Impairment in Cytotoxicity and Expression of NK Cell- Activating Receptors on Human NK Cells following Exposure to Asbestos Fibers

Asbestos is well-known for its tumorigenic activity, but its effect on anti-tumor immunity remains unclear. Therefore, we prepared a sub-line of YT-A1 human NK cells exposed to chrysotile B (CB) asbestos (YT-CB5) as an in vitromodel to analyze the effect of asbestos exposure on NK cells, and examined cytotoxicity and expressions of its related molecules. The cytotoxicity of YT-CB5 against K562 cells decreased compared with the original line of YT-A1 (YT-Org). YT-CB5 exhibited significant decreases in expressions of cell surface NKG2D, 2B4 and intracellular granzyme A. YT-CB5 also exhibited a decrease in the 2B4-dependent cytotoxicity. In addition, the degranulations stimulated via cell surface NKG2D and 2B4 also decreased in YT-CB5. Therefore, peripheral blood NK cells in patients with malignant mesothelioma (MM) were examined and compared with healthy volunteers. NK cells in patients with MM also showed decreases in cytotoxicity against K562. Although the expressions of NKG2D and 2B4 did not decrease in NK cells of MM patients, the expression of cell surface NKp46 decreased. To confirm the effect of asbestos exposure on peripheral blood NK cells, PBMCs were cultured under exposure to CB. NK cells in PBMCs exposed to CB in vitroshowed a significant decrease in the expression of NKp46, whereas NK cells in PBMCs exposed to glass wool did not show such a decrease. These results indicate that exposure to asbestos has the potential to impair the cytotoxicity of NK cells and alter the expression of NK cell-activating receptors including NKG2D, 2B4 and NKp46 and intracellular perforin/granzymes.