Asbestos exposure causes asbestosis and malignant mesothelioma, disorders which 
remain difficult to cure. We focused on alveolar macrophages (AM) and natural 
killer (NK) cells in asbestosis and mesothelioma, respectively, and examined 
their functions upon exposure to asbestos or in patients with mesothelioma. 
Exposure to asbestos caused rat AM to exhibit high production of transforming 
growth factor-beta (TGF-β) with prolonged survival in the absence of other 
cells, not simultaneously with the apoptosis caused by asbestos. The NK cell 
line showed impaired cytotoxicity with altered expression of activating 
receptors upon exposure to asbestos, and primary NK cells in culture with 
asbestos and peripheral blood NK cells in mesothelioma shared a decrease in 
expression of NKp46, a representative activating receptor. The AM finding 
indicates that AM contribute to asbestosis by playing a direct role in the 
fibrogenic response, as well as the inflammatory response. The response of NK 
cells indicates that exposure to asbestos has an immune-suppressive effect, as 
well as a tumorigenic effect. Our studies therefore reveal novel effects of 
asbestos exposure on AM and tumor immunity, which may represent valuable 
information for construction of a strategy for prevention and cure of asbestosis 
and malignant mesothelioma.