Immunotherapy suppresses both Th1 and Th2 responses by allergen stimulation, but suppression of the Th2 response is a more important mechanism related to the clinical efficacy of immunotherapy for perennial allergic rhinitis.

Increased attention has recently been directed at the possibility that the clinical efficacy of immunotherapy might be elaborated by alteration of T-cell reactivity. However, there is no general agreement among different investigators regarding the effect of immunotherapy on Th-cell reactivity. Peripheral blood mononuclear cells (PBMCs) from 15 nonatopic subjects and 76 patients with perennial allergic rhinitis (18 untreated patients and 58 patients on immunotherapy) were cultured in the absence and in the presence of a major Dermatophagoides farinae allergen, Der f 1, and the levels of IgE, interleukin-5 (IL-5), interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) in the culture supernatants were determined. The difference between the absence and presence of Der f 1 was calculated to consider the Der f 1-dependent synthesis of IgE, IL-5, IFN-gamma and TNF-alpha. The levels of Der f 1-dependent synthesis of IgE, IL-5 and TNF-alpha were significantly higher in the untreated group than in the nonatopic group, whereas Der f 1-dependent synthesis of IFN-gamma was significantly lower in the untreated group than in the nonatopic group. Immunotherapy decreased the enhanced Der f 1-dependent synthesis of IgE, IL-5 and TNF-alpha, and further decreased the suppressed Der f 1-dependent synthesis of IFN-gamma as the therapy proceeded. The levels of Der f 1-dependent synthesis of IgE and IL-5 did not differ between nonatopic individuals and patients whose duration of immunotherapy was 10 or more years. The levels of Der f 1-dependent synthesis of IgE and IL-5, but not of IFN-gamma and TNF-alpha, were correlated significantly with the levels of symptom scores. In addition, the levels of Der f 1-dependent synthesis of IgE and IL-5, but not of IFN-gamma and TNF-alpha, differed significantly between good and poor responders. In conclusion, immunotherapy for perennial allergic rhinitis may possibly work via induction of tolerance or anergy of both Th1- and Th2 cells. However, our study is likely to support a view that the mechanisms responsible for the clinically beneficial effects of immunotherapy principally involve the tolerance of Th2- rather than Th1 cells. In addition, suppression of IgE synthesis is also likely to be linked to the clinical efficacy of immunotherapy for perennial allergic rhinitis.