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Published online before print November 5, 2007

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(Journal of Leukocyte Biology. 2008;83:245-253.)
© 2008 by Society for Leukocyte Biology

Serum amyloid A mediates human neutrophil production of reactive oxygen species through a receptor independent of formyl peptide receptor like-1

Lena Björkman^*,1, Jennie Karlsson^*, Anna Karlsson^*, Marie-Josèphe Rabiet^,,, Francois Boulay^,,, Huamei Fu^*, Johan Bylund^* and Claes Dahlgren^*

^* Department of Rheumatology and Inflammation Research, The Sahlgrenska Academy at Göteborg University, Göteborg, Sweden;
CEA, DSV, iRTSV, Laboratoire Biochimie et Biophysique des Systèmes Intégrés, Grenoble, France;
CNRS, UMR 5092, Grenoble, France; and
Université Joseph Fourier, Grenoble, France

¹ Correspondence: Sahlgrenska Academy, Göteborg University, Department of Rheumatology and Inflammation Research, Guldhedsgatan 10A, 41346 Göteborg, Sweden. E-mail: lena.i.bjorkman{at}vgregion.se

Serum amyloid A (SAA) is one of the acute-phase reactants, a group of plasma proteins that increases immensely in concentration during microbial infections and inflammatory conditions, and a close relationship between SAA levels and disease activity in rheumatoid arthritis (RA) has been observed. RA is an inflammatory disease, where neutrophils play important roles, and SAA is thought to participate in the inflammatory reaction by being a neutrophil chemoattractant and inducer of proinflammatory cytokines. The biological effects of SAA are reportedly mediated mainly through formyl peptide receptor like-1 (FPRL1), a G protein-coupled receptor (GPCR) belonging to the formyl peptide receptor family. Here, we confirmed the affinity of SAA for FPRL1 by showing that stably transfected HL-60 cells expressing FPRL1 were activated by SAA and that the response was inhibited by the use of the FPRL1-specific antagonist WRWWWW (WRW4). We also show that SAA activates the neutrophil NADPH-oxidase and that a reserve pool of receptors is present in storage organelles mobilized by priming agents such as TNF- and LPS from Gram-negative bacteria. The induced activity was inhibited by pertussis toxin, indicating the involvement of a GPCR. However, based on FPRL1-specific desensitization and use of FPRL1 antagonist WRW4, we found the SAA-mediated effects in neutrophils to be independent of FPRL1. Based on these findings, we conclude that SAA signaling in neutrophils is mediated through a GPCR, distinct from FPRL1. Future identification and characterization of the SAA receptor could lead to development of novel, therapeutic targets for treatment of RA.

Key Words: FPRL1 • G protein-coupled receptor • WRW4 • rheumatoid arthritis

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