Interferons (IFNs) are key mediators of the host innate antiviral immune response. To identify IFNstimulated genes (ISGs) that instigate an antiviral state against two medically important flaviviruses, West Nile virus (WNV) and dengue virus (DENV), we tested 36 ISGs that are commonly induced by IFN-␣ for antiviral activity against the two viruses. We discovered that five ISGs efficiently suppressed WNV and/or DENV infection when they were individually expressed in HEK293 cells. Mechanistic analyses revealed that two structurally related cell plasma membrane proteins, IFITM2 and IFITM3, disrupted early steps (entry and/or uncoating) of the viral infection. In contrast, three IFN-induced cellular enzymes, viperin, ISG20, and double-stranded-RNA-activated protein kinase, inhibited steps in viral proteins and/or RNA biosynthesis. Our results thus imply that the antiviral activity of IFN-␣ is collectively mediated by a panel of ISGs that disrupt multiple steps of the DENV and WNV life cycles.West Nile virus (WNV) and dengue virus (DENV) are mosquito-borne flaviviruses that cause invasive neurological diseases and lethal hemorrhagic fever in humans, respectively (6, 32). Since its first incursion into New York City in 1999, WNV has rapidly spread throughout the continental United States and has recently reached South America (29, 34). In most cases, WNV infection of people resolves as an asymptomatic or a mild febrile illness. However, approximately 1% of infections result in severe neurological disorders, such as encephalitis and meningitis (27). Unlike WNV, for which people are only accidental hosts, DENV has fully adapted to humans (32). It has apparently lost the need for an enzootic cycle and causes a range of diseases in people, from acute febrile illness to life-threatening dengue hemorrhagic fever/dengue shock syndrome (6). Four distinct serotypes of DENV have spread throughout the tropical and subtropical parts of the world, with an estimated 50 to 100 million human cases annually and about 2.5 billion people worldwide being at risk of infection (32). Effective antiviral therapies and vaccines to treat or prevent WNV and DENV infections in humans are not yet available.Type I interferons (IFNs), represented by IFN-␣ and IFN-␤, have been demonstrated to play an essential role in defending against WNV and DENV infections. For example, mice with deficiencies in the induction of type I IFNs and the receptor or JAK-STAT signal transduction pathway of the cytokines are vulnerable to WNV and DENV infections (7,38,42,(49)(50)(51). In addition, a strain of WNV that fails to block the type I IFN signal transduction pathway is phenotypically attenuated in mice (23,50). Clinically, during acute DENV infection, innate immune responses play a key role in determining disease outcome (35), and resolution of WNV infection requires effective IFN-mediated innate host responses (23,43,53). Therefore, understanding how the IFN-mediated innate immune response functions is one of the critical frontiers in the molecular biology of WN...

Tetherin and IFITM3 are recently identified interferon-induced cellular proteins that restrict infections by retroviruses and filoviruses and of influenza virus and flaviviruses, respectively. In our efforts to further explore their antiviral activities against other viruses and determine their antiviral mechanisms, we found that the two antiviral proteins potently inhibit the infection of vesicular stomatitis virus (VSV), a prototype member of the Rhabdoviridae family. Taking advantage of this well-studied virus infection system, we show that although both tetherin and IFITM3 are plasma membrane proteins, tetherin inhibits virion particle release from infected cells, while IFITM3 disrupts an early event after endocytosis of virion particles but before primary transcription of incoming viral genomes. Furthermore, we demonstrate that both the N-terminal 21 amino acid residues and C-terminal transmembrane region of IFITM3 are required for its antiviral activity. Collectively, our work sheds light on the mechanisms by which tetherin and IFITM3 restrict infection with rhabdoviruses and possibly other pathogenic viruses.The interferon (IFN) system is the first line of defense against virus infection in vertebrates. Infection of cells by viruses can be detected by host cellular pattern recognition receptors (PRRs), such as toll-like receptors and RIG-I-like receptors (1,33,42). Engagement of the PRRs with virusassociated molecular patterns, such as 5Ј-triphosphate and/or double-stranded viral RNA, triggers signaling cascades that lead to the synthesis and secretion of type I IFNs, represented by IFN-␣ and IFN-␤ (25). Type I IFNs bind to their cognate receptors on the cell surface and activate the receptor-associated Janus kinase 1 (JAK1) and tyrosine kinase 2 (Tyk2) through tyrosine phosphorylation, which in turn stimulates the tyrosine phosphorylation of STAT1 and STAT2. Phosphorylated STAT1 and STAT2, in combination with IRF9, form a trimeric ISGF3 transcription factor that translocates into the nucleus and activates the expression of IFN-stimulated genes (ISGs), whose products limit viral replication, regulate cell proliferation, and/or modulate host innate and adaptive immune responses (34,36,39).Although IFN treatment of cells induces the expression of hundreds of ISGs, only a few ISGs have thus far been demonstrated to instigate an antiviral state in cultured cells, and only four of them, including ISG15 (IFN-stimulated protein of 15 kDa), myxovirus resistance 1 (Mx1), RNase L, and doublestranded RNA-activated protein kinase (PKR), have been shown to play a role in mediating the IFN antiviral response in vivo with gene knockout mouse models (36). While it is most likely that inhibition of the infection of any given virus by IFNs is through induction of multiple ISGs that work cooperatively to disrupt multiple steps of viral replication, identification of individual antiviral ISGs and subsequent elucidation of their modes of action are essential to uncover the antiviral mechanism of IFNs and viral pathogenesis (2...

Alpha interferon (IFN-␣) is an approved medication for chronic hepatitis B. Gamma interferon (IFN-␥) is a key mediator of host antiviral immunity against hepatitis B virus (HBV) infection in vivo.However, the molecular mechanism by which these antiviral cytokines suppress HBV replication remains elusive. Using an immortalized murine hepatocyte (AML12)-derived cell line supporting tetracycline-inducible HBV replication, we show in this report that both IFN-␣ and IFN-␥ efficiently reduce the amount of intracellular HBV nucleocapsids. Furthermore, we provide evidence suggesting that the IFN-induced cellular antiviral response is able to distinguish and selectively accelerate the decay of HBV replication-competent nucleocapsids but not empty capsids in a proteasome-dependent manner. Our findings thus reveal a novel antiviral mechanism of IFNs and provide a basis for a better understanding of HBV pathobiology.Hepatitis B virus (HBV) is a noncytopathic hepatotropic DNA virus which belongs to the family Hepadnaviridae (11,44). Despite the fact that most adulthood HBV infections are transient, approximately 5 to 10% of infected adults and more than 90% of infected neonates fail to clear the virus and develop a lifelong persistent infection, which may progress to chronic hepatitis, cirrhosis, and primary hepatocellular carcinoma (4,33,34). It has been shown by several research groups that resolution of HBV and other animal hepadnavirus infection in vivo depends on both killing of infected hepatocytes by viral antigen-specific cytotoxic T lymphocytes and noncytolytic suppression of viral replication, which is most likely mediated by inflammatory cytokines, such as gamma interferon (IFN-␥) and tumor necrosis factor ␣ (TNF-␣) (10,12,15,20,26,27,48). Moreover, together with five nucleoside or nucleotide analogs that inhibit HBV DNA polymerase, alpha IFN (IFN-␣) and pegylated IFN-␣ are currently available antiviral medications for the management of chronic hepatitis B. Compared to the viral DNA polymerase inhibitors, the advantages of IFN-␣ therapy include a lack of drug resistance, a finite and defined treatment course, and an increased likelihood for hepatitis B virus surface antigen (HBsAg) clearance (8, 39). However, only approximately 30% of treated patients achieve a sustained virological response to a standard 48-month pegylated IFN-␣ therapy (6, 32). Thus far, the antiviral mechanism of IFN-␣ and IFN-␥ and the parameters determining the success or failure of IFN-␣ therapy in chronic hepatitis B remain elusive. Elucidation of the mechanism by which the cytokines suppress HBV replication represents an important step toward understanding the pathobiology of HBV infection and the molecular basis of IFN-␣ therapy of chronic hepatitis B.Considering the mechanism by which IFNs noncytolytically control HBV infection in vivo, it is possible that the cytokines either induce an antiviral response in hepatocytes to directly limit HBV replication or modulate the host antiviral immune response to indirectly inhibit the virus infect...

Cellular α-glucosidases I and II are enzymes that sequentially trim the three terminal glucoses in the N-linked oligosaccharides of viral envelope glycoproteins. This process is essential for the proper folding of viral glycoproteins and subsequent assembly of many enveloped viruses, including dengue virus (DENV). Imino sugars are substrate mimics of α-glucosidases I and II. In this report, we show that two oxygenated alkyl imino sugar derivatives, CM-9-78 and CM-10-18, are potent inhibitors of both α-glucosidases I and II in vitro and in treated animals, and efficiently inhibit DENV infection of cultured human cells. Pharmacokinetic studies reveal that both compounds are well tolerated at doses up to 100mg/kg in rats and have favorable pharmacokinetic properties and bioavailability in mice. Moreover, we showed that oral administration of either CM-9-78 or CM-10-18 reduces the peak viremia of DENV in mice. Interestingly, while treatment of DENV infected mice with ribavirin alone did not reduce the viremia, combination therapy of ribavirin with sub-effective dose of CM-10-18 demonstrated a significantly enhanced antiviral activity, as indicated by a profound reduction of the viremia. Our findings thus suggest that combination therapy of two broad-spectrum antiviral agents may provide a practically useful approach for the treatment of DENV infection.

As an emerging infectious disease, the clinical course and virological course of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection remain to be further investigated. In this case report, we described a case of SARS-CoV-2 infection with the clinical course for more than 2 months. This patient had recovered from pneumonia after treatment. The viral RNA of throat swabs became negative and the viral-specific antibodies were produced during the recovery period. However, the viral RNA reappeared and additionally persisted in throat swabs for more than 40 days. In addition, the viral RNA was detected in multiple types of specimens with extremely high titers in the saliva. In conclusion, these findings indicate that SARS-CoV-2 can cause a long clinical course. The coexistence of viral RNA and viral-specific antibodies may imply an immune evasion of SARS-CoV-2 from the host's immune system. K E Y W O R D S coronavirus, saliva, SARS-CoV-2, virus shedding