Reversal of altered intestinal mucosal immunity in rats fed elemental diet by supplementation of oleic acid

We have previously demonstrated that elemental diet (ED) induces decreased lymphocyte transport in intestinal lymph and significant changes in T cell subsets and the number of IgA-containing cells in gut-associated lymphoid tissues of rats. In order to examine whether the low fat content contributes to the induction of immunological changes in gut-associated lymphoid tissues, the effects of additional fatty acid in the ED were investigated. Rats were divided into four groups: elemental diet alone, elemental diet supplemented with 5% oleic acid (OA), elemental diet with 10% OA and conventional diet as a control. These diets were given at the same daily calorie intake for 4 weeks. The flow rate of intestinal lymph showed no significant difference between the four groups. However, lymphocyte flux as well as the percentage of CD3(+) and CD4(+) cells were significantly greater in the control and the 10% OA groups than in the ED and 5% OA groups. Intestinal lymph showed decreased concentrations of IgG and IgA in the ED group, whereas the addition of 10% OA significantly attenuated the decrease in these levels. In mesenteric lymph nodes, the CD4(+)/CD8(+) ratio was significantly decreased in the ED group, but 10% OA reversed this change. Immunohistochemical analysis of the ileal mucosa showed that in the ED group the population of CD4(+) cells was decreased, while the number of CD8(+) cells was increased. Supplementation of OA to ED produced similar stepwise attenuation of the changes in lymphocyte subpopulations in the lamina propria, while the 10% OA group reached levels that. were not statistically different from controls. In the elemental diet group, there was a significant decrease in immunoglobulin-containing cells of the IgA class in the lamina propria of the intestine. Similarly, the addition of OA induced dose-dependent recovery in the number of IgA-containing cells. These results suggest that a low dietary concentration of fat-may be closely related to changes in lymphocyte transport in intestinal lymph and mucosal immunity of intestinal mucosa induced by the feeding of a long-term ED.