Sputum levels of transforming growth factor-beta1 in asthma: relation to clinical and computed tomography findings

BACKGROUND: Transforming growth factor (TGF) beta1 is considered to play central roles in the pathogenesis of airway remodeling in asthma. This notion is based primarily on the results of experimental studies; clinical evidence is limited. OBJECTIVES: To ascertain the involvement of TGF-beta1 in asthma. METHODS: We studied 27 patients with moderate-to-severe, but stable, asthma treated with inhaled corticosteroids and 8 healthy controls. Helical computed tomography scans were acquired at full inspiration. Airway wall thickness (WT) was assessed on the basis of wall area corrected for body surface area (WA/BSA) and absolute WT corrected for BSA (WT/square root of BSA) according to a validated method. Induced sputum concentrations of TGF-beta1 were measured by enzyme-linked immunosorbent assay. Pulmonary function was evaluated. RESULTS: Indices of expiratory airflow were significantly lower in the asthmatic patients than in the controls. WA/BSA, WT/square root of square root of BSA, and sputum concentrations of TGF-beta1 were significantly higher in the asthmatic patients. Sputum TGF-beta1 concentrations correlated positively with WA/BSA and WT/square root of BSA and negatively with forced expiratory volume in 1 second in both asthmatic and control subjects. CONCLUSIONS: Levels of TGF-beta1 in induced sputum are elevated in asthmatic patients despite treatment with inhaled corticosteroids and are associated with airflow obstruction and airway wall thickening. TGF-beta1 is involved in the pathogenesis of airway remodeling and resultant functional impairment and it may be a target for specific medical treatment.