Cytokines are a large, diverse group of soluble, peptides and proteins (mostly glycoproteins) that serves as important signalling molecules and perform regulatory functions. Cytokines are regulatory proteins that are produced and secreted by various leukocytes and non-immune cells which control immune response, hematopoiesis, inflammation, wound repair and tissue morphogesis. Cytokines can alter the behaviour of the cell from which it was produced (autocrine fucntion), of a neighbouring cell (paracrine function), or of a distant cell (endocrine function). Cytokines can be secreted but can also be expressed on the cell membrane and some are held in the intra cellular matrix. The vast network of cytokines can be loosely organised into families that share similar functionality. There are several types of cytokines and these belong to one of five families, chemokines, interferons, interleukins, growth factors and tumour necrosis factor (TNF).

The TNF ligand family includes the important cytokine TNF and other structurally related ligands such as lymphotoxin and B cell activating factor (BAFF). Growth factors are a large family of molecules that include a number of hormones involved in organogenesis. Lastly, the chemokines are a subgroup of cytokines that primarily function as chemottractants.
Cytokines are important in the immune response when the body becomes under attack. Cytokines help regulate the intensity and duration of immune responses. Together with a network of specific receptors, cytokines provide a means by which cells can communicate with each other. Cytokines bind to specific receptors on the cell surface of the target cell. Once bound to their receptors, cytokines exert their effects through the initiation of an intracellular signalling cascade, which is important in controlling the development, execution and resolution of immune responses. Therefore, cytokines are a fundamental component of the immune system, without which immune cells would cease...