2.2. Bronchoscopy and Bronchoalveolar Lavage

Guidelines for bronchoscopy and alveolar lavage were reviewed in previous literatures [16, 17]. We followed the methods described in our recent publication [18]. Children with MPP were subjected to BALF collection within 1 week after admission. For children with FB, the foreign body was removed by bronchoscopy immediately after admission, and BALF specimens were collected during the reexamination of bronchial FB. Lavage was performed with sterile saline solution. BALF was then centrifuged at 1000× g at 4°C for 5 min within 1 h of collection; the supernatant was stored at -20°C, while the precipitate was resuspended in Trizol reagent (Invitrogen, Carlsbad, USA) and stored at -80°C.