Acute phase protein

Acute-phase proteins are a class of proteins whose plasma concentrations increase (positive acute phase proteins) or decrease (negative acute phase proteins) in response to inflammation. This response is called the acute-phase reaction (also called acute phase response).

In response to injury, local inflammatory cells (neutrophil granulocytes and macrophages) secrete a number of cytokines into the bloodstream, most notable of which are the interleukins IL-1, IL-6 and IL-8, and TNF-α.

The liver responds by producing a large number of acute-phase reactants. At the same time, the production of a number of other proteins is reduced; these are therefore referred to as "negative" acute phase reactants.


Positive acute-phase proteins serve different physiological functions for the immune system. Some act to destroy or inhibit growth of microbes, e.g. C-reactive protein, Mannose-binding protein, complement factors, ferritin, ceruloplasmin, Serum amyloid A and haptoglobin. Others give negative feedback on the inflammatory response, e.g. serpins. Alpha 2-macroglobulin and coagulation factors affect coagulation.

"Positive" acute phase proteins:
Protein Immune system function
C-reactive protein Opsonin on microbes
D-dimer protein fibrin degradation product
Mannose-binding protein Mannan-binding lectin pathway
Alpha 1-antitrypsin serpin, downregulates inflammation
Alpha 1-antichymotrypsin serpin, downregulates inflammation
Alpha 2-macroglobulin

Fibrinogen, prothrombin, factor VIII, von Willebrand factor, plasminogen coagulation factors
Complement factors Complement system
Ferritin Binding iron, inhibiting microbe iron uptake
Serum amyloid P component (see amyloid)
Serum amyloid A

Ceruloplasmin Oxidizes iron, facilitating for ferritin, inhibiting microbe iron uptake
Haptoglobin Bind hemoglobin, inhibiting microbe iron uptake


"Negative" acute phase proteins:
Protein Immune system function of decrease
Transcortin Decreased binding of cortisol, upregulation of inflammation
Retinol binding protein

Clinical significance

Measurement of acute phase proteins, especially C-reactive protein, is a useful marker of inflammation in both medical and veterinary clinical pathology. It correlates with the erythrocyte sedimentation rate (ESR).

They may also indicate liver failure


See also

External links

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