NK Cells Mini Review
Natural killer (NK) cells are a subset of cytotoxic lymphocytes that function predominately in the innate immune response. They were named “natural killers” because of the initial notion that they did not require activation in order to perform their cytotoxic functions. NK cells play a major role in the rejection of cells lacking the self-markers of MHC class I, particularly tumor and virus infected cells.
NK cell function is controlled by a wide range of cell surface receptors, which either have an activating cytotoxic function, or are inhibitory having an immunoregulatory role (Mandal and Viswanathan 2014), examples of these receptors are show in the table below. The intensity of the expression of CD56 on human NK cells has been seen as an indicator of function; with CD56bright NK cells (10% of the population) being inhibitory (producing cytokines) and CD56dim NK cells (90% of the population) being cytotoxic (Caligiuri 2008). Cytotoxicity is regulated by the interplay between activating and inhibitory signals. Inhibitory receptors prevent NK activation by recognition of self MHC class I.