Natural Killer Cells

Natural Killer cells, or NK cells are probably the coolest named cells in the immune system! They circulate in the blood and are able to move into other tissues to destroy their targets. NK cells are particularly effective against our own cells that have been infected by a virus or show early signs of becoming cancerous.

NK cells share characteristics of B- and T-lymphocytes, but are unable to form immunological memory, they are therefore called innate lymphoid cells (ILCs). As well as direct killing, NK cells secrete chemical messengers that act on other immune cells like macrophages and dendritic cells. This helps these cells to initiate an immune response.

Scanning electron microscope image of a natural killer cell Colourised scanning electron microscope image of a natural killer cell at high magnification and resolution.

NK cells search for a protein structure called Major Histocompatibility Complex class I (MHC class I) on the surface of our cells. All nucleated cells in the human body express this protein, which prevents NK cells from attacking them. However, virally infected and cancerous cells often lose their MHC class I proteins allowing NK cells to destroy them.



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