anaphylactic reaction [Gk, ana, phylaxis, protection; L, re, agere, to act] , an acute allergic response involving IgE–mediated, antigen-stimulated mast cell activation resulting in histamine release. Exposure to the antigen may result in dyspnea, airway obstruction, shock, urticaria, and in some cases, death. Anaphylactic reactions may be caused by bee stings, foods, allergen extract, medications, or exercise. Rapid administration of subcutaneous epinephrine is the treatment of choice for severe reactions.
