Impairment of Microbial Killing and Superoxide-Producing Activities of Alveolar Macrophages by a Low Level of Ozone

Abstract

Male Wistar rats were exposed to 0.2 ppm ozone for up to 14 days, during which alveolar macrophages were collected by pulmonary lavage to assess the effect of ozone on their microbial killing and superoxide-producing activities. For rapid assessment of microbial killing activity, we measured the release of ³H-radioactivity into the supernatant by deoxycholate-lysis of the macrophages that had phagosytosed and killed ³H-uridine-labeled microbes. The killing activity against Escherichia coli and Candida albicans was reduced to 70-80% of control levels on day 3. However, phagocytosis by and the activity of lysosomal enzymes of the macrophages were not impaired. On day 14 the killing activity against E. coli had returned to control levels, whereas that against C. albicans was still reduced. Because active oxygen species plays an important role in microbial killing activity of macrophages, the effects of ozone on respiratory burst and superoxide production were examined. Aliquots of alveolar macrophages were stimulated with phorbol myristate acetate (PMA), opsonized zymosan, or lipopolysaccharide (LPS) plus cytochalasin E (Cyt.E). The respiratory burst, oxygen consumption for rapid superoxide production, was decreased to 60-80% of control levels on day 3. On day 14, the respiratory burst by opsonized zymosan was still 80% reduced, whereas that by PMA or LPS plus Cyt. E had returned to control levels. In addition, the superoxide-producing activity of ozone-exposed macrophages was 10-60% decreased on day 3. On day 14, the superoxide production by stimulation with opsonized zymosan was still 60% reduced, whereas that by PMA or LPS plus Cyt. E had returned to control levels. In conclusion, because of their decreased production of superoxide, the host defense activity of alveolar macrophages was impaired by in vivo exposure to 0.2 ppm ozone. In particular, the C. albicans-associated defect lasted throughout the exposure period.