What Are Natural Killer Cells?

Natural Killer Cells and Cancer Immunity

natural killer cells visualized under a microscope
Natural killer cells kill cancer cells and viral infected cells on contact. istockphoto.com

What are Natural Killer Cells? - Definition

Natural killer cells (NK cells) are an aggressive part of the immune system that plays an important role in eliminating cancer cells and viral-infected cells from the body. NK cells are a type of lymphocyte, which in turn are one of the type of white blood cells in the body

How They Work/Innate Immunity

As part of the innate immune system, natural killer cells don't have to recognize a specific abnormality (antigen) on viral-infected cells or cancer cells.

This is in contrast to some functions of immune cells which result from immunologic memory. If a cell is not recognized as being a normal part of the body, the NK cell can perform one of 2 functions.

  • NK cells may be cytotoxic (cell killing) - In this process, the NK cell penetrates the cell and releases toxic granules into the abnormal cells. These granules then create holes in the cell membrane, allowing them to swell and burst and killing the cell on contact. Instead of bursting, the cell may instead be directed in a process of controlled death called apoptosis.
  • Natural killer cells may also be used as a form of immunoregulation - In this process, the NK cells regulate the function of the immune system by producing substances known as cytokines. You can visualize cytokines as the "hormones of the immune system" which stimulate other parts of the immune system.

Natural Killer Cells and Cancer Research

Since natural killer cells are able to kill tumor cells by recognizing the difference between cancer cells and normal cells scientists are studying ways to increase the number or enhance the function of these cells in the body, as a way to treat cancer more effectively.


Learn about how research on natural killer cells and immune function is advancing the treatment of cancer in the following article:

Can You Improve the Function of Natural Killer Cells?

In one study promoting the benefit of exercise, researchers found that moderate exercise may improve the function of natural killer cells in people with cancer.

On the other side of the equation, cigarette smoking appears to interfere with the function of natural killer cells, and smoking cessation is one way to ensure that your body’s natural killer cells are working as well as possible.

Also known as: NK cells, Large Granular Lymphocyte,NK-LGL


Carotta, S. Targeting NK Cells for Anticancer Immunotherapy: Clinical and Preclinical Approaches. Frontiers in Immunotherapy. 2016. 21:7-152.

Mehta, H. et al. Cigarette smoking and innate immunity. Inflammation Research. 2008. 57(11):497-503.

Purdy, A. and K. Campbell. Natural killer cells and cancer: regulation by the kill cell Ig-like receptors (KIR). Cancer Biology & Therapy. 2009. 8(23):2211-20.

Srivastava, S. et al. Natural killer cell immunotherapy for cancer: a new hope. Cytotherapy. 2008. 10(8):775-83.

Tallerico, R., Garofalo, C., and E. Carbone. A New Biological Feature of Natural Killer Cells: The Recognition of Solid Tumor-Derived Cancer Stem Cells. Frontiers in Immunology. 2016. 10:7-179.

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