Proteolytic enzymes in joint destruction.

An increase in both neutral and acid proteolytic activity and proteinase inhibitors is reported in synovial fluid of osteoarthrotic and rheumatoid joints, compared with controls, but in subchondral bone and articular cartilage only Cathepsin D and in synovial tissue only neutral caseinolysis were elevated. Especially high proteolytic activities were found in joint compartments of seronegative rheumatoid and in sera of osteoarthrotic patients. The source of the main part of neutral caseinolytic activity in joint fluid is inflammatory cells, in the case of Cathepsin D the tissues of origin seem to be bone and cartilage.