CCL2 and chronic obstructive pulmonary disease: Alveolar macrophages are likely to be a key driver of elevated leukocyte recruitment to the lungs during COPD, with COPD sputum and bronchi-alveolar lavage (BAL) containing elevated levels of CXCL-8 (93), LTB4, growth-related oncogene (GRO) alpha (94, 95), and MCP-1 (96), amongst other inflammatory agents.