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Understanding the Immune System
Adapted by Thyroid Guide, Mary J. Shomon

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Natural Killer Cells

killer cellsNatural Killer (NK) cells are yet another type of lethal lymphocyte. Like cytotoxic T cells, they contain granules filled with potent chemicals. They are called "natural" killers because they, unlike cytotoxic T cells, do not need to recognize a specific antigen before swinging into action. They target tumor cells and protect against a wide variety of infectious microbes. In several immunodeficiency diseases, including AIDS, natural killer cell function is abnormal. Natural killer cells may also contribute to immunoregulation by secreting high levels of influential lymphokines.

Both cytotoxic T cells and natural killer cells kill on contact. The killer binds to its target, aims its weapons, and then delivers a lethal burst of chemicals that produces holes in the target cell's membrane. Fluids seep in and leak out, and the cell bursts.

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Updated 2002: This information has been made available from the National Cancer Institute and the National Institute of Allergy and Infectious Diseases.
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