Anaphylaxis after Hymenoptera stings in three patients with urticaria pigmentosa.

Three patients with urticaria pigmentosa are reported who developed symptoms of anaphylaxis after Hymenoptera stings. Serum IgE antibodies to various Hymenoptera venoms could not be detected in any of the patients. Skin tests were completely negative in one patient, and borderline reactions with honeybee and yellow jacket venom, respectively, were found in the other two. Peripheral blood leukocytes of these latter two patients did not release significant amounts of histamine after exposure to the respective venoms. In patients with mastocytosis, anaphylaxis after insect stings may not be IgE-mediated but due to mediator release by the pharmacologic action of histamine liberators normally present in Hymenoptera venoms.