Comparison of the responses of different recombinant fish type I interferons against betanodavirus infection in grouper.

The nervous necrosis virus (NNV) is an aquatic virus that can infect more than 30 species including the grouper, which is a valuable fish species in Taiwan. NNV causes up to 90-100% mortality in the aquaculture industry. Interferons (IFNs) are a family of cytokines that stimulate the expression of numerous proteins to protect the host against viruses and possess very unique specific characteristics in fish. The cross-reactivity of heterologous IFNs on grouper cells and larvae has not been well-studied to date. To evaluate and compare the anti-NNV effect of different fish IFNs in grouper, we successfully synthesized, subcloned, expressed and purified several fish type I IFNs in the present study: grouper (gIFN), salmon (sIFN), seabass (sbIFN) and tilapia (tpIFN). The gIFN and sIFN proteins up-regulated myxovirus resistance protein (Mx) gene expression in grouper kidney (GK) cells, but similar effects were not observed for sbIFN and tpIFN. Following co- and pre-treatment with the 4 types of IFNs with NNV infection in GK cells, sIFN exhibited the strongest antiviral ability to suppress NNV gene replication (especially at 24 h) and significantly reduced the cytopathic effect (CPE) at 72 h, followed by gIFN. Unsurprisingly, sbIFN and tpIFN had no significant effect on CPE but slightly suppressed NNV gene replication. The cytotoxicity of these four fish IFNs on GK cells was also examined for the first time. In the in vivo test, we confirmed that gIFN and sIFN had a significant protective effect against NNV when administered by intraperitoneal (IP) injection and the oral route in Malabar grouper (Epinephelus malabaricus) larvae. This study compared the protective effects of IFNs from various fish species against NNV and demonstrated crosstalk between sIFN and grouper cells for the first time. These results provide information concerning the efficacy of fish IFNs for possible therapeutic applications.