Fig. 5

The COPD etiology is depicted in the diagram. In addition to activating epithelial cells, cigarette smoke and other environmental stimuli can also recruit neutrophils and macrophages from the bloodstream, which release a variety of chemotactic signals that recruit inflammatory cells to the lung. For instance, the CXC-chemokine receptor (CXCR) 2 is used by CXCL1 and CXCL8 to recruit neutrophils and monocytes. CD+ 8T cells can be recruited by CXCL 9, 10, and 11. The MMPs (2, 9, and 12), elastase, and Cathepsin K, L, and S that are involved in lung fibrosis and emphysema are also secreted by activated lung epithelial cells