Threshold concentration of ragweed pollen for inducing allergic symptoms: Initial data using an allergen challenge chamber

Introduction: Climate change may increase the spread of allergenic plants such as ragweed. Ragweed pollen is assumed to be more allergenic than birch pollen. Determining pollen threshold concentrations triggering symptoms is challenging. Technical modifications to the Fraunhofer Allergen Challenge Chamber (ACC) now allow investigation of very low pollen concentrations. Based on Total Nasal Symptom Score (TNSS) data from 15 subjects with birch pollen allergic rhinitis (AR), a birch pollen threshold between 50 and 100 pollen grains/m3 of air was previously derived. This study explored threshold concentrations of ragweed pollen. Methods: Two ragweed pollen AR patients were exposed to varying concentrations of ragweed pollen for 4 hours. TNSS was recorded every 20 minutes, nasal secretion and peak nasal inspiratory flow hourly. Area under the curve values (AUC0-240) were calculated. Ex-vivo basophil activation tests with varying concentrations of ragweed pollen, Amb a 1, birch pollen and Bet v 1 were performed for both ragweed pollen AR patients and 6 of the 15 birch pollen AR patients. Mean effective concentrations (EC50) for CD63 expression were calculated. Results: Ragweed pollen exposure resulted in the following TNSS AUC0-240 values: 28/23 at 0, 18/17 at 50, 13/27 at 100, 40/40 at 200, 29/16 at 300 and 55/47 at 1,000 pollen grains/m³. For CD63 expression, the mean EC50 was 277 pollen/ml for ragweed pollen, 884 ng/ml for Amb a 1, 11 pollen/ml for birch pollen, and 0.13 ng/ml for Bet v 1. On average, the proportion of Amb a 1 in ragweed pollen was 0.17 %, the proportion of Bet v 1 in birch pollen 1.96 %. Conclusion: The modified Fraunhofer ACC can investigate pollen threshold concentrations under defined conditions. The assumed differences in threshold concentrations of ragweed and birch pollen for triggering symptoms were not confirmed. To derive reliable threshold concentrations for ragweed pollen, larger studies have to follow.