Does specific immunotherapy injection cause an increase in bronchial reactivity?

Background. Several well-controlled studies have proven the clinical benefit of specific immunotherapy (SIT) for seasonal allergic rhinitis (AR). However, whether subcutaneous SIT injection could cause a transient increase in bronchial reactivity (BR) remains unknown. Objective. To investigate whether subcutaneous SIT injection, either during or outside the pollen season, could cause an increase in BR in children with pollen allergy. Methods. Twenty-two children (mean age 13.6 ± 0.7 years) with AR who were receiving maintenance SIT for 15 months were included in the study. Pre-injection BR of the patients was evaluated with methacholine provocation test immediately before maintenance dose of SIT during the peak pollen season and outside the season. The post-injection test was administered 24 hours after SIT injection. Results. There was no difference in FEV₁ measures recorded during [98(93-109)%] and outside [102(96-111)%] the pollen season. There was no significant difference between pre- [64(7-64)mg/mL] and post-allergen injection [32(7.5-64) mg/mL] BR outside the pollen season (p = 0.9). A trend towards improvement following allergen injection [64(5.4-64)] as compared to pre-allergen injection [14.6(3.5-64)] was shown during the pollen season (p = 0.053). Although PC20 measures in the pollen season were lower than outside the season, the difference was not significant. The percentage of the patients with bronchial hyperreactivity was 62% during and 43% outside the season. Conclusion. SIT injections both during and outside the pollen season cause no increase in BR in children with AR. This calls into question the necessity of empirical dose reduction during the pollen season.