Immunological Mechanisms Operative in Allergen–Specific Immunotherapy

Specific immunotherapy (SIT) is the practice of administering increasing doses of allergen extracts to selected subjects suffering from IgE-mediated hypersensitivity, with the ultimate aim of ameliorating the symptoms associated with exposure to the causative allergen. The process is often called hyposensitization or desensitization because one consequence of the treatment is a reduction in sensitivity of the target organ after challenge with the relevant allergen. SIT has been practiced as treatment of type I allergy caused by inhalant allergens and Hymenoptera venoms for more than 80 years on an empirical basis. Today, numerous double-blind, placebo-controlled studies prove the therapeutic effect of SIT. However, the immunological mechanisms underlying successful specific immunotherapy have still not been completely elucidated. This review focuses on recent attempts to characterize the immunological events associated with SIT.