Human apo-SAA is a 104 amino acid polypeptide that circulates primarily in association with high-density lipoproteins (HDL). The level of apo-SAA, normally 1-5 μg/ml in plasma, increases 500-1000 fold within 24 hours of an inflammatory stimulus and, under these conditions, is the most abundant HDL apo-lipoprotein. The human SAA gene codes for a 122 amino acid polypeptide, which contains an 18 amino acid N-terminal signal sequence.
Serum amyloid A (SAA) is found normally at concentrations of 0.1μM in blood. However, its concentration increases up to 1000-fold under stress. It has been associated with several chronic inflammatory diseases, such as atherosclerosis. It is found to participate in the inflammatory response by facilitating chemotaxis, migration, and adhesion of inflammatory cells, particularly monocytes/macrophages. SAA is also found to induce the synthesis and secretion of multiple kinds of inflammatory cytokines, such as TNF-α (tumor necrosis factor-α), IL-1β (interleukin-1β), MCP-1 (monocyte chemoattractant protein-1), and Lp-PLA2 (lipoprotein-associated phospholipase A2).
