Suppression and Recovery of the Alveolar Macrophage Phagocytic System during Continuous Exposure to 0.5 ppm Ozone

Abstract

Short-term exposures to ozone (O₃) are known to impair pulmonary antibacterial defenses and alveolar macrophage (AM) phagocytosis in a dose-related manner. To determine the effect of prolonged O₃ exposure, Swiss mice were exposed continuously to 0.5 ppm O₃. At 1, 3, 7, and 14 days, intrapulmonary killing was assessed by inhalation challenge with Straphylococcus aureus or Proteus mirabilis and by comparing the number of viable bacteria remaining in the lungs at 4 h between O₃-exposed and control animals. To evaluate the effects of O₃ on the functional capacity of the AMs, Fc-receptor mediated phagocytosis was assessed. Ozone exposure impaired the intrapulmonary killing of S. aureus at 1 and 3 days; however, with prolonged exposure, the bactericidal capacity of the lungs returned to normal. This trend of an initial suppression followed by recovery was reflected in the phagocytic capacity of the AMs. In contrast to S. aureus, when P. mirabilis was used as the challenge organism, O₃ exposure had no suppressive effect on pulmonary bactericidal activity, which correlated with an increase in the phagocytic cell population in the lungs. Morphologic examination of the lavaged macrophages showed that after 1 day of O₃ exposure, the AMs were more foamy, and contained significantly more vacuoles. There was also a significant increase in binucleated cells at 3 days. These studies demonstrate that continuous exposure to O₃ modulates AM-dependent lung defenses and points to the importance of the challenge organism and exposure protocol in establishing the adverse effect of O₃.