Background Knowledge of the inhalable particulate matter components responsible for health effects is important for developing targeted regulation.

Objectives In a double-blind randomised cross-over trial of controlled human exposures to concentrated ambient particles (CAPs) and their endotoxin and (1→3)-β-D-glucan components, we evaluated acute inflammatory responses.

Methods 35 healthy adults were exposed to five 130-min exposures at rest: (1) fine CAPs (∼250 µg/m³); (2) coarse CAPs (∼200 µg/m³); (3) second coarse CAPs (∼200 µg/m³); (4) filtered air; and (5) medical air. Induced sputum cell counts were measured at screening and 24 h postexposure. Venous blood total leucocytes, neutrophils, interleukin-6 and high-sensitivity C reactive protein (CRP) were measured pre-exposure, 3 and 24 h postexposure.

Results Relative to filtered air, an increase in blood leucocytes 24 h (but not 3 h) postexposure was significantly associated with coarse (estimate=0.44×10⁹ cells/L (95% CI 0.01 to 0.88); n=132) and fine CAPs (0.68×10⁹ cells /L (95% CI 0.19 to 1.17); n=132), but not medical air. Similar associations were found with neutrophil responses. An interquartile increase in endotoxin (5.4 ng/m³) was significantly associated with increased blood leucocytes 3 h postexposure (0.27×10⁹ cells/L (95% CI 0.03 to 0.51); n=98) and 24 h postexposure (0.37×10⁹ cells/L (95% CI 0.12 to 0.63); n=98). This endotoxin effect did not differ by particle size. There were no associations with glucan concentrations or interleukin-6, CRP or sputum responses.

Conclusions In healthy adults, controlled coarse and fine ambient particle exposures independently induced acute systemic inflammatory responses. Endotoxin contributes to the inflammatory role of particle air pollution.