Abstract
BACKGROUND: Chronic obstructive pulmonary disease (COPD) is characterized by recurrent exacerbations. Macrophages play a critical role in immune response and tissue repair in COPD. Airway macrophages (AM) are exposed to environmental exposures which are retained in the cytoplasmic material. Both biomass and particulate matter have been linked to higher AM black carbon. It is unknown if AM black carbon is associated with COPD morbidity and macrophage phenotype. METHODS: Former smokers with COPD were enrolled and sputum induction was performed to obtain airway macrophages. Macrophages underwent black carbon quantification and flow cytometry phenotyping. Health information was obtained the same day as sputum induction and prospective exacerbations were assessed by monthly telephone calls. RESULTS: We studied 30 former smokers with COPD who had a mean age of 67 years and mean forced expiratory volume in 1 second (FEV(1))% predicted of 60.8%. Higher AM black carbon content was associated with increased total exacerbations and severe exacerbations and reduced CD80 expression. CONCLUSION: AM black carbon association with respiratory morbidity is largely unexplored and this is the first study to identify association with prospective exacerbations. Macrophages expressed reduced CD80, a surface marker providing costimulatory signals required for development of antigen-specific immune responses. Our findings suggest that reduced CD80 expression is the pathophysiologic mechanism for the association of AM black carbon content and increased exacerbations. Therefore, beyond solely serving as a marker for increased exposures, AM black carbon content may be a predictor of future exacerbations given a macrophage less equipped to respond to an acute infectious exposure.