Global warming is assumed to increase air temperature and the concentration of photochemical oxidants such as ozone (O
3) in atmosphere. Concurrent exposure to these factors during the summer may affect on human health. To determine the effects of high air temperature and O
3 on pulmonary antibacterial mechanisms and lung damage, BALB/cA mice were exposed to high temperatures (32°C, 35.5°C) for seven days followed by 0-0.5 ppm O
3 for 24 h in the inhalation chamber. Then bactericidal activity against Staphylococcus aureus (S. aureus) and Proteus mirabilis in the lung, as well as the number and profile of free pulmonary cells, total protein (TP) content and lactate dehydrogenase activity in bronchoalveolar lavage (BAL) fluid were assessed. Pulmonary bactericidal activity against S. aureus was significantly suppressed after exposure to 35.5°C or O
3 compared with the control (23°C and clean air). Bactericidal activity was suppressed more in the group exposed to O
3 with 35.5°C than in the groups exposed to either of the conditions alone. These findings indicated a synergistic effect of O
3 and 35.5 °C on pulmonary bactericidal activity. The synergistic effect was not evident in the group exposed to 32°C plus O
3. The numbers of alveolar macrophages (AMs) decreased at 35.5°C alone and at 35.5°C plus O
3 but the differences between these groups were not significant. Exposure to 0.5 ppm of O
3 with 35.5 °C seemed to worsen the pulmonary antibacterial defense mechanism compared with those groups exposed to 35.5°C or O
3 alone, but these findings did not always parallel the numbers of AMs in the BAL fluid.
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