Heterogeneity of mast cells in mastocytosis and inhibitory effect of ketotifen and ranitidine on indolent systemic mastocytosis

Background: Mastocytosis is a disorder of mast cell proliferation that occurs in both cutaneous and systemic forms. The most frequent site is the skin. Objective: The mast cell subtype of two patients with mastocytosis was investigated. Methods: Immunohistochemical studies were performed on the skin or gastric mucosa or both of the two patients. Blood and urine levels of various mediators were measured for one patient. Results: Mast cells containing tryptase and chymase were the only type seen in the skin lesions of an 11-month-old boy with urticaria pigmentosa. Mast cells containing tryptase were predominant in lesions of the skin and gastric mucosa of a 41-year-old man with indolent systemic mastocytosis. However, mast cells containing tryptase and chymase were predominant in the nonlesional and the normal skin of this patient. Tryptase-positive cells were more numerous in lesional skin than nonlesional skin and normal skin. Elevated blood and urine levels of various mediators were decreased by means of combination therapy with ketotifen and ranitidine. Conclusion: In indolent systemic mastocytosis, mast cell dynamics involve only cells containing tryptase. Release of mediators from mast cells may be inhibited by means of combination therapy with histamine H1 and H2 receptor antagonists. (J Allergy Clin Immunol 1997;100:S25-32.)