Introduction of Natural Killer Cells and their role in inflammation

Introduction of Natural Killer Cells and their role in inflammation
Shahab Rabiee Lalehdashti,^1,* Zahra Ahmadian,² Amir Arasteh,³
1. Islamic Azad University
2. Islamic Azad University
3. Islamic Azad University
Introduction: Natural Killer Cells (NK Cells) are members of the innate immunity system, which are responsible for protecting their host against tumors and pathogen-infected cells, as well as activating macrophages and maintaining immune homeostasis. The main function of NK Cells is to release perforin, followed by granzymes using effector molecules such as TNF, Fas ligand, and so on which eventually leads to the killing of infected cells. In fact, it can be said that one of the main functions of NK cells to protect the host is to secrete IFN-γ. One way to accurately identify NK Cells is through their surface proteins. For example, in the human immune system, NK Cells are identified based on the expression of CD56, but most of them express CD16. NK cells are said to have cytolytic properties, and this feature is obtained by a single evolution in the thymus without the need for re-evolution. NK Cells originate from hematopoietic stem cells in the bone marrow and are mostly lymphoid progenitor cells. They consist about 5-20% of the volume of blood lymphocytes and are present in very small amounts in tissues and lymphatic organs. NK Cells are equipped with an advanced repertoire to identify their targets. In general, three types of receptors regulate the response of NK Cells: cytokine receptors, activating receptors, and inhibitory receptors. Activation of NK Cells) There are several mechanisms for activating NK cells, but in this article, we will mention only two mechanisms. In one mechanism, NK cells can be activated using cytokines or by interacting with a pathogen. In this case, cells stimulated by pathogens through Toll-like receptors, including epithelial cells, etc., secrete cytokines that directly affect NK cells and stimulate cytokine and chemokine production. Another mechanism for activating NK cells is based on the ability of NK cells to express the activator of CD-16 in killing target cells by IGG-coated by a process called antibody-dependent cytotoxicity. NK cells are generally divided into four main subgroups: 1) The CD56 bright NK Cells represent the CD62L 2) The CD56 dim NK Cells represent the PLZF 3) The CD56 bright NK Cells with low or no expression of PLZF 4) The CD56 bright NK Cells tissue reside In response to the involvement of NK cells with target cells, these cells can produce a wide range of cytokines and interleukins such as IFN-γ and TNF, IL-5, IL-10, IL-13, GM-CSF growth factor and secrete chemokines such as CCL3, CCL4, CCL5 and, CCL8. Approximately 10% of the NK Cells in the peripheral blood express a large amount of CD56 and are thus known as CD56 bright cells. NK Cells in inflammation) Severe inflammation is associated with a wide range of diseases and in very severe forms, death. For example, in human, congenital defects in lymphocyte cell cytotoxicity cause life-threatening hyper-inflammatory syndrome, which typically occurs in infancy. Another evidence linking NK Cells to inflammation comes from asthma studies. In mild to moderate asthma, among the molecular mediators, lipoxin A4 increases eosinophil apoptosis, which is characterized by inflammation of the airways. But the same inflammation in severe asthma leads to a relative increase in CD56dim NK Cells, which is inversely related to lung function. It is thought that the suppressive action of corticosteroids may also lead to pneumonia.
Methods: In the first study, the role of NK cells in allergic inflammation was investigated. The second study was performed to investigate the effect of NK Cells on the pathology of airway diseases.
Results: In the first study, it was found that in inflammations, especially peritoneal inflammation, defects in NK cells could reduce eosinophilia and produce IL-15. In the second study, NK cells were found to be able to increase allergic airway inflammation during allergies and inflammation. It was also found that if stimulated by IFN-γ, the damage caused by allergic inflammation is reduced.
Conclusion: Our understanding of NK Cells, their structure and function has made great strides since the discovery of these cells. Various studies have confirmed the role of NK Cells in inflammation. Of course, more studies are needed to fully understand the role of NK Cells. These studies may shed light on new facts that could lead to the discovery of newer treatment opportunities.
Keywords: NK Cells, Inflammation, Cytolytic, Innate immunity