AIRWAYS OF ALLERGIC RHINITICS ARE PRIMED TO REPEATED ALLERGEN INHALATION CHALLENGE

The hypothesis that repeated exposure to a specific allergen will furt her increase bronchial responsiveness to that allergen is supported by indirect evidence. However, it has not been tested as intensely in th e laboratory setting, and in some cases, conflicting results are prese nted. In order to test the hypothesis in the atopic subjects, allergen inhalation challenge tests were performed in 29 house dust mite (Derm atophagoides pteronyssinus) sensitive subjects with allergic rhinitis. Nine subjects displayed early asthmatic responses (EARs) to the first challenge (Group I). Twenty subjects with no significant airway respo nse were submitted to the second challenge 24 h later. Thirteen subjec ts showed EARs (Group II) and two of these showed late asthmatic respo nses (LARs) as well. In Group II, there were significant changes betwe en the first and second challenge in post-allergen early phase FEV(1) (88.1 +/- 4.2 vs 71.7 +/- 4.2% baseline, P < 0.05) and in post-allerge n late phase FEV(1) (93.1 +/- 3.4 vs 86.6 +/- 7.8, P < 0.05). After th e second challenge, PD20 (provocative dose of methacholine required to produce a 20% fall in FEV(1)) decreased significantly from the baseli ne values. When challenged separately with twofold dose of allergen, o nly three and one of the Group II showed EAR and LAR respectively. PD2 0 did not change significantly after this challenge. These results ind icated that two repeated exposure to allergen dose, which is not enoug h to cause significant airway responses at a time, may provoke asthmat ic airway responses in the subjects with allergic rhinitis and that th is effect of priming is not attributed to the cumulative dose but to t he consequent effect of repeated allergen exposure.