By Ian Randall

Immune cells can reel in and kill escaping dangerous cells using a nanotube, a study by Imperial College London, has shown. The research is published in this week’s proceedings of the National Academy of Sciences.

Previous studies have shown the ability of natural killer cells to destroy their prey by latching onto them and transmitting toxic molecules across a bridge known as an immune synapse. But it was not known how they might deal with dangerous cells that try to run away.

Researchers are very interested in understanding how these cells operate – as they are our primary defence against cells which are infected by bacteria and viruses, or have become tumourous.

The new study has shown that natural killer cells can ensnare their victims with a membrane nanotube, which can then be used to kill the target from afar, or to draw them in for the regular ‘direct contact’ death.

A target cell is drawn in by the bungee-like nanotube. Video Credit: PNAS

“Natural Killer cells are cells that are very good at killing tumours and virus-infected cells. It was thought they kill these diseased cells only by sticking to them tightly for several minutes. These new movies show that in fact they also tether cells with long membrane connections and can pull diseased cells back into contact. We think they may also use these nanotubes to kill them from a distance,” said Professor Daniel Davis, from the Division of Cell and Molecular Biology at Imperial.

The researchers dyed the cells to enable them to see the membrane nanotubes in action under a microscope. Membranes were found to connect natural killers cells not only with cancerous, infected and tumour cells, but also with each other. The nanotubes were also seen to be able to pull back dangerous cells up to twice as fast as the fleeing cells are able to escape.

A natural killer cell remotely kills a target using a membrane nanotube. Video Credit: PNAS

“The next step is difficult because we have to know where and when these processes are important in your body, and the technology to see such thin nanotubes in the body hasn’t been invented yet. It’s a very new research area and we need to learn how the process works precisely so that we can then think about ways to design drugs that help immune cells kill,” Professor Davis added.

The study was funded by the Medical Research Council and the Association for Cancer Research (Association pour la recherche sur le cancer) in France.