Co-localization of tryptase and cathepsin-G in mast cells in cutaneous mastocytosis

Mastocytosis is a heterogeneous disease characterized by an abnormal growth and/or accumulation of clonal mast cells (MC) in one or more organs. The most frequent site of organ involvement is the skin. The aim of this study was to investigate the immunoreactivity to tryptase and to cathepsin-G of MC from human cutaneous mastocytosis and to compare their number in normal skin and cutaneous mastocytosis. Immunohistochemistry and dual immunofluorescence using anti-tryptase and anti-capthepsin-G antibodies was performed on biopsy specimens from 20 cases diagnosed as cutaneous mastocytosis. Tryptase-positive MC was more numerous as compared to cathepsin-G positive MC. Dual immunofluorescence for tryptase and cathepsin-G demonstrated a colocalization of tryptase and cathepsin-G in skin MC secretory granules. Morphometric evaluation of MC number demostrated that the number of both tryptase- and cathepsin-G-positive MC was significantly higher in cutaneous mastocytosis as compared to normal skin and that in both conditions the number of tryptase-positive MC was significantly higher as compared to the number of cathepsin-G-positive MC. In conclusion, in this study, for the first time we have demonstrated the presence of MC with immunoreactivity to cathepsin-G in human cutaneous mastocytosis, as well as the co-localization of tryptase and cathepsin-G in MC secretory granules.