Meta-analysis of specific immunotherapy in patients with allergic rhinoconjunctivitis

Background: Specific immunotherapy (SIT) of allergic disorders as introduced by Freeman and Noon involves the application of gradually increasing doses of extracts of the material to which the individual is sensitive. SIT represents the only specific treatment that can be offered to allergic patients besides allergen avoidance. SIT has been widely used in patients with pollen allergic rhinitis and its clinical efficacy has been demonstrated in several controlled clinical trials. The underlying mechanism of this treatment is still not understood. Previous studies have focused on changes in serum antibodies, including blunting of seasonal rises in specific IgE and increases in specific IgG antibodies, especially of the IgG4 isotype. Recent studies have suggested an effect on T-lymphocytes, leading to a switch from a predominant Th2 response - that is, interleukin (IL)-4 and IL-5 - to a Th1 response involving interferon (IFN)-gamma. The switch of a cytokine profile to a predominant IFN-gamma response results in inhibition of IL-4 dependent IgE production, which is reinforced by a decrease in the production of IL-4 by Th2 cells. Methods: In the present study a metaanalysis was performed to evaluate all double-blind placebo-controlled studies investigating the effect of SIT on clinical and immunological treatment used in patients with allergic rhinoconjunctivitis. Results: SIT was shown to be an effective treatment modality in allergic rhinoconjunctivitis, decreasing symptoms, the need for medication and reactivity in specific nasal and conjunctival provocation tests, as well as inflammatory markers. Histologically, a switch might be induced from a predominant Th2 cell profile to that of a Th1. Conclusions: In general, the efficacy of SIT is dependent on the allergen the individual patient is sensitive to, the quality and total amount of the allergen applied and the SIT schedule.