The values of the KLF5-immunopositive areas in the small airways of the COPD group were significantly correlated with those of forced expiratory volume in 1 s (FEV1) %predicted (r = −0.91, p < 0.01; Fig. 4a) and forced vital capacity (FVC) %predicted (r = −0.75, p < 0.01; Fig. 4b), but not with the diffusing capacity of the lung for carbon monoxide/alveolar volume (DLCO/VA) %predicted (Fig. 4c). This evidence concerns the gene KLF5 and chronic obstructive pulmonary disease.