New insights into the mechanisms of immunotherapy.

Allergen-specific immunotherapy retains a place in treatment in patients with allergic rhinitis who fail to respond to conventional treatment with antihistamines and topical corticosteroids. Studies on mechanisms of immunotherapy have previously focussed on changes in serum antibodies, including blunting of seasonal rises in specific IgE and increase in "blocking" specific IgG antibodies. Immunotherapy in patients with rhinitis has also been shown to inhibit effector cells with a decrease in nasal mucosal eosinophils and epithelial mast cells. Recent evidence suggests that these events may be orchestrated by an effect of immunotherapy on T lymphocytes with alteration from a predominant "Th2" response (interleukin 4 and 5) in favour of an additional "Th1" response (gamma interferon) which may decrease tissue eosinophilia and local IgE production. Novel therapeutic approaches to allergic diseases might include use of topical gamma interferon, immunosuppressive agents, anti-CD4 antibodies or strategies directed specifically against IL-4 or IL-5.