Mast cell number and phenotype in chronic idiopathic urticaria

Background: Increased levels of histamine have been previously demonstrated in patients with chronic idiopathic urticaria. Objective: The purpose of the study was to determine whether increased numbers of mast cells are present in lesional skin from such patients. Methods: Mast cells have been quantified in lesional ( n = 11) and nonlesional ( n = 9) skin from patients with chronic idiopathic urticaria and compared with site-matched skin from healthy control subjects ( n = 10). Mast cells were identified by using a sensitive, double-labeling immunohistochemical technique with specific monoclonal antibodies to mast cell tryptase and chymase and quantified under light microscopy. Results: No significant differences in mast cell numbers from lesional, nonlesional, or control skin were observed ( p > 0.1, Student's t test). In both patients with urticaria and control subjects, more than 99% of cutaneous mast cells contained tryptase and chymase. Conclusions: These data indicate that increased skin histamine in chronic idiopathic urticaria is not caused by increased mast cells and may alternatively reflect an increase in histamine content per mast cell, enhanced mast cell activation, or recruitment of basophils into skin in patients with chronic idiopathic urticaria. (J ALLERGY CLIN IMMUNOL 1995;96:360-4.)