Mesothelioma May be Triggered by Suppressed ‘Natural Killer’ Cells

A group of Japanese scientists are offering some new insights into the mechanism by which the toxic mineral asbestos may trigger mesothelioma.

For decades asbestos has been linked to malignant mesothelioma, a fast-growing cancer of the mesothelial lining around the lungs and internal organs. But only in recent years have researchers begun to understand the complex physiological responses that give rise to the disease. Because mesothelioma can take 30 years or more to develop symptoms, some scientists have concluded that there is more at work in mesothelioma than the ‘tumorigenicity’ (cancer-inducing properties) of asbestos.

Now, researchers from the Kawasaki Medical School in Japan have shown that, in addition to causing cellular inflammation, asbestos may also effectively ‘turn off’ the body’s natural killer (NK) cells, leaving people more prone to developing cancer.

Normally, NK cells serve as a natural cancer-defense mechanism, seeking out and destroying pre-cancerous cells before they can do damage. But in a new study published in the International Journal of Immunopathology and Pharmacology, the researchers report the damaging effects of chrysotile asbestos on NK cells in both mesothelioma patients and healthy people.

When healthy cells were exposed to asbestos in the lab for 5 months, the result was a decrease in cytotoxicity and low expression of two types of NK cells. Likewise, NK cells taken from patients with malignant mesothelioma also showed decreased cytotoxicity. Even tissue samples cultured with asbestos for just a week showed suppressed NK expression. Interestingly, the researchers did not get the same result when they tried substituting glass wool (fiberglass) for asbestos.

Because mesothelioma is highly resistant to standard therapies, any research that sheds light on its origin could help doctors in their efforts to find effective treatments. The Japanese researchers concluded, “These results indicate that asbestos has the potential to suppress cytotoxicity of NK cells. In particular, it is noteworthy that both NK cells from malignant mesothelioma patients and those from a culture… derived from healthy volunteers with asbestos showed the same characteristic of decreased cytotoxicity with low expression of NKp46.”

Sources:

Nishimura, Y et al, “Suppressive effect of asbestos on Cytotoxicity of human NK cells”, Jan-Mar 2011, Special Supplement, International Journal Immunopathology and Pharmacology, pp 5s-10s. Nishimura, Y et al, “Decreased cytotoxicity of human NK cells with low expression of NK cell-activating receptors upon exposure to asbestos, related with malignant mesothelioma”, International Immunology Meeting Abstracts 2010.