The lectins DC-SIGN and DC-SIGNR can augment viral infection; however, the range of pathogens interacting with these attachment factors is incompletely defined. Here we show that DC-SIGN and DC-SIGNR enhance infection mediated by the glycoprotein (GP) of Marburg virus (MARV) and the S protein of severe acute respiratory syndrome coronavirus and might promote viral dissemination. SIGNR1, a murine DC-SIGN homologue, also enhanced infection driven by MARV and Ebola virus GP and could be targeted to assess the role of attachment factors in filovirus infection in vivo.

Replication-competent recombinant vesicular stomatitis viruses (rVSVs) expressing the type I transmembrane glycoproteins and selected soluble glycoproteins of several viral hemorrhagic fever agents (Marburg virus, Ebola virus, and Lassa virus) were generated and characterized. All recombinant viruses exhibited rhabdovirus morphology and replicated cytolytically in tissue culture. Unlike the rVSVs with an additional transcription unit expressing the soluble glycoproteins, the viruses carrying the foreign transmembrane glycoproteins in replacement of the VSV glycoprotein were slightly attenuated in growth. Biosynthesis and processing of the foreign glycoproteins were authentic, and the cell tropism was defined by the transmembrane glycoprotein. None of the rVSVs displayed pathogenic potential in animals. The rVSV expressing the Zaire Ebola virus transmembrane glycoprotein mediated protection in mice against a lethal Zaire Ebola virus challenge. Our data suggest that the recombinant VSV can be used to study the role of the viral glycoproteins in virus replication, immune response, and pathogenesis.

Cellular attachment factors like the C-type lectins DC-SIGN and DC-SIGNR (collectively referred to as DC-SIGN/R) can augment viral infection and might promote viral dissemination in and between hosts. The lectin LSECtin is encoded in the same chromosomal locus as DC-SIGN/R and is coexpressed with DC-SIGNR on sinusoidal endothelial cells in liver and lymphnodes. Here, we show that LSECtin enhances infection driven by filovirus glycoproteins (GP) and the S protein of SARS coronavirus, but does not interact with human immunodeficiency virus type-1 and hepatitis C virus envelope proteins. Ligand binding to LSECtin was inhibited by EGTA but not by mannan, suggesting that LSECtin unlike DC-SIGN/R does not recognize high-mannose glycans on viral GPs. Finally, we demonstrate that LSECtin is N-linked glycosylated and that glycosylation is required for cell surface expression. In summary, we identified LSECtin as an attachment factor that in conjunction with DC-SIGNR might concentrate viral pathogens in liver and lymph nodes.

The zinc finger antiviral protein (ZAP) was recently shown to inhibit Moloney murine leukemia virus and Sindbis virus replication. We tested whether ZAP also acts against Ebola virus (EBOV) and Marburg virus (MARV). Antiviral effects were observed after infection of cells expressing the N-terminal part of ZAP fused to the product of the zeocin resistance gene (NZAP-Zeo) as well as after infection of cells inducibly expressing full-length ZAP. EBOV was inhibited by up to 4 log units, whereas MARV was inhibited between 1 to 2 log units. The activity of ZAP was dependent on the integrity of the second and fourth zinc finger motif, as tested with cell lines expressing NZAP-Zeo mutants. Heterologous expression of EBOV-and MARV-specific sequences fused to a reporter gene suggest that ZAP specifically targets L gene sequences. The activity of NZAP-Zeo in this assay was also dependent on the integrity of the second and fourth zinc finger motif. Time-course experiments with infectious EBOV showed that ZAP reduces the level of L mRNA before the level of genomic or antigenomic RNA is affected. Transient expression of ZAP decreased the activity of an EBOV replicon system by up to 95%. This inhibitory effect could be partially compensated for by overexpression of L protein.In conclusion, the data demonstrate that ZAP exhibits antiviral activity against filoviruses, presumably by decreasing the level of viral mRNA. Ebola virus (EBOV) and Marburg virus (MARV) belong to the family Filoviridae.Their genome consists of a singlestranded RNA genome of negative polarity with a length of about 19 kb. The filovirus genome is transcribed in monocistronic mRNA species, which encode seven structural proteins: a single surface protein (GP), a matrix protein (virus protein 40 [VP40]), a second minor matrix protein (VP24), and four nucleocapsid proteins (nucleoprotein [NP], L protein, VP35, and VP30) (7,15,16,18,25). Both EBOV and MARV cause severe hemorrhagic fever in humans and nonhuman primates (4,19). Infections with filoviruses are characterized by high fever, hemorrhages, and shock (19,22). For Zaire-EBOV and MARV, mortality rates up to 90% have been described; the mortality rates for Sudan-EBOV are about 60% (from the Centers for Disease Control and Prevention website [http: //www.cdc.gov/]). To date, neither a vaccine nor a therapy for treating infected patients is available.In contrast to many other viruses, no host cell proteins with antiviral activity have been identified so far for filoviruses. However, it is known that filoviruses antagonize the interferon (IFN) response (17), suggesting that the IFN pathway plays a role in the host cell response against filoviruses. Both VP35 and VP24 of EBOV have been found to be involved in the IFN antagonism (6,12,23).In an attempt to search for host cell antiviral proteins active against filoviruses, we analyzed the effect of the CCCH-type zinc finger antiviral protein (ZAP) (8) on EBOV and MARV replication. ZAP was discovered via its ability to inhibit Moloney murine leukemia virus (MMLV)...