Allergy/Immunology

Answer 1 Type I. This patient had a type I, or immediate, hypersensitivity reaction. This IgE-mediated reaction affects between 3.5% and 4% of Americans; however, not all reactions are as severe as the reaction described in the case patient. Sensitized individuals produce allergen-specific IgE molecules that attach to circulating mast cells. Reexposure to the same allergen causes cross-linking of the IgE molecules and subsequent degranulation of the primed mast cells. Histamine, leukotrienes, and other inflammatory mediators are then released, causing a spectrum of clinical features. Patients with a history of anaphylaxis after ingestion of a food should always be evaluated by an allergist/immunologist to identify the causative allergen. Testing for immediate hypersensitivity can be performed in vivo (skin prick testing) or by measuring total IgE levels and specific IgE antibody levels in vitro. Clinical history, in vivo testing, and measurement of specific IgE antibody levels allow the allergist/immunologist to predict the likelihood that a reaction will occur upon re-exposure to that food and also to predict the need for carrying an epinephrine auto-injector.1 Types II, III, and IV hypersensitivities do not manifest as described in the case. Rather, type II hypersensitivity involves complement, type III involves immune complex formation, and type IV is cell-mediated, or delayed type hypersensitivity. REFERENCES 1. Sampson HA. Update on food allergy. J Allergy Clin Immunol 2004;113:805-19. Click here to return to the questions

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