NK Cells (Third Population Cells)

(1). NK cells (third population cells) Natural killer cellsantigens or NK cells are asurface group ofantigens cells similar to lymphocytes but do not have surface like the of T cells andlater B cells. Therefore, this group of cells was previously called null cells, although it turned out that these cells had receptors for complement C3. and receptors for Fc. These cells are non-phagocytic, non-adherent and phenotypically different from SD T or B, namely they do not have CD3/TCR or SLG. To differentiate them from T cells and B cells, these cells have surface markers CD16 (which is a receptor for Fc) and CD56. The surface signature ofthat CDl6 and/or CD56 without CD3 (CDl6/CD56CD3) is currently used to confirm the cell is an NK cell. The number of NK cells varies with age.Characteristics of NK cells.NK cells have special characteristics thatare: differentiate them from other cell groups. Some characteristics of NK cells (i) The number NK compared cells in babies is less than in adults; the number increases 2 times in middleof age to newborns. (ii) This cell population can killrelying target on cellsMHC spontaneously without further sensitization first and without products, therefore they are called NK (natural killer) cells. (iii) Apart from not beingthe controlled by MHC, these cells also doThe not receptor interact for with target cells through T receptor (TCR) as well as T cells. MHC, recently identified as a ctype lectin like receptor which is specific for MHC class I; Apart from that, NK cells also have other receptors, namely immunoglobulin likeinhibitory receptors,receptors. which can function as inhibitors of killing, so they are called killer NK cells play an important role in natural defense against the growth of cancer cells and various infectious diseases, especially viral infections. Most NK cells (95%) can function as killer cells for target cells infected with viruses and other target cells coated with Ig so that NK cells function as cytotoxic cells that depend on antibodies (antibody dependent cell mediated cytotoxicity=ADCC). Origins of NK cells The origins of NK cells arecells stilland a secret and not muchwith is known. LittleItisis known about the origins of NK their relationship other cells. thought that these cells develop instem the bone marrow, butsuggested until nowthat no surface markers have been found for the cells. It has been NK cellsIf and T cells originate from the same stem cell (common thymocyte precursor). peripheral bloodIL-2, lymphocytes or thosewill fromgrow thethat spleen are cultured andall incubated with a cell population is capable of killing target cells, including cells that are are not resistant to NKbycells. Thisarepopulation of cells which carry out their functions controlled MHC called LAK cells(lymphokine activated killer). LAK cell activity is selective fornormal tumor cells or cells that express abnormal surface markers, and rarely damages cells. NK producefor IFNy and other cytokines, forresponses. example IL-1 and GMCSFcells whichcanarealsoimportant hemopoiesis and immune Mechanism of NK cell lysis Lysis of target cells byplace NK cells can occur within minutes ofbyexposure. The cytolysis mechanism takes in 4 stages, similar to cytolysis other effector cells, namely: 1)known Targetforcellcertain, binding stage. NK there cell receptors forevidence bindingthat to target cells yetis but recently has been target cell recognition occurs through receptors thatinbind to lectin-like molecules, called NKR-PI. This NKR-PI ligand is expressed almost all normal tissues, so there needs to be a mechanism to prevent lysis of these normal cells by NK cells. Several studies reveal the role of MHCis an classinhibitory I in protecting cells from being lysed by NK cells. The p58 molecule receptor for the HLA-C molecule, and NKB1 is an inhibitory receptor for the HLA-B7 molecule. (2) The effector cell activation stagecell. through signals andthe signal transduction and (3) The lethal stagehit to the target Once activated, granules polarize towards the NKrelease cell where there is close contact with the targetchondroitin cell. The granules then various substances, namely proteinase, sulphate, proteoglycan, byexample exocytosis. NKOncells are also able toislyse cells with the help of cytokines, for IL-2. the one hand, IL-2 a potent induction factor for cytokine production bysdNK but oncytotoxicity the other hand IL-2 is also a growth factor for sdNK and functions to increase and migration of sdNK. Anotherit has cytokine that plays athat roleone in increasing NKthecellTNF activity is IFN-α. Recently been discovered member of family, namely has aninimportant target cells whichFas,results apoptosis.role in launching lethal signals against (4) Thecycle stageifofanynew releasingpathogen. NK cells from target cells and then undergoing a repeat Currently, several factorsNKarecells, known thatarecanalsoinhibit NKthat cellinhibit activity.target Apartcellfrom factors that can activate there factors lysis by NK cells, including prostaglandins. Prostaglandins inhibit lysis bybyNK cells by increasing cAMP levels. The lysis function can also be inhibited substances that cause damage to cell granulesNK.