Exposure to particulate air pollution is associated with an increased risk of cardiovascular disease. The mechanism by which exposure increases risk is poorly understood but could involve changes in the flow properties of blood.OBJECTIVE: The aim of this investigation was to assess the effect, in rats, of intratracheal instillation of particulate air pollution on leukocyte flow properties by measurement of polymorphonucleocyte (PMN) and monocyte actin polymerisation.METHODS: Rats were exposed to particulate air pollution by intratracheal instillation of PM10. Blood was collected from test and control animals at 3 days (n=10) and 6 weeks (n=10) after dust instillation. Partial differential leukocyte counts were performed. The intracellular F-actin content of blood PMNs and monocytes was determined by staining with FITC-phalloidin and flow cytometric determination of mean florescence intensity (MFI).RESULTS: There were no significant changes in PMN MFI (p=0.369, ANOVA) or cell counts (p=0.753, ANOVA). There was a significant increase in monocyte MFI (p=0.004, ANOVA) and a decrease in monocyte cell count (p=0.003, ANOVA) in instilled rats.CONCLUSIONS: Intratracheal instillation of air pollution particles resulted in an increase in blood monocyte actin polymerisation, which may cause trapping of monocytes. This could be a mechanism by which exposure to air pollution increases the risk of cardiovascular disease.