CCL2 and chronic obstructive pulmonary disease: The CCR2 ligand CCL2, produced by bronchial epithelial cells, is increased in the sputum of chronic obstructive pulmonary disease (COPD) patients [17] and recent data in CCL2 knock‐out mice supports an important role of the CCL2‐CCR2 axis in the development of lung emphysema [18].