Suppression of seasonal increase in serum interleukin-5 is linked to the clinical efficacy of immunotherapy for seasonal allergic rhinitis

Although immunotherapy is recognized as a highly effective form of treatmen t for allergic rhinitis; especially pollen-induced seasonal allergic rhinit is, the mechanisms have not been fully established. In the present study, w e investigated whether immunotherapy could affect the seasonal increase in interleukin-5 (IL-5) in the serum of patients with seasonal allergic rhinit is and whether the effect on IL-5 in serum is related to the clinical effic acy of immunotherapy. Venous blood was collected twice from each patient wi th seasonal allergic rhinitis due to Japanese cedar pollens, before and dur ing the cedar pollen season in 1997, to determine the cedar pollen-specific IgE and IL-5 in serum. Both specific ISE and IL-5 in serum were significan tly increased during the pollen season, not only in the poor responders to antihistamines but also in the good responders. Neither the rate of seasona l increase in specific IgE nor the rate of seasonal increase in IL-5 differ ed significantly between the good responders and the poor responders to ant ihistamines. Both specific IgE and IL-5 were significantly increased during the pollen season in the poor responders to immunotherapy, whereas neither specific ISE nor IL-5 was increased during the pollen season in the good r esponders to immunotherapy. The rate of seasonal increase in specific IgE a s well as IL-5 was significantly smaller in the good responders than in the poor responders to immunotherapy. The rates of seasonal increase in specif ic IgE and in IL-5 were inversely correlated with the length of time on imm unotherapy. However, the rare of seasonal increase in specific IgE was not significantly correlated with the rate of seasonal increase in IL-5. In con clusion, the suppression of the seasonal increase in IL-5 in serum is a wor king mechanism of immunotherapy related to the clinical efficacy of the tre atment.