SAA4 is a constitutively expressed protein belonging to the SAA family. It is a major acute phase reactant and an apolipoprotein of the HDL complex. The serum amyloid A (SAA) superfamily comprises a number of differentially expressed genes with a high degree of homology in mammalian species. SAA4, an apolipoprotein constitutively expressed only in humans and mice, is associated almost entirely with lipoproteins of the high density range. Its physiological function is unknown and its serum co