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

Extracted soybean meal (SBM) in the diet for Atlantic salmon causes an inflammatory response in the distal intestine. The morphological changes of the epithelial cells and a characterization of the inflammatory cell infiltrate of the distal intestinal mucosa were studied using a panel of enzyme and immunohistochemical markers. The salmon used in the study were fed either a fishmeal-based diet or a diet in which 30% of the fishmeal protein was replaced with SBM protein. SBM-fed salmon had markedly reduced enzyme activities in the distal intestinal epithelial cells, both in the brush border and in intracellular structures. There appeared to be an increased presence of cells of monocytic lineage, including macrophages, as well as neutrophilic granulocytes and immunoglobulin M (IgM) in the lamina propria of SBM-fed fish. The mid intestine showed little response to the diet. The results suggest that toxic/antigenic component(s) of SBM affect the differentiation of the distal intestinal epithelial cells and may help explain the reduced nutrient digestibilities previously reported in salmonids fed extracted SBM.