NK cells are the rapid response force of the immune system, capable of taking action without waiting for orders.
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Most immune cells need to verify an enemy's ID card before deciding whether to attack. NK cells are different.
NK stands for Natural Killer. It doesn't care who the enemy is; it looks at whether the counterpart is acting abnormally. If a cell behaves unlike a normal cell—such as being infected by a virus or beginning to turn cancerous—the NK cell will strike immediately, without waiting for any instructions.
This makes NK cells your fastest first line of defense against viral infections and early malignant transformations. However, its activity declines by about 15% to 20% every decade after the age of 40, which is one of the core immunological reasons why cancer risks rise with age.
