Natural killer cell

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Natural NK cells are cytotoxic; they weaken the target cell's plasma membrane by inserting proteins called perforins, causing water and ions to diffuse into the cell and cause it to swell. Under this large pressure, the target cell lyses. Natural killer cells may also be able to induce apoptosis.

NK cells are characterised immunohistochemically by the presence of CD56 and/or CD16 and the absence of CD3 on the cell membrane in humans.

NK cells are activated in response to interferons or macrophage-derived cytokines. They serve to contain viral infections while the adaptive immune response is generating antigen specific cytotoxic T cells that can clear the infection. Patients deficient in NK cells prove to be highly susceptible to early phases of herpes virus infection.

If NK cells defend the body against viruses and other pathogens, they must possess mechanisms to decide if a cell is infected or not. The exact mechanisms are as yet unknown, but recognition of 'altered self' is thought to be involved. To control their cytotoxic activity, they possess two types of surface receptors: 'activating receptors' and 'inhibitory receptors'.

These 'inhibitory receptors' recognize MHC (major histocompatibility complex) class I alleles, which could explain why NK cells kill cells with low levels of MHC class I molecules - a concept that is known as "missing-self" recognition.

Different families of NK receptors exist and many of these receptors seem to have evolved recently.

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See also

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Literature

  • Immunobiology The Immune System In Health And Disease by Janeway, Travers, Walport & Shlomchik Churchchill Livingstone Copyright 2005
  • Cellular and Molecular Immunology by Abbul K. Abbas & Andrew Lichtman Saunders Copyright 2003
  • How the Immune System Works, 2nd edition, by Lauren Sompayrac, PhD Blackwell Publishing 2003
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External links

Blood - Blood plasma - edit
Pluripotential hemopoietic stem cell | Red blood cells (Reticulocyte, Normoblast) | White blood cells
Lymphocytes (Lymphoblast)
T cells (Cytotoxic, Helper, Regulatory T cell) | B cells (Plasma cells & Memory B cells) | Natural killer cell
Myelocytes (Myeloblast)
Granulocytes (Neutrophil, Eosinophil, Basophil) | Mast cell precursors | Monocytes (Histiocyte, Macrophages, Dendritic cells, Langerhans cells, Microglia, Kupffer cells, Osteoclasts) | Megakaryoblast | Megakaryocyte | Platelets
cs:NK buňky

fr:Cellule tueuse naturelle he:תא NK tr:Doğal öldürücü hücre zh:自然杀伤细胞

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