Sammendrag
Unknown component(s) of full-fat and extracted soybean meal (SBM) cause an inflammatory response in the distal intestine of all salmonids examined to date, limiting its use as an alternative protein source to fishmeal in formulated feeds. The pathogenic mechanisms underlying the SBM-induced enteropathy in salmon are not clear, although hypersensitivity is thought to play a role. Atlantic salmon post-smolts in seawater were fed extracted SBM (25% inclusion level) compared to fish fed a control diet containing fishmeal (FM) as the sole protein source. Following a 3-week feeding trial, immunohistochemical reactivity of markers for putative T cells and immunoglobulin (IgM) as well as apoptosis, protein degenerative/regenerative processes, and proliferation, were investigated in formalin-fixed, paraffin-embedded tissue sections from the distal intestine. Real-time (rt) PCR with primers for the T cell markers CD3?, CD4, CD8?, and CD8? was also carried on RNA extracted from thymus and distal intestine homogenates. The Dako A0452 anti-human CD3? appeared to react to putative T cells in salmon since characteristic staining was observed in cells of the thymus as well as distal intestine, skin, gills, and spleen. These cells were IgM negative. A dramatic increase in the number of CD3?-positive was observed in the SBM-fed fish. Real-time PCR confirmed the RNA expression of CD3?, CD4, CD8?, and CD8? in thymus and distal intestine as well as up-regulation in the distal intestine of SBM-fed fish. Intestinal intraepithelial lymphocytes (IEL) at the base of the epithelium were CD3? positive. During the SBM-induced enteropathy, the positive IELs kept a somewhat less regular position than in FM controls, often occupying a position closer to the apex of the epithelial cells. An increased number of epithelial cells reactive to anti-caspase-3, heat shock protein 70, and proliferating cell nuclear antigen (PCNA) was observed in salmon with SBM-induced enteropathy.
Vis fullstendig beskrivelse
