Glycoprotein 96 perpetuates the persistent inflammation of rheumatoid arthritis.
OBJECTIVE
The mechanisms that contribute to the persistent activation of macrophages in rheumatoid arthritis (RA) are incompletely understood. The aim of this study was to determine the contribution of endogenous gp96 in Toll-like receptor (TLR)-mediated macrophage activation in RA.


METHODS
RA synovial fluid was used to activate macrophages and HEK-TLR-2 and HEK-TLR-4 cells. Neutralizing antibodies to TLR-2, TLR-4, and gp96 were used to inhibit activation. RA synovial fluid macrophages were isolated by CD14 negative selection. Cell activation was measured by the expression of tumor necrosis factor α (TNFα) or interleukin-8 messenger RNA. Arthritis was induced in mice by K/BxN serum transfer. The expression of gp96 was determined by immunoblot analysis, enzyme-linked immunosorbent assay, and immunohistochemistry. Arthritis was treated with neutralizing anti-gp96 antiserum or control serum.


RESULTS
RA synovial fluid induced the activation of macrophages and HEK-TLR-2 and HEK-TLR-4 cells. RA synovial fluid-induced macrophage and HEK-TLR-2 activation was suppressed by neutralizing anti-gp96 antibodies only in the presence of high (>800 ng/ml) rather than low (<400 ng/ml) concentrations of gp96. Neutralization of RA synovial fluid macrophage cell surface gp96 inhibited the constitutive expression of TNFα. Supporting the role of gp96 in RA, joint tissue gp96 expression was induced in mice with the K/BxN serum-induced arthritis, and neutralizing antibodies to gp96 ameliorated joint inflammation, as determined by clinical and histologic examination.


CONCLUSIONS
These observations support the notion that gp96 plays a role as an endogenous TLR-2 ligand in RA and identify the TLR-2 pathway as a therapeutic target.
Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA.
Qi-Quan
QQ
Huang
Renee E
RE
Koessler
Robert
R
Birkett
Andrea
A
Dorfleutner
Harris
H
Perlman
G Kenneth
GK
Haines
Christian
C
Stehlik
Christopher V
CV
Nicchitta
Richard M
RM
Pope
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D057134:Antibodies, Neutralizing / Q000276:immunology; D001172:Arthritis, Rheumatoid / Q000276:immunology* / Q000378:metabolism; D004195:Disease Models, Animal; D005260:Female; D057809:HEK293 Cells; D006801:Humans; D008264:Macrophages / Q000276:immunology / Q000378:metabolism; D008297:Male; D008562:Membrane Glycoproteins / Q000276:immunology* / Q000378:metabolism; D051379:Mice; D008815:Mice, Inbred Strains; D008875:Middle Aged; D015398:Signal Transduction / Q000276:immunology*; D013583:Synovial Membrane / Q000276:immunology* / Q000378:metabolism; D051195:Toll-Like Receptor 2 / Q000276:immunology* / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000276:immunology / Q000378:metabolism
D057134:Antibodies, Neutralizing; D008562:Membrane Glycoproteins; C495342:TLR2 protein, human; C495345:TLR4 protein, human; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; C053387:endoplasmin