Results
Patients
Among 23 screened participants, 16 met the inclusion criteria and performed two consecutive EEC exposures. Eight patients who responded at Expo 2 were included in step 2 (Figure 1). Patient characteristics are given in Table 1. Roughly, sensitization to birch pollen was evidenced by the skin prick test wheal diameter of 7.4 ± 1.6 mm and specific IgE value of 61.3 ± 109.3 kUI/L for the total study population. Co-sensitizations were frequent, as only one patient was mono-sensitized to birch pollen. Approximately 90% of patients had concomitant rhinitis, and 43% presented with asthma according to GINA 1 classification.
Conjunctival outcomes during CAC and EEC exposures (step 1)
Among the 16 patients included in step 1, 12 presented a conjunctival response during allergen exposure in the EEC during Expo 1 or Expo 2. In the EEC, the mean TOSS was 5.7 ± 0.8 in Expo 1 and 5.5 ± 0.6 in Expo 2, whereas the mean TOSS during the CAC was 6.2 ± 1.1. No correlation was observed between the TOSS in the EEC versus CAC (r= 0.05). The maximal TOSS was 9 for both types of exposure (CAC and EEC). The mean time needed to obtain a positive conjunctival challenge was not significantly different between Expo 1 (81.2 ± 33.9 min) and Expo 2 (101.6 ± 57 min). During the CAC, positivity was obtained in 36 ± 15 min. The estimated quantity of Bet v 1 inducing a conjunctival response was 980 ng in the CAC and 0.07 ± 0.03 ng during Expo 1 and 0.07 ± 0.07 ng during Expo 2. This level was significantly lower with the EEC than the CAC (Table 2).
Reproducibility of EEC exposures (step 2)
The eight patients included in step 2 had identical characteristics to the whole cohort from step 1 (Table 1). One patient dropped out of the study before the last exposure and was not analyzed here. This patient left the EEC before reaching a positive TOSS due to an early asthma response. Among the seven remaining patients, all except one exhibited a positive conjunctival response to the entire course of six designed exposures (Expo 1 to Expo 6; Table 3). The clinical response was identical throughout the six exposures in terms of TOSS. Moreover, the time necessary to reach TOSS ≥ 5 was <2 hours for all exposures. The amount of Bet v 1 inducing a positive conjunctival response was similar in all six exposures. Reproducibility was studied regarding the time and quantity of allergen necessary for a positive challenge. Time exposition was highly reproducible (Table 3) with a Pearson correlation coefficient of 0.78 (p<0.05) between Expo 1 and Expo 4. As for the quantity of allergen inducing a positive response, reproducibility was also assessed between Expo 1 and Expo 4 with a Pearson correlation coefficient 0.81 (p= 0.028).