[Fibronectin in the synovium and synovial fluid in rheumatoid arthritis and in osteoarthritis]

Fibronectin (FN) in the rheumatoid, and osteoarthritic, synovium was examined by light microscopy using immunostaining by fluorescein-labeled anti-fibronectin, or by peroxidase-labeled anti-fibronectin. Immunofluorescent FN was found more in the rheumatoid synovium than in the osteoarthritic synovium. The mean fluorescence intensity in a given area of the synovium including the synovial surface in rheumatoid arthritis was significantly higher than in osteoarthritis. As there was a significant correlation between the fluorescence intensity in the synovium and the number of synovial lining cells immunostained with peroxidase-labeled anti-fibronectin, the fluorescence intensity appeared to depend on the number of synovial lining cells containing FN. FN in the rheumatoid synovium and synovial fluid cells was examined by electron microscopy after immunoperoxidase staining. Immunoelectron microscopy of the rheumatoid synovium demonstrated FN on the surface of both type-A and type-B cells, the collagen fibers, and within the mitochondria, in the endoplasmic reticulum of type-B cells, and in the intercellular contact zone. These findings suggested that FN was mainly produced in the type-B cells, and played a role in maintaining the synovial structure. Immunoelectron microscopy of the rheumatoid synovial fluid cells confirmed the presence of FN on their surfaces. This suggested that FN opsonized by adhering debris to FN on the cell surfaces in the synovial fluid. The concentration of FN in the rheumatoid, and osteoarthritic, synovial fluids was measured by single radial immunodiffusion. The FN concentration in the rheumatoid synovial fluids was significantly higher than in the osteoarthritic synovial fluids. However, it was not significantly correlated with the indices of inflammatory activity such as with the C-reactive protein, the erythrocyte sedimentation rate, or catalase activity measured by a gasometry, or with the number of polymorphonucleated cells.