title: Porcine reproductive and respiratory syndrome virus field isolates differ in in vitro interferon phenotypes.
abstract: Type I interferons (IFN-alpha and -beta) play an important role in the innate host defense against viral infection by inducing antiviral responses. In addition to direct antiviral activities, type I IFN serves as an important link between the innate and adaptive immune response through multiple mechanisms. Therefore, the outcome of a viral infection can be affected by IFN induction and the IFN sensitivity of a virus. North American porcine reproductive and respiratory syndrome virus (PRRSV) field isolates were studied with regard to IFN-alpha sensitivity and induction in order to understand the role of type I IFN in PRRSV pathogenesis. PRRSV isolates were differentially sensitive to porcine recombinant IFN-alpha (rIFN-alpha) and varied in their ability to induce IFN-alpha in porcine alveolar macrophages (PAM) cultures as measured by a porcine IFN-alpha specific ELISA on cell culture supernatants. Fifty-two plaques were purified from three PRRSV isolates (numbers 3, 7, and 12) and tested for IFN sensitivity and IFN induction. Plaque-derived populations were composed of heterogeneous populations in terms of IFN-inducing capacity and sensitivity to rIFN-alpha. When macrophages infected with isolates 3, 7, or 12 were treated with polycytidylic acid (polyI:C), IFN-alpha production was enhanced. Cells infected with isolate 3 and treated with polyI:C showed the most consistent and strongest enhancement of IFN-alpha production. It was demonstrated that the relatively low concentrations of IFN-alpha produced by isolate 3 contributed to the enhanced IFN-alpha synthesis in response to polyI:C. Isolates 7 and 12 significantly suppressed the enhanced IFN-alpha production by isolate 3 in polyI:C treated cells. To determine if suppression was at the level of IFN-alpha transcription, quantitative RT-PCR was performed for IFN-alpha mRNA and compared to GAPDH and cyclophilin mRNA quantification. However, the relative number of IFN-alpha transcript copies did not correlate with IFN-alpha protein levels, suggesting a post-transcriptional mechanism of suppression. In summary, these results demonstrate that PRRSV field isolates differ both in IFN-alpha sensitivity and induction. Furthermore, a PRRSV field isolate strongly enhance polyI:C-induced IFN-alpha production in PAM cultures and this priming effect was suppressed by other PRRSV isolates.
authors.affiliation: Department of Veterinary Pathobiology, College of Veterinary Medicine, University of Missouri, 1600 E. Rollins, Columbia, MO 65211, USA.
authors.forename: Sang-Myeong
authors.initials: SM
authors.lastname: Lee
authors.forename: Susan K
authors.initials: SK
authors.lastname: Schommer
authors.forename: Steven B
authors.initials: SB
authors.lastname: Kleiboeker
mesh_terms: D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D014644:Genetic Variation; D016898:Interferon-alpha / Q000096:biosynthesis / Q000276:immunology*; D016676:Macrophages, Alveolar; D010641:Phenotype; D019318:Porcine Reproductive and Respiratory Syndrome / Q000821:virology; D019316:Porcine respiratory and reproductive syndrome virus / Q000187:drug effects / Q000235:genetics / Q000276:immunology*; D013552:Swine / Q000276:immunology / Q000821:virology; D013997:Time Factors
chemical_list: D016898:Interferon-alpha