Acute-phase proteins

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).

Overview

The acute-phase reaction characteristically involves fever, an increase in circulating leukocytes, and a variety of metabolic and hormonal changes. The reaction is part of the body's immune system response to injury or inflammation. The increase in acute-phase proteins is primarily due to increased production by the liver.

Positive Acute-Phase Proteins

Positive acute-phase proteins include C-reactive protein, serum amyloid A, fibrinogen, procalcitonin, haptoglobin, and alpha 1-antitrypsin. These proteins show increased plasma concentration during inflammation.

Negative Acute-Phase Proteins

Negative acute-phase proteins include albumin, transferrin, transthyretin, and retinol-binding protein. These proteins show decreased plasma concentration during inflammation.

Function

The function of acute-phase proteins is generally defensive. They aid in the immune response by increasing local inflammation and recruiting macrophages and neutrophils. Some acute-phase proteins bind microbial products and prevent their spread.

Clinical Significance

Changes in the levels of acute-phase proteins in the blood can be used as markers of inflammation or infection. They are used in clinical medicine to assess disease activity and the effectiveness of treatment.