How nanotubes suppress the immune function

Carbon nanotubes are the multi-purpose material of the future, but new research published today in Nature Nanotechnology reinforces concerns that the tiny carbon cylinders might represent a health risk.

The researchers found that inhalation of carbon nanotubes, which can measure only a few nanometres across, activates cellular signals in the lung, which in turn activate signals in the spleen to suppress the immune function of mice.

This finding provides an insight into the immune-system response of mice exposed to nanotubes, and highlights health concerns for those working with these materials.

Jacob McDonald and colleagues report that activation and release of a signalling molecule from the lung after inhalation of low levels of nanotubes has a direct effect on the immune function of T cells in the spleen. The signalling molecule from the lung activates certain enzymes in the spleen that induce the release of other molecules that can cause T-cell dysfunction.

Across the range of nanotube concentrations examined in this study, only mice exposed to 1 mg m^-3 showed suppressed immune function for up to 30 days.

Because accurate levels of occupational exposures remain unknown, it should be noted that rough estimates indicate that if humans are exposed to 1 mg m^-3 nanotubes in a similar setup, the burden on the lungs of humans would be approximately 7.5 times less than the burden experienced by the mice in this study.

However, the authors suggest that with increasing production of carbon nanotubes and possible occupational exposures that will persist for much longer than the duration of this study, immune dysfunction may be a concern for those working in the industry.

“This paper suggests that inhalation of carbon nanotubes, as well as potentially causing a persistent inflammatory reaction resembling mesothelioma, at sufficient concentration may also produce a unique suppression of the systemic immune system," says Thomas Faunce, Director of the Globalization and Health Project and Associate Professor in the College of Law and Medical School at The Australian National University.

"One needs to be cautious about overreacting to what is in many ways a preliminary finding but if this research is supported by subsequent studies it supports the case for specific exposure regulation applied to these nanoparticles.”