| Summary: | The current study investigated the detrimental effects of SBM on gut integrity of rainbow trout (<i>Oncorhynchus mykiss)</i> by focusing on the response of immune-related genes and other relevant genes. Results were compared with the transcriptomic response in the intestine during<i> Aeromonas salmonicida</i> infection. During a 12 week feeding trial, a diet containing a high concentration of SBM (HSBM) caused reduced weight gain and specific growth rate. A diet containing a low concentration of SBM (LSMB) also caused reduced weight gain, although not as significant as the HSBM diet. Both the HSBM and the LSBM diet caused morphological changes in the distal intestine. SBM induced TNF-α2 gene expression in the distal intestine; COX-2 and IFN-γ expression levels were also increased at higher levels of soybean meal inclusion. Expression levels of TGF-β and IL-8 were decreased in the distal intestine. A different profile was observed in the proximal intestine. Soybean meal induced the expression of COS-2, IL-8 and IFN-γ. At higher inclusion levels of soybean meal, IL-1β expression was also increased, while TGF-β expression was decreased. Bacterial infection with <i>Aeromonas salmonicida </i>by intraperitoneal (i.p.) injection and by bath challenge induced differential cytokine expression in the head kidney and intestine. i.p. injection caused 29% mortality. Increased expression of COX-2 and decreased expression of TGF-β was observed in the distal intestine. COX-2 was also induced in the proximal intestine, while expression of TGF-β was decreased. Bath challenge caused 24% mortality. Increased expression of IL-1β, IL-8, TNF-α2, iNOS, COX2 and IFNγ was observed in the proximal intestine, as well as downregulation of TGF-β. IL-8 and COX-2 were significantly upregulated in the distal intestine and TGF-β gene expression was decreased. Differential gene expression in the intestine during infection with <i>A. salmonicida </i>by i.p. injection was investigated using SSH. Potentially upregulated immune system-related genes including MHC class I and II proteins, β-2 microglobulin type I, lysozyme II, CD83 and several lectins. Extracellular matrix-related genes included integrin, CD9, thrombospondin, fibronectin, matrix metalloproteinase, meprin A and gap junction protein β 2 were also induced, suggesting that <i>A. salmonicida</i> adheres to and invades the extracellular matrix. The transcriptomic response in the intestine of rainbow trout during SBM-induced enteritis was investigated by means of SSH and microarray. Increased expression was observed of immune system-related genes including perforin, natural killer cell enhancement factor, interleukin-1β, thioredoxin, β-thymosin and galectin, while decreased expression was observed of C-type lectin 2, eosinophil chemotactic cytokine, T-cell antigen receptor β-chain, defender against cell death 1 and iNOS.
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