Effect of serum amyloid A on selected in vitro functions of isolated human neutrophils

Abstract

Serum amyloid A (SAA) is an acute phase reactant whose levels in the blood rise as part of the body's response to stress and inflammation. Previous studies have suggested that SAA may carry an anti-inflammatory potential. We evaluated the effects of SAA on human neutrophils activated by N-formyl-methionyl-leucylphenylalanine (fMLP) in vitro. At concentrations higher than 10 μg/mL, SAA inhibited neutrophil myeloperoxidase (MPO) release. This effect was located in the N-terminal—that is, amino acid residues 1–14—of the SAA molecule. Directed neutrophil migration was inhibited at the same SAA concentrations. Several amino acid residues (1–14, 15–104, 83–104) contributed to this effect. Neutrophil O 2 production was inhibited at low concentrations of SAA (0.1 to 1 μg/ml) and was stimulated at concentrations higher than 50 μg/mL. Neutrophil O 2 − production induced by phorbol myristate acetate (PMA) and O 2 − generated by the xanthine—xanthine oxidase reaction were not affected by SAA. These results add to previous data suggesting that SAA, at concentrations recorded in the serum during inflammation, modulates neutrophil function; thus it may play a role in the down-regulation of the inflammatory process.