Characterization and functional analysis of the interferon regulatory factor 5 (IRF5) from the GIFT Oreochromis niloticus.

The genetically improved farmed tilapia (GIFT, Oreochromis niloticus) is an economically important fresh water fish globally. Tilapia lake virus (TiLV) causes TiLV disease (TiLVD) in GIFT with a high mortality rate. In this study, interferon regulatory factor 5 (IRF5) was identified from GIFT, and its antiviral and immunoregulatory roles were explored. The IRF5 protein of GIFT is 474 amino acids (aa) in length, containing a conserved DNA binding domain (DBD) and an IRF-association domain (IAD), and sharing 85.7%-96.6% sequence identity with the IRF5 protein of other vertebrates. qPCR analysis demonstrated that GIFT IRF5 was ubiquitously expressed in all selected tissues, and could be upregulated in head kidney (HK) following pathogen-associated molecular patterns (PAMPs) (lipopolysaccharide (LPS) or polyriboinosinic polyribocytidylic acid (polyI:C)) stimulation and pathogens (Streptococcus agalactiae and TiLV) infection. Overexpression of IRF5 significantly decreased the expressions of TiLV-S8 and TiLV-S10 and increased the expressions of interferon (IFN)-c, IRF3, IRF7, Mx and viperin genes in the tilapia brain (TiB) cells. These results demonstrated that IRF5 plays an essential role in the antiviral immunity of GIFT, providing support to elucidate the IFN signaling pathway of fish.