Soluble interleukin-6 receptor in plasma and in lymphocyte culture supernatants of healthy individuals and patients with systemic lupus erythematosus and rheumatoid arthritis.

The soluble IL-6 receptor (sIL-6R) occurring in various body fluids of healthy persons and patients with various diseases is an agonist since its complex with IL-6 binds to gp130 making IL-6 receptor negative cells responsive for IL-6. The generation as well as the functional role of soluble IL-6 receptor is poorly understood. We measured the sIL-6R levels by ELISA sandwich technology in sera and in supernatants of lymphocyte cultures without and after incubations with dexamethasone. Our results indicate, that the sIL-6R levels in sera of patients with inactive systemic lupus erythematosus (SLE) and active rheumatoid arthritis (RA) were higher than those of the control group, active SLE and inactive RA. In vitro dexamethasone treatment stimulated generation of sIL-6R in both healthy persons and in active SLE, however it strongly suppressed sIL-6R in both RA groups. At mRNA level, we found that in SLE both the mRNA coding the cell-bound and an alternatively spliced variant corresponding to soluble IL-6R transcript increases, however the strong decrease of sIL6R protein in RA was not found at mRNA level.