Manganese dioxide induces alveolar macrophage chemotaxis for neutrophils in vitro

Workers exposed to airborne manganese dioxide (MnO2) may develop pneumonia resistant to chemotherapy. Previous animal experiments have demonstrated that exposure to airborne MnO2 induces an invasion of neutrophils into the airways 4-12 h after exposure. Experiments were undertaken to further study the role of alveolar macrophage (AM) in the development of this response. Guinea pig lung lavage fluid was centrifuged and washed, and cell suspension incubated on one side of a leukocyte migration chamber. MnO2 (2.5 mg/ml) was incubated with the cells for different time periods. Peritoneal neutrophils from guinea pigs were isolated and incubated on the other side of the chamber. Observations of the free lung cells demonstrated that phagocytosis of the MnO2 particles commenced immediately and was virtually completed within 30 min. Cells from control animals caused small directional migration across the filter. Cells which had phagocytosed MnO2 particles showed a significantly higher degree of neutrophil migration. The data suggest that pneumonia, in terms of neutrophil invasion into the lungs after MnO2 exposure, is associated with an activation of AM with subsequent release of neutrophil recruiting factor.