A protocol for conducting a challenge in an allergen exposure chamber (AEC) facility is presented. AECs have proven to be safe and effective tools for the induction of allergic symptoms or as an endpoint in the efficacy testing of allergen immunotherapy due to their ability to maintain stable particle concentrations and environmental conditions.
Allergen exposure chambers allow controlled exposure to allergenic and non-allergenic urban particles in a confined environment. They are used for controlled challenges and mimicking natural exposure. The allergen exposure chamber facilitates the observation of various clinical endpoints, particularly objective measures such as nasal obstruction or secretion, and subjective parameters evaluated by the patient.
Allergen exposure chambers are available tool for the assessment of primary endpoints in clinical studies especially in allergen-specific immunotherapy and pharmacotherapy of allergic respiratory diseases. To begin, vacuum all the surfaces, including the furniture and the floor, with a high-efficiency particulate air filter vacuum cleaner. Clean all washable surfaces with a moisture wipe including the furniture, the walls, windows, and floor.
Turn on the compressor which circulates air through the allergen exposure chamber or AEC system and then turn on the floor and ceiling fans so that the incoming air is regularly mixed under turbulent conditions. Set the injection length and break between injections of the feeder control station to their maximum values to blow the allergen supply duct with clean air for 30 minutes. To check the contamination by the allergen, go to the main menu on the laser particulate counter and select configuration, followed by sample, zero cycles, one-minute delay.
Hold to one minute. Set sample to one minute and units to cubic meters. Again, go to the main menu and select configuration followed by particles, then select all options.
Turn on the compressor, which circulates air through the AEC, and adjust the temperature to 21 plus or minus 0.5 degrees Celsius on the temperature control system. Turn on the floor and ceiling swirl fans and the humidifier on the feeder control station. Set the knob air supply to the position between 40 to 100%to set the air change per hour to between 50 and 20.
Then control the relative humidity and carbon dioxide concentration during the trial by adjusting the air supply. After setting the laser particle counter to count the particles for one minute, go to the main menu and select configuration followed by particles. Take 5, 10, and 20 micrometers to set the value for the monitored particles in the range of zero to 20 micrometers.
Place the allergen in the feeder and set the injection length to 100 milliseconds and the break between injections to 1.5 minutes on the feeder control station. Before the participants enter the AEC, request them to put on disposable coveralls with a hood to guard against the infiltration of non-allergen particles and the potential contamination of clothing. Give them a containing all the necessary instrument disposable tips for use during the examination:a remote controller for the questionnaire, one pack of handkerchiefs and a biohazard plastic bag for nasal secretion.
Instruct the participants to place any used handkerchiefs in the plastic bag. Each participant would spend a total of 120 minutes inside the AEC. All the tests will be performed during this time.
For the participant's comfort, perform the tests individually in a room next to the AEC. For the symptoms survey, display the questions on the TV screen and ask the participants to self-assess before the challenge and every 30 minutes during the challenge by selecting the number on the remote that corresponds to the severity of each symptom. For the acoustic rhinometry, place the appropriate tip of the rhinometer head against the participant's nostril.
Check if it is tight. Ask the participants to hold their breath for three seconds and then start the program. Repeat for the other nostril with the appropriate tip.
Perform the acoustic rhinometry test three times before the challenge, 60 minutes after the challenge, and 120 minutes after the challenge. For the peak nasal inspiratory flow test, ask the participants to deflate their lungs deeply. Place the disposable inspiratory flow meter mask connected with the flow meter onto their face and then breathe in through the nose to the maximum.
For the peak expiratory flow rate, ask the participants to take in as deep a breath as possible. Put their lips around the peak flow matter disposable tip and exhale quickly and forcefully. For spirometry, put the disposable tip on the spirometer and then put on the nose plug.
Finally, instruct them to take a deep breath and a strong exhalation without unnecessary delay which can only be interrupted when the spirometer gives a signal. After the trial is over, instruct the participants to place the unused handkerchiefs in the same bag and collect all the bags. To determine the weight of nasal secretions, weigh used handkerchiefs in plastic bags and subtract the weight of the unused handkerchiefs and plastic bags from each measurement.
Check the measured data. And after each trial, download the data from the computer to an external drive and analyze it. The results of the stability of the environment in the AEC during the trial are shown in this figure.
The particle concentration was assessed and found to be in the range of zero to 20 micrometers by the laser particle counter. The target value for the concentration of house dust mites allergens was 5, 000 particles per cubic meter. For comparison, a trial where no allergen was used is shown.
The AEC environment was monitored throughout the operation time for humidity, carbon dioxide concentration, and temperature. The house dust might triggered allergy subjects with allergic rhinitis and healthy controls including eight and seven participants were exposed to house dust mite allergen concentrations of 5, 000 particles per cubic meter in the AEC. Nasal secretion weight, nasal symptoms, minimal cross-sectional area in acoustic rhinometry, peak nasal inspiratory flow, peak expiratory flow rate, and forced expiratory volume in the first second were evaluated and the results are presented as individual replicates with the mean value.
It is essential to provide stable and sufficiently high allergen concentrations throughout the whole trial in the allergen exposure chamber. The validation of allergen exposure chambers against other allergens, especially rare ones like cat, dog dander, molds, weeds, or similar, will enable assessment of other sensitizations in various subjects.
