Bronchoscopy and processing of samples
Bronchoscopy was performed six hours after both exposures using a flexible video bronchoscope (Olympus BF IT160, Tokyo, Japan). Endobronchial mucosal biopsies were taken either from the anterior aspect of the main carina and the subcarinae of the 3rd and 4th generation airways of the right side or from the posterior aspect of the main carina and the corresponding subcarinae on the left side. Bronchial wash (BW, 2 × 20 ml) and bronchoalveolar lavage (BAL, 3 × 60 ml) with saline were carried out on the contra-lateral side, in a pre-determined randomized way. The aspirates recovered from the first and second 20 ml instillations of the BW and the pooled BAL were collected into separate siliconized containers placed on ice. All lavage samples were filtered through a nylon filter (pore diameter 100 µm) and centrifuged at 400 g for 15 min. Cell pellets were re-suspended in PBS at a cell concentration of 10