Journal
CURRENT MEDICINAL CHEMISTRY
Volume 23, Issue 17, Pages 1725-1755Publisher
BENTHAM SCIENCE PUBL LTD
DOI: 10.2174/0929867323666160418114600
Keywords
SAA variants; FPR2; TLR2; leukocytes; chemotaxis; cytokines; inflammatory diseases; amyloidosis
Funding
- Fund for Scientific Research of Flanders (F.W.O.-Vlaanderen)
- Interuniversity Attraction Poles Program
- Concerted Research Actions of the Regional Government of Flanders [G.O.A. 2013/014]
- Belgian Science Policy Office (I.A.P. project) [P7/40]
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Serum amyloid A (SAA) is, like C-reactive protein (CRP), an acute phase protein and can be used as a diagnostic, prognostic or therapy follow-up marker for many diseases. Increases in serum levels of SAA are triggered by physical insults to the host, including infection, trauma, inflammatory reactions and cancer. The order of magnitude of increase in SAA levels varies considerably, from a 10- to 100-fold during limited inflammatory events to a 1000-fold increase during severe bacterial infections and acute exacerbations of chronic inflammatory diseases. This broad response range is reflected by SAA gene duplications resulting in a cluster encoding several SAA variants and by multiple biological functions of SAA. SAA variants are single-domain proteins with simple structures and few post-translational modifications. SAA1 and SAA2 are inducible by inflammatory cytokines, whereas SAA4 is constitutively produced. We review here the regulated expression of SAA in normal and transformed cells and compare its serum levels in various disease states. At low concentrations (10-100 ng/ml), early in an inflammatory response, SAA induces chemokines or matrix degrading enzymes via Toll-like receptors and functions as an activator and chemoattractant through a G protein-coupled receptor. When an infectious or inflammatory stimulus persists, the liver continues to produce more SAA (>= 1000 ng/ml) to become an antimicrobial agent by functioning as a direct opsonin of bacteria or by interference with virus infection of host cells. Thus, SAA regulates innate and adaptive immunity and this information may help to design better drugs to treat specific diseases.
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