Background: Bronchiolitis obliterans syndrome(BOS)often develops in transplant patients and results in injury to the respiratory and terminal airway epithelium.Owing to its rising incidence,the pathogenesis of BOS is currently an area of intensive research.Studies have shown that injury to the respiratory epithelium results in dysregulation of epithelial repair.Airway epithelial regeneration is supported by stromal cells,including fibroblasts.This study aimed to investigate whether the supportive role of lung fibroblasts is altered in BOS.Methods: Lung progenitor cells(LPCs)were separated by fluorescence-activated cell sorting.Lung fibroblasts from patients with BOS or healthy controls were mixed with sorted mouse LPCs to compare the colony-forming efficiency of LPCs.Statistical analyses were performed using the SPSS 17.0 software(SPSS Inc.,USA).The paired Students t test was used to test for statistical significance.Results: The colony-forming efficiency of LPCs was significantly reduced when co-cultured with fibroblasts isolated from patients with BOS.The addition of SB431542 increasedthe colony-forming efficiency of LPCs to1.8%; however,it was still significantly less than that in co-culture with healthy control fibroblasts.Conclusions:The preliminary data indicate that the epithelial-supportive capacity of fibroblasts is impaired in the development of BOS and suggest that inefficient repair of airway epithelium could contribute to persistent airway inflammation in BOS.