Asbestos Fiber and Immunological Effects: Do Immunological Effects Play Any Role in Asbestos-Related Diseases?

The immune system functions to eliminate abnormal cells that may arise for a variety of reasons. This process can help prevent tumor formation and is referred to as anti-tumor immunity. Inhaled asbestos fibers can accumulate in the non-lymphoid organ of the lungs as well as draining lymph nodes, exposing immune cells to the inhaled asbestos and thereby triggering potential immunological effects. On the basis of that idea, we have been investigating various kinds of asbestos exposure-mediated functional alterations in natural killer (NK), CD4+ T helper (Th), CD8+ cytotoxic T lymphocyte (CTL), and macrophage cells by in vitro experiments. The findings obtained indicate that exposure to asbestos causes decreased cytotoxicity of NK and CTL cells and decreased expression of cell surface activating receptors (NKp46, NKG2D), intracellular perforin levels, and IFN- γ production. Furthermore, an enhanced immune-suppressive role of Th (regulatory T (Treg)) cell function results, with increases in cell surface CTLA-4, and increased production of IL-10 and TGF-β cells as well as fibrogenic/immune-suppressive macrophages with high and lasting production of TGF-β. Interestingly, patients with malignant mesothelioma also show similar characteristics with respect to findings relating to peripheral blood mononuclear cells. Taken together, those data suggest that asbestos fibers elicit immune-suppressive potential, which might contribute to immune escape of abnormal mesothelial cells arising transiently, and promote the development of malignant mesothelioma in people exposed to asbestos. Continued investigations of these events may facilitate the development of early intervention strategies from an immunological perspective to mitigate the development of mesothelioma.