MICROFIBRILLAR ELEMENTS IN THE SYNOVIAL JOINT - PRESENCE OF TYPE-VI COLLAGEN AND FIBRILLIN-CONTAINING MICROFIBRILS

Objectives-The aims were to isolate and positively identify the microf ibrillar elements which have been observed in the synovial lining. In addition, synovial fluid was examined for these elements to improve th e understanding of the role of these structures in health and disease. Methods-Bacterial collagenase digestion of bovine synovial linings an d human and bovine synovial fluids was used to release intact, non-den atured microfibrillar elements. The microfibrils were isolated by Seph arose CL-2B chromatography and viewed by rotary shadowing. They were c haracterised by immunogold labelling with specific antibodies. Results -Intact type VI collagen microfibrils and fibrillin-containing microfi brils were isolated and positively identified in the synovial lining f rom bovine ankle joints by immunogold labelling. Type VI collagen micr ofibrils were also present in the synovial fluid. Conclusions-The role of the microfibrillar elements in vivo is not fully understood, but t heir distribution in the synovial lining suggests they have an importa nt role in the mechanical and physical properties of this tissue. The presence of type VI collagen microfibrils in synovial fluid poses the intriguing possibility that it may represent a product of microfibril turnover and a potential early marker for rheumatoid arthritis. Altern atively, type VI collagen may be specifically secreted into the synovi al fluid to interact with hyaluronan and form part of the structure of synovial fluid.