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

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	inhibitor of coagulation by inhibiting thrombin. inhibitor of fibrinolysis by inhibiting plasmin
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	recruitment of immune cells to inflammatory sites induction of enzymes that degrade extracellular matrix
Ceruloplasmin	Oxidizes iron, facilitating for ferritin, inhibiting microbe iron uptake
Haptoglobin	Bind hemoglobin, inhibiting microbe iron uptake

Negative

"Negative" acute phase proteins:

Protein	Immune system function of decrease
Albumin
Transferrin
Transthyretin
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

References

See also

External links