IFNa of black carp is an antiviral cytokine modified with N-linked glycosylation.

Type I interferons (IFNs) play an important role in the antiviral immune response in teleost fish. In this study, one type I interferon (bcIFNa) of black carp (Mylopharyngodon piceus) has been cloned and characterized. The full-length cDNA of bcIFNa gene consists of 783 nucleotides and the predicted bcIFNa protein contains 185 amino acids. Semi-quantitative RT-PCR analysis demonstrated that bcIFNa mRNA transcription level in all the selected tissues of black carp was greatly increased at 33 h post spring viremia of carp virus (SVCV) infection. The protein of bcIFNa could be detected in both the whole cell lysate and the supernatant media of HEK293T cells transfected with plasmids expressing bcIFNa through immunoblot assay. EPC cells showed greatly increased antiviral ability when the cells were treated with the bcIFNa-containing conditioned media for 24 h before SVCV infection. Mass spectrum assay and glycosidase digestion analysis determined that bcIFNa is modified with N-linked glycosylation, which occurs on the Asn (N) of 38 site of this cytokine. The un-glycosylated mutant bcIFNa-N38Q could be secreted out of the cell and showed the similar antiviral ability against SVCV as that of wild type bcIFNa, which suggested that N-linked glycosylation does not contribute directly to the antiviral property of this fish cytokine.