Soluble vascular cell adhesion molecule 1 mediation of monocyte chemotaxis in rheumatoid arthritis.
OBJECTIVE
Rheumatoid arthritis (RA) is characterized by infiltration of leukocytes, including monocyte/ macrophages, into synovial tissue (ST), but factors mediating the ingress of these cells are poorly understood. Vascular cell adhesion molecule 1 (VCAM-1) plays an important role in adhesion of leukocytes to the vasculature. This study was undertaken to test the hypothesis that soluble VCAM-1 (sVCAM-1) might mediate chemotaxis of monocytes in RA.


METHODS
Chemotaxis assays were performed using a modified Boyden chamber to determine the effects of sVCAM-1 on and the role of very late activation antigen 4 (VLA-4) in peripheral blood (PB) monocyte migration. Synovial fluids (SF) were immunodepleted of sVCAM-1 to identify a role for sVCAM-1 in RA. Immunohistochemistry and flow cytometry analyses were performed to show the expression of VLA-4 in ST, SF, and PB. Tyrosine phosphorylation was studied by Western blot analysis on PB monocyte lysates in the presence of signaling inhibitors.


RESULTS
Soluble VCAM-1 induced monocyte migration in the nM range, in a concentration-dependent manner. Anti-VLA-4 significantly inhibited sVCAM-1-induced monocyte migration, suggesting that sVCAM-1 acts in part via a VLA-4-dependent mechanism. In RA SF, incubation with anti-VCAM-1 resulted in a reduction in the ability to induce monocyte migration (mean 28%). VLA-4 immunolocalized to RA ST, SF, or PB, monocytes, macrophages, and lymphocytes. Soluble VCAM-1 stimulated tyrosine phosphorylation in monocytes, and pertussis toxin, chelerythrine chloride, and staurosporine significantly reduced sVCAM-1-mediated monocyte chemotaxis, suggesting that signaling pathways via G proteins and protein kinase C are required for sVCAM-1-mediated monocyte migration.


CONCLUSIONS
These results demonstrate a novel function for sVCAM-1 as a monocyte chemotactic agent in RA and suggest a new potential target for modulating monocyte ingress into inflamed RA ST.
Tokuhira
M
M
Northwestern University Medical School, Chicago, Illinois 60611, USA.
Hosaka
S
S
Volin
M V
MV
Haines
G K
GK
Katschke
K J
KJ
Kim
S
S
Koch
A E
AE
D001172:Arthritis, Rheumatoid / Q000378:metabolism / Q000473:pathology* / Q000503:physiopathology; D002634:Chemotaxis, Leukocyte / Q000187:drug effects*; D006801:Humans; D039041:Integrin alpha4beta1; D016023:Integrins / Q000096:biosynthesis / Q000502:physiology; D008264:Macrophages / Q000378:metabolism; D009000:Monocytes / Q000166:cytology* / Q000378:metabolism; D016201:Receptors, Lymphocyte Homing / Q000096:biosynthesis / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D012995:Solubility; D013582:Synovial Fluid / Q000166:cytology; D015854:Up-Regulation; D019010:Vascular Cell Adhesion Molecule-1 / Q000494:pharmacology* / Q000502:physiology
D039041:Integrin alpha4beta1; D016023:Integrins; D016201:Receptors, Lymphocyte Homing; D019010:Vascular Cell Adhesion Molecule-1