Studies on YKL-40 in knee joints of patients with rheumatoid arthritis andosteoarthritis. Involvement of YKL-40 in the joint pathology

Objective: The presence of YKL-40 (human cartilage glycoprotein 39) in syno vium, cartilage and synovial fluid (SF) from knee joints of patients with r heumatoid arthritis and osteoarthritis (OA) were related to histopathologic al changes in synovium and cartilage and to serum YKL-40 and other biochemi cal markers. Methods: The localization of YKL-40 in synovium and cartilage was determine d by immunohistochemistry. Synovial inflammation was estimated histological ly and by magnetic resonance imaging (MRI). Biochemical markers of inflamma tion, neutrophil activation and cartilage metabolism were analysed. YKL-40 concentrations in serum and SF were determined by RIA and ELISA. Results: In the synovium YKL-40 positive cells were found in lining and str omal cells (macrophages) and the number of YKL-40 positive cells was relate d to the degree of synovitis. in arthritic cartilage, YKL-40 was located to chondrocytes. YKL-40 levels in SF were higher in RA patients with moderate /severe or none/slight synovitis of the knee joint compared to OA patients with moderate/severe or none/slight synovitis. SF YKL-40 correlated with th e synovial membrane and the joint effusion Volumes determined by magnetic r esonance imaging (MRI) and with other biochemical markers of intercellular matrix metabolism. SF YKL-40 was higher than serum YKL-40, and a relationsh ip existed between the YKL-40 levels in SF and serum. Intraarticular glucoc orticoid injection was followed by clinical remission and a decrease in ser um YKL-40, which increased again at clinical relapse. Conclusions: YKL-40 in SF is derived from cells in the inflamed synovium, c hondrocytes and SF neutrophils. Joint derived YKL-40 influences serum YKL-4 0. YKL-40 may be involved in the pathophysiology of the arthritic processes and reflect local disease activity. (C) 2001 OsteoArthritis Research Socie ty International.