The effect and underlying mechanism of yeast β-glucan on antiviral resistance of zebrafish against spring viremia of carp virus infection

beta-glucan has been used as immunostimulant for fish. However, the effect of yeast beta-glucan on viral infections has been less studied in fish. In this study, we investigated the effects of beta-glucan on the resistance of zebrafish against spring viraemia of carp virus (SVCV) and elucidated the underlying mechanisms. Zebrafish were fed with a control diet or diet supplemented with 0.01% and 0.025% beta-glucan for 2 weeks, and were challenged by SVCV. Zebrafish embryonic fibroblast (ZF4) cells were treated with 5 mu g/mL beta-glucan and were infected by SVCV. We further investigated the effect of beta-glucan on autophagy level post SVCV infection. The intestinal microbiota was evaluated by 16S rRNA gene pyrosequencing. Results showed that dietary supplementation of 0.025% beta-glucan significantly increased survival rate of zebrafish compared with control group after SVCV challenge (P < 0.05). Dietary beta-glucan significantly increased the expression of genes related to type I IFN antiviral immune pathway in the spleen of zebrafish after viral infection, including type I IFN genes (ifn phi 1, ifn phi 2, ifn phi 3), IFN-stimulated genes (mxb, mxc), as well as other genes involved in the IFN signaling pathway, including tlr7, rig1, mavs, irf3 and irf7. Morpholino knockdown of type I IFN receptors dampened the antiviral effect of beta-glucan in zebrafish larvae, indicating that beta-glucan-mediated antiviral function was at least partially dependent on IFN immune response. Furthermore, beta-glucan can inhibit the replication of SVCV in ZF4 cells. However, beta-glucan did not stimulate type I IFN antiviral response in ZF4 cells, and the antiviral effect of beta-glucan in ZF4 was independent of Myd88. Interestingly, beta-glucan induced autophagy in ZF4 cells after SVCV infection. Inhibition of autophagy blocked the antiviral effect of beta-glucan in ZF4 cells. Lastly, dietary beta-glucan changed the composition of intestinal microbiota in zebrafish, with reduced abundance of Proteobacteria and an enrichment of Fusobacteria and Firmicutes. To sum up, our results indicate that the beta-glucan enhanced resistance of zebrafish against SVCV and the mechanism involved stimulation of type I IFN antiviral immune response of fish after viral infection.

Automated summary

Beta-glucan can enhance the resistance of zebrafish against spring viraemia of carp virus (SVCV) by stimulating the type I interferon (IFN) antiviral immune response.