Cytokines

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## Contents

* 1 Categorizing by source
* 2 Categorizing by target
* 3 Categorizing by structure
* 4 Categorizing by receptor
* 5 Categorizing by hybrid, functional organization
* 6 References

In medicine, cytokines are the primary intercellular chemical messengers of the immune system. Chemically, they are water-soluble proteins and glycoproteins with a mass of 8 to 30 kDaltons (kDa). These protein messengers are produced and released by cells of the immune system such as B-lymphocytes, macrophages and T-lymphocytes. Their actions are essential to the the activation and control of immune responses and the development of blood cells. Once they attach to the surface of a target cell, they may invoke a second messenger system, which causes a release, inside the cell, of chemical messenger(s) that cause specific activities. Those activities may include the extracellular release of additional, usually differentiated cytokines, so cells amplify cytokines. Mammalian cytokines are "non-antibody proteins secreted by inflammatory leukocytes and some non-leukocytic cells, that act as intercellular mediators. They differ from classical hormones in that they are produced by a number of tissue or cell types rather than by specialized glands. They generally act locally in a paracrine or autocrine rather than endocrine manner."[1] Examples include growth factors,interferons, interleukins, and tumor necrosis factor.

Plants may synthesize cytokines, which affect the plants, but some, such as abscisic acid, also affect humans.[2] In botany, however, the cytokinins are a group distinct from animal cytokines.

Cytokine is not the universal name for the group.[3] Other name refer to sources of specific kinds of cytokines, or their categorizing by target of action. Once the amino acid sequence of a cytokine is known, by convention, it is reclassified as an interleukin. [4]

## Categorizing by source[edit]

They may be named by their source:

* lymphokine (cytokines made by lymphocytes)
* monokine (cytokines made by monocytes)
* chemokine (cytokines with chemotactic activities)
* interleukin (cytokines made by one leukocyte and acting on other leukocytes).

## Categorizing by target[edit]

They also may be categorized by their target; some cytokines have more than one of the type:

* On the secreting cell: autocrine cytokine
* on nearby cells: paracrine
* on distant cells: endocrine action. This last group overlaps releasing factors and hormones.

## Categorizing by structure[edit]

Structurally, cytokines can be classified into several classes: [5]

* four alpha-helix bundle family consisting of the IL-2 subfamily (including erythropoietin and thrombopoietin,
* interferon subfamily (approximately 20 α-interferon and 1 β-interferon in Type I, one β-interferon in Type II) and the IL-10 subfamily[6]
* IL-1 family (primarily IL-1 and IL-18)
* IL-17 family
* chemokine family

## Categorizing by receptor[edit]

* Immunoglobulin (Ig-x) superfamily are found throughout the body (eg, IL-1 receptor types)
* Interferon (type 2) family includes IFN beta and gamma receptors.
* Tumor necrosis factor (TNF) (type 3) family is composed of receptors sharing a cystein-rich extracellular binding domain and includes non-cytokine ligands such as CD40, CD27, and CD30 in addition to TNF.
* 7-transmembrane helix family that includes all G-protein coupled receptors (GPCRs), such as the chemokine receptors CXCR4 and CCR5 (HIV binding proteins) belong to this family.

## Categorizing by hybrid, functional organization[edit]

Major chemical families include:

* Interleukins (IL) (formally called lymphocyte activating factor)
* Interferons (INF)
* Tumor necrosis factors (TNF)
* Granulocyte-Monocyte Colony Stimulating Factor
* Erythrocyte Stimulating Factor
* Macrophage chemotactic protein (MCP)
* Macrophage inflammatory protein (MIP)

Selected cytokines Name(s)  | Source  | Target  | Function

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Il-1a, IL-1b  | monocytes, macrophages, B-lymphocytes, DC  | Th cells, B cells, NK cells, general inflammation-susceptible  | Th cell co-stimulation, B-lymphocyte maturation and proliferation, NK cell activation, general inflammation
IL-2  | Th1 cells  | activated T- and B-lymphocytes, NK cells  | growth, proliferation, activation
IL-3  | Th cells, NK cells  | stem cells, mast cells  | stem cell growth and differentiation, mast cells growth and histamine release
IL-4  | Th2 cells  | activated B cells, macrophages, T cells  | IgG1 and IgE synthesis ,macrophage MHC Class II, T cell growth, B cell growth
IL-5  | Th2 cells  | activated B cells  | proliferation and differentiation, IgA synthesis
IL-6  | monocytes, macrophages, T-helper subtype 2 lymphocytes (Th2 cells), stromal cells  | activated B cells, plasma cells, stem cells,  | differentiate B lymphocytes (B cells) into plasma cells, plasma cell antibody secretion, stem cell differentiation, general acute phase response, increases hepcidin secretion
IL-7  | marrow and thymus stroma  | stem cells  | differentiation
IL-8  | macrophages and endothelial cells  | neutrophils  | chemotaxic attraction of neutrophils
IL-10  | Th2 cells  | macrophages, B-cells  | downregulate cytokine production by macrophages, activate B-lymphocytes
IL-12  | macrophages, B cells  | activated Tc cells, natural killer cells  | In combination with IL-2, differentiate Tc cells into CTL; activate NK
IL-13  | TH2 cells  |  | Similar to IL-4
GM-CSF  | Th cells  | progenitor cells  | growth and differentiation of monocytes and dendritic cells (DC)
|  |  |

## References[edit]

1. ↑ Anonymous (2025), Cytokines (English). Medical Subject Headings. U.S. National Library of Medicine.
2. ↑ Nicole LeBrasseur (23 April 2007), "Plant hormone is human cytokine", J Cell Biol 177, DOI:10.1083/jcb.1772rr1.
3. ↑ Decker, Janet, Cytokines, Welcome to webImmunology 419!, University of Arizona
4. ↑ Ganong, William F. (Nineteenth edition, 1999), Review of Medical Physiology, Appleton & Lange,pp. 498-499
5. ↑ What are cytokines?, Ion Channel Media Group Ltd.
6. ↑ The International Society for Interferon and Cytokine Research (ISICR), Interferons: A primer for the non-scientist