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...

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Virus neutralization remains the gold standard for determining antibody efficacy. Therefore, a high-throughput assay to measure SARS-CoV-2 neutralizing antibodies is urgently needed for COVID-19 serodiagnosis, convalescent plasma therapy, and vaccine development. Here, we report on a fluorescence-based SARS-CoV-2 neutralization assay that detects SARS-CoV-2 neutralizing antibodies in COVID-19 patient specimens and yields comparable results to plaque reduction neutralizing assay, the gold standard of serological testing. The fluorescence-based neutralization assay is specific to measure COVID-19 neutralizing antibodies without cross reacting with patient specimens with other viral, bacterial, or parasitic infections. Collectively, our approach offers a rapid platform that can be scaled to screen people for antibody protection from COVID-19, a key parameter necessary to safely reopen local communities.

Flavivirus RNA replication occurs within a replication complex (RC) that assembles on ER membranes and comprises both non-structural (NS) viral proteins and host cofactors. As the largest protein component within the flavivirus RC, NS5 plays key enzymatic roles through its N-terminal methyltransferase (MTase) and C-terminal RNA-dependent-RNA polymerase (RdRp) domains, and constitutes a major target for antivirals. We determined a crystal structure of the full-length NS5 protein from Dengue virus serotype 3 (DENV3) at a resolution of 2.3 Å in the presence of bound SAH and GTP. Although the overall molecular shape of NS5 from DENV3 resembles that of NS5 from Japanese Encephalitis Virus (JEV), the relative orientation between the MTase and RdRp domains differs between the two structures, providing direct evidence for the existence of a set of discrete stable molecular conformations that may be required for its function. While the inter-domain region is mostly disordered in NS5 from JEV, the NS5 structure from DENV3 reveals a well-ordered linker region comprising a short 310 helix that may act as a swivel. Solution Hydrogen/Deuterium Exchange Mass Spectrometry (HDX-MS) analysis reveals an increased mobility of the thumb subdomain of RdRp in the context of the full length NS5 protein which correlates well with the analysis of the crystallographic temperature factors. Site-directed mutagenesis targeting the mostly polar interface between the MTase and RdRp domains identified several evolutionarily conserved residues that are important for viral replication, suggesting that inter-domain cross-talk in NS5 regulates virus replication. Collectively, a picture for the molecular origin of NS5 flexibility is emerging with profound implications for flavivirus replication and for the development of therapeutics targeting NS5.

Virus–host interactions determine an infection outcome. The Asian lineage of Zika virus (ZIKV), responsible for the recent epidemics, has fixed a mutation in the NS1 gene after 2012 that enhances mosquito infection. Here we report that the same mutation confers NS1 to inhibit interferon-β induction. This mutation enables NS1 binding to TBK1 and reduces TBK1 phosphorylation. Engineering the mutation into a pre-epidemic ZIKV strain debilitates the virus for interferon-β induction; reversing the mutation in an epidemic ZIKV strain invigorates the virus for interferon-β induction; these mutational effects are lost in IRF3-knockout cells. Additionally, ZIKV NS2A, NS2B, NS4A, NS4B, and NS5 can also suppress interferon-β production through targeting distinct components of the RIG-I pathway; however, for these proteins, no antagonistic difference is observed among various ZIKV strains. Our results support the mechanism that ZIKV has accumulated mutation(s) that increases the ability to evade immune response and potentiates infection and epidemics.

West Nile virus is a mosquito-borne flavivirus originally isolated in 1937 from the blood of a febrile woman in the West Nile province of Uganda. The virus is widely distributed in Africa, Europe, Australia, and Asia, and, since 1999, it has spread rapidly throughout the western hemisphere, including the USA, Canada, Mexico, and the Caribbean and into parts of Central and South America. Before 1994, outbreaks of West Nile virus were sporadic and occurred primarily in the Mediterranean region, Africa, and east Europe. Since 1994, outbreaks have occurred with a higher incidence of severe human disease, particularly affecting the nervous system. In North America, the virus has caused meningitis, encephalitis, and poliomyelitis, resulting in significant morbidity and mortality. The goal of this Review is to highlight recent advances in our understanding of West Nile virus virology, ecology, clinical disease, diagnosis, and development of potential vaccines and antiviral therapies.

SUMMARY The emergence of Zika virus (ZIKV) and its association with congenital malformations has prompted the rapid development of vaccines. Although efficacy with nucleic acid or inactivated viral vaccine platforms has been established in animals, no study has addressed protection during pregnancy. We tested in mice two vaccine platforms, a lipid nanoparticle-encapsulated modified mRNA vaccine encoding ZIKV prM and E genes and a live-attenuated ZIKV strain encoding an NS1 protein without glycosylation, for their ability to protect against transmission to the fetus. Vaccinated dams challenged with a heterologous ZIKV strain at embryo day 6 (E6) and evaluated at E13 showed markedly diminished levels of viral RNA in maternal, placental, and fetal tissues, which resulted in protection against placental damage and fetal demise. As modified mRNA and live-attenuated vaccine platforms can restrict in utero transmission of ZIKV in mice, their further development in humans to prevent congenital ZIKV syndrome is warranted.