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Ebola and Marburg filoviruses cause deadly outbreaks of haemorrhagic fever. Despite considerable efforts, no essential cellular receptors for filovirus entry have been identified. We showed previously that Niemann-Pick C1 (NPC1), a lysosomal cholesterol transporter, is required for filovirus entry. Here, we demonstrate that NPC1 is a critical filovirus receptor. Human NPC1 fulfills a cardinal property of viral receptors: it confers susceptibility to filovirus infection when expressed in non-permissive reptilian cells. The second luminal domain of NPC1 binds directly and specifically to the viral glycoprotein, GP, and a synthetic single-pass membrane protein containing this domain has viral receptor activity. Purified NPC1 binds only to a cleaved form of GP that is generated within cells during entry, and only viruses containing cleaved GP can utilize a receptor retargeted to the cell surface. Our findings support a model in which GP cleavage by endosomal cysteine proteases unmasks the binding site for NPC1, and GP-NPC1 engagement within lysosomes promotes a late step in entry proximal to viral escape into the host cytoplasm. NPC1 is the first known viral receptor that recognizes its ligand within an intracellular compartment and not at the plasma membrane.

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Ebola virus (EBOV) and Marburg virus (MARV) cause rapidly progressive hemorrhagic fever with high mortality and may possess specialized mechanisms to evade immune destruction. We postulated that immune evasion could be due to the ability of EBOV and MARV to interfere with dendritic cells (DCs), which link innate and adaptive immune responses. We demonstrate that EBOV and MARV infected and replicated in primary human DCs without inducing cytokine secretion. Infected DC cultures supported exponential viral growth without releasing interferon (IFN)-alpha and were impaired in IFN-alpha production if treated with double-stranded RNA. Moreover, EBOV and MARV impaired the ability of DCs to support T cell proliferation, and infected, immature DCs underwent an anomalous maturation. These findings may explain the profound virulence of EBOV and MARV--DCs are disabled, and an effective early host response is delayed by the necessary reliance on less-efficient secondary mechanisms.

The matrix protein VP40 plays a critical role in Ebola virus assembly and budding, a process that utilizes specialized membrane domains known as lipid rafts. Previous studies with purified protein suggest a role for oligomerization of VP40 in this process. Here, we demonstrate VP40 oligomers in lipid rafts of mammalian cells, virus-like particles, and in the authentic Ebola virus. By mutagenesis, we identify several critical C-terminal sequences that regulate oligomerization at the plasma membrane, association with detergent-resistant membranes, and vesicular release of VP40, directly linking these phenomena. Furthermore, we demonstrate the active recruitment of TSG101 into lipid rafts by VP40. We also report the successful application of the biarsenic fluorophore, FlAsH, combined with a tetracysteine tag for imaging of Ebola VP40 in live cells.rafts ͉ FlAsH ͉ TSG101 ͉ filovirus