Deoxynivalenol decreased intestinal immune function related to NF-κB and TOR signalling in juvenile grass carp (Ctenopharyngodon idella)

Deoxynivalenol (DON) is one of the most common mycotoxins in animal feed worldwide and causes significant threats to the animal production. The intestine is an important mucosal immune organ in teleost, and it is also the first target for feed-borne toxicants in animal. However, studies concerning the effect of DON on fish intestine are scarce. This study explored the effects of DON on intestinal immune function in juvenile grass carp (Ctenopharyngodon idella). A total of 1440 juvenile grass carp (12.17 +/- 0.01 g) were fed six diets containing graded levels of DON (27, 318, 636, 922, 1243 and 1515 mu g/kg diet) for 60 days. After the growth trial, fish were challenged with Aeromonas hydrophila. The results were analysed by the Duncan's multiple-range test (P < 0.05), indicating that compared with the control group (27 mu g/kg diet), dietary DON levels up to 318 mu g/kg diet: (1) decreased lysozyme (LZ) and acid phosphatase (ACP) activities, as well as complement 3 (C3), C4 and immunoglobulin M (IgM) content in the proximal intestine (PI), middle intestine (MI) and distal intestine (DI) of juvenile grass carp (P < 0.05); (2) down-regulated the mRNA levels of anti-microbial substance: liver expressed antimicrobial peptide (LEAP) -2A, LEAP-2B, hepcidin, beta-defensin-1 and mucin2 in the PI, MI and DI of juvenile grass carp (P < 0.05); (3) up regulated the mRNA levels of pro inflammatory cytokines [interleukin 1 beta (IL 1 beta), tumour necrosis factor alpha (TNF alpha), interferon gamma 2 (INF-gamma 2), IL 6 (only in PI), IL-8, IL-12p35, IL-12p40, IL-15 and IL-17D) in the PI, MI and DI of juvenile grass carp (P < 0.05), which might be partly related to nuclear factor kappa B (NF-kappa B) signalling [I kappa B kinase beta (IKK beta) and IKK gamma/inhibitor of kappa B alpha (I kappa B alpha)/NF-kappa B (p65 and c Rel)); and (4) down-regulated the mRNA levels of anti-inflammatory cytokines [IL-10, IL-11, IL-4/13A (not IL-4/13B), transforming growth factor beta 1 (TGF-beta 1) (not TGF-beta 2)] in the PI, MI and DI of juvenile grass carp (P < 0.05), which might be partly related to target of rapamycin (TOR) signalling [TOR/ribosomal protein S6 kinases 1 (S6K1) and eIF4E-binding proteins (4E-BP)]. All data indicated that DON could impair the intestinal immune function, and its potential regulation mechanisms were partly associated with NF-kappa B and TOR signalling pathways. Finally, based on the enteritis morbidity, and the LZ and ACP activities as well as IgM content in the PI, the reasonable dose of DON for grass carp were estimated to be 251.66, 305.83, 252.34 and 309.94 mu g/kg diet, respectively.