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

Natural killer cells have received a lot of attention in recent years for the roles they play in immunity alone but also their role in fighting cancer. If you've been listening to the latest news on immunotherapy drugs, including the latest advances in cancer treatments, you will see these cells appear often. What exactly are natural killer cells, what is their function in the immune system, and how do they help fight cancer?

Definition of Natural Killer Cells (NK Cells)

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 types of white blood cells in the body

How They Work and 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 (the kind of functions for which immunizations are designed). If a cell is not recognized as being a normal part of the body, the NK cell can perform one of two 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. It is these other parts of the immune system that, once stimulated, result in the death of the cancer cell or viral-infected cell.

    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.  

    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.

    Bottom Line 

    Natural killer cells are a critical part of your immune system, especially with the roles they play in eliminating both viral-infected cells and cancer cells. Research is in progress looking at ways to both boosts the function of these cells and increase their numbers as a method of fighting cancers.

    Of note is that there are things you can do yourself that may affect your natural killer cells. Exercise appears to increase their numbers and smoking lowers them.

    As we learn about the immunology of cancer we are learning not only new methods to fight tumors but the ways that we can support our own immune system in fighting these cancers for us.

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

    Sources:

    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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