An immunohistochemical study on the effects of cyclosporin on the gut-associated lymphoid tissue of rats.

The effect of Cyclosporin (CS) on the gut-associated lymphoid tissue (GALT) of inbred WKA rats was immunohistochemically studied by the immunoperoxidase method. CS in olive oil was orally administered daily for seven days at the dose of 25, 50 and 100 mg/kg/day. On days 1, 4 and 7 of CS administration, rats were sacrificed under ether anesthesia. By CS administration, the decrease and disappearance of Ia antigen expression were dose-dependently recognized on the epithelial cells and the overlaying cells of Peyer's patches. The reduced cellular population and Ia expression of lymphocytes of the follicle and the disappearance of the germinal center also occurred, and Ia-positive dendritic non-lymphoid cells in Peyer's patches and endothelial cells of capillaries in the lamina propria disappeared on day 7 of CS administration. In addition, a temporary increase of W3/25-positive cells and the appearance of Ia-positive intra-epithelial cells were observed on day 4. Simultaneously, interleukin 2 receptor (IL-2R)-positive cells gradually decreased on day 4, and almost disappeared on day 7. From these results, it is speculated that CS suppresses not only interleukin 2 (IL-2) production as previously reported, but also the expression of Ia antigens and IL-2R. It may well suppress the immune system at the point of recognition and presentation of alloantigen, and the proliferation and differentiation of B cells.