Natural Killer Research Paper

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1.2.0 Natural Killer Cells NK cells are one of the most sophisticated weapons in the innate immune systems arsenal however, they a short lived. Cytotoxic effector cell which resemble NK cells have been a part of the innate immune system for approximately 500 million years, long before the arrival of T and B cells of the adaptive immune system (Caligiuri, 2008). NK cells are best known for their role in the innate defense against viral infection and potential tumour cells. However, more recently they are being recognized with roles in the coordination of immunity, immunoregulation and the modulation of autoreactivity. NK cells got their name ‘natural killer’ due to the nature of being able to cause cell death instantly without priming, effector…show more content…
Although presence of CD56 can alter between NK cells and leads to subsets. In the peripheral blood, mature NK cells express low levels of CD56 including CD16 an IgG Fc receptor FcγRIIIA. These are given the name CD56 dim, this means that fluorescent intensity is slightly higher then then cell which are CD56 negative. A small amount approximately 10% in blood and 100% in secondary lymphoid tissue of peripheral blood NK cells express high levels of CD56 without CD16 present of the cell surface and these are considered immature however, functionally enabled NK cell subset or CD56 bright (Orange, 2013). CD56 bright NK cells can produce and high levels of cytokines and chemokines within a few minutes of their activation. Although, they show little or no ability to spontaneously kill tumour or virally infected cell targets. Contrary CD56 dim show lesser ability to produce cytokines in response to activation, however the majority can instantly lyse susceptible targets. The population of human NK cells are phenotypically and functionally heterogenous. Although, CD56 bright mature into CD56 dim as they develop they both have key roles within the human immune system (Caligiuri,…show more content…
IFN-γ is a prototypic NK cell cytokine and its production within the cell influences the T helper 1 cells response, up regulates MHC class 1 expression on antigen presenting cells and activates macrophages while having antiproliferative effects on viral and transformed tumour cells (Caligiuri, 2008). Mature NK cells specialize against T cell elusive pathogens, this is mostly viruses. Most viruses evade cytotoxic T lymphocytes by downregulating the class I MHC in infected cells also seen in tumours, this prevents the presenting of derived viral proteins by the cell. However, by doing this it becomes susceptible to NK cell defenses. NK cells can become activated by many activation receptors however, they are inhibited by killer cell immunoglobulin-like receptors (KIRs). These are ligated by class I MHC. Activation receptors can directly recognize viral antigens which include natural cytotoxicity receptors which binds to viral hemagglutinin. Some viruses and tumours induce specific cell stress molecules that serve as ligands to NK activation receptors (Orange, 2013). This relationship between KIRs and activating receptors can be seen below in figure

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