Carbon load in airway macrophages, a biomarker for traffic related air pollution. Repeated measurements over one year.

Abstract

Introduction Carbon load in airway macrophages (AM) has been proposed as a biomarker of past long-term individual exposure to traffic-derived particulate matter (PM) air pollution. However, the repeatability of this measurement has not been formally assessed. This work was designed to study the kinetics of AM carbon over one year follow-up. Methods In 14 healthy non-smokers (aged 28 ± 5.7 years), having resided in Belgium for at least one year, we performed sputum induction to retrieve AM every 6 weeks and up to 8 times. Spirometry and blood and urine samples were also obtained. Carbon load was quantified by assessing the median area (µm2) occupied by black inclusions in 25 AM, using light microscopy and ImageJ. Average residential PM2.5 values were estimated for lags of 1 week, 1 month, 3 months, 6 months, and one year, based on interpolated levels of PM2.5 for each home address. The association of the median carbon content with previous PM2.5 levels and country of origin was calculated using mixed regression models. Results AM carbon was measured in 105 samples (94%). The mean (±SD) carbon content for 8 successive measurements amounted to 0.32 (±0.24), 0.29 (±0.25), 0.30 (±0.23), 0.26 (±0.19), 0.39 (±0.24), 0.37 (±0.22), 0.38 (±0.32), and 0.32 (±0.24) µm2. Daily PM2.5 values ranged from 2.8 to 70.8 µg/m3, with the highest median levels observed over one year lag (13 µg/m3; IQR=0.4). The individual median AM carbon was not associated with residential PM2.5. However, the median carbon load in the immigrants (n=7) was 0.26 µm2 higher (95% CI: 0.06-0.46) than in the locals (n=7). Conclusions Measurements of carbon load in AM proved to be stable over one year regardless of variations in air pollution. The unexpectedly large difference of carbon load between immigrants and locals suggests that AM carbon load reflects an exposure window even longer than one year.