Natural killer (NK) cells are key components of our immune system. They attach to unhealthy cells and then destroy them. Inside the NK cell a package of toxic chemicals called a lytic granule (here coloured yellow and 20,000 times bigger than normal) is on its way to kill a diseased cell. The closed structure stops the deadly chemicals within from harming the healthy NK cell. Surrounding the granule are actin filaments (shown in blue), which are part of the cytoskeleton, a complex network of protein filaments that helps the cell keep its shape. The network also helps things move around. The lytic granules use it to travel to the NK cell membrane, fuse with it, and then eject their contents onto the diseased cell.
Written by Sarah McLusky
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