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 fermentation 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 different levels of fermentability fiber on immune function. Sixteen adult mongrel dogs (23 +/- 2 kg) were fed (14 days) in a randomized cross over design two isoenergetic isonitrogenous diets containing 8.3 g/kg non-fermentable or 8.7 g/kg fermentable fibers. Lymphocytes were isolated from blood prior to starting the study and at the end of each diet period. At study completion, lymphocytes were isolated from the gut associated lymphoid tissue (GALT) of the small intestine for characterization by immunofluorescence and to 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 natural killer cell activity or the response to mitogens. Mesenteric lymph node 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) response to mitogens. Intraepithelial, Peyer's patches and lamina propria cells contained a greater (P < 0.05) proportion of CD8+ cells when dogs were fed 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 little effect on the type and function of immune cells in peripheral blood. However, 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 conclusion, the level of fermentable fiber in the diet appears to alter GALT properties. Further studies are required to determine the direct contribution of a high or low fiber diet to these changes and the physiological implications to the health of the animal.