Quantitative analysis of tryptase- and chymase-containing mast cells in eosinophilic conditions of cats

The presence and density of tryptase-positive/chymase-positive mast cells (MCs) (MCTC), chymase-positive/tryptase-negative MCs (MCC), and tryptase-positive/chymase-negative MCs (MCT) in lesional skin from cats with eosinophilic conditions were investigated. Skin biopsy specimens from eight cats with eosinophilic plaque (three cats), eosinophilic granuloma (two cats), and eosinophilic dermatitis (three cats) were studied. Toluidine blue staining and a double-enzyme-immunohistochemical staining technique were performed to determine MC density and MC subtypes, respectively. MC density varied from 170.3 to 503 cells/mm(2) (mean value of 314.9 cells/mm(2)). In the superficial dermis, 5.9% of the MC belonged to the MCT, 12.8% to the MCC, and 81.2% to the MCTC subtype. In the deep dermis, 12.8% belonged to the MCT, 12.8% to the MCC, and 73.8% to the MCTC subtype. It is the first time that MCC have been identified. The double-labeling procedure proved to be a reliable tool for identifying simultaneously the presence of MC subtypes in feline skin.