RANKL was also more obviously detected in the cytoplasm of cells within the small airways, bronchiolar walls, and the lung parenchyma in COPD group compared with never-smoker group or smoker group (Figures 2D–F), and a similar pattern was observed for RANK expression (Figures 2G–I). This evidence concerns the gene TNFRSF11A and chronic obstructive pulmonary disease.