Changes in immune and enzyme histochemical phenotypes of cells in the intestinal mucosa of Atlantic salmon, Salmo salar L., with soybean meal-inducedenteritis

Extracted soybean meal (SBM) in the diet for Atlantic salmon, Salmo salar L ., causes an inflammatory response in the distal intestine. The morphologic al changes of the epithelial cells and a characterization of the inflammato ry cell infiltrate of the distal intestinal mucosa were studied using a pan el of enzyme and immunohistochemical markers. The salmon (average body weig ht 927 g) used in the study were fed either a fishmeal-based diet (control diet) or a diet in which 30% of the fishmeal protein was replaced with SBM protein (SBM diet). In salmon fed SBM, there were markedly reduced enzyme r eactivities in the distal intestinal epithelial cells, both in the brush bo rder [5'-nucleotidase (5'N), Mg2+-ATPase, alkaline phosphatase (ALP) and le ucine aminopeptidase (LAP)] and in the intracellular structures [alkaline a nd acid phosphatase, non-specific esterase (NSE) and alanine aminopeptidase (APIP)]. There appeared to be an increased presence of cells of monocytic lineage, including macrophages, as well as neutrophilic granulocytes and im munoglobulin (Ig) M in the lamina propria of the SBM-fed fish. The mid inte stine showed little response to the diet. The results suggest that toxic/an tigenic component(s) of SBM affect the differentiation of the distal intest inal epithelial cells and may help explain the reduced nutrient digestibili ties previously reported in salmonids fed extracted SBM.