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.
Table of Contents
Types of Cytokines
Cytokines coordinate and regulate various physiological responses, including inflammation, immune responses, and hematopoiesis (the formation of blood cells). Here are some common types of cytokines:
Interleukins (IL)
Interleukins are a large group of cytokines that act as signaling molecules between leukocytes (white blood cells). They play critical roles in regulating immune responses, inflammation, and communication between different immune cells. Examples include IL-1, IL-2, IL-6, and IL-12.
Tumor Necrosis Factors (TNF)
Tumor Necrosis Factors are cytokines that aids in regulating immune cells and inflammation. TNF-alpha and TNF-beta are examples of cytokines within this family. TNF-alpha, in particular, plays a central role in the inflammatory response.
Interferons (IFN)
Interferons are useful in antiviral defense and modulating immune responses. They can be further categorized into Type I (IFN-alpha and IFN-beta) and Type II (IFN-gamma). The production of Type I interferons is a response to viral infections, while IFN-gamma production involves in immune regulation.
Chemokines
Chemokines are cytokines that attract immune cells to specific sites in the body. They have a crucial role in cell migration and positioning during immune responses. Examples include CCL (C-C motif ligand) and CXCL (C-X-C motif ligand) chemokines.
Transforming Growth Factors (TGF)
Transforming Growth Factors involve various cellular processes, including cell growth, differentiation, and immune regulation. TGF-beta is a well-known cytokine in this family with immunosuppressive properties.
Colony-stimulating factors (CSF)
Colony-stimulating factors (CSFs) regulate the production and differentiation of white blood cells (WBCs) in the bone marrow and have a crucial role in hematopoiesis. Examples include granulocyte-colony stimulating factor (G-CSF) and macrophage-colony stimulating factor (M-CSF).
Interleukin-1 Family
IL-1 family cytokines include IL-1 alpha, IL-1 beta, and IL-18. They are involved in inflammatory responses and immune regulation. IL-1, in particular, plays a central role in initiating inflammation.
Interleukin-17 Family
IL-17 family cytokines, including IL-17A and IL-17F, are associated with inflammatory and autoimmune responses. They help recruit immune cells and induce pro-inflammatory mediators.
Interleukin-10 (IL-10)
IL-10 is an anti-inflammatory cytokine that suppresses immune responses. It aids in regulating the balance between pro-inflammatory and anti-inflammatory signals.
IL-12 Family
IL-12 and IL-23 are members of the IL-12 family and play essential roles in immune responses. They differentiate T cells and activate natural killer (NK) cells.
These are just a few examples of the diverse range of cytokines, and many more have been identified, each with specific functions in regulating immune responses and maintaining homeostasis in the body. The balance and coordination of cytokine signaling are critical for a properly functioning immune system. Dysregulation of cytokine production and signaling can contribute to various diseases, including autoimmune disorders and chronic inflammatory conditions.
Function of Cytokines
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.
References
- Levinson. (2010). Review of Medical Microbiology and Immunology. McGraw-Hill.
- Zhang, J. M., & An, J. (2007). Cytokines, inflammation, and pain. International anesthesiology clinics, 45(2), 27–37. https://doi.org/10.1097/AIA.0b013e318034194e