Background |
Acute phase proteins (APPs) are blood proteins that are an integral part of acute phase responses (APR). The APR is a part of the innate host defense system which is triggered by tissue damage and inflammation caused by infectious, immunologic, or neoplastic agents. One of the well-characterized APPs, serum amyloid A (SAA) is a 11.4 - 12.5 kDa protein consisting of 104 - 112 amino acids in different species. The protein is well-conserved in the evolution of eutherian mammals, indicating an important role in biological functions. The N-terminus of the molecule is hydrophobic and probably responsible for its lipid-binding properties which allows SAA to form complexes with high-density lipoproteins as well as apoproteins. In inflamed tissues, macrophages serve as a major source of SAA. In fact, during APR, SAA levels in plasma increase 1000-fold in human and other species, suggesting it may be an important indicator of disease status. Elevated SAA levels are also seen in rheumatoid arthritis, atherosclerosis, Crohn’s disease, and Type 2 diabetes. These findings suggest that SAA may play an active and/or a protective role in inflammatory disorders. |