebola virus transmission and persistence is severely limited by its virulence; Ebola virus essentially requires host encoded protein Niemann–Pick C1 (NPC1) for host’s cell’ entry; Ebola virus essentially requires host encoded proteins (TIM-1) for cell’ entry; Relative abundance of Ebolavirus Nucleoprotein than the other virion components; The Opportunities harnessed by ebola virus include: Lack of infection control practices in African health-care facilities and paucity of health infrastructures, especially in the endemic zones; Permissiveness of circulating Monocytes, Macrophages and dendritic cells in virus mobilization and dissemination; Collection, consumption and trade of wild games (bushmeats); Pertubation and drastic changes in forest ecosystems present opportunities for Ebola virus; Use of dogs in hunting predisposes man and animals to inter-species contact; Poverty, malnutrition, crowding, social disorder, mobility and political instability; Ease of travel and aviation as potentials for global spread; Possible mechanical transmission by arthropod vectors; No vaccines or therapeutics are yet approved for human treatment; The Threats to ebola virus include: Avoidance of direct contact with infected blood and other bodily fluids of infected patient; Appropriate and correct burial practices; Adoption of barrier Nursing; Improved surveillance to prevent potential spread of epidemic; Making Available Rapid laboratory equipment and procedures for prompt detection (ELISA, Western Blot, PCR); Sterilization or disinfection of equipment and safe disposal of instrument; Prompt hospitalization, isolation and quarantine of infected individual; Active contact tracing and monitoring, among others.

Conclusion:

The identified capacities and gaps presented in this study are inexhaustive framework to combat the ebola virus. To undermine and overcome the virus, focus should be aimed at strategically decreasing the identified strengths and opportunities, while increasing on the weaknesses of, and threats to the virus.

The Glycoproteins of All Filovirus Species Use the Same Host Factors for Entry into Bat and Human Cells but Entry Efficiency Is Species Dependent

Ebola and marburgviruses, members of the family Filoviridae, can cause severe hemorrhagic fever in humans. The ongoing Ebola virus (EBOV) disease epidemic in Western Africa claimed more than 11,300 lives and was associated with secondary cases outside Africa, demonstrating that filoviruses pose a global health threat. Bats constitute an important natural reservoir of filoviruses, including viruses of the recently identified Cuevavirus genus within the Filoviridae family. However, the interactions of filoviruses with bat cells are incompletely understood. Here, we investigated whether filoviruses employ different strategies to enter human and bat cells. For this, we examined host cell entry driven by glycoproteins (GP) from all filovirus species into cell lines of human and fruit bat origin. We show that all GPs were able to mediate entry into human and most fruit bat cell lines with roughly comparable efficiency. In contrast, the efficiency of entry into the cell line EidNi/41 derived from a straw-colored fruit bat varied markedly between the GPs of different filovirus species. Furthermore, inhibition studies demonstrated that filoviruses employ the same host cell factors for entry into human, non-human primate and fruit bat cell lines, including cysteine proteases, two pore channels and NPC1 (Niemann-Pick C1 molecule). Finally, processing of GP by furin and the presence of the mucin-like domain in GP were dispensable for entry into both human and bat cell lines. Collectively, these results show that filoviruses rely on the same host cell factors for entry into human and fruit bat cells, although the efficiency of the usage of these factors might differ between filovirus species.

Characterization of the inhibitory effect of an extract of Prunella vulgaris on Ebola virus glycoprotein (GP)-mediated virus entry and infection

Currently, no approved antiviral therapeutic is available for treatment or prevention of Ebola virus (EBOV) infection. In this study, we characterized an EBOV-glycoprotein (GP) pseudotyped HIV-1-based vector system in different cell cultures, including human umbilical vein endothelial cells (HUVECs) and human macrophages, for the screening of anti-EBOV-GP agent(s). Based on this system, we demonstrated that an aqueous extract (CHPV) from the Chinese herb Prunella vulgaris displayed a potent inhibitory effect on EBOV-GP pseudotyped virus (EBOV-GP-V)-mediated infection in various cell lines, including HUVEC and macrophage. In addition, our results indicated that CHPV was able to block an eGFP-expressing Zaire ebola virus (eGFP-ZEBOV) infection in VeroE6 cells. The anti-EBOV activity of CHPV was exhibited in a dose-dependent manner. At a 12.5 μg/ml concentration, the CHPV showed a greater than 80% inhibition of EBOV-GP-V and eGFP-EBOV infections. Likewise, our studies suggested that the inhibitory effect of CHPV occurred by binding directly to EBOV-GP-Vs and blocking the early viral events. Interestingly, our results have shown that CHPV was able to enhance the anti-EBOV activity of the monoclonal antibody MAb 2G4 against EBOV-GP. Overall, this study provides evidence that CHPV has anti-EBOV activity and may be developed as a novel antiviral approach against EBOV infection.

Ebola vaccine, therapeutics, and diagnostics

Ebolaviruses, members of the family Filoviridae, cause severe hemorrhagic fever in humans and nonhuman primates, with human case fatality rates of up to 90%. No effective prophylaxis or treatment for Ebola virus disease (EVD) is yet commercially available. During the latest outbreak of EVD in West Africa, several unapproved drugs were used for the treatment of patients. This outbreak has indeed accelerated efforts to develop antiviral strategies and some of the vaccine and drug candidates have undergone clinical trials. This article reviews previous researches and recent advances on the development of vaccine, therapeutics, and diagnostics for EVD.

MGL Receptor and Immunity: When the Ligand Can Make the Difference

C-type lectin receptors (CLRs) on antigen-presenting cells (APCs) facilitate uptake of carbohydrate antigens for antigen presentation, modulating the immune response in infection, homeostasis, autoimmunity, allergy, and cancer. In this review, we focus on the role of the macrophage galactose type C-type lectin (MGL) in the immune response against self-antigens, pathogens, and tumor associated antigens (TAA). MGL is a CLR exclusively expressed by dendritic cells (DCs) and activated macrophages (MØs), able to recognize terminal GalNAc residues, including the sialylated and nonsialylated Tn antigens. We discuss the effects on DC function induced throughout the engagement of MGL, highlighting the importance of the antigen structure in the modulation of immune response. Indeed modifying Tn-density, the length, and steric structure of the Tn-antigens can result in generating immunogens that can efficiently bind to MGL, strongly activate DCs, mimic the effects of a danger signal, and achieve an efficient presentation in HLA classes I and II compartments.

A sensitive and efficient method for determination of N-acetylhexosamines and N-acetylneuraminic acid in breast milk and milk-based products by high-performance liquid chromatography via UV detection and mass spectrometry identification

A sensitive and efficient method of high performance liquid chromatography using 1-(2-naphthyl)-3-methyl-5-pyrazolone (NMP) as pre-column derivatization reagent coupled with UV detection (HPLC-UV) and online mass spectrometry identification was established for determination of the most common N-Acetylhexosamines (N-acetyl-d-glucosamine (GlcNAc) and N-acetyl-d-galactosamine (GalNAc)) and N-acetylneuraminic acid (Neu5Ac). In order to obtain the highest liberation level of the three monosaccharides without destruction of Neu5Ac or conversion of GlcNAc/GalNAc to GlcN/GalN in the hydrolysis procedure, the pivotal parameters affecting the liberation of N-acetylhexosamines/Neu5Ac from sample were investigated with response surface methodology (RSM). Under the optimized condition, maximum yield was obtained. The effects of key parameters on derivatization, separation and detection were also investigated. At optimized conditions, three monosaccharides were labeled fast and entirely, and all derivatives exhibited a good baseline resolution and high detection sensitivity. The developed method was linear over the calibration range 0.25-12μM, with R(2)>0.9991. The detection limits of the method were between 0.48 and 2.01pmol. Intra- and inter-day precisions for the three monosaccharides (GlcNAc, GalNAc and Neu5Ac) were found to be in the range of 3.07-4.02% and 3.69-4.67%, respectively. Individual monosaccharide recovery from spiked milk was in the range of 81%-97%. The sensitivity of the method, the facility of the derivatization procedure and the reliability of the hydrolysis conditions suggest the proposed method has a high potential for utilization in routine trace N-acetylhexosamines and Neu5Ac analysis in biological samples.

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.

Ebola virus entry into host cells: identifying therapeutic strategies

Filoviruses cause severe hemorrhagic fever in humans. The archetypal virus of this group, Ebola virus, is responsible for the current filovirus epidemic in West Africa. Filoviruses infect most mammalian cells, resulting in broad species tropism and likely contributing to rapid spread of virus throughout the body. A thorough understanding of filovirus entry events will facilitate the development of therapeutics against these critical steps in the viral life cycle. This review summarizes the current understanding of filovirus entry and discusses some of the recent advancements in therapeutic strategies that target entry.

Predictive and comparative analysis of Ebolavirus proteins

Ebolavirus is the pathogen for Ebola Hemorrhagic Fever (EHF). This disease exhibits a high fatality rate and has recently reached a historically epidemic proportion in West Africa. Out of the 5 known Ebolavirus species, only Reston ebolavirus has lost human pathogenicity, while retaining the ability to cause EHF in long-tailed macaque. Significant efforts have been spent to determine the three-dimensional (3D) structures of Ebolavirus proteins, to study their interaction with host proteins, and to identify the functional motifs in these viral proteins. Here, in light of these experimental results, we apply computational analysis to predict the 3D structures and functional sites for Ebolavirus protein domains with unknown structure, including a zinc-finger domain of VP30, the RNA-dependent RNA polymerase catalytic domain and a methyltransferase domain of protein L. In addition, we compare sequences of proteins that interact with Ebolavirus proteins from RESTV-resistant primates with those from RESTV-susceptible monkeys. The host proteins that interact with GP and VP35 show an elevated level of sequence divergence between the RESTV-resistant and RESTV-susceptible species, suggesting that they may be responsible for host specificity. Meanwhile, we detect variable positions in protein sequences that are likely associated with the loss of human pathogenicity in RESTV, map them onto the 3D structures and compare their positions to known functional sites. VP35 and VP30 are significantly enriched in these potential pathogenicity determinants and the clustering of such positions on the surfaces of VP35 and GP suggests possible uncharacterized interaction sites with host proteins that contribute to the virulence of Ebolavirus.

Emerging intracellular receptors for hemorrhagic fever viruses

Ebola virus and Lassa virus belong to different virus families that can cause viral hemorrhagic fever, a life-threatening disease in humans with limited treatment options. To infect a target cell, Ebola and Lassa viruses engage receptors at the cell surface and are subsequently shuttled into the endosomal compartment. Upon arrival in late endosomes/lysosomes, the viruses trigger membrane fusion to release their genome into the cytoplasm. Although contact sites at the cell surface were recognized for Ebola virus and Lassa virus, it was postulated that Ebola virus requires a critical receptor inside the cell. Recent screens for host factors identified such internal receptors for both viruses: Niemann-Pick disease type C1 protein (NPC1) for Ebola virus and lysosome-associated membrane protein 1 (LAMP1) for Lassa virus. A cellular trigger is needed to permit binding of the viral envelope protein to these intracellular receptors. This 'receptor switch' represents a previously unnoticed step in virus entry with implications for host-pathogen interactions and viral tropism.

Ebola virus outbreak, updates on current therapeutic strategies

Filoviruses are enveloped negative‐sense single‐stranded RNA viruses, which include Ebola and Marburg viruses, known to cause hemorrhagic fever in humans with a case fatality of up to 90%. There have been several Ebola virus outbreaks since the first outbreak in the Democratic Republic of Congo in 1976 of which, the recent 2013–2015 epidemic in Guinea, Liberia, and Sierra Leone is the largest in recorded history. Within a few months of the start of the outbreak in December 2013, thousands of infected cases were reported with a significant number of deaths. As of March 2015, according to the Centers for Disease Control and Prevention, there have been nearly 25 000 suspected cases, with 15 000 confirmed by laboratory testing, and over 10 000 deaths. The large number of cases and the high mortality rate, combined with the lack of effective Food and Drug Administration‐approved treatments, necessitate the development of potent and safe therapeutic measures to combat the current and future outbreaks. Since the beginning of the outbreak, there have been considerable efforts to develop and characterize protective measures including vaccines and antiviral small molecules, and some have proven effective in vitro and in animal models. Most recently, a cocktail of monoclonal antibodies has been shown to be highly effective in protecting non‐human primates from Ebola virus infection. In this review, we will discuss what is known about the nature of the virus, phylogenetic classification, genomic organization and replication, disease transmission, and viral entry and highlight the current approaches and efforts, in the development of therapeutics, to control the outbreak. Copyright © 2015 John Wiley & Sons, Ltd.

Analysis of Ebola Virus Entry Into Macrophages

Ebolaviruses constitute a public health threat, particularly in Central and Western Africa. Host cell factors required for spread of ebolaviruses may serve as targets for antiviral intervention. Lectins, TAM receptor tyrosine kinases (Tyro3, Axl, Mer), T cell immunoglobulin and mucin domain (TIM) proteins, integrins, and Niemann-Pick C1 (NPC1) have been reported to promote entry of ebolaviruses into certain cellular systems. However, the factors used by ebolaviruses to invade macrophages, major viral targets, are poorly defined. Here, we show that mannose-specific lectins, TIM-1 and Axl augment entry into certain cell lines but do not contribute to Ebola virus (EBOV)-glycoprotein (GP)-driven transduction of macrophages. In contrast, expression of Mer, integrin αV, and NPC1 was required for efficient GP-mediated transduction and EBOV infection of macrophages. These results define cellular factors hijacked by EBOV for entry into macrophages and, considering that Mer and integrin αV promote phagocytosis of apoptotic cells, support the concept that EBOV relies on apoptotic mimicry to invade target cells.

Interaction between TIM-1 and NPC1 Is Important for Cellular Entry of Ebola Virus

Multiple host molecules are known to be involved in the cellular entry of filoviruses, including Ebola virus (EBOV); T-cell immunoglobulin and mucin domain 1 (TIM-1) and Niemann-Pick C1 (NPC1) have been identified as attachment and fusion receptors, respectively. However, the molecular mechanisms underlying the entry process have not been fully understood. We found that TIM-1 and NPC1 colocalized and interacted in the intracellular vesicles where EBOV glycoprotein (GP)-mediated membrane fusion occurred. Interestingly, a TIM-1-specific monoclonal antibody (MAb), M224/1, prevented GP-mediated membrane fusion and also interfered with the binding of TIM-1 to NPC1, suggesting that the interaction between TIM-1 and NPC1 is important for filovirus membrane fusion. Moreover, MAb M224/1 efficiently inhibited the cellular entry of viruses from all known filovirus species. These data suggest a novel mechanism underlying filovirus membrane fusion and provide a potential cellular target for antiviral compounds that can be universally used against filovirus infections.

IMPORTANCE

Filoviruses, including Ebola and Marburg viruses, cause rapidly fatal diseases in humans and nonhuman primates. There are currently no approved vaccines or therapeutics for filovirus diseases. In general, the cellular entry step of viruses is one of the key mechanisms to develop antiviral strategies. However, the molecular mechanisms underlying the entry process of filoviruses have not been fully understood. In this study, we demonstrate that TIM-1 and NPC1, which serve as attachment and fusion receptors for filovirus entry, interact in the intracellular vesicles where Ebola virus GP-mediated membrane fusion occurs and that this interaction is important for filovirus infection. We found that filovirus infection and GP-mediated membrane fusion in cultured cells were remarkably suppressed by treatment with a TIM-1-specific monoclonal antibody that interfered with the interaction between TIM-1 and NPC1. Our data provide new insights for the development of antiviral compounds that can be universally used against filovirus infections.

Comparative Analysis of Host Cell Entry of Ebola Virus From Sierra Leone, 2014, and Zaire, 1976

The ongoing Ebola virus (EBOV) disease (EVD) epidemic in Western Africa is the largest EVD outbreak recorded to date and requires the rapid development and deployment of antiviral measures. The viral glycoprotein (GP) facilitates host cell entry and, jointly with cellular interaction partners, constitutes a potential target for antiviral intervention. However, it is unknown whether the GPs of the currently and previously circulating EBOVs use the same mechanisms for cellular entry and are thus susceptible to inhibition by the same antivirals and cellular defenses. Here, we show that the GPs of the EBOVs circulating in 1976 and 2014 transduce the same spectrum of target cells, use the same cellular factors for host cell entry, and are comparably susceptible to blockade by antiviral interferon-induced transmembrane proteins and neutralizing antibody KZ52. Thus, the viruses responsible for the ongoing EVD epidemic should be fully susceptible to established antiviral strategies targeting GP and cellular entry factors.

Ebola virus. Two-pore channels control Ebola virus host cell entry and are drug targets for disease treatment

Ebola virus causes sporadic outbreaks of lethal hemorrhagic fever in humans, but there is no currently approved therapy. Cells take up Ebola virus by macropinocytosis, followed by trafficking through endosomal vesicles. However, few factors controlling endosomal virus movement are known. Here we find that Ebola virus entry into host cells requires the endosomal calcium channels called two-pore channels (TPCs). Disrupting TPC function by gene knockout, small interfering RNAs, or small-molecule inhibitors halted virus trafficking and prevented infection. Tetrandrine, the most potent small molecule that we tested, inhibited infection of human macrophages, the primary target of Ebola virus in vivo, and also showed therapeutic efficacy in mice. Therefore, TPC proteins play a key role in Ebola virus infection and may be effective targets for antiviral therapy.

Identifying the pattern of molecular evolution for Zaire ebolavirus in the 2014 outbreak in West Africa

The current Ebola virus disease (EVD) epidemic has killed more than all previous Ebola outbreaks combined and, even as efforts appear to be bringing the outbreak under control, the threat of reemergence remains. The availability of new whole-genome sequences from West Africa in 2014 outbreak, together with those from the earlier outbreaks, provide an opportunity to investigate the genetic characteristics, the epidemiological dynamics and the evolutionary history for Zaire ebolavirus (ZEBOV). To investigate the evolutionary properties of ZEBOV in this outbreak, we examined amino acid mutations, positive selection, and evolutionary rates on the basis of 123 ZEBOV genome sequences. The estimated phylogenetic relationships within ZEBOV revealed that viral sequences from the same period or location formed a distinct cluster. The West Africa viruses probably derived from Middle Africa, consistent with results from previous studies. Analysis of the seven protein regions of ZEBOV revealed evidence of positive selection acting on the GP and L genes. Interestingly, all putatively positive-selected sites identified in the GP are located within the mucin-like domain of the solved structure of the protein, suggesting a possible role in the immune evasion properties of ZEBOV. Compared with earlier outbreaks, the evolutionary rate of GP gene was estimated to significantly accelerate in the 2014 outbreak, suggesting that more ZEBOV variants are generated for human to human transmission during this sweeping epidemic. However, a more balanced sample set and next generation sequencing datasets would help achieve a clearer understanding at the genetic level of how the virus is evolving and adapting to new conditions.

Role of EXT1 and Glycosaminoglycans in the Early Stage of Filovirus Entry

Filoviruses, including both Ebola virus (EBOV) and Marburg virus (MARV), can infect humans and other animals, causing hemorrhagic fever with a high mortality rate. Entry of these viruses into the host is mediated by a single filoviral glycoprotein (GP). GP is composed of two subunits: GP1, which is responsible for attachment and binding to receptor(s) on susceptible cells, and GP2, which mediates viral and cell membrane fusion. Although numerous host factors have been implicated in the entry process, the initial attachment receptor(s) has not been well defined. In this report, we demonstrate that exostosin 1 (EXT1), which is involved in biosynthesis of heparan sulfate (HS), plays a role in filovirus entry. Expression knockdown of EXT1 by small interfering RNAs (siRNAs) impairs GP-mediated pseudoviral entry and that of infectious EBOV and MARV in tissue cultured cells. Furthermore, HS, heparin, and other related glycosaminoglycans (GAGs), to different extents, can bind to and block GP-mediated viral entry and that of infectious filoviruses. These results strongly suggest that HS and other related GAGs are attachment receptors that are utilized by filoviruses for entry and infection. These GAGs may have therapeutic potential in treating EBOV- and MARV-infected patients.

IMPORTANCE

Infection by Ebola virus and Marburg virus can cause severe illness in humans, with a high mortality rate, and currently there is no FDA-approved vaccine or therapeutic treatment available. The ongoing 2014 outbreak in West Africa underscores a lack of our understanding in the infection and pathogenesis of these viruses and the urgency of drug discovery and development. In this study, we provide several pieces of evidence that demonstrate that heparan sulfate and other closely related glycosaminoglycans are the molecules that are used by filoviruses for initial attachment. Furthermore, we demonstrate that these glycosaminoglycans can block entry of and infection by filoviruses. Thus, this work provides mechanistic insights on the early step of filoviral infection and suggests a possible therapeutic option for diseases caused by filovirus infection.

Bi- to tetravalent glycoclusters presenting GlcNAc/GalNAc as inhibitors: from plant agglutinins to human macrophage galactose-type lectin (CD301) and galectins

Emerging insights into the functional spectrum of tissue lectins leads to identification of new targets for the custom-made design of potent inhibitors, providing a challenge for synthetic chemistry. The affinity and selectivity of a carbohydrate ligand for a lectin may immensely be increased by a number of approaches, which includes varying geometrical or topological features. This perspective leads to the design and synthesis of glycoclusters and their testing using assays of physiological relevance. Herein, hydroquinone, resorcinol, benzene-1,3,5-triol and tetra(4-hydroxyphenyl)ethene have been employed as scaffolds and propargyl derivatives obtained. The triazole-containing linker to the α/β-O/S-glycosides of GlcNAc/GalNAc presented on these scaffolds was generated by copper-catalysed azide-alkyne cycloaddition. This strategy was used to give a panel of nine glycoclusters with bi-, tri- and tetravalency. Maintained activity for lectin binding after conjugation was ascertained for both sugars in solid-phase assays with the plant agglutinins WGA (GlcNAc) and DBA (GalNAc). Absence of cross-reactivity excluded any carbohydrate-independent reactivity of the bivalent compounds, allowing us to proceed to further testing with a biomedically relevant lectin specific for GalNAc. Macrophage galactose(-binding C)-type lectin, involved in immune defence by dendritic cells and in virus uptake, was produced as a soluble protein without/with its α-helical coiled-coil stalk region. Binding to ligands presented on a matrix and on cell surfaces was highly susceptible to the presence of the tetravalent inhibitor derived from the tetraphenylethene-containing scaffold, and presentation of GalNAc with an α-thioglycosidic linkage proved favorable. Cross-reactivity of this glycocluster to human galectins-3 and -4, which interact with Tn-antigen-presenting mucins, was rather small. Evidently, the valency and spatial display of α-GalNAc residues is a key factor to design potent and selective inhibitors for this lectin.

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.

Chemical and Structural Aspects of Ebola Virus Entry Inhibitors

The Ebolaviruses are members of the family Filoviridae (“filoviruses”) and cause severe hemhorragic fever with human case fatality rates as high as 90%. Infection requires attachment of the viral particle to cells and triggering of membrane fusion between the host and viral membranes, a process that occurs in the host endosome and is facilitated by the envelope glycoprotein (GP). One potential strategy for therapeutic intervention is the development of agents (antibodies, peptides, and small molecules) that can interfere with viral entry aspects such as attachment, uptake, priming, or membrane fusion. This paper highlights recent developments in the discovery and evaluation of therapeutic entry inhibitors and identifies opportunities moving forward.

[Ebola virus host cell entry]

Ebola virus is an enveloped virus with filamentous structure and causes a severe hemorrhagic fever in human and nonhuman primates. Host cell entry is the first essential step in the viral life cycle, which has been extensively studied as one of the therapeutic targets. A virus factor of cell entry is a surface glycoprotein (GP), which is an only essential viral protein in the step, as well as the unique particle structure. The virus also interacts with a lot of host factors to successfully enter host cells. Ebola virus at first binds to cell surface proteins and internalizes into cells, followed by trafficking through endosomal vesicles to intracellular acidic compartments. There, host proteases process GPs, which can interact with an intracellular receptor. Then, under an appropriate circumstance, viral and endosomal membranes are fused, which is enhanced by major structural changes of GPs, to complete host cell entry. Recently the basic research of Ebola virus infection mechanism has markedly progressed, largely contributed by identification of host factors and detailed structural analyses of GPs. This article highlights the mechanism of Ebola virus host cell entry, including recent findings.

Less is more: Ebola virus surface glycoprotein expression levels regulate virus production and infectivity

The Ebola virus (EBOV) surface glycoprotein (GP1,2) mediates host cell attachment and fusion and is the primary target for host neutralizing antibodies. Expression of GP1,2 at high levels disrupts normal cell physiology, and EBOV uses an RNA-editing mechanism to regulate expression of the GP gene. In this study, we demonstrate that high levels of GP1,2 expression impair production and release of EBOV virus-like particles (VLPs) as well as infectivity of GP1,2-pseudotyped viruses. We further show that this effect is mediated through two mechanisms. First, high levels of GP1,2 expression reduce synthesis of other proteins needed for virus assembly. Second, viruses containing high levels of GP1,2 are intrinsically less infectious, possibly due to impaired receptor binding or endosomal processing. Importantly, proteolysis can rescue the infectivity of high-GP1,2-containing viruses. Taken together, our findings indicate that GP1,2 expression levels have a profound effect on factors that contribute to virus fitness and that RNA editing may be an important mechanism employed by EBOV to regulate GP1,2 expression in order to optimize virus production and infectivity.

IMPORTANCE

The Ebola virus (EBOV), as well as other members of the Filoviridae family, causes severe hemorrhagic fever that is highly lethal, with up to 90% mortality. The EBOV surface glycoprotein (GP1,2) plays important roles in virus infection and pathogenesis, and its expression is tightly regulated by an RNA-editing mechanism during virus replication. Our study demonstrates that the level of GP1,2 expression profoundly affects virus particle production and release and uncovers a new mechanism by which Ebola virus infectivity is regulated by the level of GP1,2 expression. These findings extend our understanding of EBOV infection and replication in adaptation of host environments, which will aid the development of countermeasures against EBOV infection.

Novel insights into the immunomodulatory role of the dendritic cell and macrophage-expressed C-type lectin MGL

Based on their ability to balance tolerance and inflammation, antigen presenting cells, such as dendritic cells and macrophages contribute to the maintenance of immune homeostasis as well as the instigation of immune activation. Acting as key sensors of tissue integrity and pathogen invasion, they are well equipped with a wide variety of pattern recognition receptors, to which the C-type lectin family also belongs. C-type lectins are glycan-binding receptors that mediate cell-cell communication and pathogen recognition, besides participating in the endocytosis of antigens for presentation to T cells and the fine-tuning of immune responses. Here we review the current state-of-the-art on the dendritic cell and macrophage-expressed C-type lectin macrophage galactose-type lectin (MGL), highlighting the binding specificities, signaling properties and modulation of innate and adaptive immunity by its human and murine orthologues.

Hsa-miR-1246, hsa-miR-320a and hsa-miR-196b-5p inhibitors can reduce the cytotoxicity of Ebola virus glycoprotein in vitro

Ebola virus (EBOV) causes a highly lethal hemorrhagic fever syndrome in humans and has been associated with mortality rates of up to 91% in Zaire, the most lethal strain. Though the viral envelope glycoprotein (GP) mediates widespread inflammation and cellular damage, these changes have mainly focused on alterations at the protein level, the role of microRNAs (miRNAs) in the molecular pathogenesis underlying this lethal disease is not fully understood. Here, we report that the mi-RNAs hsa-miR-1246, hsa-miR-320a and hsa-miR-196b-5p were induced in human umbilical vein endothelial cells (HUVECs) following expression of EBOV GP. Among the proteins encoded by predicted targets of these miRNAs, the adhesion-related molecules tissue factor pathway inhibitor (TFPI), dystroglycan1 (DAG1) and the caspase 8 and FADD-like apoptosis regulator (CFLAR) were significantly downregulated in EBOV GP-expressing HUVECs. Moreover, inhibition of hsa-miR-1246, hsa-miR-320a and hsa-miR-196b-5p, or overexpression of TFPI, DAG1 and CFLAR rescued the cell viability that was induced by EBOV GP. Our results provide a novel molecular basis for EBOV pathogenesis and may contribute to the development of strategies to protect against future EBOV pandemics.

A negative effect of Campylobacter capsule on bacterial interaction with an analogue of a host cell receptor

BACKGROUND

Campylobacter jejuni (C. jejuni) is the leading causative agent of bacterial gastrointestinal infections. The rise of antibiotic resistant forms of this pathogen necessitates the development of novel intervention strategies. One approach is the design of drugs preventing bacterial attachment to host cells. Although some putative C. jejuni adhesins have been identified, the molecular mechanisms of their interaction with host cells and their role in pathogenesis remain to be elucidated. C. jejuni adhesion may also be modulated by a bacterial capsule. However, the role of this structure in adhesion was not clear due to conflicting results published by different research groups. The aim of this study was to clarify the role of capsule in bacterial interaction with host cells by using an in vitro model of adhesion and an analogue of a host cell receptor.

RESULTS

In this study, we developed an in vitro bacterial adhesion assay, which was validated using various tests, including competitive inhibition studies, exoglycosydase treatment and site-directed mutagenesis. We demonstrate that PEB3 is one of the cell surface glycoproteins required for bacterial interaction with an analogue of a host cell receptor. In contrast, JlpA glycoprotein adhesin is not required for such interaction. We demonstrate that the production of capsule reduces bacterial attachment, and that the genes involved in capsule and PEB3 adhesin biosynthesis are differentially regulated.

CONCLUSIONS

In this study we report an in vitro model for the investigation of bacterial interaction with analogs of host cell receptors. The results suggest an interfering effect of capsule on bacterial attachment. In addition, using a liquid culture, we demonstrate differential expression of a gene involved in capsule production (kpsM) and a gene encoding a glycoprotein adhesin (peb3). Further studies are required in order to establish if these genes are also differentially regulated during the infection process. The results will assist in better understanding of the mechanism of pathogenesis of C. jejuni in general and the role of capsule in the process in particular.

The clinically approved drugs amiodarone, dronedarone and verapamil inhibit filovirus cell entry

Objectives

Filoviruses such as Ebola virus and Marburg virus cause a severe haemorrhagic fever syndrome in humans for which there is no specific treatment. Since filoviruses use a complex route of cell entry that depends on numerous cellular factors, we hypothesized that there may be drugs already approved for human use for other indications that interfere with signal transduction or other cellular processes required for their entry and hence have anti-filoviral properties.

Methods

We used authentic filoviruses and lentiviral particles pseudotyped with filoviral glycoproteins to identify and characterize such compounds.

Results

We discovered that amiodarone, a multi-ion channel inhibitor and adrenoceptor antagonist, is a potent inhibitor of filovirus cell entry at concentrations that are routinely reached in human serum during anti-arrhythmic therapy. A similar effect was observed with the amiodarone-related agent dronedarone and the L-type calcium channel blocker verapamil. Inhibition by amiodarone was concentration dependent and similarly affected pseudoviruses as well as authentic filoviruses. Inhibition of filovirus entry was observed with most but not all cell types tested and was accentuated by the pre-treatment of cells, indicating a host cell-directed mechanism of action. The New World arenavirus Guanarito was also inhibited by amiodarone while the Old World arenavirus Lassa and members of the Rhabdoviridae (vesicular stomatitis virus) and Bunyaviridae (Hantaan) families were largely resistant.

Conclusions

The ion channel blockers amiodarone, dronedarone and verapamil inhibit filoviral cell entry.

Interaction of L-SIGN with hepatitis C virus envelope protein E2 up-regulates Raf-MEK-ERK pathway

Liver/lymph node-specific intercellular adhesion molecule-3-grabbing integrin (L-SIGN) facilitates hepatitis C virus (HCV) infection through interaction with HCV envelope protein E2. Signaling events triggered by the E2 via L-SIGN are poorly understood. Here, kinase cascades of Raf-MEK-ERK pathway were defined upon the E2 treatment in NIH3T3 cells with stable expression of L-SIGN. The E2 bound to the cells through interaction with L-SIGN and such binding subsequently resulted in phosphorylation and activation of Raf, MEK, and ERK. Blockage of L-SIGN with antibody against L-SIGN reduced the E2-induced phosphorylation of Raf, MEK, and ERK. In the cells infected with cell culture-derived HCV, phosphorylation of these kinases was enhanced by the E2. Up-regulation of Raf-MEK-ERK pathway by HCV E2 via L-SIGN provides new insights into signaling cascade of L-SIGN, and might be a potential target for control and prevention of HCV infection.

Ebola hemorrhagic Fever: novel biomarker correlates of clinical outcome

BACKGROUND

Ebola hemorrhagic fever (EHF) outbreaks occur sporadically in Africa and result in high rates of death. The 2000-2001 outbreak of Sudan virus-associated EHF in the Gulu district of Uganda led to 425 cases, of which 216 were laboratory confirmed, making it the largest EHF outbreak on record. Serum specimens from this outbreak had been preserved in liquid nitrogen from the time of collection and were available for analysis.

METHODS

Available samples were tested using a series of multiplex assays to measure the concentrations of 55 biomarkers. The data were analyzed to identify statistically significant associations between the tested biomarkers and hemorrhagic manifestations, viremia, and/or death.

RESULTS

Death, hemorrhage, and viremia were independently associated with elevated levels of several chemokines and cytokines. Death and hemorrhage were associated with elevated thrombomodulin and ferritin levels. Hemorrhage was also associated with elevated levels of soluble intracellular adhesion molecule. Viremia was independently associated with elevated levels of tissue factor and tissue plasminogen activator. Finally, samples from nonfatal cases had higher levels of sCD40L.

CONCLUSIONS

These novel associations provide a better understanding of EHF pathophysiology and a starting point for researching new potential targets for therapeutic interventions.

Comprehensive functional analysis of N-linked glycans on Ebola virus GP1

Ebola virus (EBOV) entry requires the virion surface-associated glycoprotein (GP) that is composed of a trimer of heterodimers (GP1/GP2). The GP1 subunit contains two heavily glycosylated domains, the glycan cap and the mucin-like domain (MLD). The glycan cap contains only N-linked glycans, whereas the MLD contains both N- and O-linked glycans. Site-directed mutagenesis was performed on EBOV GP1 to systematically disrupt N-linked glycan sites to gain an understanding of their role in GP structure and function. All 15 N-glycosylation sites of EBOV GP1 could be removed without compromising the expression of GP. The loss of these 15 glycosylation sites significantly enhanced pseudovirion transduction in Vero cells, which correlated with an increase in protease sensitivity. Interestingly, exposing the receptor-binding domain (RBD) by removing the glycan shield did not allow interaction with the endosomal receptor, NPC1, indicating that the glycan cap/MLD domains mask RBD residues required for binding. The effects of the loss of GP1 N-linked glycans on Ca(2+)-dependent (C-type) lectin (CLEC)-dependent transduction were complex, and the effect was unique for each of the CLECs tested. Surprisingly, EBOV entry into murine peritoneal macrophages was independent of GP1 N-glycans, suggesting that CLEC-GP1 N-glycan interactions are not required for entry into this important primary cell. Finally, the removal of all GP1 N-glycans outside the MLD enhanced antiserum and antibody sensitivity. In total, our results provide evidence that the conserved N-linked glycans on the EBOV GP1 core protect GP from antibody neutralization despite the negative impact the glycans have on viral entry efficiency.

IMPORTANCE

Filovirus outbreaks occur sporadically throughout central Africa, causing high fatality rates among the general public and health care workers. These unpredictable hemorrhagic fever outbreaks are caused by multiple species of Ebola viruses, as well as Marburg virus. While filovirus vaccines and therapeutics are being developed, there are no licensed products. The sole viral envelope glycoprotein, which is a principal immunogenic target, contains a heavy shield of glycans surrounding the conserved receptor-binding domain. We find that disruption of this shield through targeted mutagenesis leads to an increase in cell entry, protease sensitivity, and antiserum/antibody sensitivity but is not sufficient to allow virion binding to the intracellular receptor NPC1. Therefore, our studies provide evidence that filoviruses maintain glycoprotein glycosylation to protect against proteases and antibody neutralization at the expense of efficient entry. Our results unveil interesting insights into the unique entry process of filoviruses and potential immune evasion tactics of the virus.

The macrophage galactose-type lectin can function as an attachment and entry receptor for influenza virus

Specific protein receptors that mediate internalization and entry of influenza A virus (IAV) have not been identified for any cell type. Sialic acid (SIA), the primary attachment factor for IAV hemagglutinin, is expressed by numerous cell surface glycoproteins and glycolipids, confounding efforts to identify specific receptors involved in virus infection. Lec1 Chinese hamster ovary (CHO) epithelial cells express cell surface SIA and bind IAV yet are largely resistant to infection. Here, we demonstrate that expression of the murine macrophage galactose-type lectin 1 (MGL1) by Lec1 cells enhanced Ca(2+)-dependent IAV binding and restored permissivity to infection. Lec1 cells expressing MGL1 were infected in the presence or absence of cell surface SIA, indicating that MGL1 can act as a primary receptor or as a coreceptor with SIA. Lec1 cells expressing endocytosis-deficient MGL1 mediated Ca(2+)-dependent IAV binding but were less sensitive to IAV infection, indicating that direct internalization via MGL1 can result in cellular infection. Together, these studies identify MGL1 as a cell surface glycoprotein that can act as an authentic receptor for both attachment and infectious entry of IAV.

Characterization of the envelope glycoprotein of a novel filovirus, lloviu virus

Lloviu virus (LLOV), a novel filovirus detected in bats, is phylogenetically distinct from viruses in the genera Ebolavirus and Marburgvirus in the family Filoviridae. While filoviruses are known to cause severe hemorrhagic fever in humans and/or nonhuman primates, LLOV is biologically uncharacterized, since infectious LLOV has never been isolated. To examine the properties of LLOV, we characterized its envelope glycoprotein (GP), which likely plays a key role in viral tropism and pathogenicity. We first found that LLOV GP principally has the same primary structure as the other filovirus GPs. Similar to the other filoviruses, virus-like particles (VLPs) produced by transient expression of LLOV GP, matrix protein, and nucleoprotein in 293T cells had densely arrayed GP spikes on a filamentous particle. Mouse antiserum to LLOV VLP was barely cross-reactive to viruses of the other genera, indicating that LLOV is serologically distinct from the other known filoviruses. For functional study of LLOV GP, we utilized a vesicular stomatitis virus (VSV) pseudotype system and found that LLOV GP requires low endosomal pH and cathepsin L, and that human C-type lectins act as attachment factors for LLOV entry into cells. Interestingly, LLOV GP-pseudotyped VSV infected particular bat cell lines more efficiently than viruses bearing other filovirus GPs. These results suggest that LLOV GP mediates cellular entry in a manner similar to that of the other filoviruses while showing preferential tropism for some bat cells.