Immunoprotection of grass carp (Ctenopharyngodon idella) with recombinant interferon (rCiIFN) against GCHV infection

The immunostimulatory effect and antiviral activity of grass carp (Ctenopharyngodon idella) recombinant interferon (rCiIFN) were investigated in the present study. The rCiIFN fusion protein (≈ 38 kD) was expressed and purified from BL21 Escherichia coli. To evaluate in vivo protective efficacy of rCiIFN against grass carp hemorrhagic virus (GCHV) infection, we administered it by intraperitoneal (ip) injection and oral feeding in our experiments. Intraperitoneal injections with three different rCiIFN dosages (0.1, 1, 10 μg/g fish body weight) at 24 h prior to GCHV infection all improved the survival rate of the fish. The relative percentage survival (RPS) from 1 μg/g fish body weight injection was higher than those from other two dosages. Fish were fed with pellets mixed with rCiIFN at 1 μg/g fish body weight once daily for 1, 2 and 5 days before GCHV infection. The results indicated that the RPS from feeding for 2 consecutive days was higher than those from feeding for just 1 d or 5 consecutive days. Additionally, we observed that several IFN-stimulated genes (ISGs) were greatly up-regulated. After stimulation with rCiIFN, the expression levels of Mx and IFN genes in grass carp kidney cells (CIK) were highly enhanced and peaked within 6 and 12 h, respectively. By comparison with gene expression levels observed in PBS-injected controls, expressions of IFN, IRF1, IRF7, PKR, Mx and STAT3 were found to be significantly up-regulated in tested tissues of rCiIFN-injected fish, and most of these ISGs reached the highest level within 12 h post-treatment and declined within 72 h. After feeding fish once daily for 1–5 days with pellets mixed with rCiIFN at 1 μg rCiIFN/g fish body weight, it was found that the expression level of IFN was significantly up-regulated and reached its peak level in tissues of those fish treated for 1 or 2 days. These results demonstrated that rCiIFN had antiviral activity and ip injection as well as oral administration of rCiIFN was effective in protecting grass carp against GCHV infection.