Immunology NK Cells Receptors

Question: Describe the functions of NK cells receptors? Answer: NK cells or natural killer cells are cytototoxic lymphocytes, significant to the vertebrate innate immune system. They act similar like cytotoxic T cells. NK cells give swift responses to infected cells and also react during tumor formation. Immune cells have the capacity to detect major histocompatibility complex or MHC, presented on the infected cellular surfaces, trigger cytokine release and this leads to cell apoptosis or cell lysis. NK cells have capacity to identify stressed cells without the presence of major histocompatibility complex and antibodies and also they allow for much rapid immune reaction inside the human system. Thus, these cells are named as natural killers, as they do not need cellular activation to destroy cells. This function is typically vital as harmful cells, those do not have MHC 1 markers cannot be identified and destroyed by different other immune cells, for example: T lymphocyte cells. NK cell receptors Functions Ly49 Activating receptors, human have pseudogenic Ly49 for polymorphic MHC I molecules. NCR/ Natural Cytotoxic Receptors Activating receptors; upon stimulation release gamma interferon and mediate NK killing. CD94 Activating receptors; identify nonclassical or nonpolymorphic MHC I molecules, for example: HLA-E. Expression of major histocompatibility complex. Class I, E on the cellular surfaces is reliant on the existence of nonamer peptide epitope (Lieto, 2005). These are derived from signal sequence associated with classical MHC I molecules. This sequence is generated by chronological action of signal peptidase and proteasome. This mechanism is considered as indirect and is said to be a good way to inspect the quantity of polymorphic HLA molecules. CD16 Activating receptors; these receptors can bind with immunoglobulin G and contribute to the function of antibody-dependent cell- mediated cytotoxicity. These receptors are low affinity Fc receptors and attach to Fc region of antibodies immunoglobulin G. This complex then activates natural killer cells for of antibody-dependent cell- mediated cytotoxicity (Kramer, Winger and Reuben, 2009). If CD16 is not present in a particular neutrophil population, it could be assumed as the indication of prematurity, which could have taken place because of left-shift caused by neutrophilic leukocytosis stimulated by bacterial infection or tissue necrosis. KIRs or killer-cell immunoglobulin-like receptors Inhibitory receptors; these are the main receptors for classical and nonclassical MHCs. Classical MHCs are HLA-A, HLA-B, HLA-C; nonclassical MHCs are HLA-G (Zhang, Tong and Wu, 2009). Some of these receptors are particular for specific HLA subtypes. Most of these receptors are dominant. Regular cells show MHC 1 class, hence are recognized by these receptors and natural killing is inhibited. LIR or ILT or leukocyte inhibitory receptors Work as inhibitory receptors on human natural killer cells. These receptors get expressed on mononuclear leukocyte cells of human. Cytotoxic activity of newly isolated T cell replicas can be inhibited by the anti-LIR-1mAb (Lebbink et al., 2007). These receptors provide regulation mechanism of T effector cells and inhibit unwanted responses arbitrated by antigen specific T cells. References Kramer, P., Winger, V. and Reuben, J. (2009). PI3K limits TNF- production in CD16-activated monocytes.European Journal of Immunology, 39(2), pp.561-570. Lebbink, R., de Ruiter, T., Kaptijn, G., Bihan, D., Jansen, C., Lenting, P. and Meyaard, L. (2007). Mouse leukocyte-associated Ig-like receptor-1 (mLAIR-1) functions as an inhibitory collagen-binding receptor on immune cells.International Immunology, 19(8), pp.1011-1019. Lieto, L. (2005). CD94 1A/1B: a window opens into NK-cell development.Blood, 106(10), pp.3338-3339. Zhang, X., Tong, C. and Wu, T. (2009). 178-P: The effect of inhibitory and activating KIRs on haploidentical hematopoietic stem cell transplantation.Human Immunology, 70, p.S101.