Ozone-induced inflammation is attenuated with multiday exposure

It is well known that ozone (O-3) causes acute lung inflammation. What is not known is whether there is progression of the inflammatory response in humans with repeated short-term exposures. Our study was designed to test the hypothesis that repeated exposures to a high-ambient concentration of O-3 (0.2 ppm) over several days would cause more inflammation than a single exposure. Fifteen healthy volunteers were exposed in random fashion to 0.2 ppm ozone for 4 h on a single day and to 0.2 ppm O-3 for 4 h on 4 consecutive days while exercising moderately for 30 min of each hour. Pulmonary function tests were obtained immediately before and after each 4-h exposure. Bronchoscopy was performed 20 h after the completion of each exposure arm to obtain bronchoalveolar lavage (BAL) for measurement of markers of inflammation. Our results show initial progression followed by attenuation of the acute physiologic response to O-3 with repeated daily exposures. We found a significant difference in percent change in FEV1, FVC, and specific airway resistance (SRaw) across the single-day exposure when compared with the change across Day 4 of the 4-d exposure. Bronchial fraction (the first 15 mi of BAL return) and BAL were analyzed for the following end points: total and differential cell counts, total protein, lactate dehydrogenase (LDH), fibronectin, interleukin-6 (IL-6), interleukin-8 (IL-8), and granulocyte-macrophage colony-stimulating factor (CM-CSF). In the bronchial fraction the number of polymorphonuclear cells (PMN)s and fibronectin concentration were significantly decreased after 4-d exposure compared with single-day exposure. In BAL, significant decreases in the number of PMNs, fibronectin, and IL-6 were found after 4-d exposure versus single-day exposure. These results suggest that there is attenuation of the O-3-induced inflammatory response in both proximal airways and distal lung with repeated daily exposures.