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).