N K cells activity is enhanced by ?
Ans. is 'c' i.e., IL-2 IL-2 acts as a growth factor for N K cells. Null cells (Large granular lymphocytes) Null cells are called so because they lack features of surface markers of both B and T lymphocytes. The account for 5 to 10% of peripheral blood lymphocytes. They are also called "large granular lymphocytes (LGL)"as they contain large azurophilic cytoplasmic granules. They express Surface receptors for the Fc poion of IgG (CD-16) NCAM-I (CD56) They proliferate in response to IL-2 Many LGL express some lineage marker paicularly CD-8, CD-2. LGLs arise in both bone marrow and thymic microenvironment. Members of this group are : 1. Antibody dependent cytotoxic cells (ADCC) ADCC possess surface receptors for the Fc pa of Ig. Capable of lysing or killing target cells sensitized with IgG. 2. Natural killer cells (NK Cells) Possess spontaneous cytotoxicity towards various target cells : - Virus infected cells Malignant cells Transplanted foreign cells Cytotoxicity is not antibody dependent or MHC restricted Activity is nonimmune as it does not require sensitization by prior antigenic contact. They have CD-56 and CD-16 on their surface IL-2 acts as a growth factor Natural killer cell activity is augmented by interferon. They release perforin which causes transmembrane pores through which TNF-f3 enters the cell and induce apoptosis. NK cells are activated to LAK cells in the presence of IL-2 Usually CD-3 negative but subset of NK cells are CD-3 positive called NK/T cells. NK cells secrete TNF-a, GMCSF, perforin, IL-4. NK cells do not kill normal cells. Why is it so? lets see : ? The NK cells express activating and inhibiting receptors. The functional activity of the NK cells is regulated by a balance between signal from these receptors. MHC class I molecules has inhibiting signal on NK cells and normal cell are not killed because inhibiting signals from normal MHC class I molecules overside activating signals. The ability of NK cells to kill target cells is inversly related to target cell expression of MHC class I molecule. If virus infection or neoplastic transformation reduces the expression of MHC I, inhibitory signals are interrupted and lysis of target cells occur. 3. Lymphokine activated killer (LAK) cells These are NK - cells treated with IL-2 Kill tumor cells more efficiently than unstimulated NK cents.
IL-1
TNF
1L-2
TGP-I3