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Introduction
The term cytokine is a generic name for the soluble molecules that mediate reactions between cells, acting via specific receptors on those cells. They are particularly important during effector stages of the immune system and the development of haematopoietic cells
Nomenclature and classification
Nomenclature of the cytokines was first based on their activity both in vivo and in vitro, with the name being abbreviated to acronyms. For example, when a factor isolated from antigen-activated lymphocytes was added to non-immune peritoneal macrophages, their migration from capillary tubes was inhibited. This led to the factor being named migration inhibition factor, or MIF for short. It was then discovered that many biological functions were being produced by the same chemicals, which led to the classification of cytokines based on either the cell populations that secrete them or their function:
- Monokines- produced by myeloid cells (macrophages, monocytes)
- Lymphokines- produced primarily by lymphocytes
- Interleukins- produced by leukocytes in general
- Chemokines- directing cell migration, activating cells in response to infectious agents/tissue damage
- Interferons- produced by many different cells in response to viral infection
Common cytokines and nomenclature
| Name | Abbreviation | Examples |
|---|---|---|
| interleukins | IL | IL-1, IL-2 |
| interferons | IFN | IFN-alpha |
| tumour necrosis factors | TNF | TNF-alpha |
| growth factors | GF | NGF, EGF |
| colony stimulating factors | CSF | M-CSF, G-CSF |
| chemokines | - | RANTES, MCP-1 |
Functions of cytokines
Mediating and regulating innate immunity: bacterial and viral products, such as LPS, stimulate macrophages and natural killer cells to secrete cytokines that primarily act on endothelial cells and leukocytes. They stimulate the early stages of the inflammatory reaction to microbes. Mediating and regulating adaptive immunity: in response to specific recognition by T lymphocytes, cytokines are produced that have a wide range of functions, including:
- regulating the growth and differentiation of some lymphocyte populations
- recruitment, activation and regulation of specialised effector cells, e.g. mononuclear phagocytes, neutrophils, eosinophils
Stimulating haematopoiesis: produced primarily by bone marrow stromal cells and leukocytes, these cytokines stimulate the growth and differentiation of immature leukocytes