Nk Cells - Natural Killers

See Science Daily for their definition and explanation of Nk Cells.

Key points:

• NK cells play a major role in the elimination of both tumours and virally infected cells.
• NK cells are cytotoxic; small granules in their cytoplasm contain special proteins such as perforin and proteases known as granzymes.  Granzymes are enzymes that break down proteins and are released by natural killer cells. Their purpose is to induce cell-death within virus-infected cells, thus destroying them.
• Upon release in close proximity to a cell slated for killing, perforin forms pores in the cell membrane of the target cell through which the granzymes and associated molecules can enter, inducing cell-death (apoptosis).
• The distinction between apoptosis and cell lysis is important in immunology - lysing a virus-infected cell would only release the virions, whereas apoptosis leads to destruction of the virus inside. NK cells are activated in response to interferons or macrophage-derived cytokines.

Check the video out on NK cells

A small fraction (~2%) of the lymphocytes circulating in the blood are neither T cells nor B cells.  Most of these are called natural killer (NK) cells because they are already specialized to kill certain types of target cells, especially

• host cells that have become infected with virus;

• host cells that have become cancerous.