Serum amyloid A apolipoprotein family consists of three members that in human beings are coded by different genes: SAA1, SAA2, and SAA4 (reviewed in 1-3). SAA1 and SAA2 are so-called acute phase isoforms. Their expression is increased in response to inflammation. SAA4 is a constitutive isoform, the expression of which does not change during an acute-phase response. In addition, one more related gene (SAA3) has been identified, although this gene is not expressed in human beings.