Dietary yeast culture modulates immune response related to TLR2-MyD88-NF-kβ signaling pathway, antioxidant capability and disease resistance against Aeromonas hydrophila for Ussuri catfish (Pseudobagrus ussuriensis)

The aim of the present study was to investigate effects of dietary yeast culture on immune response related to TLR2-MyD88-NF-kβ signaling pathway, antioxidant capability and disease resistance against Aeromonas hydrophila for Ussuri catfish (Pseudobagrus ussuriensis). A total of 240 Ussuri catfish (mean weight of 7.39 ± 0.32 g) were randomly distributed into four groups that fed diets containing 0 (Y0), 10 (Y1), 20 (Y2) and 30 (Y3) g kg-1 yeast culture for 8 weeks. The results indicated that dietary 10 g kg-1 yeast culture supplementation significantly down-regulated mRNA levels of TLR2, MyD88, NF-kβ p65, IL-1β and IL-8 in the liver tissue compared with the control group (P < 0.05). Simultaneously, serum lysozyme (LZM) activity, respiratory burst activity (RBA) of phagocytes, plasma alkaline phosphatase (AKP) activity and immunoglobulin M (IgM) content were significantly improved in fish fed Y1 diet (P < 0.05). Fish fed Y1 diet had significantly higher serum alternative complement pathway activity (ACH50) and plasma complement 3 (C3) content than the Y3 group (P < 0.05). However, no significant differences were observed in plasma acid phosphatase (ACP) activity and complement 4 (C4) content among the groups (P > 0.05). Fish cumulative mortality rate (CMR) in the Y1 and Y2 groups were significantly lower than that in Y0 and Y3 groups (P < 0.05), and the lowest CMR was observed in the Y1 group after challenge by A. hydrophila. The highest hepatic superoxide dismutase and glutathione peroxidase activities, total antioxidant capacity and the lowest malondialdehyde content were found in Y1 group, but no significant difference was found in hepatic catalase activity among the groups (P > 0.05). These results demonstrate that dietary 10 g kg-1 yeast culture could effectively improve the immunity, antioxidant capability and disease resistance against A. hydrophila for Ussuri catfish and could down-regulate the mRNA expression levels of pro-inflammatory cytokines modulated by TLR2-MyD88-NF-kβ signaling pathway.