The fermentable fiber content of the diet alters the function and composition of canine gut associated lymphoid tissue

The ingestion of plant fibers and their susceptibility to microbial ferment ation in the large bowel modulate intestinal morphology but little is known about effects on the gut associated lymphoid tissue (GALT). The aim of the present study was to determine the effect of consuming diets containing di fferent levels of fermentability fiber on immune function, Sixteen adult mo ngrel dogs (23 +/- 2 kg) were fed (14 days) in a randomized cross over desi gn two isoenergetic isonitrogenous diets containing 8.3 g/kg non-fermentabl e or 8.7 g/kg fermentable fibers, Lymphocytes were isolated from blood prio r to starting the study and at the end of each diet period. At study comple tion, lymphocytes were isolated from the gut associated lymphoid tissue (GA LT) of the small intestine for characterization by immunofluorescence and t o determine their ability to respond to mitogenic stimulation. Feeding high fermentable fibers increased (P < 0.05) the CD4/ CD8 ratio and decreased ( P < 0.05) the proportion of B cells in peripheral blood without changing na tural killer cell activity or the response to mitogens. Mesenteric lymph no de cells from dogs fed the low then high fermentable fiber diet contained a higher (P < 0.05) proportion of CD4(+) cells and a higher (P < 0.05) respo nse to mitogens. Intraepithelial, Peyer's patches and lamina propria cells contained a greater (P < 0.05) proportion of CD8(+) cells when dogs were fe d a low fermentable fiber diet followed by a high fermentable fiber diet. T cell mitogen responses in vitro were higher for intraepithelial but lower for Peyer's patches and lamina propria cells from dogs who were fed the low fermentable fiber diet followed by the high fermentable fiber diet (P < 0. 05). In conclusion, the fermentable fiber content of the diet had very litt le effect on the type and function of immune cells in peripheral blood. How ever, feeding dogs a high fermentable fiber diet for 2 weeks (after 2 weeks of consuming a low fermentable fiber diet) altered the T-cell composition of GALT and produced a higher mitogen response in the predominantly T cell tissues and a lower response in areas involved in B cell functions. in conc lusion, the level of fermentable fiber in the diet appears to alter GALT pr operties. Further studies are required to determine the direct contribution of a high or low fiber diet to these changes and the physiological implica tions to the health of the animal. (C) 1999 Published by Elsevier Science B .V. all rights reserved.