The role of allergen immunotherapy in asthma management

Immunotherapy (IT) using extracts of inhalant allergen has been used world-wide for more than 75 years in the management of allergic respiratory disorders including asthma. Good clinical results with IT depend on careful patient selection and the use of standardized, high-quality extracts that have only become widely available in the last 20 years. The immunologic and clinical consequences of effective IT include 'desensitization' of antigen- driven IgE-dependent mast cell activation, attenuation of specific T cell responses, and down regulation of inflammatory cells and cytokines in the respiratory mucosa, all leading to reduced end-organ responsiveness to the treatment allergens. Many controlled clinical trials support the effectiveness of IT in reducing upper airway symptoms and antihistamine use in allergic rhinoconjunctivitis. Effectiveness in controlling symptoms of allergic asthma has been more difficult to demonstrate, especially in multiply sensitive perennial asthmatics with moderate or severe disease. The risk of fatal anaphylaxis from IT treatment in the United States is apparently very low, but three quarters of these fatalities occur in asthmatic patients. Recent evidence suggests that the risk is greatest and the benefit is minimal for perennial persistent asthmatics requiring inhaled or oral steroids. Whether IT can be uniquely helpful in preventing the emergence of allergic asthma in high-risk, atopic children remains to be determined.