A novel mechanism of neutrophil recruitment in a coculture model of the rheumatoid synovium.
OBJECTIVE
Rheumatoid arthritis (RA) is classically thought of as a Th1, T lymphocyte-driven disease of the adaptive immune system. However, cells of the innate immune system, including neutrophils, are prevalent within the diseased joint, and accumulate in large numbers. This study was undertaken to determine whether cells of the rheumatoid stromal microenvironment could establish an inflammatory environment in which endothelial cells are conditioned in a disease-specific manner to support neutrophil recruitment.


METHODS
Human umbilical vein endothelial cells (ECs) and fibroblasts isolated from the synovium or skin of RA patients were established in coculture on opposite sides of porous transwell filters. After 24 hours of EC conditioning, the membranes were incorporated into a parallel-plate, flow-based adhesion assay and levels of neutrophil adhesion to ECs were measured.


RESULTS
ECs cocultured with synovial, but not skin, fibroblasts could recruit neutrophils in a manner that was dependent on the number of fibroblasts. Antibody blockade of P-selectin or E-selectin reduced neutrophil adhesion, and an antibody against CD18 (the beta2 integrin) abolished adhesion. Blockade of CXCR2, but not CXCR1, also greatly inhibited neutrophil recruitment. Interleukin-6 (IL-6) was detectable in coculture supernatants, and both IL-6 and neutrophil adhesion were reduced in a dose-dependent manner by hydrocortisone added to cocultures. Antibody blockade of IL-6 also effectively abolished neutrophil adhesion.


CONCLUSIONS
Synovial fibroblasts from the rheumatoid joint play an important role in regulating the recruitment of inflammatory leukocytes during active disease. This process may depend on a previously unsuspected route of IL-6-mediated crosstalk between fibroblasts and endothelial cells.
Lally
Frank
F
Department of Physiology, Medical School, The University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
Smith
Emily
E
Filer
Andrew
A
Stone
Michael A
MA
Shaw
John S
JS
Nash
Gerard B
GB
Buckley
Christopher D
CD
Rainger
G Ed
GE
D019138:Antibodies, Blocking / Q000494:pharmacology; D001172:Arthritis, Rheumatoid / Q000276:immunology / Q000473:pathology*; D018821:CD18 Antigens / Q000276:immunology; D002448:Cell Adhesion / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D018920:Coculture Techniques; D004305:Dose-Response Relationship, Drug; D019040:E-Selectin / Q000276:immunology; D004730:Endothelium, Vascular / Q000166:cytology / Q000502:physiology*; D005347:Fibroblasts / Q000166:cytology / Q000502:physiology; D006801:Humans; D006854:Hydrocortisone / Q000494:pharmacology; D015850:Interleukin-6 / Q000378:metabolism; D007719:Knee Joint / Q000473:pathology; D020556:Neutrophil Infiltration / Q000187:drug effects / Q000502:physiology*; D009504:Neutrophils / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D019007:P-Selectin / Q000276:immunology; D012867:Skin; D013583:Synovial Membrane / Q000187:drug effects / Q000276:immunology / Q000473:pathology*
D019138:Antibodies, Blocking; D018821:CD18 Antigens; D019040:E-Selectin; D015850:Interleukin-6; D019007:P-Selectin; D006854:Hydrocortisone