Cytokines: Types and Functions

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.

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