Cytokines are bioactive hormones, normally glycoproteins, which exercise a wide variety of biological effects on those cells which express the appropriate receptors. Cytokines are designated by their cellular origin such that
- Monokines include those interleukins produced by macrophages/ monocytes,
- lymphokines include those interleukins produced by lymphocytes.
- Interleukins is used for cytokines which mostly influence cellular interactions.
All cytokines are cyto-regulatory proteins with molecular weights under 60 kDa (in most cases under 25 kDa). They are produced locally, have very short half-lives (a matter of seconds to minutes), and are effective at picomolar concentrations. The effects of cytokines may be:
- paracrine (acting on cells near the production locus), or
- autocrine (the same cell both produces, and reacts to, the cytokine).
By way of interaction with highly specific cell surface receptors, cytokines can induce cell-specific or more general effects (including mediator release, expression of differentiation molecules and regulation of cell surface molecule expression). The functions of cytokines are usually pleiotropic, in that they display a number of effects of the same, or of a different, nature on one or more cell types.
Below is a summary of cytokine functions:
- Promotion of inflammation: IL-1, IL-6, TNFα, chemokines (e.g., IL-8).
- Inhibition of inflammation: IL-10, TGFß.
- Promotion of hematopoiesis: GM-CSF, IL-3, G-CSF, M-CSF, IL-5, IL-7.
- Activating B cells: CD40L, IL-6, IL-3, IL-4.
- Activating T cells: IL-2, IL-4, IL-10, IL-13, IL-15.
- Anti-infectious: IFNα, IFNß, IFNγ, TNFα.
- Anti-proliferative: IFNα, IFNß, TNFα, TGFß.