MAST-CELL NUMBER AND PHENOTYPE IN CHRONIC IDIOPATHIC URTICARIA

Background: Increased levels of histamine have been previously demonst rated in patients with chronic idiopathic urticaria. Objective: The pu rpose of the study was to determine whether increased numbers of mast cells are present in lesional skin from such patients. Methods: Mast c ells have been quantified in lesional (n = 11) and nonlesional (n = 9) skirt from patients with chronic idiopathic urticaria and compared wi th site-matched skin from healthy control subjects (n = 10). Mast cell s were identified by using a sensitive, double-labeling immunohistoche mical technique with specific monoclonal antibodies to mast cell trypt ase and chymase and quantified under light microscopy. Results: No sig nificant differences in mast cell numbers from lesional, nonlesional, or control skin were observed (p > 0.1, Student's t test). In both pat ients with urticaria and control subjects, more than 99% of cutaneous mast cells contained tryptase and chymase. Conclusions: These date: in dicate that increased skin histamine in chronic idiopathic urticaria i s not caused by increased mast cells and may alternatively reflect an increase in histamine content per mast cell, enhanced mast cell activa tion, or recruitment of basophils into skin in patients with chronic i diopathic urticaria.