Identification of a type I interferon (IFN) gene from Japanese eel and its expression analysis in vivo and in vitro

Type I interferon (IFN) is a key cytokine of innate immune response for viral infection in teleost fish. In present study we report the identification of a type I IFN gene (AjIFN) from Japanese eel (Anguilla japonica) and provide evidence that AjIFN has been involved in Japanese eel host response against not only the virus but also the bacterial infection. The full-length cDNA of AjIFN (826 bp) has an ORF of 531 bp. The analysis of NCBI CDD showed that the AjIFN protein had the typical conserved domains, including IFabd conserved domain, and two conserved cysteine residues potentially forming disulphide bridges. Based on the phylogenetic analysis, AjIFN was classified into type I IFNs families belonging to the subgroup-a of the 2Cys group. In vivo, the AjIFN expressions in liver and kidney were induced following injection with LPS, the viral mimic poly I:C, and Aeromonas hydrophila infection. In vitro, the AjIFN transcripts of Japanese eel liver cells were enhanced by LPS, poly I:C and CpG-DNA stimulation and no change of the expression level was found post PGN treatment. Following A. hydrophila infection, the low concentration of 1 × 10⁶ cfu/mL failed to induce the expression of AjIFN whereas the concentration of 1 × 10⁷ cfu/mL and 1 × 10⁸ cfu/mL successfully induced the expression of AjIFN. These results collectively suggested AjIFN is an inducible gene possibly involved in Japanese eel defense against viral and bacterial infection.