515 Veterinarni Medicina, 60 , 2015 (9): 515–521 Original Paper doi: 10.17221/8443-VETMED Effect of the mycotoxin deoxynivalenol on the immune responses of rainbow trout ( Oncorhynchus mykiss ) I. Matejova 1,2 , M. Vicenova 2 , L. Vojtek 3 , H. Kudlackova 2 , K. Nedbalcova 2 , M. Faldyna 2 , E. Sisperova 1 , H. Modra 1 , Z. Svobodova 1 1 University of Veterinary and Pharmaceutical Sciences, Brno, Czech Republic 2 Veterinary Research Institute, Brno, Czech Republic 3 Masaryk University, Brno, Czech Republic ABSTRACT : The trichothecene mycotoxin deoxynivalenol (DON) is commonly found as a natural contaminant in cereals such as wheat, barley, and corn, and exhibits various toxicological effects when present in animal feeds. The effects of DON at a nominal 2 mg/kg feed on immune responses of rainbow trout were investigated, includ - ing relative gene expression of important cytokines (TNF-alfa, IL-8, IL-1beta, IL-10), lysozyme concentration in skin mucus, and level of antigen-specific IgM in blood plasma after vaccination with the commercial vaccine AquaVac ERM containing Yersinia ruckeri type 1 (Hagerman strain). Twenty one-year-old rainbow trout Oncorhynchus mykiss were randomly divided into two groups. The control received a commercial feed with a naturally occurring low level of DON (225 ug /kg feed), while an experimental group was fed the same formulation with DON added to 1964 ug /kg feed. The trial continued for 23 days. Consumption of feed with added DON showed a significant effect on the immune system, as indicated by a higher level of pro-inflammatory cytokine TNF-alfa ( P < 0.05) and of IL-8 (non-significant) in head kidney. Expression of the pro-inflammatory gene IL-1beta and the expression of a gene encoding anti-inflammatory cytokine (IL-10) were not influenced by DON treatment. Effects on the concentration of skin mucus lysozyme and specific IgM antibody levels were not observed during this experiment. These results suggest that prolonged ingestion of low doses of DON may influence the immune responses of rainbow trout.