Serum amyloid A protein which belongs to the SAA family is encoded by the SAA gene in humans. It is expressed by the liver and secreted in plasma. Serum amyloid A is the major acute phase reactant and apolipoprotein of the HDL complex. Elevated serum SAA protein levels may be associated with lung cancer. 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. Recombinant human Apo-SAA1 is an 11.7 kDa protein containing 104 amino acid residues.