Dynamics of interleukin (IL)-18 in serum, synovial fluid and synovial membrane in the patients with rheumatoid arthritis]

OBJECTIVES: IL-18 is a novel cytokine that plays an important role in the Th1 response. The aim of this study is to investigate the dynamics of IL-18 in serum, synovial fluid and synovial membrane in the patients with rheumatoid arthritis. MATERIALS AND METHODS: The serum, synovial fluid and synovial membrane were obtained from RA patients at operation. The levels of IL-18 in the serum and synovial fluid were measured by ELISA. We then examined the expression of IL-18 in synovial tissues using anti-human IL-18 monoclonal antibody in immunohistochemical study. RESULTS: The levels of IL-18 in serum and synovial fluid in RA patients were 193.7 +/- 109.7 pg/ml and 258.8 +/- 238.0 pg/ml, respectively. Compared with OA patients and normal volunteers, the level of IL-18 in RA patients was higher in both serum and synovial fluid. (P < 0.05) In synovial membrane, the cells positive for anti IL-18 antibody were confirmed not only in RA (n = 26) but also in OA (n = 7) patients. The positive cells were the synovial lining cells, macrophages, fibroblasts and endothelial cells. However, a large number of positive cells were demonstrated in synovial tissues in RA compared with OA patients.