Natural killer

Natural killer cells (or NK cells) are a type of Cytotoxic lymphocyte crucial to the immune system. The role NK cells play is analogous to that of cytotoxic T cells. The primary function of NK cells is to mediate immune response against cells infected with viruses and growing tumors.

Function

NK cells are unique as they have the ability to recognize stressed cells in the absence of antibody and Major histocompatibility complex (MHC), allowing for a much faster immune reaction. They were named "natural killers" because of the initial notion that they do not require activation to kill cells that are missing "self" markers of MHC class 1.

Development

NK cells are derived from hematopoietic stem cells (HSCs) in the bone marrow. They then undergo a process of maturation in the bone marrow, lymph nodes, and spleen with interleukin 15 (IL-15) as the key driver of NK cell development and maturation.

Clinical significance

NK cells play a major role in the rejection of tumors and cells infected by viruses. They kill on contact. The cell to be killed is identified by a 'flag' that is found on its surface called MHC class I. NK cells are 'turned off' by the presence of MHC class I. A decrease of NK cells activity is found in HIV infection, while an increase is found in Erythema nodosum, rheumatoid arthritis, asthma and systemic lupus erythematosus.

See also

• Cytotoxic T cell
• Immune system
• Major histocompatibility complex
• Hematopoietic stem cell

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