A direct involvement of collagenases in type II collagen degradation was recently demonstrated in human articular cartilage.41 Antibodies were developed that recognize the carboxy-terminal and the amino-terminal neoepitopes generated by cleavage of native human type II collagen by the three collagenases 1, 2, and 3. When the antibodies were used to immunoassay cartilage extracts, significantly more neoepitope was present in OA cartilage compared to nonOA cartilages. The neoepitope reflecting collagenase activity within the tissue is detectable particularly in areas depleted of PGs. Collagenases have been detected in the synovial fluid of patients with traumatic arthritis, rheumatoid arthritis as well as OA.42-45 While in other arthritic diseases the cellular source of the MMPs may be the cells of the synovial membrane, in OA chondrocytes are the cellular source and are capable of expressing and secreting all three collagenases.38
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