Anti-IHNV activities of recombinant rainbow trout IFNa and its influence on interferon response gene expression in vitro

Our research aimed to evaluate the antiviral activities of prokaryotic-expressed rainbow trout recombinant interferon-a (rtrIFNa) against infectious hematopoietic necrosis virus (IHNV), and the expression change of interferon response genes in vitro following IHNV infection or early stage rtrIFNa stimulation. The antiviral activities of rtrIFNa were evaluated based on cytopathic effect (CPE) reduction assays. Our results showed that the anti-IHNV activity of rtrIFNa was dose related and about 1 × 104 U/mg. RtrIFNa significantly reduced the copy number of the IHNV N gene after infection (P<0.01), indicating that rtrIFNa could suppress replication of the IHNV genome. In addition, rtrIFNa could significantly up-regulate most IFN-stimulated genes early (within 8 h). The strongest significant response was observed in the Mx3 and ISG15 genes. After IHNV infection, these IFN related genes were also significantly induced and then began to decrease within 72 h. The transcript level of these genes in the rtrIFNa-injected group was significantly higher (P<0.05) than in the rpET32a-injected group. Additionally, we observed that the transcription of IFNa and PKR genes was inhibited at early stages after IHNV infection in the absence of rtrIFNa. Finally, we conclude that refolded rtrIFNa has good biological activity, as it could effectively inhibit IHNV replication and activate IFN signaling. The kinetics of interferon related gene expression, elicited by IHNV or rtrIFNa, will facilitate a better understanding of the anti-IHNV activity of rtrIFNa in vitro.