Synovial fluid concentrations of interleukin-1β and proteoglycans are inversely related

Abstract

Interleukin-1β (IL-1β) and proteoglycans have been quantified by radio-immunoassay (IL-1β) and enzyme linked immunosorbent assay (proteoglycans) in synovial fluids and sera from patients with rheumatoid arthritis (RA) and reactive arthritis. All fluids were also tested for their ability to influence proteoglycan metabolism in a cartilage explant culture system. Synovial fluid IL-1β concentrations were inversely related to proteoglycan concentrations in samples from both RA and reactive arthritis patients ( P < 0.002 for all patients). There was no statistically significant relation between immunoreactive IL-1β concentration and proteoglycan synthesis or degradation in explants cultured in synovial fluid containing medium. Synovial fluid IL-1β concentrations were not related to erythrocyte sedimentation rate or joint total leukocyte count. IL-1β was not detectable (limit 250 pg/ml) in any unextracted sera. Although it appears likely that IL-1β is involved in the inflammatory and degenerative processes in joint disease, our findings indicate that there is no simple positive relationship between immunoreactive levels of this cytokine in synovial fluid and liberation of proteoglycans from articular cartilage as reflected in synovial fluid proteoglycan concentration.