Klin Wochenschr (1990) 68:685-691 Klinische Wochen- schrift 9 Springer-Verlag 1990 Correlation of Anti-Cytoskeleton Antibody Activities in Synovial Fluid with Interleukin-6 in Patients with Osteoarthritis and Inflammatory Joint Disease W.-J. Mayet 1, E. Hermann 1, M. Bachmann z, M. Manns 1, and K.-H. Meyer zum Biischenfelde1 1 I. Medizinische Klinik, Johannes Gutenberg Universit/it Mainz, 2 Institut ffir Physiologische Chemic, Johannes Gutenberg Universit/it Mainz Summary. Synovial fluids and sera from patients with rheumatoid arthritis, psoriatic arthritis, yer- sinia arthritis, Behget's syndrome, Crohn's disease, and osteoarthritis were tested for antinuclear anti- bodies and antibodies to five cytoskeletal compo- nents in sensitive enzyme-linked immunosorbent assay (ELISA) systems and for IL-6 concentrations in a proliferation assay (IL-6 dependent hybri- doma cell line B13.29, subclone B9). Statistically significant correlations between antibody activities and IL-6 levels were found for vimentin antibodies (r=0.56; p<0.05) and actin antibodies (r=0.44; p <0.05). In patients with chronic and active dis- ease like rheumatoid arthritis and psoriatic arthri- tis, optical densities measured by vimentin- and actin-ELISA were significantly different from those measured in patients with osteoarthritis. To date only a few reports exist concerning the inci- dence of antibodies in synovial fluids. We have shown to our knowledge for the first time that IL-6 seems to induce synovial fluid antibody activi- ties restricted to cytoskeletal components of syno- viocytes (i.e., vimentin and actin). Synovial fluid antibody activities against vimentin and actin ap- pear to be markers of activity in patients with in- flammatory joint disease. Key words: Synovial fluid - IL-6 - Cytoskeleton - Antibodies - ELISA Abbreviations: ELISA=enzyme-linked immunosorbent assay; ANA = antinuclear antibodies; ACA = antibodies against cyto- plasmic components; RA = rheumatoid arthritis; OA = os- teoarthritis; SF = synovial fluid; RF = rheumatoid factors; FCS = fetal calf serum; IFT = immunofluoreseence microscopy; PBS=phosphate buffered saline; BSA=bovine serum albu- min; OD=optical density; SLE=systemic lupus erythemato- sus; IL-6=interleukin-6; HGF=hybridoma growth factor; BSF-2 = B-cell-stimulatory factor; DMEM = Dulbecco's modi- fied Eagles Medium Antibodies to nuclear and cytoplasmic compo- nents (ANA and ACA) have gained importance as diagnostic markers of several connective tissue diseases. To date, diseases like rheumatoid arthritis (RA) and osteoarthritis (OA) seem to lack typical autoantibody profiles. While antibody screening usually is done in serum samples from peripheral blood, little is known about the incidence of au- toantibodies in synovial fluid (SF). Recently, we confirmed that SF of patients with RA may con- tain excessive amounts of IL-6, whereas in patients with OA only weak IL-6 activities could be demon- strated (Hermann et al. 1989; Houssiau et al. 1988; Kitani et al. 1987; Hirano et al. 1986). IL-6, also named hybridoma growth factor (HGF) or B-cell- stimulatory factor (BSF-2), enhances the produc- tion of both immunoglobulins predominantly of the IgG type and antibodies such as rheumatoid factors (RF). The aim of the present work was first to search for antibody activities in the SF of patients with RA, other inflammatory joint dis- eases, and OA, and then to look for any correla- tions to IL-6 concentrations and SF-IgG. This ap- proach should give more information about the local effect of IL-6 in the joint and the role of antibodies besides a network of cytokines involved in chronic synovitis. Patients and Methods Patients SF was obtained from 8 patients with classic or definite RA (6 females and 2 males, mean age 57 years, range 31-72 years) 3 patients with psor- iatic arthritis (2 females and 1 male, mean age 42 years, range 35-48 years), 3 patients with acute yersinia arthritis (2 females and 1 male, mean age