Malignant mesothelioma is caused by exposure to asbestos, which is known to have 
carcinogenic effects. However, the development of mesothelioma takes a long 
period and results from a low or intermediate dose of exposure. These findings 
have motivated us to investigate the immunological effects of asbestos exposure 
and analyze immune functions of patients with mesothelioma and pleural plaque, a 
sign of exposure to asbestos. Here, we review our knowledge concerning natural 
killer (NK) cells and cytotoxic T lymphocytes (CTL). NK cells showed impaired 
cytotoxicity with altered expression of activating receptors upon exposure to 
asbestos, while induction of granzyme(+) cells in CD8(+) lymphocytes was 
suppressed by asbestos exposure. It is interesting that a decrease in NKp46, a 
representative activating receptor, is common between NK cells in PBMC culture 
with asbestos and those of mesothelioma patients. Moreover, it was observed that 
CD8(+) lymphocytes may be stimulated by some kind of "nonself" cells in 
plaque-positive individuals and in mesothelioma patients, whereas CTL in 
mesothelioma is impaired by poststimulation maintenance of cytotoxicity. These 
findings suggest that analysis of immunological parameters might contribute to 
the evaluation of health conditions of asbestos-exposed individuals and to a 
greater understanding of the pathology of malignant mesothelioma.