Asbestos-induced lung inflammation. Role of local macrophage-derived chemotactic factors in accumulation of neutrophils in the lungs.

In a recently developed sheep model of progressive low-dose pulmonary exposure to asbestos, initial alveolar lymphocyte and macrophage activation was followed by pulmonary neutrophilia in higher-dose exposed animals. This was observed after 18 months of exposure to intratracheal instillations of asbestos fibers and coincided with progressive alveolitis and decreased lung compliance. Alveolar macrophages from those animals were found to produce a chemotactic factor which attracted in vitro peripheral blood neutrophils. It attracted neutrophils more efficiently from higher-exposure than lower-exposure animals. Supernatants of control macrophages exposed to asbestos in vitro were also chemotactic for PMN. Similarly, bronchoalveolar lavage fluids from the animals showed chemotactic activity for peripheral blood neutrophils. It is suggested that chronic exposure to asbestos activates alveolar macrophages to produce chemotactic factors which in turn attract neutrophils from the vascular compartment and may thus contribute to the inflammatory process in asbestosis.