Effect of β-glucan on activity of antioxidant enzymes and Mx gene expression in virus infected grass carp

The effects of β-glucan, an immunostimulatory agent, on the superoxide dismutase (SOD) and catalase (CAT) activities of erythrocytes and Mx gene expression were studied from grass carp that were challenged with grass carp hemorrhage virus (GCHV). The SOD and CAT activities in erythrocytes and Mx gene expression in spleen from the fish were detected by spectrophotometry and RT-PCR, respectively. Negative control fish were injected with PBS; positive control groups were injected with either β-glucan or GCHV only; and the experimental groups were pre-injected with β-glucan 15 days prior to injection with GCHV. The results show that the SOD and CAT activities were higher in fish injected with β-glucan for 15 days than the negative control group injected with PBS. The SOD and CAT activities significantly decreased when the fish were challenged with GCHV, but it was higher in the group pre-treated with β-glucan than in infected fish not pre-treated, 15 days after GCHV infection. Mx gene expression levels increased during the early stages (at 12 h and 36 h) of GCHV infection, and it remained at higher levels from the 6th till the 10th day in the β-glucan pre-treated group, but it was falling from the 6th day in the β-glucan untreated group. The GCHV-infected group pre-treated with β-glucan had a higher survival rate (60%) than the group not pre-treated with β-glucan (20%), suggesting that β-glucan possesses or enhances anti-viral responses.