Inflammatory responses in the lungs of rats exposed to amosite asbestos

Studies with a long fibre sample of amosite asbestos demonstrated its deposition in the terminal bronchi and alveolar ducts and its phagocytosis by macrophages. Rats inhaling UICC amosite asbestos showed accumulation of inflammatory leukocytes and evidence of toxicity, indicated by increased levels of the cytoplasmic enzyme lactate dehydrogenase, in the bronchoalveolar region. We believe this inflammatory response to be due to long fibres present in the UICC amosite. We investigated possible consequences of these events for the inflammatory response by assessing the ability of two amosite samples, one long fibre and one short fibre, to induce release of the proinflammatory cytokine, tumour necrosis factor (TNF) from alveolar macrophages in vitro. The long fibre preparation was much more active in causing the release of TNF. Furthermore, 1 mg of the long fibre sample, instilled into rat lungs, produced marked cell proliferation leading to severe fibrosis at 1 month. The short fibre sample, by contrast, produced lung inflammation but little cell proliferation or fibrosis.