lnterleukin-6 (IL-6) in Synovial Fluid and Serum of Patients with Rheumatic Diseases

Swaak AJ, van Rooyen A, Nieuwenhuis E, Aarden LA. Interleukin-6 (IL-6) in synovial fluid and serum of patients with rheumatoid disease. Scand J Rheumatology 1988; 17: 469-474.Interleukin-6 (IL-6) is a monokine with a number of biological activities, which are intimately related to inflammatory responses. We have measured IL-6 levels in synovial fluid (SF) and serum (Se) of patients with rheumatic diseases. SF-IL-6 levels were a thousand-fold higher than corresponding Se levels and a positive correlation was found between SF and Se levels suggesting that Se-IL-6 is derived from IL-6 produced in the joint. Se levels of IL-6 were also positively correlated to C-reactive protein (CRP) levels, supporting the in vitro experiments showing that IL-6 stimulates hepatocytes to produce CRP. Finally we observed a positive corelation between SF-IL-6 levels and the local activity score.A. J. G. Swaak, Department of Rheumatology, The Dr Daniel den Hoed Clinic, Groene Hill-edijk 301, NL-3075 EA Rotterdam, The Netherlands.