Mannan oligosaccharides supplementation enhanced head-kidney and spleen immune function in on-growing grass carp (Ctenopharyngodon idella).

This research investigates the influences of dietary mannan oligosaccharides (MOS) on the head-kidney and spleen immune function in on-growing grass carp (Ctenopharyngodon idella) and its related mechanism. Fish were fed during 60 days at different levels of MOS (0, 200, 400, 600, 800 and 1000 mg kg). Subsequently, 14 days after the feeding trial was injected intraperitoneally with Aeromonas hydrophila, the immune function was studied. The results are as follows: (1) appropriate MOS supplementation could increase the content of antibacterial compound and immunoglobulin (Ig), up-regulate antimicrobial peptides transcriptional levels in these two organs; (2) appropriate MOS supplementation attenuated inflammatory response in these two organs by regulating cytokines (pro- and anti-inflammatory cytokines) and related signalling pathways (NF-κB and TOR). The interesting points though, was, no differences were found in liver-expressed antimicrobial peptide (LEAP)-2A, interleukin (IL)-8, IL-4/13B, IκB kinase (IKK) α and nuclear factor kappa B (NF-κB) p52 gene expression in these two organs. Consequently, the present research suggests that MOS supplementation can enhance head-kidney and spleen immune function. Finally, we obtained these appropriate MOS dose (538.5 and 585.8 mg kg) by quadratic regression analysis of lysozyme activity (head-kidney) and phosphatase activity (spleen), respectively.