Definition:
A type of cell in the immune system that destroys tumor cells or cells that are infected with some types of organisms. NK cells play a "front line" role in controlling infection by keeping it under control until the body can mount a full immune response.
Research suggests that some people with chronic fatigue syndrome have decreased function of NK cells, which is one piece of evidence supporting one chronic fatigue syndrome theory that attributes symptoms to chronic immune system activation possibly triggered by infection.
