Recruitment, distribution and phenotypes of mast cells in interstitial cystitis

Interstitial cystitis (IC) is a chronic disabling condition of unknown etiology. One of its major characteristics is an increase in mast cells (MC) showing signs of activation. It has been suggested that the proteinase content defines two MC types: MC(TC), containing chymase and tryptase, and MC(T), which contains tryptase but lacks chymase. Here, we investigated the MC distribution and the MC proteinase expression in IC together with the tissue expression of the major MC growth factors, stem cell factor (SCF) and interleukin-6 (IL-6).

MC were enumerated in bladder specimens from patients with classic IC, nonulcer IC and controls. MC were visualized in terms of metachromasia, reflecting glycosaminoglycan content, and immunohistochemically, visualizing tryptase, chymase and IL-6 as well as the surface markers CD117 and SCF.

Classic IC displayed a 6 to 10-fold increase of MC identified by proteinase content while in nonulcer IC there were twice as many MC as in controls. In contrast to nonulcer IC and controls, classic IC displayed an abundance of epithelial MC. Fewer CD117+ than proteinase+ MC were detected in IC but not in controls. Classic IC coexpressed SCF and IL-6 in the epithelium and displayed numerous SCF and IL-6+ cells in the mucosa and detrusor muscle, many of which were MC.

Redistribution of MC into the epithelium and a high bladder wall MC density distinguish classic IC from nonulcer IC. Our findings suggest an SCF/IL-6-driven MC response in IC. They also indicate a downregulation of the SCF receptor in IC.