Early changes of ileoanal pouch mucosa in patients with ulcerative colitis

Following closure of the protective ileostomy the mucosa of ileoanal pouches undergoes characteristic changes, which are thought to be caused by the new luminal environment Conventional histopathology and immunohistochemical markers were compared in serial pouch biopsies from patients with ulcerative colitis (UC) in the early period of function.

Biopsy specimens were obtained from nine patients during ileostomy closure, 24 h after the first bowel action, then 6 days, 6 weeks and 3 months postoperatively. Cryostat sections were stained with haematoxylin and eosin (H&E) for assessment of mucosal inflammation and morphometry, and for lymphocyte subtypes (CD3, CD4, CD8), macrophages (CD68), common leucocyte antigen (CD45), and HLA-DR, using a three-stage immunoperoxidase reaction.

Within 5 days of pouch function the index for mucosal atrophy (villous height/total mucosal thickness ratio) decreased significantly from a median (range) of 0.66 (0.39-0.69) to 0.52 (0.37-0.61)(P = 0.02). Intraepithelial lymphocyte counts diminished from 10.1 (5.6-21.1) to 7.0 (2.2-8.2)(P = 0.007) per 100 epithelial cells and remained so. In the lamina propria, apart from a transient increase in CD3 positive cells at 5 days (from 92.7 (58-165) to 100.5 (57-234) per unit area; P = 0.038), no significant changes were observed. H&E grading and HLA-DR expression remained unchanged.

While there was no significant change in mucosal morphology and mucosal leucocyte subpopulations after 24 h of pouch function, the ileal pouch mucosa in UC patients had responded significantly within 5 days. Further studies into cell function and signalling are required.