METAPLASTIC TRANSFORMATION OF URINARY-BLADDER EPITHELIUM - EFFECT ON MAST-CELL RECRUITMENT, DISTRIBUTION, AND PHENOTYPE EXPRESSION

Mucosal mast cells (MCs) are normally found in the connective tissue s troma but are redistributed into the epithelium in conditions associat ed with immunoglobulin E responses, such as allergic inflammation and nematode infections, as well as in interstitial cystitis, a condition of unknown etiology. The potential role of epithelium-derived factors in this response prompted this inquiry into growth and differentiation signaling in normal tissue as well as in tissues from five different metaplastic conditions of the urothelium (cystitic cystica, cystitis g landularis, colonic metaplasia, squamous cell metaplasia, and nephroge nic metaplasia). Expression of the two major human MC growth factors, stem cell factor (or kit ligand) and interleukin 6, was detected using immunohistochemistry. In the case of interleukin 6, its mRNA expressi on was also detected using in situ reverse transcription-polymerase ch ain reaction. Among the different metaplastic lesions, nephrogenic met aplasia was the only one associated with an abundance of MCs, which we re distributed within or in close relationship to the epithelium. Unli ke in the other types of metaplasia, the epithelium strongly co-expres sed interleukin 6 and stem cell factor. The MCs expressed the stem cel l factor receptor CD117 and exhibited a variable tryptase immunoreacti vity, but lacked chymase. They also displayed a relative deficiency of granular glycosaminoglycan, as indicated by a lack of metachromasia, and were sensitive to strong aldehyde fixation. The findings suggest t hat the MC response in nephrogenic metaplasia may be the result of loc al epithelial stem cell factor/interleukin 6 expression.