M-cells are damaged and increased in number in inflamed human ileal mucosa.

Ileocolonoscopy and biopsies of patients with spondylarthropathy reveal gut inflammation in 62% of cases. In order to better understand the pathogenetic mechanisms of spondylarthropathy-related gut inflammation, the follicle-associated epithelium was examined. Biopsies from nine controls and 18 patients with spondylarthropathy were studied by electronmicroscopy. Membranous (M) cells were investigated in normal and inflamed ileum. In normal mucosa, M-cells were scarce whereas in inflamed mucosa their number was increased (up to 24% of follicle-associated epithelial cells). They showed a thin rim of cytoplasm covering groups of lymphocytes. In chronic ileitis, necrotic M-cells, rupture of M-cells and lymphocytes entering the gut lumen were observed. The bursting of M-cells at the top of the lymphoid follicles leads to interruption of the gut epithelial lining and gives the luminal content access to the lymphoid tissue. This pathogenetic mechanism may cause aphthoid ulcers.