Machupo Virus Glycoprotein Determinants for Human Transferrin Receptor 1 Binding and Cell Entry

Machupo virus (MACV) is a highly pathogenic New World arenavirus that causes hemorrhagic fever in humans. MACV, as well as other pathogenic New World arenaviruses, enter cells after their GP1 attachment glycoprotein binds to their cellular receptor, transferrin receptor 1 (TfR1). TfR1 residues essential for this interaction have been described, and a co-crystal of MACV GP1 bound to TfR1 suggests GP1 residues important for this association. We created MACV GP1 variants and tested their effect on TfR1 binding and virus entry to evaluate the functional significance of some of these and additional residues in human and simian cells. We found residues R111, D123, Y122, and F226 to be essential, D155, and P160 important, and D114, S116, D140, and K169 expendable for the GP1-TfR1 interaction and MACV entry. Several MACV GP1 residues that are critical for the interaction with TfR1 are conserved among other New World arenaviruses, indicating a common basis of receptor interaction. Our findings also open avenues for the rational development of viral entry inhibitors

Host-Species Transferrin Receptor 1 Orthologs Are Cellular Receptors for Nonpathogenic New World Clade B Arenaviruses

The ability of a New World (NW) clade B arenavirus to enter cells using human transferrin receptor 1 (TfR1) strictly correlates with its ability to cause hemorrhagic fever. Amapari (AMAV) and Tacaribe (TCRV), two nonpathogenic NW clade B arenaviruses that do not use human TfR1, are closely related to the NW arenaviruses that cause hemorrhagic fevers. Here we show that pseudotyped viruses bearing the surface glycoprotein (GP) of AMAV or TCRV can infect cells using the TfR1 orthologs of several mammalian species, including those of their respective natural hosts, the small rodent Neacomys spinosus and the fruit bat Artibeus jamaicensis. Mutation of one residue in human TfR1 makes it a functional receptor for TCRV, and mutation of four residues makes it a functional receptor for AMAV. Our data support an in vivo role for TfR1 in the replication of most, if not all, NW clade B arenaviruses, and suggest that with modest changes in their GPs the nonpathogenic arenaviruses could use human TfR1 and emerge as human pathogens

Junín Virus Infection of Human Hematopoietic Progenitors Impairs In Vitro Proplatelet Formation and Platelet Release via a Bystander Effect Involving Type I IFN Signaling

Argentine hemorrhagic fever (AHF) is an endemo-epidemic disease caused by Junín virus (JUNV), a member of the arenaviridae family. Although a recently introduced live attenuated vaccine has proven to be effective, AHF remains a potentially lethal infection. Like in other viral hemorrhagic fevers (VHF), AHF patients present with fever and hemorrhagic complications. Although the causes of the bleeding are poorly understood, impaired hemostasis, endothelial cell dysfunction and low platelet counts have been described. Thrombocytopenia is a common feature in VHF syndromes, and it is a major sign for its diagnosis. However, the underlying pathogenic mechanism has not yet been elucidated. We hypothesized that thrombocytopenia results from a viral-triggered alteration of the megakaryo/thrombopoiesis process. Therefore, we evaluated the impact of JUNV on megakaryopoiesis using an in vitro model of human CD34+ cells stimulated with thrombopoietin. Our results showed that CD34+ cells are infected with JUNV in a restricted fashion. Infection was transferrin receptor 1 (TfR1)-dependent and the surface expression of TfR1 was higher in infected cultures, suggesting a novel arenaviral dissemination strategy in hematopoietic progenitor cells. Although proliferation, survival, and commitment in JUNV-infected cultures were normal, viral infection impaired thrombopoiesis by decreasing in vitro proplatelet formation, platelet release, and P-selectin externalization via a bystander effect. The decrease in platelet release was also TfR1-dependent, mimicked by poly(I:C), and type I interferon (IFN α/β) was implicated as a key paracrine mediator. Among the relevant molecules studied, only the transcription factor NF-E2 showed a moderate decrease in expression in megakaryocytes from either infected cultures or after type I IFN treatment. Moreover, type I IFN-treated megakaryocytes presented ultrastructural abnormalities resembling the reported thrombocytopenic NF-E2−/− mouse phenotype. Our study introduces a potential mechanism for thrombocytopenia in VHF and other diseases associated with increased bone marrow type I IFN levels

Ebola Virion Attachment and Entry into Human Macrophages Profoundly Effects Early Cellular Gene Expression

Zaire ebolavirus (ZEBOV) infections are associated with high lethality in primates. ZEBOV primarily targets mononuclear phagocytes, which are activated upon infection and secrete mediators believed to trigger initial stages of pathogenesis. The characterization of the responses of target cells to ZEBOV infection may therefore not only further understanding of pathogenesis but also suggest possible points of therapeutic intervention. Gene expression profiles of primary human macrophages exposed to ZEBOV were determined using DNA microarrays and quantitative PCR to gain insight into the cellular response immediately after cell entry. Significant changes in mRNA concentrations encoding for 88 cellular proteins were observed. Most of these proteins have not yet been implicated in ZEBOV infection. Some, however, are inflammatory mediators known to be elevated during the acute phase of disease in the blood of ZEBOV-infected humans. Interestingly, the cellular response occurred within the first hour of Ebola virion exposure, i.e. prior to virus gene expression. This observation supports the hypothesis that virion binding or entry mediated by the spike glycoprotein (GP1,2) is the primary stimulus for an initial response. Indeed, ZEBOV virions, LPS, and virus-like particles consisting of only the ZEBOV matrix protein VP40 and GP1,2 (VLPVP40-GP) triggered comparable responses in macrophages, including pro-inflammatory and pro-apoptotic signals. In contrast, VLPVP40 (particles lacking GP1,2) caused an aberrant response. This suggests that GP1,2 binding to macrophages plays an important role in the immediate cellular response

Genetic Detection and Characterization of Lujo Virus, a New Hemorrhagic Fever–Associated Arenavirus from Southern Africa

Lujo virus (LUJV), a new member of the family Arenaviridae and the first hemorrhagic fever–associated arenavirus from the Old World discovered in three decades, was isolated in South Africa during an outbreak of human disease characterized by nosocomial transmission and an unprecedented high case fatality rate of 80% (4/5 cases). Unbiased pyrosequencing of RNA extracts from serum and tissues of outbreak victims enabled identification and detailed phylogenetic characterization within 72 hours of sample receipt. Full genome analyses of LUJV showed it to be unique and branching off the ancestral node of the Old World arenaviruses. The virus G1 glycoprotein sequence was highly diverse and almost equidistant from that of other Old World and New World arenaviruses, consistent with a potential distinctive receptor tropism. LUJV is a novel, genetically distinct, highly pathogenic arenavirus