TGFB1 and chronic obstructive pulmonary disease: The levels of IL-6 increased after TGF-β stimulation in lung fibroblasts from control subjects at both normoxic (p = 0.018) and hypoxic (p = 0.0008) conditions, and in lung fibroblasts from COPD patients at both normoxic (p = 0.049) and hypoxic (p = 0.013) conditions (Fig. 4a).