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Interleukin-18 levels in synovial fluid of patients with rheumatoid arthritis and in patients with osteoarthritis

Background: Interleukin-18 (IL-18) was first described in 1989 as IFN-gama inducing factor and the molecule was subsequently cloned. Many of biological properties of IL-18 are similar to those of IL-1. IL-18 is clearly a proinflammatory cytokine. Its role in rheumatoid arthritis (RA) is due to its abilities to increase gene expresion for IL-6, iNOS, COX-2 and the matrix metalloprotease stromelysin in chondrocytes. The aim of these study was to determine IL-18 in synovial fluid from patients with seropositive RA and osteoarthritis (OA). Also, we had analysed the morphologic composition of the cell population in joint fluid of RA and OA patients.Materials and methods: Synovial fluid was aseptically taken from joint 17 patients with seropositive RA and 15 patients with OA. The fluid was stored at &#8211; 20 0 C until determination of IL-18 concentration. Since most samples were viscous all samples were incubated at 37 0 C for 30 minutes in the presence of hyaluronidase (Sigma) and centrifuged at 12 000 g for 5 minutes and the cytokine was than determined in the supernatants. The concentration IL-18 was determined by ELISA assay using R&D kits and prescribed procedure of manufacture was followed.Results: Generally, the concentration of IL-18 was significantly higher in patients with RA than in patients with OA (2631.9 &plusmn ; 1199.0 pg/ml vs 620.9 &plusmn ; 276.9 pg/ml, respectively ; p< 0, 01). It appears that concentration of IL-18 is dependent on the type of synovial effusion i.e. on the type of cells present in the joint effusion with the tendency to be the highest in the synovial effusion type II i.e. with preponderance of lymphocites. However, more samples should be analysed to support this conclusion. We also plan to determine in the same samples (patients) the concentration of NO and PGE 2, in correlation with type of cells present in the joint effusions.Conclusion: The level of IL-18 is significantly higher in synovial fluid of patients with RA than in patients with OA, most probably because of higher absolut and relative number of lymphocites in effusions of former patients.

Interleukin-18; synovial fluid; rheumatoid arthritis; osteoarthritis

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