IMMUNOGLOBULIN-G AND SERUM-ALBUMIN ISOLATED FROM THE ARTICULAR-CARTILAGE OF PATIENTS WITH RHEUMATOID-ARTHRITIS OR OSTEOARTHRITIS CONTAIN COVALENT HETEROPOLYMERS WITH PROTEOGLYCANS

The present study was undertaken to identify the cartilage matrix mole cules that are bound with intermolecular disulfide bonds to IgG and se rum albumin molecules recovered from the articular cartilage of patien ts with rheumatoid arthritis (RA) or osteoarthritis (OA). The cartilag e specimens were extracted sequentially with three changes of neutral buffer, three changes of 6 M guanidine hydrochloride and then partiall y degraded with bacterial collagenase. The extracted IgG and albumin, along with matrix molecules bound to these proteins, were isolated wit h affinity chromatography using antibodies to IgG or human serum album in conjugated to agarose beads. The isolated materials were characteri zed with sodium dodecyl sulfate polyacrylamide gel electrophoresis and transfer blotting, using specific antibodies to IgG, albumin, and pro teoglycans. In the isolated materials, heteropolymers with IgG or albu min wer identified. These polymers contained keratan sulfate and less frequently chondroitin-4-sulfate and chondroitin-6-sulfate. These find ings identified the keratan sulfate rich proteoglycans, prevalent at t he surface of joint cartilage, as the most common cartilage matrix mol ecules that are covalently bound to IgG or to serum albumin by disulfi de bonds in the articular cartilage of patients with RA or OA.