Determining the Threshold Concentration of Birch Pollen for Inducing Allergic Symptoms Using an Allergen Challenge Chamber

Abstract

Introduction: To determine threshold concentrations of pollen inducing symptoms in seasonal allergic rhinitis patients has been a challenge for decades. Allergen challenge chambers (ACC) allow a controlled, reproducible experimental design to address this problem. Hitherto, ACCs were only run with high pollen concentrations. Methods: The Fraunhofer ACC was technically modified to deploy very low pollen concentrations. Then, adults with birch pollen-induced allergic rhinitis were challenged with varying birch pollen concentrations using a patient-blinded, sham challenge-controlled, part-randomized, titrate-to-effect clinical study setting. Mean increase in Total Nasal Symptom Score (TNSS) ≥0.55 compared to sham challenge was regarded as minimal clinically important difference (MCID). Further endpoints were nasal secretion weight, exhaled nitric oxide (FeNO), and inflammatory cells from nasal lavage. Results: Fifteen participants with mild to moderate allergic rhinitis participated in the experimental study part (mean age 45 years [22–64]; 7 females). Mean TNSS was: 1.08 at 0 pollen/m3; 1.05 at 10 pollen/m3; 1.2 at 50 pollen/m3; 1.74 at 100 pollen/m3; 1.61 at 200 pollen/m3; 2.79 at 1,000 pollen/m3. MCID of TNSS was observed at 100, 200, and 1,000 pollen/m3. More than half of the study population showed a lack of response at 10, 50, and 200 pollen/m3. Nasal secretion increased slightly with concentration. No clinically meaningful results could be derived from FeNO and inflammatory cells. Conclusions: The applied technical modification of the Fraunhofer ACC produced stable, low pollen concentrations. Based on mean TNSS data, the threshold concentration for inducing symptoms with birch pollen was 50–100 pollen/m3. © 2025 The Author(s).