1. Health
Send to a Friend via Email
You can opt-out at any time. Please refer to our privacy policy for contact information.

What Are Natural Killer Cells?


Updated October 08, 2012

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Question: What Are Natural Killer Cells?

Natural killer cells (NK cells) are a part of the immune system that plays an important role in eliminating cancer cells from the body. These cells combine with cancer cells or cells infected with viruses and release toxic granules into the abnormal cells to kill them. In this role they are cytotoxic -- that is, “cell killing.” Natural killer cells also produce substances known as cytokines (one example is interferon g), which assist the body in removing viruses and tumor cells.

The term “natural” before killer cells, means that natural killer cells don’t have to recognize a specific abnormality on a cell to be able to do their job. This is also called “innate immunity.” Natural killer cells are a type of lymphocyte, which is in turn one of the types of white blood cells in the body.

Since natural killer cells are able to kill tumor 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. 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


Sharon heard from a friend that moderate exercise may improve the function of natural killer cells in the body, so she decided she would ask her oncologist what exercise he would recommend for her during her cancer treatment.


Anderson, S. Biology of Natural Killer Cells: What Is the Relationship between Natural Killer Cells and Cancer? Will an Increased Number and/or Function of Natural Killer Cells Result in Lower Cancer Incidence?. The Journal of Nutrition. 2005. 135:291 0S.

Knols, R. et al. Physical Exercise in Cancer Patients During and After Medical Treatment: A Systematic Review of Randomized and Controlled Clinical Trials. Journal of Clinical Oncology. 2005. 23(16):3830-3842.

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.

©2014 About.com. All rights reserved.

We comply with the HONcode standard
for trustworthy health
information: verify here.