Today it was announced in PLoS Biology that researchers at Imperial College, London have discovered the mechanism by which our body’s frontline defence system is able to distinguish between good and evil.
Researchers from the university’s Department of Life Sciences and the National Heart and Lung Institute at Imperial studied the ‘Natural Killer’ (NK) immune cells in the human body identifying how they know which cells are diseased and must be destroyed and which are normal cells. They believe that this work could help scientists develop new ways of boosting the body’s natural defences.
NK cells are a fundamental part of our body’s immune system – in fact over 1,000 NK cells are found in every drop of our blood. By latching onto harmful cells they can protect our bodies against tumours, viruses and bacteria.
However, up until now it was not understood how NK cells would know to leave our own normal cells unharmed.
Professor Dan Davis, the principal investigator of the study, and his colleagues used high speed microscopy imahing techniques to observe first-hand how the NK cells decide which cells and good and which are evil.
They found that NK cells have two types of receptors on their surface that are capable of interacting with proteins on the surface of the captured cell. One set of these receptors are ‘activators’ (capable of turning the killing mechanism on), whilst the others are ‘inhibitors’ (which prevent the captured cell being killed).
A series of sill images showing Nk cells at work, coutresy of Imperial College, London. This series of images show the time course of an NK cell killing a diseased cell. The top row of panel shows the cells in black and white and below are the same cells with the NK cell marked with a red dye and the target cell marked green. The NK cell attaches to the target and spreads over it before delivering a lethal dose of toxins. The death of the target cell can be seen in the last image as the surface of the cell is seen to bubble. The whole process takes about 15 minutes.
If an NK cell finds a harmful cell, such as a cancerous one, more of its activator receptor cells interact and the killing signal dominates, causing the NK cell to maintain contact with the harmful cell and eventually kill it. Conversely, if a normal cell is captured, the inhibitor receptors dominate the the NK cell knows to quickly move off in search of other cells.
“Our research has shown that information gleaned from its surface receptors tells the Natural Killer cell whether to stop patrolling and commence killing, or to move off quickly, and harmlessly, in search of another target,” said Professor Davis.
This work is a significant step forward in our understanding of how our body’s natural defence system works.