To investigate whether soluble interleukin-2 receptor (sIL-2R) could be a useful marker of disease activity in rheumatoid arthritis (RA); sIL-2R levels in serum and in synovial fluid were determined by enzyme-linked immunosorbent assay.
Sixty five serum and 27 synovial fluid samples were obtained from patients with RA. Twenty five serum and 28 synovial fluid samples from patients with osteoarthritis (OA) were used as controls. Furthermore, 10 synovial fluid samples from healthy volunteers were also examined. Variable laboratory and clinical data were compared with serum sIL-2R levels, in 26 patients with RA and serial samples from some patients were examined.
Concentrations of sIL-2R in serum (median 81, range 40-350 pM) and synovial fluid (median 125, range 52-460 pM) from patients with RA were significantly higher than in serum (median 45, range 13-100 pM) and synovial fluid (median 37, range 15-140 pM) from patients with OA, and healthy control synovial fluid (median 2.5, range 0-10 pM). Serum sIL-2R levels correlated strongly with serum levels of C-reactive protein (p = 0.0001), and a significant correlation with erythrocyte sedimentation rate (ESR) (p = 0.048), IgG levels (p = 0.028), IgA levels (p = 0.044) and Lansbury Index (p = 0.037) was observed. However, serum sIL-2R levels showed no significant correlation with rheumatic factor, IgM or T cell subsets.
These findings indicate that sIL-2R levels in patients with RA reflect disease activity.