Cytokines are important in the communication between cells of multicellular organisms. They are pleiotropic intercellular mediators in controling the survival, growth, proliferation, differentiation and effector functions of cells, and play a key role in normal homeostatic tissue function as well as the regulation of the immune response, particularly during infections, inflammation, neurological and endocrinological autoimmune diseases.
The activation stimulus (such as bacteria, viruses, fungi and parasites, as well as
mechanical injury and toxic stimuli) leads to the immune response. It is called specific,
because recognition molecules should ideally be specific for a single ligand. The cells
responsible for these immune responses include monocyte, mast cell, macrophage,
neutrophil, eosinophil, basophil, B and T lymphocyte. These cells secret cytokines
which are small proteins providing cells with the ability to communicate with one
another and orchestrate complex multicellular behavior, therefore regulating diverse
functions in the immune response including proliferation, differentiation, migration
and function of immunocytes.
The potency of cytokines, and the potential for amplification and damage which
excessive cytokine production carries, has resulted in elaborate controls on cytokine
production and action. Cytokines include interleukins (IL), interferons (IFN),
chemokines, tumor necrosis factors (TNF) and growth factors that have been
classified on the basis of their biological responses into pro- or anti-inflammatory
catalogs, depending on their effects on immunocytes.