Cytokines are small molecules that are released by cells to modify the behaviour of the surrounding cells. Cytokines play a major role in modulating the immune system. Among the large number of cytokines are the interferons, tumour necrosis factor and the interleukins.

Cytokines are manufactured and released by cells of the immune system and perform a variety of functions including cell activation, inflammation, tissue breakdown and repair and cell death.

Cytokines belong to a group of molecules called proteins. They are directly coded for in the DNA. Cytokines are relatively small proteins and often comprise of just a single chain of amino acids.

A sub-group of cytokines are the chemokines. These attract more cells of the immune system and play an important role in the initiation of the inflammatory response.

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