Immunotherapy: rationale and mechanisms

Immunotherapy is defined as the controlled exposure to known allergens to reduce the severity of the allergic response. Although available since 1910, its exact mechanisms of action is not known but may involve an increase in allergen-specific IgG antibodies, a decrease in IgE synthesis, and alteration in T-lymphocyte activity. Immunotherapy is indicated in patients with proven allergy who have significant symptoms. It may be used together with pharmacologic measures but is relatively contraindicated in patients receiving beta-blocker therapy. Immunotherapy may be continued during pregnancy and should not be initiated in patients with autoimmune diseases or in human immunodeficiency virus-positive patients. Selection of appropriate diagnostic tests is important. Before immunotherapy is considered, there are two recommended in vivo tests (combined prick and intradermal skin test, and skin end point titration) and two recommended in vitro tests (radioallergosorbent test [RAST] and enzyme-linked immunosorbent assays [ELISA]), all equally safe and sensitive. After appropriate test interpretation, treatment is initiated with slowly escalating doses of allergen. Effects are often apparent in 3 to 6 months and, after continuation for 3 to 5 years, patients usually achieve lasting benefit.