Abstract
Background: Interferon (IFN) regulatory factors (IRF) are the crucial transcription factors for IFN expression and leading host cells response to viral infection. IRF8 in mammals plays vital roles in the innate and adaptive immune systems. In this study, we identified and characterized the common carp (Cyprinus carpio. L) IRF8 gene (ccIRF8) to further clarify the function of IRF8 in teleost fish. Results: The complete cDNA sequence of ccIRF8 was 1431 bp and encodes a polypeptide of 431 amino acids. Analysis of the putative amino acid sequence showed that ccIRF8 encodes structures typical of the IRF family, including a DNA-binding domain (DBD), an IRF-association domain (IAD) and two nuclear localization signals (NLS). Comparison with homologous proteins showed that the deduced protein has the highest sequence identity to grass carp IRF8 (92.7%). Phylogenetic analysis grouped ccIRF8 with other IRF8s of teleosts. Quantitative RT-PCR analysis showed that ccIRF8 transcripts were detectable in all investigated tissues of healthy fish with the highest level in spleen. Following poly I: C and Aeromonas hydrophila challenge, ccIRF8 transcripts were induced significantly in immune relevant tissues. In addition, ccIRF8 was induced by poly I: C and ipopolysaccharide (LPS), peptidoglycan (PGN) and flagellin in HKLs. Overexpression of ccIRF8 increased the expression of IFN and IFN-stimulated genes (ISGs), and a dual-luciferase reporter assay revealed that ccIRF8 decreased the activation of NF-κB though TRAF6. Conclusions: Overall, our findings provide a new perspective on the role of IRF8 in innate immunity in fish, as well as insights that will help the prevention and control of disease in the common carp farming industry.