Mast cells (MC) are tissue-resident immune cells that participate in first line host defense, responding to allergic challenge and pathogen attacks. Following appropriate stimulation they release immuno-modulators, and vaso- and neuroactive compounds. Early reports suggest that MCs are innervated [1] and their anatomical proximity to vasculature and nerve fibers underpin the likelihood of functioning neuro-immune interfaces. The biological role of MCs is diversified.

MCs have been in the focus of interstitial cystitis research for a long time and it has been repeatedly suggested that histo-pathologic demonstration of MC hyperplasia represents a momentous diagnostic tool. In the 80-ties the critical number of 28 MCs/mm² was by many suggested as the proof of the diagnosis [2, 3]. It has to be remembered, though, that MC counts in the specimen of bladder mucosa and detrusor muscle does not disclose the absolute number of cells residing in the biopsy. Certainly, the degree of MC expansion is determinative but laboratory techniques have a considerable impact as to numbers, too. During the last decades, there has been a significant development of technologies resulting in increasing accuracy of MC demonstration. Naphtolesterase staining [2] was replaced by the more sensitive toluidine blue staining, reinforced by more appropriate fixation techniques to overcome blocking of dye-binding [4, 5]. Currently, immunohistochemical tryptase labeling has been found superior and more robust comparing to earlier methods [6, 7] and is the method recommended today [8].