Evaluating carbon content in airway macrophages as a biomarker of personal exposure to fine particulate matter and its acute respiratory effects

It remains unclear whether carbon content in airway macrophages (AM) can predict personal short-term exposure to fine particulate matter (PM2.5) air pollution and its respiratory health effects. We aimed to evaluate the pathway from personal PM2.5 exposure to adverse respiratory outcomes through AM carbon content. We designed a longitudinal panel study with 3 scheduled follow-ups among 113 non-smoking patients of chronic obstructive pulmonary disease in Shanghai, China, from April 2017 to January 2019. We quantified AM carbon content from induced sputum by image analysis, tested lung function and measured sputum levels of 4 pro-inflammatory cytokines and 2 anti-inflammatory cytokines. We applied the “meet in the middle” approach incorporating linear mixed-effect models to evaluate the associations from external PM2.5 exposure to respiratory outcomes through AM carbon content. Our results indicated that personal exposure to PM2.5 within 24 h was significantly associated with decreased forced expiratory volume in 1s and anti-inflammatory cytokines, as well as increased macrophages and pro-inflammatory cytokines. These changes were accompanied by increased areas of AM carbon and higher percentage of AM area occupied by carbon, both of which were associated with increased levels of pro-inflammatory cytokines and decreased levels of anti-inflammatory cytokines. Exposure to ambient black carbon and organic carbon in PM2.5 within 2 days was significantly associated with increased AM carbon area and percentage of AM area occupied by carbon. Our findings reinforced the causality in respiratory health effects of PM2.5 in which increased AM carbon content might serve as a valid exposure biomarker. •Acute PM2.5 exposure increases AM carbon content and leads to respiratory effects.•The percentage of carbon area in AM may be a better exposure biomarker of PM2.5.•This study reinforces the causality for the acute respiratory effects of PM2.5.