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Human coronavirus-EMC (hCoV-EMC) is a new coronavirus that has killed around half of the few humans infected so far; this study now identifies DPP4 as the receptor that this virus uses to infect cells. Supplementary information The online version of this article (doi:10.1038/nature12005) contains supplementary material, which is available to authorized users., Human receptor for emerging coronavirus The emerging pathogenic coronavirus hCoV-EMC, first identified in September 2012, has been fatal in about half of the few humans infected so far. Bart Haagmans and colleagues have now identified the receptor that this virus uses to infect cells. In contrast to the related virus SARS-CoV, which uses angiotensin converting enzyme 2, the functional receptor for hCoV-EMC is dipeptidyl peptidase 4 (DPP4, also known as CD26), an exopeptidase found on non-ciliated cells in the lower respiratory tract. This enzyme is highly conserved across different species, and hCoV-EMC can also use bat DPP4 as a functional receptor — a possible clue as to the host range and epidemiological history of this new virus. The findings may also be important for the development of intervention strategies. Supplementary information The online version of this article (doi:10.1038/nature12005) contains supplementary material, which is available to authorized users., Most human coronaviruses cause mild upper respiratory tract disease but may be associated with more severe pulmonary disease in immunocompromised individuals1. However, SARS coronavirus caused severe lower respiratory disease with nearly 10% mortality and evidence of systemic spread2. Recently, another coronavirus (human coronavirus-Erasmus Medical Center (hCoV-EMC)) was identified in patients with severe and sometimes lethal lower respiratory tract infection3,4. Viral genome analysis revealed close relatedness to coronaviruses found in bats5. Here we identify dipeptidyl peptidase 4 (DPP4; also known as CD26) as a functional receptor for hCoV-EMC. DPP4 specifically co-purified with the receptor-binding S1 domain of the hCoV-EMC spike protein from lysates of susceptible Huh-7 cells. Antibodies directed against DPP4 inhibited hCoV-EMC infection of primary human bronchial epithelial cells and Huh-7 cells. Expression of human and bat (Pipistrellus pipistrellus) DPP4 in non-susceptible COS-7 cells enabled infection by hCoV-EMC. The use of the evolutionarily conserved DPP4 protein from different species as a functional receptor provides clues about the host range potential of hCoV-EMC. In addition, it will contribute critically to our understanding of the pathogenesis and epidemiology of this emerging human coronavirus, and may facilitate the development of intervention strategies. Supplementary information The online version of this article (doi:10.1038/nature12005) contains supplementary material, which is available to authorized users.

The recent emergence of a novel human coronavirus (HCoV-EMC) in the Middle East raised considerable concerns, as it is associated with severe acute pneumonia, renal failure, and fatal outcome and thus resembles the clinical presentation of severe acute respiratory syndrome (SARS) observed in 2002 and 2003. Like SARS-CoV, HCoV-EMC is of zoonotic origin and closely related to bat coronaviruses. The human airway epithelium (HAE) represents the entry point and primary target tissue for respiratory viruses and is highly relevant for assessing the zoonotic potential of emerging respiratory viruses, such as HCoV-EMC. Here, we show that pseudostratified HAE cultures derived from different donors are highly permissive to HCoV-EMC infection, and by using reverse transcription (RT)-PCR and RNAseq data, we experimentally determined the identity of seven HCoV-EMC subgenomic mRNAs. Although the HAE cells were readily responsive to type I and type III interferon (IFN), we observed neither a pronounced inflammatory cytokine nor any detectable IFN responses following HCoV-EMC, SARS-CoV, or HCoV-229E infection, suggesting that innate immune evasion mechanisms and putative IFN antagonists of HCoV-EMC are operational in the new host. Importantly, however, we demonstrate that both type I and type III IFN can efficiently reduce HCoV-EMC replication in HAE cultures, providing a possible treatment option in cases of suspected HCoV-EMC infection. IMPORTANCE A novel human coronavirus, HCoV-EMC, has recently been described to be associated with severe respiratory tract infection and fatalities, similar to severe acute respiratory syndrome (SARS) observed during the 2002-2003 epidemic. Closely related coronaviruses replicate in bats, suggesting that, like SARS-CoV, HCoV-EMC is of zoonotic origin. Since the animal reservoir and circumstances of zoonotic transmission are yet elusive, it is critically important to assess potential species barriers of HCoV-EMC infection. An important first barrier against invading respiratory pathogens is the epithelium, representing the entry point and primary target tissue of respiratory viruses. We show that human bronchial epithelia are highly susceptible to HCoV-EMC infection. Furthermore, HCoV-EMC, like other coronaviruses, evades innate immune recognition, reflected by the lack of interferon and minimal inflammatory cytokine expression following infection. Importantly, type I and type III interferon treatment can efficiently reduce HCoV-EMC replication in the human airway epithelium, providing a possible avenue for treatment of emerging virus infections.

Significance Hepatitis delta virus (HDV) aggravates hepatitis B virus (HBV) infection of liver cells. Although the viruses are evolutionarily unrelated, HDV depends on HBV because it requires the HBV envelope protein for its transmission. HDV is only described in humans, which has triggered diverse hypotheses regarding its evolution and origins. Here we show that spiny rats (Proechimys semispinosus) carry a counterpart to HDV that surprisingly does not cause hepatitis and is not linked to HBV. The rodent deltavirus finding alone, but also taken together with the recent deltavirus findings in snakes and other vertebrates and invertebrates, suggests that a deltavirus precursor may have infected mammals before it acquired dependence on HBV as seen in humans., Hepatitis delta virus (HDV) is a human hepatitis-causing RNA virus, unrelated to any other taxonomic group of RNA viruses. Its occurrence as a satellite virus of hepatitis B virus (HBV) is a singular case in animal virology for which no consensus evolutionary explanation exists. Here we present a mammalian deltavirus that does not occur in humans, identified in the neotropical rodent species Proechimys semispinosus. The rodent deltavirus is highly distinct, showing a common ancestor with a recently described deltavirus in snakes. Reverse genetics based on a tandem minus-strand complementary DNA genome copy under the control of a cytomegalovirus (CMV) promoter confirms autonomous genome replication in transfected cells, with initiation of replication from the upstream genome copy. In contrast to HDV, a large delta antigen is not expressed and the farnesylation motif critical for HBV interaction is absent from a genome region that might correspond to a hypothetical rodent large delta antigen. Correspondingly, there is no evidence for coinfection with an HBV-related hepadnavirus based on virus detection and serology in any deltavirus-positive animal. No other coinfecting viruses were detected by RNA sequencing studies of 120 wild-caught animals that could serve as a potential helper virus. The presence of virus in blood and pronounced detection in reproductively active males suggest horizontal transmission linked to competitive behavior. Our study establishes a nonhuman, mammalian deltavirus that occurs as a horizontally transmitted infection, is potentially cleared by immune response, is not focused in the liver, and possibly does not require helper virus coinfection.