Role of lysozyme in the microbicidal activity of rat alveolar macrophages.

Lysozyme release from alveolar macrophages is stimulated by exposure to particles, such as latex and zymosan, and to bacteria. Rat alveolar marcophages contain 10-fold-greater intracellualr concentrations of lysozyme and release more lysozyme after stimulation than rat blood neutrophils. During 30 min of incubation in vitro, alveolar macrophages kill more than 99% of Micrococcus lysodeikticus in the incubation mixture, whereas neutrophils kill approximately 50% of the bacteria. The bactericidal capacity of alveolar macrophages for M. lysodeikticus exceeds that of neutrophils at all bacteria-to-cell ratios tested. This bacterial killing by alveolar macrophages is inhibited when specific rabbit antirat lysozyme serum is added to the incubation mixture. Electron microscopy studies indicate that bacterial killing occurs extracellularly. Initial degradation of bacteria occurs within 5 min, and lysis is complete by 25 to 30 min. Phagocytosis of lysed bacteria is maximum after 25 to 30 min. The greater quantities of lysozyme, both intracellularly and released into the extracellular environment by alveolar macrophages, suggest that this factor may be a mechanism by which alveolar macrophages contribute to pulmonary defense.