Cigarette smoke triggers macrophage adhesion and activation: role of lipid peroxidation products and scavenger receptor

Pulmonary emphysema in chronic obstructive pulmonary disease (COPD) is characterized by the destruction of the alveolar walls leading to permanent enlargement of distal respiratory air spaces. A major causal factor is cigarette smoking, which produces conditions of chronic oxidative stress within the lungs. At a cellular level, increased macrophage accumulation and retention within the alveolar interstitial spaces is pivotal to the development of emphysema. To date it has been unclear as to the underlying mechanisms relating chronic oxidative stress to macrophage accumulation and retention. Our study was initiated to ascertain the role of modification of extracellular matrix proteins with cigarette smoke and products of lipid peroxidation on macrophage adhesion and activation. Increased numbers of macrophages were seen adhering to cigarette smoke-modified collagen IV as compared to unmodified collagen, where little or no adherent macrophages were observed. Similar observations were made when collagen was modified with either acrolein or 4-hydroxy-2-nonenal. Adhesion could be blocked with either fucoidan or a monoclonal antibody against the Type A macrophage scavenger receptor. Also, modified collagen triggered both oxidative burst and MCP-1 release in macrophages. These results, therefore, highlight a potential mechanism by which oxidative stress through the production of reactive carbonyls promotes macrophage accumulation, retention, and activation, independently of other proinflammatory stimuli. The implications of this for the development of emphysema in COPD are discussed.