Increased production of TGF-β1 from sputum cells of COPD: Relationship with airway obstruction
Chronic obstructive pulmonary disease (COPD) is a chronic airway disease characterized by a profound airway remodelling that leads to airway obstruction. A role for transforming growth factor-β1 (TGF-β1) has been proposed in airway remodelling of COPD. Regarding the TGF-β1 production at local level, the results seemed to be controversial. In this study, an original model of sputum cell culture thought to maintain important cells interactions, was used.
We investigated the production of TGF-β1 from sputum cell culture in 33 COPD encompassing the whole severity spectrum and compared the results with those found in 39 healthy controls. Sputum was induced by inhalation of saline, the cellular fraction cultured for 24 h and the spontaneous production of total TGF-β1 was assessed by ELISA. Using, a TGF-β1 reporter cell assay, we also compared the levels of active and total TGF-β1 in the sputum cell culture supernatants of COPD and controls. Moreover, as a combination of tumor necrosis factor-α (TNF-α) and TGF-β1 have been shown to have a cumulative impact on the severity of airflow limitation in COPD, the TNF-α release was also measured in a representative subgroup of patients.
Our results indicated that the use of sputum cell culture was a reliable and reproducible method to assess TGF-β1 production at airway level. Sputum cells from COPD produced greater amount of total TGF-β1 than those of healthy controls (p < 0.001). This result was confirmed using the cell reporter assay which also showed a higher level of active TGF-β1 in the COPD group compared to controls. In addition, total TGF-β1 production was increased according to GOLD stage and was inversely related to FEV1/FVC ratio (p < 0.05). By contrast, the production of this growth factor was not correlated with the functional markers of emphysema nor with demographic characteristics such as age, BMI or smoking status. Interestingly, the production of total TGF-β1 was inversely related to that of TNF-α (r = −0.53, p < 0.05) which was decreased in COPD. In summary, COPD patients displayed a raised production of total and active TGF-β1 from their airway cells. Total TGF-β1 correlates with the severity of airway obstruction without evidence of a link with emphysema.