Metaplastic transformation of urinary bladder epithelium: effect on mast cell recruitment, distribution, and...

Mucosal mast cells (MCs) are normally found in the connective tissue stroma but are redistributed into the epithelium in conditions associated 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 glandularis, colonic metaplasia, squamous cell metaplasia, and nephrogenic 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 expression was also detected using in situ reverse transcription-polymerase chain reaction. Among the different metaplastic lesions, nephrogenic metaplasia was the only one associated with an abundance of MCs, which were distributed within or in close relationship to the epithelium. Unlike in the other types of metaplasia, the epithelium strongly co-expressed interleukin 6 and stem cell factor. The MCs expressed the stem cell factor receptor CD117 and exhibited a variable tryptase immunoreactivity, 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 that the MC response in nephrogenic metaplasia may be the result of local epithelial stem cell factor/interleukin 6 expression.