Soluble interleukin-2 receptor in sera and synovial fluids of rheumatoid patients: correlations with disease activity

The measurement of serum soluble interleukin-2 receptor (sIL-2R), a sensitive marker of lymphocyte activation, has been proposed as an indicator of disease activity and "outcome" in patients with inflammatory diseases characterized by the activation of immune cells. Serum sIL-2R levels have been reported higher in rheumatoid patients than in controls. Using an enzyme-linked immunoabsorbent assay (ELISA), we evaluated soluble IL-2R levels in the serum of 34 patients with RA and in the synovial fluid of 25 of these patients and we compared it with levels found in the serum of 13 healthy controls. Serum sIL-2R levels were significantly elevated in RA patients compared with the healthy age-matched control group (P < 0.005). The mean level of soluble IL-2R in synovial fluids was significantly higher than the mean sera levels in RA patients (P < 0.0001). Moreover, we examined the correlation between serum and synovial fluid sIL-2R levels and disease activity measures. Serum sIL-2R correlated only with ESR (P < 0.04). The synovial fluid sIL-2R correlated with ESR (P < 0.02) and a visual analogue scale (VAS) pain score (P < 0.04). Both serum and synovial fluid sIL-2R levels correlated with the chronic arthritis systemic index (CASI; P < 0.04 and P < 0.005, respectively). Our data suggested that in RA the measurement of sIL-2R may certainly mirror the degree of chronic inflammation and the continuous activation of the immune cells in the joint, although the role of this molecule in the immune response is still unclear.