Clinical Evidence Of A Priming Mechanism For Insect Sting Anaphylaxis

RATIONALE: We have presented evidence of basophil activation during initial sting challenge (SC) in patients experiencing no systemic reaction (SR) to SC, suggesting that venom exposure may prime the subject with increased risk for a SR to a subsequent sting. This study aims to determine if the frequency of a SR to SC increases with venom exposure (skin test or sting) during the previous 4-8 weeks. METHODS: Volunteers (n=153) with a previous SR to a sting and positive venom skin tests or RAST consented to undergo SC, which occurred from 1week to 2 years later. Of the subjects experiencing no reaction to the initial SC, 52 repeated SC either 4-8 weeks later or in a subsequent year. RESULTS: Among 38 patients stung < 4 weeks after skin test, the sting reaction rate was significantly higher (34%) than in 115 patients whose skin test were < 4 weeks earlier (18%) (p=.04). However, reaction rates were equivalent when comparing stings < 8 weeks, and > 8 weeks after skin tests. When a second sting was performed the same summer a systemic reaction occurred in 4/27 patients (16%), significantly more than when the second sting occurred in a later year (0/25) (p=0.02). CONCLUSIONS: The higher frequency of reaction to a sting within weeks after previous venom exposure, either skin test or sting, suggests a priming mechanism that enables the anaphylactic event. Together with in vitro basophil and dendritic cell evidence, this suggests the need for further investigation of the priming mechanism in anaphylaxis.