Coronaviruses (CoVs) are important human and animal pathogens that induce fatal respiratory, gastrointestinal and neurological disease. The outbreak of the severe acute respiratory syndrome (SARS) in 2002/2003 has demonstrated human vulnerability to (Coronavirus) CoV epidemics. Neither vaccines nor therapeutics are available against human and animal CoVs. Knowledge of host cell proteins that take part in pivotal virus-host interactions could define broad-spectrum antiviral targets. In this study, we used a systems biology approach employing a genome-wide yeast-two hybrid interaction screen to identify immunopilins (PPIA, PPIB, PPIH, PPIG, FKBP1A, FKBP1B) as interaction partners of the CoV non-structural protein 1 (Nsp1). These molecules modulate the Calcineurin/NFAT pathway that plays an important role in immune cell activation. Overexpression of NSP1 and infection with live SARS-CoV strongly increased signalling through the Calcineurin/NFAT pathway and enhanced the induction of interleukin 2, compatible with late-stage immunopathogenicity and long-term cytokine dysregulation as observed in severe SARS cases. Conversely, inhibition of cyclophilins by cyclosporine A (CspA) blocked the replication of CoVs of all genera, including SARS-CoV, human CoV-229E and -NL-63, feline CoV, as well as avian infectious bronchitis virus. Non-immunosuppressive derivatives of CspA might serve as broad-range CoV inhibitors applicable against emerging CoVs as well as ubiquitous pathogens of humans and livestock.

Virus-infected cells secrete a broad range of interferons (IFN) which confer resistance to yet uninfected cells by triggering the synthesis of antiviral factors. The relative contributions of the various IFN subtypes to innate immunity against virus infections remain elusive. IFN-␣, IFN-␤, and other type I IFN molecules signal through a common, universally expressed cell surface receptor, whereas type III IFN (IFN-) uses a distinct cell-typespecific receptor complex for signaling. Using mice lacking functional receptors for type I IFN, type III IFN, or both, we found that IFN-plays an important role in the defense against several human pathogens that infect the respiratory tract, such as influenza A virus, influenza B virus, respiratory syncytial virus, human metapneumovirus, and severe acute respiratory syndrome (SARS) coronavirus. These viruses were more pathogenic and replicated to higher titers in the lungs of mice lacking both IFN receptors than in mice with single IFN receptor defects. In contrast, Lassa fever virus, which infects via the respiratory tract but primarily replicates in the liver, was not influenced by the IFN-receptor defect. Careful analysis revealed that expression of functional IFN-receptor complexes in the lung and intestinal tract is restricted to epithelial cells and a few other, undefined cell types. Interestingly, we found that SARS coronavirus was present in feces from infected mice lacking receptors for both type I and type III IFN but not in those from mice lacking single receptors, supporting the view that IFN-contributes to the control of viral infections in epithelial cells of both respiratory and gastrointestinal tracts.The interferon (IFN) system represents a major element of the innate immune response against viral infections (10,13,14). Virus-induced IFN is a complex mixture of biologically active molecules, which includes type I and type III IFN. Type I IFN consists of 14 different IFN-␣ subtypes in the mouse as well as IFN-␤, IFN-, IFN-ε, and limitin, which all signal through the same universally expressed cell surface receptor complex (IFNAR) (30). Type III IFN includes IFN-1, IFN-2, and IFN-3 (21, 28), of which only the latter two are encoded by genes that are expressed in the mouse (22). Type III IFN uses a distinct receptor complex (IL28R) for signaling (21, 28), which appears to be expressed on only a few cell types, including epithelial cells (29). Binding of type I IFN and type III IFN to their cognate receptor complexes triggers signaling cascades that result in the activation of a large number of genes, many of which encode antiviral proteins (10, 32). Type I IFN and type III IFN trigger highly similar gene expression profiles in responsive cells, suggesting that both IFN types might serve similar functions. However, it has to date been largely unclear to which extent IFN-might contribute to innate immunity.Using knockout mouse strains that lack receptors for type I IFN (IFNAR1 0/0 ), type III IFN (IL28R␣ 0/0 ), or both (IFNAR1 0/0 IL28R␣ 0/0 ), we have recently ...

During the outbreak of SARS in 2002/3, a prototype virus was isolated from a patient in Frankfurt/Germany (strain Frankfurt-1). As opposed to all other SARS-Coronavirus strains, Frankfurt-1 has a 45-nucleotide deletion in the transmembrane domain of its ORF 7b protein. When over-expressed in HEK 293 cells, the full-length protein but not the variant with the deletion caused interferon beta induction and cleavage of procaspase 3. To study the role of ORF 7b in the context of virus replication, we cloned a full genome cDNA copy of Frankfurt-1 in a bacterial artificial chromosome downstream of a T7 RNA polymerase promoter. Transfection of capped RNA transcribed from this construct yielded infectious virus that was indistinguishable from the original virus isolate. The presumed Frankfurt-1 ancestor with an intact ORF 7b was reconstructed. In CaCo-2 and HUH7 cells, but not in Vero cells, the variant carrying the ORF 7b deletion had a replicative advantage against the parental virus (4- and 6-fold increase of virus RNA in supernatant, respectively). This effect was neither associated with changes in the induction or secretion of type I interferon, nor with altered induction of apoptosis in cell culture. However, pretreatment of cells with interferon beta caused the deleted virus to replicate to higher titers than the parental strain (3.4-fold in Vero cells, 7.9-fold in CaCo-2 cells).In Syrian Golden Hamsters inoculated intranasally with 10e4 plaque forming units of either virus, mean titers of infectious virus and viral RNA in the lungs after 24 h were increased 23- and 94.8-fold, respectively, with the deleted virus. This difference could explain earlier observations of enhanced virulence of Frankfurt-1 in Hamsters as compared to other SARS-Coronavirus reference strains and identifies the SARS-CoV 7b protein as an attenuating factor with the SARS-Coronavirus genome. Because attenuation was focused on the early phase of infection in-vivo, ORF 7b might have contributed to the delayed accumulation of virus in patients that was suggested to have limited the spread of the SARS epidemic.

HBoV causes severe respiratory tract infections in infants and young children. Its role as a copathogen and many other open questions has to be defined in further prospective studies.

Human metapneumovirus (hMPV) infections occur frequently despite high rates of perpetual seroprevalence for all age groups. Analyses of ϳ2,000 archived, randomly selected serum samples demonstrated that neutralizing capacities remain high, with a minor decrease for individuals over 69 years of age, leading to the hypothesis that reinfections occur because humoral immune responses play minor roles in the clearance of hMPV infections.