CFTR is decreased in the lung of GOLD 4 COPD patients. (A) CFTR protein was detected in the lung of GOLD 0 (Control 1 and 2) and GOLD 4 (Patient 1 and 2) patients. Formalin fixed paraffin embedded lung tissue sections from GOLD 0 and GOLD 4 patients were immunostained using a specific CFTR antibody (red) (A) or non-immune control (B). (C) Intensity of CFTR signal was scored as described in the Methods section. (D) The CFTR mRNA level was measured by quantitative RT-PCR and expressed as Relative Copy Number (RCN). N = 7 for number of patients GOLD 0 and N = 8 for number of patients COPD GOLD 4. Statistically significant differences were assessed using Mann–Whitney U test.