Proliferation of immature plasma cells in pouchitis mucosa in patients with ulcerative colitis

Pouchitis is the most common complication of restorative proctocolectomy in patients with ulcerative colitis (UC). The etiology of pouchitis is not known. We have previously reported the specific and significant proliferation of immature plasma lineage cells in the ulcer bases and inflamed mucosa of UC. In the present study we report the results of a phenotypic study of ileal pouch mucosa. Biopsy samples were taken from the ileal pouch of 22 patients with UC (12 with pouchitis, 10 with a normal pouch) and 5 patients with familial adenomatous polyposis (FAP) (with a normal pouch) who underwent restorative proctocolectomy, and normal ileum of 10 patients with UC yet to undergo pouch surgery. Frozen sections were cut from fixed samples and reacted with various lymphocyte markers and anti-Ki-67 antibodies. Ki-67+ cells, CD19+ cells, and CD138+ cells were significantly increased in the pouchitis mucosa of patients with UC. Immunological double staining revealed significantly increased numbers of CD19+Ki-67+ cells and CD138+Ki-67+ cells in the pouchitis mucosa of patients with UC compared to noninflamed UC pouch, FAP pouch, and normal ileum of UC patients. The number of CD19+CD138+ cells was significantly increased in inflamed pouch mucosa. The increased number of CD19+CD138+ cells we observed represents proliferation of immature plasma cells. Moreover, the increase in labeling for Ki-67 among CD19 cells and CD138 cells suggests proliferative activity of these cells, consistent with their immaturity. Proliferation of these immature plasma cells suggests the possibility of involvement of UC-derived abnormality in the pathogenesis of pouchitis.