PHENOTYPIC CHARACTERIZATION OF SKIN-LESIONS IN URTICARIA PIGMENTOSA AND MASTOCYTOMAS

In order to identify possible cellular abnormalities in human mastocyt osis, sections from 13 urticaria pigmentosa lesions and 5 mastocytomas were compared with 5 normal skin specimens using histochemical, enzym e histochemical and immunohistochemical techniques. All toluidine blue -positive mast cells also reacted with Fc epsilon RI and c-kit antibod ies, almost all stained for tryptase, many for chymase and the myeloid workshop mast cell antibodies, few for Fc epsilon RII and none for th e proliferation marker Ki-67. Urticaria pigmentosa lesions contained f ewer epidermal Langerhans cells and a lower percentage of avidin-posit ive mast cells than mastocytomas and normal skin. Mastocytomas exhibit ed generally weaker staining for mast cell markers and mostly lacked F c epsilon RI-bound IgE on mast cells and Langerhans cells, although th e receptor was able to bind IgE in tissue sections. Most of the mast c ell antibodies also reacted with other cell types. Only toluidine blue , avidin, tryptase and chymase stains were mast cell specific. Mast ce lls in mastocytosis thus differed only to a minor degree from normal m ast cells, although distinct pathomechanisms may play a role in urtica ria pigmentosa and mastocytosis.