Environmental exposure chamber effectively assesses birch allergy

Use of environmental exposure chambers to test for conjunctivitis response from birch appeared to be closer to natural exposure vs. use of conjunctival allergen challenge, according to data published in Clinical and Translational Allergy.

“Environmental exposure chambers (EECs) have been in development since 1985 to study new therapeutics for allergic pathologies, including conjunctivitis,” Alina Gherasim, MD, of the ALYATEC Environmental Exposure Chamber in France, and colleagues wrote. “EECs have the advantage of achieving reproducible and safe exposure with controlled levels of allergen for several hours in several subjects simultaneously by avoiding confounding factors during exposure.”

Gherasim and colleagues noted that the ALYATEC EEC was previously validated for mite- and cat-induced allergic asthma. This study was designed to validate its use for birch pollen among patients affected by seasonal allergic conjunctivitis.

They added that, in France, the prevalence of seasonal allergic rhinoconjunctivitis is 13% among 10-year-old children and approximately 20% among adults, with birch being one of the most frequent sources, at 4.7% for the general adult population.

The study comprised 16 patients (mean age, 26.4 years; 62.5% male) who had a positive conjunctival allergen challenge (CAC) and consisted of two steps. The first step included two initial EEC exposures to the same birch pollen extract (Bet v 1) over consecutive days. The second step included two additional consecutive exposures for patients who responded during the first step, followed by two more exposures to test for reproducibility. Each pair of EEC exposures in the second step was separated by 14 days.

Among the 16 patients enrolled, eight patients had a conjunctival response to EEC based on a Total Ocular Symptom Score (TOSS) of 5 or higher during the first exposure (mean TOSS = 5.7 ± 0.8). Twelve patients had a positive conjunctival response during the second exposure (mean TOSS = 5.5 ± 0.6).

In comparison, the mean TOSS after CAC was 6.2 ± 1.1, indicating there was no correlation between the TOSS after use of EEC compared with CAC (r = .05).

The maximal TOSS was higher after CAC than EEC (9 vs. 7), and mean time to obtain a positive conjunctival challenge was shorter after CAC (35 ± 15 minutes) compared with the two EEC exposures (first exposure, 81.2 ± 33.9 minutes; second exposure, 101.6 ± 57 minutes).

The estimated quantity of Bet v 1 that induced a conjunctival positive score was significantly lower with EEC, at 0.07 ± 0.03 ng during the first exposure and 0.07 ± 0.07 ng during the second, compared with 980 ng in the CAC (P < .001).

One of the eight patients with a response during the first step dropped out of the study. Among the seven remaining patients, all except one exhibited a conjunctival positive scoring to all six exposures.

Researchers also studied reproducibility based on time and quantity of allergen necessary for a positive challenge and found time of exposure was highly reproducible with a Pearson correlation coefficient of 0.78 (P < .05) between the second and fourth exposure. The quantity of allergen needed to induce a positive response also was highly reproducible between the second and fourth exposures, with a Pearson correlation coefficient of 0.81 (P = .028).

The researchers noted the limitation of a small study population, but highlighted the high reproducibility estimates.

“The estimation of the amount of allergen deposition on the ocular surface could be discussed, but the calculation took into account the different physiological factors involved in the pathophysiology of conjunctivitis,” they wrote. “Nevertheless, one can suggest that EEC exposures is closer to natural exposure than the CAC exposure.”