Allergen immunotherapy: definition, indications, and reactions.

Specific allergen immunotherapy is the administration of increasing amounts of specific allergens to which the patient has type I immediate hypersensitivity. It is a disease-modifying therapy, indicated for the treatment of allergic rhinitis, allergic conjunctivitis, allergic asthma, and Hymenoptera hypersensitivity. Specific immunoglobulin E (IgE) antibodies for appropriate allergens for immunotherapy must be documented. Indications for allergen immunotherapy include (1) inadequate symptom control despite pharmacotherapy and avoidance measures; (2) a desire to reduce the morbidity from allergic rhinitis and/or asthma, or reduce the risk of anaphylaxis from a future insect sting; (3) when the patient experiences undesirable adverse effects from pharmacotherapy; and (4) when avoidance is not possible. Several studies reported that immunotherapy in allergic rhinitis seems to prevent the development of new allergic sensitizations and/or new onset asthma. Humoral-, cellular-, and tissue-level changes occur with allergen immunotherapy, including induction of allergen-specific regulatory T and B cells, interleukin 10, and transforming growth factor β production; suppression of T-helper type 2 cell proliferation; large increases in anti-allergen IgG4 antibodies; and reduction in basophil, mast cell, and eosinophil mediator release. Allergen immunotherapy can be administered either subcutaneously in the physician's office or sublingually by the patient at home. The use of immunotherapy in food allergy is still under investigation.