Objective: Our study was undertaken to determine the quantity and pattern of distribution of vitronectin (Vn) in the synovial fluid and tissue of patients with rheumatic disease.
Methods: We quantitated synovial fluid Vn levels in 37 patients (17 with rheumatoid arthritis (RA), 12 with crystal induced arthritis (CIA), and 8 with osteoarthritis (OA)) using a competitive-binding ELISA: Immunofluorescence studies were performed on synovial pannus tissue specimens from 3 RA patients. SDS-PAGE analysis of the synovial fluids was performed to demonstrate the molecular forms of Vn present in inflammatory and noninflammatory synovial fluids. Albumin levels of synovial fluids were determined using an automated chemistry analyzer.
Results: Immunoreactive Vn was detected in 36 of 37 synovial fluid specimens examined, over a wide range of dilutions. Concentrations of Vn in inflammatory synovial fluid were significantly elevated compared to non-inflammatory synovial fluid and normal human plasma (NHP). Immunofluorescence studies revealed immunoreactive Vn most heavily concentrated in the lining layers of RA pannus tissue. Similar to NHP, molecular forms of Vn were heterogeneous in the synovial fluid; however, the inflammatory milieu appears to predispose Vn to cleavage at its protease-sensitive site. Overall there was a positive correlation of synovial fluid Vn to albumin. CIA and OA revealed a very strong relationship, whereas RA synovial fluid Vn levels correlated poorly to the levels of albumin.
Conclusion: Vitronectin is present in synovial fluid. Levels are significantly enhanced in the inflamed joint and in the RA synovial lining, where it may influence cell adhesion and modulate tissue repair.