Acute phase protein

Overview
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.

Examples
The notable are:
 * D-dimer protein
 * C-reactive protein
 * Mannose-binding protein
 * Alpha 1-antitrypsin
 * Alpha 1-antichymotrypsin
 * Alpha 2-macroglobulin
 * some coagulation factors (Fibrinogen, prothrombin, factor VIII, von Willebrand factor, plasminogen)
 * Complement factors
 * Ferritin
 * Serum amyloid P component (see amyloid)
 * Serum amyloid A
 * Prealbumin

Serum albumin concentrations fall in acute disease states. For this reason albumin is sometimes referred to as a negative acute phase protein.

Clinical significance
Measurement of acute phase proteins is a useful marker of inflammation in both medical and veterinary clinical pathology. It correlates with the erythrocyte sedimentation rate (ESR).