Effect of CRISPR/Cas9-mediated Knockout of Either IRF-3 or IRF-5 Gene in Epithelioma Papulosum Cyprini Cells on Type I Interferon Response and NF-κB Activity.

Transcription factors related to the activation of type I interferons (IFNs) and nuclear factor-kappa B (NF-κB) are known to be critical in innate immune responses. Interferon regulatory factors (IRFs) are a family of transcription factors. IRF-3 is known to act as the primary regulator in type I IFN signaling in response to viral infections, and the upregulation of IRF5 by virus infection has been reported in various fish species. One of the ways to know the functional role of certain genes is the production of target gene(s) knockout cells or organisms. In the present study, we produced either IRF3 or IRF5 gene knockout Epithelioma papulosum cyprini (EPC) cells using a CRISPR/Cas9 system, and investigated the effect of IRF3 gene and IRF5 gene knockout on polyinosinic:polycytidylic acid (ploly (I:C))-mediated and viral hemorrhagic septicemia virus (VHSV) infection-mediated type I IFN response and NF-κB activation. Both IRF3 knockout and IRF5 knockout EPC cells showed severely decreased type I IFN responses measured by ISRE activity and the expression of Mx1 and ISG15 genes when stimulated with poly (I:C), while the decreased level of type I IFN responses was not high as by poly (I:C) stimulation when infected with VHSV. Different from type I IFN response, NF-κB activities in IRF3 and IRF5 knockout cells were not highly different between poly (I:C) stimulated cells and VHSV-infected cells. Further studies are needed to elucidate pathways responsible for the type I IFN responses and NF-κB activation by VHSV infection.