ELISA FOR THE CORE PROTEIN OF THE CARTILAGE LARGE AGGREGATING PROTEOGLYCAN, AGGRECAN - COMPARISON WITH THE CONCENTRATIONS OF IMMUNOGENIC KERATAN SULFATE IN SYNOVIAL-FLUID, SERUM AND URINE

Immunological assays for fragments of the cartilage large aggregating proteoglycan, aggrecan, have been widely used to monitor cartilage tur nover. These assays have commonly employed the monoclonal keratan sulp hate antibody, 5D4. Keratan sulphate, however, is present in many tiss ues and 5D4 affinity is critically dependent on antigen structure. We have therefore raised and characterized a monoclonal antibody (1-F21) that reacts with the core protein of aggrecan without interference fro m the glycosaminoglycan side chains and, using this antibody, we have optimized a sensitive, competitive ELISA. The within-assay and between -assay coefficients of variation were 4.9-8.9% and 11.1-13.0%, respect ively. The mean concentrations of core protein in synovial fluid, seru m and urine were 76.4 pg/ml, 104.0 ng/ml and 81.0 ng/ml, respectively. In synovial fluids the concentrations were closely correlated with th e concentrations of keratan sulphate as determined by 5D4 (r = 0.94), whereas in serum and urine there was no obvious correlation between th e determinations. These findings show that measurement of both core pr otein and keratan sulphate results in a more precise description of ag grecan turnover.