[Serum amyloid A (SAA)--pathogenicity and implication of appearance in plasma].

Serum amyloid A, SAA, is a plasma precursor of reactive amyloid fibrils and a sensitive acute phase reactant. The prolonged high production of SAA in chronic inflammation is the most essential for amyloidogenesis. In addition, impaired catabolism of SAA and SAA polymorphism may enhance disease development. SAA1 polymorphism affects the plasma concentration of SAA, probably because of differences in plasma clearance. Interestingly, amyloidogenic polymorphism (SAA1.3) does not show a high plasma SAA concentration. The true significance of SAA polymorphism in amyloidogenesis and physiological function is under investigation. Although SAA is produced primarily in the liver, attention has recently focused on extra-hepatic production and its physiological significance. In non-inflammatory conditions, the extrahepatic sites may constantly produce SAA while the expression may be suppressed in the liver. Therefore, it is possible that some parts of SAA in non-inflamed plasma are derived from extrahepatic sites such as adipose tissues and cells in the vascular wall.