Synthesis of IFN-β by Virus-Infected Chicken Embryo Cells Demonstrated with Specific Antisera and a New Bioassay

Transcripts of interferon-α(IFN-α) and IFN-β genes are present in virus-infected chicken cells, but because of a lack of appropriate assays and reagents, it was unclear if biologically active IFN-β is secreted. We have established a nonviral bioassay for the sensitive detection of chicken IFN (ChIFN). This assay is based on a quail cell line that carries a luciferase gene that is controlled by the IFN-responsive chicken Mx promoter. Luciferase activity was strongly stimulated when the indicator cells were incubated with ChIFN-α, ChIFN-β, or ChIFN-γ but not with chicken interleukin-1β (ChIL-1β). Unlike the classic antiviral assay that preferentially detects ChIFN-α, the Mx-luciferase assay detected ChIFN-α and ChIFN-β with similar sensitivity. With the help of this novel assay and with rabbit antisera specific for either IFN-α or IFN-β, we analyzed the composition of IFN in supernatants of virus-infected chicken embryo cells. Virtually all IFN produced in response to Newcastle disease virus (NDV) was IFN-α. However, IFN produced in response to influenza A or vaccinia virus (VV) was a mixture of usually more than 80% IFN-α and up to 20% IFN-β. Thus, IFN-α and IFN-β both contribute to the cytokine activity in supernatants of virus-infected chicken cells. Furthermore, the infecting virus appears to determine the IFN subtype composition