Functions of Natural Killer Cells

Question: What is Functions of Natural Killer Cells? Answer: Functions of natural killer cells Natural Killer cells are a kind of cytotoxic lymphocyte that are both important for innate and adaptive immunity[1]. They are the one which response to the cells that are infected by viruses and pathogens and response to the formation of tumor cells. All this is done after three days from infection. The natural killer cells are efficient to phagocytes both the exogenous and the endogenous antigens without the need of prior stimulation by anybody. The functions are underlined below: Cytolytic granzymes that mediates lysis or apoptosis of cells: They are cytotoxic cells. They contain granzymes which enters by forming pores in the cell membrane of the target cells, and thereby causing apoptosis or osmotic lysis of the cell. Cytotoxicity mediated by antigen antibody binding : The infected cell are opsonized with their antibodies by the immunity cells[2]. The antigen binding antibodies are easily recognized by CD16 receptor that is expressed on NK cells. This causes activation of NK cells releasing cytolytic granules and thus causing apoptosis. CTL and NK cells activation by cytokines: Cytokines like IL 2, IL 5, IL 8 etc. activates NK cells. They contains viral infection. In response to this body secretes cytotoxic T cells and NK cells secretes IFN and TNF to kill the target infectious cells[3]. NK cells as tumor cells surveillance: The NK cells sometimes lacks antigen specific cell surface receptor so they often react immediately without any pathogen exposure and thus functions by causing a direct death of the tumor cell. Adaptive responses by NK cells: They function is contractions, expansions, memory maintaining, and recalling. Natural killer cells initiates their activation in response to the interferons or the cytokines that are derived by macrophages. These Macrophages phagocytose the endogenous antigens by the support provided by stimulating TNF, cytokine and various other interleukins. The macrophages generally consume invading microorganisms. They here carry out various functions like phagocytosis ,antigen processing and antigen representation and secreting the chemical factors. Functions during pregnancy: The NK cells secretes cytokines like TNF , IL 10, IFN and TGF that mediates various functions[4]. Like dilation of the walls of maternal arteries so as to increase blood flow at the implantation point. The NK cells are evaded by tumor cell: In the case of prostate cancer the evasion is carried by NK cells. The tumor cells shed NKG2D ligands so as to avoid the responses from the immune system[5]. These ligands bind to the NKG2D cell receptor present on the NK cell so to activate a fake NK response and thus competing for the receptor sites. The NK cells defends the human body against any viral or pathogenic infections. They adopt mechanism to identify a cell is infected or not. The mechanism is not yet understood but it is believed it is altering the self mechanism[6]. These mechanism of cytotoxicity are carried out by the inhibitory and activating receptors like the killer cell immunoglobulin like receptor. References 1. Lodoen, M.,B. Lanier, L.,L.; Lanier (2005). "Viral modulation of NK cell immunity". Nature Reviews Microbiology 3: 59692. Arina, A., Murillo, O., Dubrot, J., Azpilikueta, A., Alfaro, C., Prez-Gracia, J.,L., Bendandi, M., Palencia, B., Hervs-Stubbs, S. Melero, I.; Murillo; Dubrot; Azpilikueta; Alfaro; Prez-Gracia; Bendandi; Palencia; Hervs-Stubbs; Melero (2007). "'Cellular liaisons of natural killer lymphocytes in immunology and immunotherapy of cancer'". Expert Opinion on Biological Therapy 5 (5): 599615.3. Bulmer, Judith N.; Williams, Paula J.; Lash, Gendie E. (2010). "Immune cells in the placental bed". Int J Dev Biol 54 (23): 281294.4. Seshadri, S.; Sunkara, S. K. (2013). "Natural killer cells in female infertility and recurrent miscarriage: a systematic review and meta-analysis". Human Reproduction Update 20 (3): 4294385. O'Leary, J.,G., Goodarzi, M., Drayton, D.,L. von Andrian, U.,H.; Goodarzi; Drayton; von Andrian (2006). "'T cell-and B cell-independent adaptive immunity mediated by natural killer cells'". Nature Immunology 7 (5): 507516.6. Roitt I, Brostoff J, Male D (2001). Immunology (6th ed.), 480p. St. Louis: Mosby,