Cytokines

Cytokines are small proteinmolecules that regulate communication among immune systemcells and between immune cells and those of other tissuetypes. These chemicals are actively secreted by immune cells as well as other cell types in response to external stimuli. Lymphokinesare a subset of cytokines.

Effects

Cytokines mediate many important physiological functions including growth, development, wound healingand immune response. They may affect local tissues (paracrineeffects) or more distant ones (endocrineeffects) (Clark, 2005).

Cytokines act by binding to their cell-specific receptors. These receptors are located in the cell membrane, and each allows a distinct signal transductioncascade to start in the cell, that eventually will lead to biochemical and phenotypical changes in the target cell. Typically, receptors for cytokines are also tyrosine kinases.

Cytokines are said to be pleiotropic, meaning that the same cytokine can have different effects on a cell depending on the state of the cell. For instance, there are several known cytokines that have both stimulating and suppressing action on lymphocytecells and immune response.

To make things even more complicated, cytokines often regulate the expression of other cytokines (either upwards or downwards), often triggering cascadesof other cytokines. The cytokines in these cascades can interact with each other and the cells that produced them in complicated fashions to form cytokine networks. Cytokines often act together in ways that are synergisticor antagonistic.

Some studies have shown links between cytokine levels and clinical depression[1].

In the inflammatory response, white blood cells release cytokines, which also recruit more lymphocytes and allow them to pass through blood vessel walls into the inflamed area (Clark, 2005). Their release triggers stages in the wound-healing cascade. They are also implicated in brain tissue damagedue to reperfusion injuryin stroke(Clark, 2005).

The excessive production of cytokines is what leads to the death of individuals that are infected with avian flu. The cytokines are produced by the immune system as a defensive reaction (much like an allergic reaction), and excessive levels cause the airways to become blocked. The young and healthy are more likely to succumb to avian flu because the vigorous response of their immune systems leads to excessive levels of cytokines.

Types

There are three classes of cytokines. Hundreds of cytokines have been discovered, and the rate of discovery shows no sign of slowing. Some of the better-known cytokines include: TNF-α, IL-1, and IL-6.

Most cytokines are not growth factors.

Characteristics

Cytokines weigh from 8 to 30 kDaand are active in picomolarconcentrations (Clark, 2005).

History

The first lymphokines were identified in the mid-1960's, with the best-known being migration inhibition factor (MIF), simultaneously discovered by John David and Barry Bloom. The first cytokines were identified in cultures of kidney cells, by Stanley Cohen and his colleagues, in 1974.

See also

• Adipokines
• Apoptosis
• Chemokines
• Cytokine secretion assay
• Cytokine storm
• ELISPOT
• Interleukins
• Interferon
• Granulocyte-colony stimulating factor
• Signal transduction
• Tumor necrosis factor

External links

• Cytokine Tutorial
• Cell Interactions: Cytokines
• Reperfusion Injury in Stroke.
• Cytokines Online Pathfinder Encyclopaediade:Zytokin

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This article is licensed under the GNU Free Documentation License.
It uses material from the http://en.wikipedia.org/wiki/Cytokines Wikipedia article Cytokines.