Cloning and characterization of type IV interferon from black carp Mylopharyngodon piceus

From mammals to fish, interferons (IFNs) play vital roles in the immune response. In this study, a newly identified type IV interferon (bcIFN-υ) from black carp (Mylopharyngodon piceus) has been cloned and characterized. The CDS of bcIFN-υ consists of 489 nucleotides, encoding 163 amino acids, with the first 20 amino acids predicted to be the signal peptide region. The immunoblot and immunofluorescence assays verified that bcIFN-υ was a secreted cytokine. qPCR analysis and reporter assay demonstrated that bcIFN-υ participated in innate immune defense and activated the transcription of fish ISRE promoter under spring viremia of carp virus (SVCV) stimulation. Additionally, compared with control group, EPC cells transfected with bcIFN-υ or incubated with the bcIFN-υ-containing conditioned media before SVCV infection showed greatly enhanced antiviral activity, and the transcription levels of MX1, PKR, ISG15 and Viperin genes were significantly increased. The subsequential co-immunoprecipitation assay identified the interaction between bcIFN-υ proteins. Collectively, our data conclude that bcIFN-υ is a kind of secretory protein with self-interaction and triggering the expression of downstream ISGs to enhance the antiviral activity of host cells.