Anaphylatoxin

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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.^[1]

Functions

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 too strong, 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.

See also

• Allergy
• Anaphylatoxin receptors
• Anaphylaxis
• Complement system
• Inflammation
• Immune system
• Nervous system

References

Janeway et al. Immunobiology Garland Science Publishing 2005

External links

• MeSH Anaphylatoxin
• Anaphylatoxin at eMedicine Dictionary