Abstract
Natural Killer (NK) cells are innate immune lymphocytes that are important for early and effective immune responses against infections and cancer. The antitumor immunity mediated by NK cells can be exerted through several direct or indirect “immunosurveillance” mechanisms that control tumor growth and prevent the rapid dissemination of metastatic tumors. NK cells express an array of activating and inhibitory receptors that enable them to recognize and bind non-self as well as self-ligands expressed on the surface of malignant or virally infected cells. The family of Natural Cytotoxicity Receptors (NCRs) comprises three activating receptors; NKp30, NKp44, and NKp46 that are important for the stimulation of NK cell effector functions. This review summarizes the mechanisms of antitumor immunity mediated by natural killer cells with focus on the role of the family of the NCRs and their tumor associated ligands.
Highlights
The histologic and functional definition of a natural killer cell (NK cell) was that of a Large Granular Lymphocyte (LGL) that could kill a target cell “naturally”, that is, spontaneously without any prior sensitization and without restriction by the Major Histocompatibility Complex (MHC) [1, 2]
Natural Killer (NK) cells can be divided into CD56dim and CD56bright NK cell subsets based on levels of cell surface expression of CD56
CD56dim NK cells are the predominant NK subset in peripheral blood, while CD56bright NK cells which are more abundant in lymphoid organs [9]
Summary
The histologic and functional definition of a natural killer cell (NK cell) was that of a Large Granular Lymphocyte (LGL) that could kill a target cell “naturally”, that is, spontaneously without any prior sensitization and without restriction by the Major Histocompatibility Complex (MHC) [1, 2]. NK cells are regarded as innate immune lymphocytes because unlike T and B lymphocytes, NK cells’ effector functions are controlled by a repertoire of germline-encoded receptors that do not undergo somatic recombination [3]. Despite these known innate immune cell functions, there is some evidence that NK cells possess some features as an “adaptive” immune component as well. CD56dim NK cells are the predominant NK subset in peripheral blood, while CD56bright NK cells which are more abundant in lymphoid organs [9]
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