Serum amyloid A (SAA) is a family of apolipoproteins related to plasma high-density lipoprotein (HDL). Different isoforms of SAA are constitutively expressed at different levels or in response to inflammatory stimuli (acute phase SAAs). These proteins are mainly produced by the liver. The mouse SAA gene family is located on chromosome 7. In mice, five SAA genes and four protein products have been identified, the acute-phase isoforms SAA1, SAA2, and SAA3, the constitutively expressed gene SAA5, and the pseudogene of SAA4. SAAs belong to the acute-phase proteins, including C-reactive protein (CRP), haptoglobin, cuprocyanin, complement components C3 and C4, a1-acid glycoprotein, a1-protease inhibitor and fibrinogen.