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Demonstration of lysozyme by the immunoperoxidase method was used to determine whether ozone-induced defects in phagocytic killing of inhaled Staphylococcus aureus by rat alveolar macrophages were associated with absence of this important bactericidal enzyme. Rats were infected with aerosols of S. aureus and then exposed for 5 hr to 2.5 ppm of ozone. Left lungs were cultured for staphylococci; right lungs were stained for lysozyme and bacteria. Compared with control animals, rats exposed to ozone showed diminished rates of bacterial killing; a larger percentage of extracellular, uningested bacteria; an increased number of intracellular staphylococcal clumps; and absence of lysozyme in macrophages permitting staphylococcal proliferation. These results, in which absence of enzyme activity occurred in macrophages subjected to the dual insults of ozone exposure and ingested bacteria, provide an explanation for the inability of phagocytes to kill ingested bacteria after exposure to ozone.
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