Clinical Validation of House Dust Mite Allergen Exposure in the Environmental Exposure Unit

The Environmental Exposure Unit (EEU) is a controlled indoor allergen exposure model of allergic rhinitis (AR), historically used with seasonal pollens such as ragweed, birch, and grass. We sought to clinically validate the EEU for exposure with the perennial house dust mite (HDM) allergen. Healthy volunteers with a 2-year history of perennial AR symptoms and a positive skin prick test result for both Dermatophagoides pteronyssinus and Dermatophagoides farinae (defined as a wheal size greater than 5 mm over the diluent control) attended a 3 hour EEU HDM exposure session. Non-atopic controls were also recruited. Participants assessed rhinoconjunctivitis symptoms, tallied as the Total Nasal Symptom Score (TNSS), and recorded their Peak Nasal Inspiratory Flow (PNIF). Both were collected at baseline, every 30 mins while in the EEU, and were subsequently recorded hourly until 12 hours post-exposure, followed by a final evaluation at the 24 hour mark. Fifty-five participants between the ages of 13-65 years were eligible after the screening process (44 allergics, 11 non-atopics). Mean TNSS values for allergic participants were significantly elevated compared to controls for the first 6 hrs following HDM exposure (p<0.05), with a mean value of 7.1 observed at 3 hours post-exposure (p<0.0001). There was also a significant decrease in the %PNIF change from baseline noted at the 2 and 3hr points (both p<0.05). The non-atopic controls were asymptomatic. The EEU is capable of inducing nasal symptoms in HDM allergic participants, proving it to be a robust HDM allergen exposure model.