Allergen-induced changes in airway responsiveness are not related to indices of airway edema

Background: The mechanisms behind airway hyperresponsiveness in asthma are unknown, Airway wall edema has been proposed as one possible culprit of thi s phenomenon. Objective: To test the hypothesis that airway edema may be the cause of all ergen-induced increases in airway responsiveness in asthma, this trial aime d at determining the relationship between allergen-induced changes in airwa y responsiveness to inhaled methacholine and indirect indices of edema, nam ely peripheral airway resistance and the levels of the plasma protein fibri nogen in bronchoalveolar lavage (BAL) fluids. Methods: Twenty-six atopic individuals with mild asthma were subjected to b ronchoscopy at baseline and 28 hours after allergen inhalation, Before each bronchoscopy, methacholine bronchoprovocation was performed. During bronch oscopy, peripheral airway resistance measurements were obtained by wedged b ronchoscopy, BAL fluids were analyzed for fibrinogen, as well as for eosino philic cationic protein. Cytology was performed, and cytokine gene expressi on was assessed with competitive reverse transcriptase PCR from cell pellet s. Results: A significant increase in airway responsiveness to methacholine wa s recorded after allergen, but this did not correlate with changes in perip heral airway resistance (which was not affected) or with BAL fibrinogen (wh ich decreased after allergen), Other BAL outcomes confirmed that airway inf lammation was produced and was characterized by a T(H)2 cytokine pattern. Conclusions: Airway responsiveness in asthma increases after exposure to al lergen in the absence of increased indirect indices of edema. The role of e dema in this phenomenon should therefore be tested more vigorously.