Acute-phase protein
Acute-phase proteins (APPs) are a class of
In response to
Regulation of synthesis
Positive
Positive acute-phase proteins serve (as part of the innate immune system) different physiological functions within the
Protein | Immune system function |
---|---|
C-reactive protein | Opsonin on microbes[4] (not an acute-phase reactant in mice) |
Serum amyloid P component | Opsonin |
Serum amyloid A |
|
Complement factors | Opsonization, lysis and clumping of target cells. Chemotaxis
|
Mannan-binding lectin | Mannan-binding lectin pathway of complement activation
|
Coagulation factors , trapping invading microbes in blood clots.Some cause chemotaxis | |
Plasminogen activator inhibitor-1 (PAI-1) | Prevents the degradation of blood clots by inhibiting tissue Plasminogen Activator (tPA)
|
Alpha 2-macroglobulin |
|
Ferritin | Binding iron, inhibiting microbe iron uptake[6] |
Hepcidin[7] | Stimulates the internalization of macrophages
|
Ceruloplasmin | Oxidizes iron, facilitating for ferritin, inhibiting microbe iron uptake |
Haptoglobin | Binds hemoglobin, inhibiting microbe iron uptake and prevents kidney damage |
Orosomucoid (Alpha-1-acid glycoprotein, AGP) |
Steroid carrier |
Alpha 1-antitrypsin
|
Serpin, downregulates inflammation |
Alpha 1-antichymotrypsin | Serpin, downregulates inflammation |
Lipopolysaccharide binding protein (LBP) | Attaches to bacterial pattern recognition receptors[8]
|
Negative
"Negative" acute-phase proteins decrease in inflammation. Examples include albumin,[9] transferrin,[9] transthyretin,[9] retinol-binding protein, antithrombin, transcortin. The decrease of such proteins may be used as markers of inflammation. The physiological role of decreased synthesis of such proteins is generally to save amino acids for producing "positive" acute-phase proteins more efficiently. Theoretically, a decrease in transferrin could additionally be decreased by an upregulation of transferrin receptors, but the latter does not appear to change with inflammation.[10]
While the production of C3 (a complement factor) increases in the liver, the plasma concentration often lowers because of an increased turn-over, therefore it is often seen as a negative acute-phase protein.[citation needed]
Clinical significance
Measurement of acute-phase proteins, especially C-reactive protein, is a useful marker of inflammation in both medical and veterinary
References
- ^ PMID 21430962.
- ^ Abbas A, Lichtman A, Pillai S (2012). Basic immunology Functions and Disorders of the Immune System (4th ed.). Philadelphia, PA: Saunders/Elsevier. p. 40.
- PMID 19438602.
- ISBN 978-0-7817-9543-2. Page 182
- PMID 7693593.
- PMID 20711357.
- PMID 19679815.
- PMID 11502220.
- ^ PMID 10633294.
- PMID 10627880.
- PMID 15966220.
External links
- http://eclinpath.com/chemistry/proteins/acute-phase-proteins/
- Acute-Phase+Proteins at the U.S. National Library of Medicine Medical Subject Headings (MeSH)