Correlation of rectum-associated lymph nodules with the development of experimentally induced acute colonic...

The mechanisms of inflammation in ulcerative colitis occurring initially in the rectum and then extending throughout the colon are still unknown. The aim of this study is to investigate the correlation of rectum-associated lymph nodules (RALN) and the development of a dextran sulfate sodium-induced experimentally acute colonic inflammation in rats.

We immunohistochemically analyzed the lymph nodules in the rectal region of rats using monoclonal antibodies to specific markers.

Rectum-associated lymph nodules resembled the Peyer's patches, where CD4+, CD8+ lymphocytes and Mar 1+ macrophages were observed. After the administration of dextran-sulfate sodium (DSS), RALN showed hypertrophy with an increase in the number of CD4+, CD8+, and interleukin (IL)-2R+ lymphocytes in the periphery, as well as Mar 1+ macrophages in the entire region. Concurrently, platelet/endothelin cell adhesion molecule-1 (PECAM-1+) blood vessels, including high-endothelial venules (HEV), were increased in number in the interfollicular areas. Furthermore, a number of small lymph nodules varying in size were observed in the upper region of the rectum. Some of them were initially confined to the lamina propria mucosae, and became large enough to extend deeper into the tela submucosa. These DSS-induced lymph nodules contained large numbers of CD4+ lymphocytes, IL-2R+ lymphocytes, and Mar 1+ macrophages.

The pathological changes of ulcerative colitis were well correlated with the development of both RALN and DSS-induced lymph nodules. The immunological reaction that occurred in DSS-induced lymph nodules is significantly associated with the expansion of colitis from the lower region of rectum to the upper region of rectum and colon.