Passive sensitization
Isolated airways were rotated overnight at room temperature in tubes containing KH buffer solution in the presence of 10% vol-1 sensitizing serum (passively sensitized bronchi) or 10% vol-1 non-sensitizing serum (non-sensitized bronchi). Sensitizing and non-sensitizing sera were prepared by centrifugation from the whole blood. Sensitizing serum was obtained from a patient suffering from severe atopic asthma (total IgE 1,000 U ml-1 specific against common aeroallergens), whereas non-sensitizing serum was obtained from a non-atopic donor (total IgE 45 U ml-1). The serum from the non-atopic donor was used as a negative control (C-). The subjects provided signed consent for serum donation. Sera were frozen at -80°C in 250 µl aliquots until required. The next morning bronchial tissues were transferred into the isolated organ bath system containing KH buffer solution (37°C) and continuously gassed with O2/CO2(95:5%). The passive sensitization is a model that closely mimics important functional characteristics of AHR in asthmatic patients, as previously reported (Schaafsma et al., 2006; Schmidt et al., 1999).