Proliferation and transepithelial migration of mucosal mast cells in interstitial cystitis

The distribution and abundance of mast cells, as well as their fixation, staining and ultrastructural properties, were studied in the urinary bladders of 16 patients with interstitial cystitis (IC) and in 14 normal subjects. Tissues were fixed in both standard formaldehyde solution and a special fixative, IFAA, optimized for the preservation of mucosal mast cells. An expansion of two distinct mast cell populations was observed in IC. One of these, comprising formaldehyde-sensitive cells, was found only in the mucosa underlying lesions of IC. They were most numerous in the lamina propria but were also frequent in the epithelial layer as well as in the bladder washings, indicating a migratory capacity for these cells. The other mast cell population was visualized equally well irrespective of fixation and staining procedure. In control subjects, such cells were found both in the lamina propria and detrusor muscle, but not in the epithelium nor in bladder washings. In lesions of IC they were increased in the detrusor muscle only. Both types of mast cell contained granules with the highly characteristic lamellar arrays and scrolls, distinguishing human mast cell granules from those of blood basophils. The proliferation and intraepithelial distribution of mucosal mast cells are unusual findings, but prominent features of helminth responses and human mucosal allergic reactions. These findings thus suggest that the mucosal mast cell-IgE system may be involved in the pathogenesis and/or aetiology of IC.