Immunodetection and characterization of the degradation of cartilage proteoglycans in vitro and in vivo.

The large aggregating cartilage proteoglycans can be detected immunologically using antibodies directed against the hyaluronic acid-binding region, core protein, keratan sulfate, chondroitin sulfate, and hyaluronic acid. With radioimmunoassays we have detected proteoglycans released from adult human articular cartilage in vitro and in vivo. In vitro cleavage appears to occur mainly adjacent to the hyaluronic acid binding region with the release of the rest of the molecule. Two distinct populations have been observed, the larger of which is chondroitin sulfate-rich and the smaller keratan sulfate-rich. Although they are a little smaller and probably aggregate less with hyaluronic acid, these populations correspond in size and composition to two similar populations detected in situ in healthy adult human articular cartilage. In vivo studies of synovial fluid have revealed that the proteoglycan fragments are smaller and the most commonly detected fragment is the hyaluronic acid binding region. This suggests that in vivo further degradation occurs, probably due to degradation mediated by the inflamed synovium and polymorphonuclear leucocytes present in the synovial fluid of inflamed joints.