Identification and characterization of interferon regulatory factor 8 (IRF8) in Nile tilapia (Oreochromis niloticus)

Interferon regulatory factor 8 (IRF8) participates in the defense against pathogens. In this study, we cloned and characterized OnIRF8 from Nile tilapia (Oreochromis niloticus) and investigating its immune response functions both in vivo and in vitro. The encoded open reading frame comprises of 420 amino acids, with a predicted molecular weight of 47.645 kDa. It exhibits a high degree of sequence homology (ranging from 50.57 % to 98.81 %) with IRF8 orthologs from other vertebrates. Ubiquitous OnIRF8 expression was detected across tissues, with the highest expression observed in the spleen. Both in vivo and in vitro analyses revealed that the transcription levels of OnIRF8 were significantly up-regulated in response to treatments with Streptococcus agalactiae, Aeromonas hydrophila, Lipopolysaccharide (LPS) and polyinosinic acid:polycytidylic acid (poly (I:C)) in the head kidney and spleen. Furthermore, overexpression of OnIRF8 in Nile tilapia significantly enhanced immune-related gene expression in head kidney monocytes/macrophages. Overexpression of OnIRF8 also reduced bacterial load in head kidney and spleen post-S. agalactiae infection, with up-regulation of inflammatory factor production. OnIFN-γ recombinant protein and poly (I:C) could both markedly amplified OnIRF8 expression, implying its potential dual role in modulating both OnIFN-γ and TLR signaling pathways. These findings indicate that OnIRF8 may serve a protective function against bacterial infections and act as an immunomodulatory factor in Nile tilapia.