Alveolar macrophage-stimulated neutrophil and monocyte migration: effects of in vitro ozone exposure

The ability of rabbit alveolar macrophages (AM) to release factors which stimulate the migration of peripheral blood neutrophils and monocytes was examined, and the influence of in vitro ozone exposure on this secretory activity was investigated. To evaluate the ability of AM to release leukocyte chemotactic activity, AM obtained by bronchoalveolar lavage were established in monolayer or suspension culture, with and without added zymosan, for 2 and 6 hr. The resulting macrophage-conditioned medium was tested for chemotactic activity using modified Boyden-type chambers and rabbit peripheral blood neutrophils or monocytes as the responding cells. The results demonstrate that substrate attachment (monolayer culture) and/or zymosan phagocytosis can stimulate AM to release chemoattractants for monocytes and neutrophils. Additionally, the results suggest that AM are constitutively producing low levels of monocyte chemotactic factors. The effects of in vitro ozone exposure on the secretion of chemotactic activity was investigated by exposing monolayer cultures of AM to air, 0.1, 0.3, or 1.2 ppm ozone for 2 hr. Macrophage-conditioned medium was harvested immediately, 2 and 6 hr postexposure, and tested for chemotactic activity. Exposure to 0.3 and 1.2 ppm ozone significantly increased the AM secretion of factors which stimulated neutrophil migration; additionally, the results strongly suggest that ozone can augment the ability of AM to stimulate monocyte migration. These results imply a role for the AM in the recruitment of inflammatory cells after ozone inhalation.