Duffy antigen receptor for chemokines and CXCL5 are essential for the recruitment of neutrophils in a multicellular model of rheumatoid arthritis synovium.
OBJECTIVE
The role of chemokines and their transporters in rheumatoid arthritis (RA) is poorly described. Evidence suggests that CXCL5 plays an important role, because it is abundant in RA tissue, and its neutralization moderates joint damage in animal models of arthritis. Expression of the chemokine transporter Duffy antigen receptor for chemokines (DARC) is also up-regulated in early RA. The aim of this study was to investigate the role of CXCL5 and DARC in regulating neutrophil recruitment, using an in vitro model of RA synovium.


METHODS
To model RA synovium, RA synovial fibroblasts (RASFs) were cocultured with endothelial cells (ECs) for 24 hours. Gene expression in cocultured cells was investigated using TaqMan gene arrays. The roles of CXCL5 and DARC were determined by incorporating cocultures into a flow-based adhesion assay, in which their function was demonstrated by blocking neutrophil recruitment with neutralizing reagents.


RESULTS
EC-RASF coculture induced chemokine expression in both cell types. Although the expression of CXC chemokines was modestly up-regulated in ECs, the expression of CXCL1, CXCL5, and CXCL8 was greatly increased in RASFs. RASFs also promoted the recruitment of flowing neutrophils to ECs. Anti-CXCL5 antibody abolished neutrophil recruitment by neutralizing CXCL5 expressed on ECs or when used to immunodeplete coculture-conditioned medium. DARC was also induced on ECs by coculture, and anti-Fy6 antibody or small interfering RNA targeting of DARC expression effectively abolished neutrophil recruitment.


CONCLUSIONS
This study is the first to demonstrate, in a model of human disease, that the function of DARC is essential for editing the chemokine signals presented by ECs and for promoting unwanted leukocyte recruitment.
Smith
Emily
E
Department of Physiology, Medical School, University of Birmingham, Edgbaston, Birmingham, UK. E.Smith.1@bham.ac.uk
McGettrick
Helen M
HM
Stone
Michael A
MA
Shaw
John S
JS
Middleton
Jim
J
Nash
Gerard B
GB
Buckley
Christopher D
CD
Ed Rainger
G
G
D001172:Arthritis, Rheumatoid / Q000276:immunology*; D054365:Chemokine CXCL5 / Q000096:biosynthesis*; D018925:Chemokines / Q000276:immunology; D004375:Duffy Blood-Group System / Q000096:biosynthesis*; D042783:Endothelial Cells; D005260:Female; D005347:Fibroblasts; D015870:Gene Expression; D006801:Humans; D008297:Male; D020556:Neutrophil Infiltration / Q000276:immunology*; D009504:Neutrophils / Q000502:physiology; D011956:Receptors, Cell Surface / Q000096:biosynthesis*; D013583:Synovial Membrane / Q000276:immunology; D015854:Up-Regulation
C473745:ACKR1 protein, human; C486263:CXCL5 protein, human; D054365:Chemokine CXCL5; D018925:Chemokines; D004375:Duffy Blood-Group System; D011956:Receptors, Cell Surface