Carbon loading in airway macrophages as a biomarker for individual exposure to particulate matter air pollution - A critical review

Exposure to particulate matter (PM) is associated with adverse health effects, including chronic lung diseases, lung cancer and cardiovascular disease. Personal exposure varies depending on the generation of particles locally, background levels, activity patterns and meteorology. Carbon loading in airway macrophages (AM) is a novel marker to assess personal exposure to combustion-derived particles. This review summarizes the published evidence and describes the validity and reliability of this marker with a focus on the technical aspects. Carbon loading in AM is reported in nine published studies assessing personal exposure to particulate air pollution. The carbon content is quantified by image analysis and is suggested to be suited to assess cumulative exposures. While there is some variation in study technique, these studies each indicate that internal AM carbon reflects either external exposure or important health effects. However, some uncertainty remains regarding potentially confounding materials within particles, the time frame of exposures that this technique reflects, and the optimal strategy to accurately quantify AM carbon. These aspects need to be clarified or optimized before applying this technique in larger populations.