A small protein released by cells that has a specific effect on the interactions between cells, on communications between cells or on the behavior of cells. The cytokines includes the interleukins, lymphokines and cell signal molecules, such as tumor necrosis factor and the interferons, which trigger inflammation and respond to infections.
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Any of numerous hormonelike, low-molecular-weight proteins, secreted by various cell types, that regulate the intensity and duration of immune response and mediate cell-cell communication. See interferon, interleukin, lymphokine, chemokines. See entries under various growth factors. SEE ALSO: interferon, interleukin, lymphokine. [cyto- + G. kinesis, movement] Cytokines are produced by macrophages, B and T lymphocytes, mast cells, endothelial cells, fibroblasts, and stromal cells of the spleen, thymus, and bone marrow. They are involved in mediating immunity and allergy and in regulating the maturation, growth, and responsiveness of particular cell populations, sometimes including the cells that produce them (autocrine activity). A given c. may be produced by more than one type of cell. Some cytokines enhance or inhibit the action of other cytokines. The first cytokines to be identified were named according to their functions (e.g., T cell growth factor), but this nomenclature became awkward because several cytokines can have the same function, and the function of a c. can vary with the circumstances of its elaboration. Later, as the chemical structure of each c. was determined, it was designated an interleukin and assigned a number (e.g., interleukin-2 [IL-2], formerly T cell growth factor). Cytokines have been implicated in the generation and recall of long-term memory and the focusing of attention. Some of the degenerative effects of aging may be due to a progressive loss of regulatory capacity by cytokines. Because cytokines derived from the immune system (immunokines) are cytotoxic, they have been used against certain types of cancer.
- c. network a group of cytokines which together modulate and regulate key cellular functions.

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cy·to·kine 'sīt-ə-.kīn n any of a class of immunoregulatory proteins (as interleukin, tumor necrosis factor, and interferon) that are secreted by cells esp. of the immune system

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cy·to·kine (siґto-kīn) [cyto- + kinesis] a generic term for nonantibody proteins released by one cell population (e.g., primed T lymphocytes) on contact with specific antigen, which act as intercellular mediators, as in the generation of an immune response. Examples include lymphokines and monokines.

Medical dictionary. 2011.

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