Elevated IL-6 levels in the synovial fluid of osteoarthritis patients stem from plasma cells.
OBJECTIVE
To analyse the levels of interleukin-6 (IL-6) in the synovial fluids and sera of patients with osteoarthritis (OA) and to identify the IL-6-secreting cells.


METHODS
Serum, synovial fluid, synovial tissue, and articular cartilage samples were collected from 49 OA patients with end-stage knee or hip OA who underwent joint replacement surgery. Serum and synovial fluid levels of IL-6 were measured by enzyme-linked immunosorbent assay (ELISA) and IL-6-secreting cells were identified by immunohistochemistry.


RESULTS
Eight out of 49 patients (16%) exhibited elevated IL-6 levels in the synovial fluids, averaging at 2022+/-526 pg/mL, while the levels in the rest of the patients averaged at 132+/-19 pg/mL. The sera levels of all patients were comparable in the 10 pg/mL range. Immunohistochemical analyses revealed plasma cells in the synovial lining of the high producers as the source of IL-6.


CONCLUSIONS
Synovial fluid IL-6 levels may help to classify OA patients and may point to a subgroup with a particular impact from their immune system.
Doss
F
F
Institute of Immunology, Medical Faculty, University of Rostock, Berlin.
Menard
J
J
Hauschild
M
M
Kreutzer
H-J
HJ
Mittlmeier
T
T
Müller-Steinhardt
M
M
Müller
B
B
D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D015850:Interleukin-6 / Q000097:blood / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D015207:Osteoarthritis, Hip / Q000276:immunology*; D020370:Osteoarthritis, Knee / Q000276:immunology*; D010950:Plasma Cells / Q000378:metabolism*; D013582:Synovial Fluid / Q000737:chemistry* / Q000276:immunology; D013583:Synovial Membrane / Q000276:immunology / Q000378:metabolism*
D015415:Biomarkers; D015850:Interleukin-6