Determinants of the proinflammatory action of ambient particulate matter in immortalized murine macrophages.

Background: Proximity to traffic-related pollution has been associated with poor respiratory health in adults and children.
Objectives: We wished to test the hypothesis that particulate matter (PM) from high-traffic sites would display an enhanced capacity to elicit inflammation.
Methods: We examined the inflammatory potential of coarse [2.5-10 µm in aerodynamic diameter (PM(2.5-10))] and fine [0.1-2.5 µm in aerodynamic diameter (PM(0.1-2.5))] PM collected from nine sites throughout Europe with contrasting traffic contributions. We incubated murine monocytic-macrophagic RAW264.7 cells with PM samples from these sites (20 or 60 µg/cm²) and quantified their capacity to stimulate the release of arachidonic acid (AA) or the production of interleukin-6 and tumor necrosis factor-α (TNFα) as measures of their inflammatory potential. Responses were then related to PM composition: metals, hydrocarbons, anions/cations, and endotoxin content.
Results: Inflammatory responses to ambient PM varied markedly on an equal mass basis, with PM(2.5-10) displaying the largest signals and contrasts among sites. Notably, we found no evidence of enhanced inflammatory potential at high-traffic sites and observed some of the largest responses at sites distant from traffic. Correlation analyses indicated that much of the sample-to-sample contrast in the proinflammatory response was related to the content of endotoxin and transition metals (especially iron and copper) in PM(2.5-10). Use of the metal chelator diethylene triamine pentaacetic acid inhibited AA release, whereas recombinant endotoxin-neutralizing protein partially inhibited TNFα production, demonstrating that different PM components triggered inflammatory responses through separate pathways.
Conclusions: We found no evidence that PM collected from sites in close proximity to traffic sources displayed enhanced proinflammatory activity in RAW264.7 cells.