Anaphylatoxin
McGraw-Hill Science & Technology Dictionary:
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anaphylatoxin
(¦an·ə′fil·ə′täk·sən)
(immunology) The vasodilator principal, a toxic substance released by tissues of sensitized animals when antigen and antibody react.
American Heritage Stedman's Medical Dictionary:
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an·a·phyl·a·tox·in
or an·a·phyl·o·tox·in (ăn'ə-fĭl'ə-tŏk'sĭn)
n.
n.
A substance that may cause the release of histamine and other compounds that cause hypersensitivity, thus triggering some or all of the symptoms of anaphylaxis.
Oxford Dictionary of Biochemistry:
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anaphylatoxin
any of a group of substances that mediate inflammation and are produced in serum during the fixation of complement, especially during the production of C3a and C5a. They cause mast cell degranulation and histamine release.
| anaphylactoid reaction, anaphylactic shock, anaphase promoting complex | |
| anaphylaxis, anaplasia, anaplerosis |
Saunders Veterinary Dictionary:
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anaphylatoxin
A substance produced in blood serum when complement is activated; serves as a mediator of inflammation by inducing mast cell degranulation, histamine release and increased vascular permeability, and on injection into animals, it causes anaphylactic shock.
- a. inhibitor — a specific serum carboxypeptidase, one of the complement proteins.
Wikipedia on Answers.com:
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Anaphylatoxin
| Anaphylotoxin-like domain | |||||||||
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| Structure of porcine C5adesArg.[1] | |||||||||
| Identifiers | |||||||||
| Symbol | ANATO | ||||||||
| Pfam | PF01821 | ||||||||
| InterPro | IPR000020 | ||||||||
| SMART | ANATO | ||||||||
| PROSITE | PDOC00906 | ||||||||
| SCOP | 1c5a | ||||||||
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Anaphylatoxins, or anaphylotoxins, are fragments ( C3a, C4a and C5a) that are produced as part of the activation of the complement system.[2]. Complement components C3, C4 and C5 are large glycoproteins that have important functions in the immune response and host defense.[3] They have a wide variety of biological activities and are proteolytically activated by cleavage at a specific site, forming a- and b-fragments.[4] A-fragments form distinct structural domains of approximately 76 amino acids, coded for by a single exon within the complement protein gene. The C3a, C4a and C5a components are referred to as anaphylatoxins.[4][5]: they cause smooth muscle contraction, histamine release from mast cells, and enhanced vascular permeability.[5] They also mediate chemotaxis, inflammation, and generation of cytotoxic oxygen radicals.[5] The proteins are highly hydrophilic, with a mainly alpha-helical structure held together by 3 disulphide bridges.[5]
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Contents
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Function
Anaphylatoxins are able to trigger degranulation (release of substances) of endothelial cells, mast cells or phagocytes, which produce a local inflammatory response. If the degranulation is widespread, it can cause a shock-like syndrome similar to that of an allergic reaction.
Anaphylatoxins indirectly mediate:
- smooth muscle cells contraction, for example bronchospasms
- increase in the permeability of blood capillaries
- chemotaxis — receptor-mediated movement of leukocytes in the direction of the increasing concentration of anaphylatoxins
Examples
Important anaphylatoxins:
- C5a has the highest specific biological activity and is able to act directly on neutrophils and monocytes to speed up the phagocytosis of pathogens.
- C3a works with C5a to activate mast cells, recruit antibody, complement and phagocytic cells and increase fluid in the tissue, all of which contribute to the initiation of the adaptive immune response.
- C4a is the least active anaphylatoxin.
Terminology
Although some drugs (morphine, codeine, synthetic ACTH) and some neurotransmitters (norepinephrine, substance P) are important mediators of degranulation of mast cells or basophils, they are generally not called anaphylatoxins. This term is reserved only for fragments of the complement system.
Human proteins containing this domain
C3, C4A, C4B, C4B-1, C5, FBLN1, FBLN2
See also
- Allergy
- Anaphylatoxin receptors
- Anaphylaxis
- Complement system
- Inflammation
- Immune system
- Nervous system
References
- ^ Williamson MP, Madison VS (March 1990). "Three-dimensional structure of porcine C5adesArg from 1H nuclear magnetic resonance data". Biochemistry 29 (12): 2895–905. doi:10.1021/bi00464a002. PMID 2337573.
- ^ Hugli TE (1986). "Biochemistry and biology of anaphylatoxins". Complement 3 (3): 111–27. PMID 3542363.
- ^ Fritzinger DC, Petrella EC, Connelly MB, Bredehorst R, Vogel CW (1992). "Primary structure of cobra complement component C3". J. Immunol. 149 (11): 3554–3562. PMID 1431125.
- ^ a b Rosa PA, Ogata RT, Zepf NE (1989). "Sequence of the gene for murine complement component C4". J. Biol. Chem. 264 (28): 16565–16572. PMID 2777798.
- ^ a b c d Gennaro R, Simonic T, Negri A, Mottola C, Secchi C, Ronchi S, Romeo D (1986). "C5a fragment of bovine complement. Purification, bioassays, amino-acid sequence and other structural studies". Eur. J. Biochem. 155 (1): 77–86. doi:10.1111/j.1432-1033.1986.tb09460.x. PMID 3081348.
Janeway et al. Immunobiology Garland Science Publishing 2005
External links
- MeSH Anaphylatoxin
- Anaphylatoxin at eMedicine Dictionary
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This article incorporates text from the public domain Pfam and InterPro IPR000020
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McGraw-Hill Science & Technology Dictionary
McGraw-Hill Dictionary of Scientific and Technical Terms. Copyright © 2003, 1994, 1989, 1984, 1978, 1976, 1974 by McGraw-Hill Companies, Inc. All rights reserved.
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American Heritage Stedman's Medical Dictionary
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company.
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Oxford Dictionary of Biochemistry
Oxford University Press. Oxford Dictionary of Biochemistry and Molecular Biology © 1997, 2000, 2006 All rights reserved.
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Saunders Veterinary Dictionary
Saunders Comprehensive Veterinary Dictionary 3rd Edition. Copyright © 2007 by D.C. Blood, V.P. Studdert and C.C. Gay, Elsevier. All rights reserved.
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