title: Alpha interferon and not gamma interferon inhibits salmonid alphavirus subtype 3 replication in vitro.
abstract: Salmonid alphavirus (SAV) is an emerging virus in salmonid aquaculture, with SAV-3 being the only subtype found in Norway. Until now, there has been little focus on the alpha interferon (IFN-alpha)-induced antiviral responses during virus infection in vivo or in vitro in fish. The possible involvement of IFN-gamma in the response to SAV-3 is also not known. In this study, the two IFNs were cloned and expressed as recombinant proteins (recombinant IFN-alpha [rIFN-alpha] and rIFN-gamma) and used for in vitro studies. SAV-3 infection in a permissive salmon cell line (TO cells) results in IFN-alpha and IFN-stimulated gene (ISG) mRNA upregulation. Preinfection treatment (4 to 24 h prior to infection) with salmon rIFN-alpha induces an antiviral state that inhibits the replication of SAV-3 and protects the cells against virus-induced cytopathic effects (CPE). The antiviral state coincides with a strong expression of Mx and ISG15 mRNA and Mx protein expression. When rIFN-alpha is administered at the time of infection and up to 24 h postinfection, virus replication is not inhibited, and cells are not protected against virus-induced CPE. By 40 h postinfection, the alpha subunit of eukaryotic initiation factor 2 (eIF2alpha) is phosphorylated concomitant with the expression of the E2 protein as assessed by Western blotting. Postinfection treatment with rIFN-alpha results in a moderate reduction in E2 expression levels in accordance with a moderate downregulation of cellular protein synthesis, an approximately 65% reduction by 60 h postinfection. rIFN-gamma has only a minor inhibitory effect on SAV-3 replication in vitro. SAV-3 is sensitive to the preinfection antiviral state induced by rIFN-alpha, while postinfection antiviral responses or postinfection treatment with rIFN-alpha is not able to limit viral replication.
authors.affiliation: Department of Basic Sciences and Aquatic Medicine, Norwegian School of Veterinary Science, N-0033 Oslo, Norway.
authors.forename: Cheng
authors.initials: C
authors.lastname: Xu
authors.forename: Tz-Chun
authors.initials: TC
authors.lastname: Guo
authors.forename: Stephen
authors.initials: S
authors.lastname: Mutoloki
authors.forename: Øyvind
authors.initials: Ø
authors.lastname: Haugland
authors.forename: Inderjit S
authors.initials: IS
authors.lastname: Marjara
authors.forename: Øystein
authors.initials: Ø
authors.lastname: Evensen
mesh_terms: D000524:Alphavirus / Q000235:genetics / Q000502:physiology*; D018354:Alphavirus Infections / Q000276:immunology / Q000662:veterinary* / Q000821:virology; D000818:Animals; D000998:Antiviral Agents / Q000276:immunology*; D002460:Cell Line; D005393:Fish Diseases / Q000276:immunology* / Q000821:virology; D015967:Gene Expression Regulation, Viral; D016898:Interferon-alpha / Q000235:genetics / Q000276:immunology*; D007371:Interferon-gamma / Q000235:genetics / Q000276:immunology*; D011994:Recombinant Proteins; D012487:Salmonidae / Q000276:immunology* / Q000821:virology; D014779:Virus Replication
chemical_list: D000998:Antiviral Agents; D016898:Interferon-alpha; D011994:Recombinant Proteins; D007371:Interferon-gamma