Mitogen

A mitogen is a chemical substance that encourages a cell to commence cell division, triggering mitosis. A mitogen is usually some form of a protein. Mitogenesis is the induction (triggering) of mitosis, typically via a mitogen. Mitogens trigger signal transduction pathways in which mitogen-activated protein kinase (MAPK) is involved, leading to mitosis.

Use in immunology

Lymphocytes can enter mitosis when they are activated by mitogens or antigens. B cells specifically can divide when they encounter an antigen matching their immunoglobulin. T cells undergo mitosis when stimulated by mitogens to produce small lymphocytes that are then responsible for the production of lymphokines, which are substances that modify the host organism to improve its immunity. B cells, on the other hand, divide to produce plasma cells when stimulated by mitogens, which then produce immunoglobulins, or antibodies.^[1] Mitogens are often used to stimulate lymphocytes and thereby assess immune function. The most commonly used mitogens in clinical laboratory medicine are:

Name	Acts upon T cells?	Acts upon B cells?
phytohaemagglutinin (PHA)	yes	no
concanavalin A (conA)	yes	no
lipopolysaccharide (LPS)	no	yes
pokeweed mitogen (PWM)	yes	yes

Lipopolysaccharide toxin from gram-negative bacteria is thymus-independent. They may directly activate B cells, regardless of their antigenic specificity. Plasma cells are terminally differentiated and, therefore, cannot undergo mitosis. Memory B cells can proliferate to produce more memory cells or plasma B cells. This is how the mitogen works, that is, by inducing mitosis in memory B cells to cause them to divide, with some becoming plasma cells.

Mitogens in human physiology

Insulin-like Growth Factor 1 mediates the major growth-promoting effect of Human Growth Hormone as a paracrine agent at growth plates in the skeletal system. Another example for mitogen agent is G-CSF.

Other uses

Mitogen-activated protein kinase (MAPK) pathways can induce enzymes such as the COX-2 enzyme.^[2] MAPK pathways may also play a role in the regulation of PTGS2.^[3]

References

↑ Barret, James (1980). Basic Immunology and its Medical Application (2 ed.). St.Louis: The C.V. Mosby Company. p. 52-3. ISBN 0-8016-0495-8.
↑ Font-Nieves, M; Sans-Fons, MG (2012). "Induction of COX-2 enzyme and down-regulation of COX-1 expression by lipopolysaccharide (LPS) control prostaglandin E2 production in astrocytes". Journal of Biological Chemistry. 24;287: 6454–68. doi:10.1074/jbc.M111.327874. PMID 22219191.
↑ Casciani, V; Marinoni, E (2008). "Opposite effect of phorbol ester PMA on PTGS2 and PGDH mRNA expression in human chorion trophoblast cells". Reproductive Sciences. 15: 40–50. doi:10.1177/1933719107309647. PMID 18212353.

External links

Mitogens at the US National Library of Medicine Medical Subject Headings (MeSH)

MAP kinase activation

Initiation	Mitogen

MAP kinase kinase kinase (MAP3K or MKKK)	MAP kinase kinase kinases MAP3K1 MAP3K2 MAP3K3 MAP3K4 MAP3K5 MAP3K6 MAP3K7 MAP3K8 RAFs RAF1 ARAF BRAF KSR1 KSR2) MLKs MAP3K12 MAP3K13 MAP3K9 MAP3K10 MAP3K11 MAP3K7 ZAK CDC7

MAP kinase kinase (MAP2K or MKK)	MAP2K1 MAP2K2 MAP2K3 MAP2K4 MAP2K5 MAP2K6 MAP2K7

MAP kinase	Extracellular signal-regulated kinases MAPK1 MAPK3 C-Jun N-terminal kinases MAPK8 MAPK9 MAPK10 P38 mitogen-activated protein kinases MAPK11 MAPK12 MAPK13 MAPK14 ERK5 kinase MAPK7 Atypical MAPKs MAPK4 MAPK6 MAPK15 NLK

Phosphatase	MAPK phosphatase

Protein: lectins

Animal

C-type lectins	Asialoglycoprotein receptor KLRD1 Collectin Mannan-binding lectin Mannose receptor proteochondroitin sulfate Aggrecan Versican Brevican Neurocan

Other	Calnexin Calreticulin CD22 CD33 Galectin Myelin-associated glycoprotein N-Acetylglucosamine receptor Selectin Sialoadhesin

Plant

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