Early effects of low-doses exposure to asbestos on local cellular immune responses in the lung.

We recently developed an animal model to study the pulmonary reactions after exposure to environmental pollutants. In this model, sheep received monthly intratracheal instillations of a suspension of varying amounts of chrysotile asbestos in saline. All animals were studied by pulmonary function tests, transbronchial biopsies, and bronchoalveolar lavage. During the 6 mo of the study, no changes were seen in the 2 former tests, but bronchoalveolar lavage yielded leukocytes that responded with enhanced proliferative activity to concanavalin A, pokeweed mitogen, and staphylococcal lysate. The response to phytohemagglutinin was poor but also enhanced in the asbestos-exposed animals. Enhanced responsiveness was dose-related, except for the highest dose used, 128 mg, which was associated with a less enhanced proliferative response or none. Our data suggest that the initial response to low-dose exposure to asbestos consists in a stimulation of lymphocyte function; the possibility that this phenomenon may be linked to the eventual fibrogenic response of asbestosis warrants further studies.