Does allergen immunotherapy alter the natural course of allergic disorders?

Allergy in patients with atopy is caused by clinical adverse reactions to environmental antigen, which is often associated with allergen-specific immunoglobulin (Ig)E production. Since allergy reflects an inappropriate immunological reaction, a therapeutic approach related to immunology is likely to actively alter the natural course of allergic disorders. Allergen immunotherapy, known at various times as desensitisation or hyposensitisation, is very recently defined by the World Health Organization as therapeutic vaccines for allergic diseases. At present, it has become a common clinical practice in selected patients for the treatment and prevention of the recurrence of allergic disorders caused by insect venoms and has proven to be effective in changing the course of allergic responses induced by grass and tree pollen, animal hair and dander, house dust mite and mold, as demonstrated by improvement in clinical symptoms, skin prick test and medication scores. Reported effects of allergen immunotherapy on the natural course of allergic disorders include (i) prevention of reaction following re-sting in insect venom allergy; (ii) prevention or decrease the rate of the natural progress of allergic rhinitis to asthma; and (iii) inhibition of new sensitisation in monosensitised children. Many aspects of the immune responses associated with allergic disorders, including antibody production, cytokine secretion, T cell activation and local inflammatory reactions, are found to be significantly altered during and/or after immunotherapy. Specifically, the ratio of allergen-specific IgG4 to IgG1 correlates well with positive clinical outcome caused by allergen immunotherapy in patients with pollen-allergy. Allergen immunotherapy affects the cytokine profile of allergen-specific T cells and switches T(H)2 type immune responses in patients with atopy towards T(H)0 or T(H)1 type responses. Although the changes in the absolute value of T(H)1 or T(H)2 cytokines appear quite variable, the increase in the ratio of T(H)1/T(H)2 cytokines is very consistent among published reports, especially in the late stage of treatment. Accumulating evidence indicates that appropriate immunotherapy prevents the onset of new sensitisation and prevents the progress of allergic rhinitis to asthma. Although the changes in B cell and T cell responses, especially IgG antibodies and T(H)1/T(H)2 cytokine production, may be the major mechanism underlying the clinical efficacy of allergen immunotherapy and the prevention of the development of allergic phenotypic changes, multiple mechanisms may be involved in the outcome of alteration of the natural course of allergic disorders.