To measure levels of oncostatin M (OSM) in the synovial fluid of rheumatoid arthritis (RA) patients and to examine the activities of human OSM in the regulation of human synovial fibroblast (HSF) production of chemokines and matrix metalloproteinases (MMP-1 and MMP-3) in vitro.
We examined the levels of OSM in the synovial fluids of patients with arthritis by an enzyme-linked immunosorbent assay (ELISA). ELISA of cell culture supernatants and Northern blots were used to assess responses of HSF to interleukin-1alpha (IL-1alpha), OSM, and other members of the IL-6/leukemia inhibitory factor (IL-6/LIF) family of cytokines.
We detected variable levels of OSM antigen in 9 of 10 RA patient synovial fluids, but levels were not detectable in 9 of 10 osteoarthritis (OA) patient fluids. Upon examining the responses of HSF in culture, OSM stimulated monocyte chemoattractant protein 1 (MCP-1), whereas RANTES secretion (regulated upon activation, normal T expressed and presumably secreted) was not altered by OSM alone. In IL-1alpha-induced cells, OSM costimulation further enhanced MCP-1 release, but inhibited the release of RANTES and IL-8. Other members of the IL-6/LIF family of cytokines did not show these effects. OSM induced a small elevation of MMP-1 production over 2 and 3 days of stimulation (2-fold), and acted significantly to enhance IL-1alpha-induced production of MMP-1 (to 8-fold and 9-fold at 48 and 72 hours, respectively). No effect of OSM was seen on MMP-3 secretion, either alone or in IL-1alpha-costimulated cells.
These results suggest that OSM has potentially important functions in the modulation of chemokine and metalloproteinase production by synovial cells of the joint.