Airway inflammation following exposure to diesel exhaust: a study of time kinetics using induced sputum

The adverse health effects of particulate matter pollution are of increasin g concern. In a recent bronchoscopic study in healthy volunteers, pronounce d airway inflammation was detected following exposure to diesel exhaust (DE ), The present study was conducted in order to evaluate the time kinetics o f the inflammatory response following exposure to DE using induced sputum f rom healthy volunteers. Fifteen healthy nonsmoking volunteers were exposed to DE particles,vith a 5 0% cut-off aerodynamic diameter of 10 mu m 300 mu g.m(-3) and air for 1 h o n two separate occasions. Sputum induction with hypertonic saline was perfo rmed 6 and 24 h after each exposure. Analyses of sputum differential cell c ounts and soluble protein concentrations were performed. Six hours after exposure to DE, a significant increase was found in the per centage of sputum neutrophils (37.7 versus 26.2% p=0.002) together with inc reases in the concentrations of interleukin-6 (12.0 versus 6.3 pg.mL(-1), p =0.006) and methylhistamine (0.11 versus 0.12 mu g.L-1, p=0.024). Irrespect ive of exposure, a significant increase was found in the percentage of sput um neutrophils at 24 as compared to 6 h. indicating that the procedure of s putum induction itself may change the composition of sputum. This study demonstrates that exposure to diesel exhaust induces inflammator y response in healthy human airways, represented by an early increase in in terleukin-6 and methylhistamine concentration and the percentage of neutrop hils. Induced sputum provides a safe tool for the investigation of the infl ammatory effects of diesel exhaust, but care must be taken when interpretin g results from repeated sputum inductions.