IFNa2 of triploid hybrid of gold fish and allotetraploid is an intracellular antiviral cytokine against SVCV and GCRV

Sterile triploid hybrids (3n = 150) of gold fish (Carassius auratus red var., ♀, 2n = 100) and allotetroploid (♂, 2n = 100) display obviously improved disease resistance and much enhanced growth rate than their parents, which have been cultured widely in China. In this paper, one of the type I IFNs of triploid hybrid (3nIFNa2) has been cloned and characterized. The full-length cDNA of 3nIFNa2 gene consists of 715 nucleotides and the predicted 3nIFNa2 contains 183 amino acids. The transcription of 3nIFNa2 gene was detected in all the examined tissues of triploid hybrid and the mRNA level of 3nIFNa2 was obviously enhanced in response to SVCV and GCRV infection. 3nIFNa2 has been detected in the whole cell lysate of HEK293T cells transfected with plasmids expressing 3nIFNa2 but not in the supernatant media. EPC cells transfected with plasmid expressing 3nIFNa2 at 24 h before SVCV and GCRV infection showed obviously decreased cytopathic effect; and the virus titers in the supernatant media were much lower than those of the control cells. Glycosidase digestion analysis demonstrates that 3nIFNa2 is modified with N-linked glycosylation, which occurs on the asparagine (N) of residue 177 of this cytokine. The un-glycosylated mutant 3nIFNa2-N177Q shows the similar antiviral ability as that of 3nIFNa2, which suggests that the N-linked glycosylation does not contribute directly to its antiviral property. All the above data support the conclusion that 3nIFNa2 is an intracellular cytokine functioning importantly in host antiviral innate immunity.