Acute phase reactant

Acute phase reactants are a class of proteins whose plasma concentrations increase (positive acute phase reactants) or decrease (negative acute phase reactants) 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 injury, infection, or inflammation. The liver primarily produces acute phase reactants, although all body tissues can produce some. The reaction is characterized by the increased production of a large number of proteins in the liver, which are then released into the blood.

Positive Acute Phase Reactants

Positive acute phase reactants are proteins whose serum levels increase in response to inflammation. Examples include C-reactive protein (CRP), fibrinogen, serum amyloid A (SAA), haptoglobin, and procalcitonin. These proteins play various roles in the immune response, including activating the complement system, neutralizing enzymes, and binding free hemoglobin.

Negative Acute Phase Reactants

Negative acute phase reactants are proteins whose serum levels decrease in response to inflammation. Examples include albumin, transferrin, transthyretin, and retinol-binding protein. The decrease in these proteins' levels is thought to be due to their being used up in the inflammatory response or being broken down more quickly.

Clinical Significance

Acute phase reactants are often measured in clinical medicine to assess the presence and intensity of inflammation or tissue injury. They can also be used to monitor the progress of disease or the effectiveness of treatment. For example, a high level of CRP is a marker of inflammation and can be used to monitor inflammatory diseases such as rheumatoid arthritis or lupus.

See Also

• Inflammation
• Innate immune system
• C-reactive protein
• Fibrinogen
• Serum amyloid A
• Haptoglobin
• Procalcitonin
• Albumin
• Transferrin
• Transthyretin
• Retinol-binding protein