['Platelet-derived growth factor (PDGF) may have a significant role in airway remodeling in asthma, because it is a powerful inductor of many airway fibroblast activities such as collagen synthesis.', 'To determine whether PDGF is a significant contributor to airway remodeling in patients with asthma by enhancing airway fibroblast procollagen I expression.', 'Six normal controls without asthma, 10 subjects with mild to moderate asthma, and 5 subjects with severe asthma underwent bronchoscopy with endobronchial biopsy. Biopsies were placed in Dulbecco modified Eagle medium and fibroblasts cultured in the presence and absence of PDGF isoforms -AA, -BB, and -AB (1, 5, 10, 100 ng/mL) and insulin-like growth factor 1 (100 ng/mL). Fibroblast procollagen I and PDGF receptors (PDGFRs) alpha and beta expression were determined by ELISA.', 'Platelet-derived growth factor BB significantly enhanced fibroblast procollagen I expression in patients with severe asthma compared with patients with mild/moderate asthma and normal controls. Furthermore, the baseline fibroblast expression of PDGFR-beta was significantly greater in patients with severe asthma compared with the other groups.'] Do airway fibroblasts exhibit a synthetic phenotype in severe asthma?