Background There is no in vitro test to predict the induction of long-term tolerance in patients treated with venom immunotherapy (VIT). The aim of this study was to investigate whether immunotherapy-induced changes in basophil responsiveness reflect a state of protection and the induction of a tolerance. Methods Twenty-three patients with allergic reaction after Hymenoptera sting (11 wasp and 12 honeybee) were treated with VIT. In all patients, a CD63 basophil activation test was performed before the beginning of immunotherapy, after 1 year and after completing 46.5 years of immunotherapy (approximately 1 year after stopping). The tolerance was then evaluated by a sting challenge test. The basophil activation test was repeated 36 months after the challenge. Results Twenty-two subjects showed a negative sting challenge, and one subject, a positive sting challenge. Allergen-specific basophil response remained unchanged after 1 year of immunotherapy. However, after immunotherapy, a significant and approximately fourfold decrease was demonstrated in all tolerant subjects mainly in response to submaximal 0.1 mu g/ml allergen concentration. This depression was sustained and did not change with the sting challenge test. In a nontolerant patient with a positive sting challenge, basophil response did not change. Conclusions Our results suggest that the depression of allergen-specific basophil response seems to be associated with the induction of a tolerance after completing a course of VIT.
