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).

Overview

The acute phase reaction is a part of the innate immune system's response to infection, tissue injury, or inflammatory disease. It is characterized by changes in the concentrations of several plasma proteins, known as acute phase proteins. These proteins are primarily produced in the liver and released into the bloodstream in response to cytokines such as interleukin-6 (IL-6), interleukin-1 (IL-1), and tumor necrosis factor-alpha (TNF-alpha).

Positive Acute Phase Proteins

Positive acute phase proteins increase in concentration during the acute phase reaction. Examples include C-reactive protein (CRP), serum amyloid A (SAA), fibrinogen, procalcitonin, and mannose-binding lectin (MBL). These proteins play various roles in the immune response, such as activating the complement system, promoting phagocytosis, and aiding in cell adhesion.

Negative Acute Phase Proteins

Negative acute phase proteins decrease in concentration during the acute phase reaction. Examples include albumin, transferrin, and transthyretin. The decrease in these proteins is thought to be due to a redirection of the liver's resources towards the production of positive acute phase proteins.

Clinical Significance

Changes in the levels of acute phase proteins can be used as biomarkers for various conditions. For example, elevated levels of CRP are used as a marker of inflammation and infection, and can also indicate a higher risk of cardiovascular disease. Similarly, decreased levels of albumin can indicate malnutrition or liver disease.

See Also

• Inflammation
• Innate immune system
• Cytokines
• Biomarkers