ALTERATION OF MUCOSAL IMMUNITY AFTER LONG-TERM INGESTION OF AN ELEMENTAL DIET IN RATS

The effects of an elemental diet on lymphocyte transport in intestinal lymph and immune responses of gut-associated lymphoid tissue were inv estigated in rats. The control animals were fed a conventional diet. A fter 4 week of feeding, the total calorie intake and body weight gain showed no differences between the two groups. The number and total are a of Peyer's patches and the ratio of height of villi to height of cry pt showed no significant differences between the two groups. The rate of lymph flow in intestinal lymphatics showed no significant change in treated animals compared with the control rats. However, an elemental diet induced a significant decrease in lymphocyte flux in intestinal lymphatics compared with that in control rats. Lymphocyte subsets in i ntestinal lymph revealed a significant decrease in CD3-positive cells, especially CD4-positive cells in the elemental diet-treated group. A significant decrease in the number of immunoglobulin A-containing cell s and a decreased CD4/CD8 ratio in T-cell subsets were observed in the lamina propria of ileal mucosa in the elemental diet-treated group by morphometric analysis in the immunohistochemical study. Specific anti body-secreting cells in intestinal lymph were also investigated after rats were intraduodenally primed with cholera toxin and challenged wit h the same toxin after an interval Of 2 weeks. No significant differen ce was seen between the two groups in any of the numbers of anti-chole ra toxin immunoglobulin-secreting cells in any immunoglobulin A, immun oglobulin G, or immunoglobulin M class as determined by the enzyme-lin ked immunospot assay. These results suggest that the elemental diet we used might have an inhibitory effect on several aspects of the mucosa l immunologic system of the gut without significant reduction m its ab ility to produce specific antibodies.