natural killer (NK) cells

Last reviewed 01/2018

• cells of the inate immune system
• are mononuclear and have lymphocyte morphology
• their different surface characteristics however prevent them from being classified as either B or T cells.
• also known as “large granular lymphocytes” (LGLs)
• mainly found in the circulation
• comprise between 5-11% of the total lymphocyte fraction
• possess receptors for immunoglobulin type G (IgG)
• also contain two unique cell surface receptors known as killer activation receptor and killer inhibition receptor
  • activation of killer activation receptor initiates cytokine (“communication”) molecules from the cell
  • activation of the killer inhibition receptor inhibits the cytokines
• have an important role in attacking virally-infected cells in addition to certain tumour cells
• destruction of infected cells is achieved through the release of perforins and granyzymes from its granules, which induce apoptosis (programmed cell death)
• able to secrete interferon-alpha
  • interferon alpha prevents healthy host cells from becoming infected by a virus; and augments the T cell response to other virally infected cells
• cells lyse antibody-coated cells in the absence of complement by attaching to the Fc potion of the antibody molecule