Serum levels of interleukin-6 type cytokines and soluble interleukin-6 receptor in patients with rheumatoid arthritis

WE investigated the serum concentrations of interleukin-6 (IL-6) and two IL -6 family of cytokines (leukaemia inhibitory factor (LIF) and ciliary neuro trophic factor (CNTF) as well as IL-6 soluble receptor (sIL-6R) using an en zyme-linked immunosorbent assay (ELISA) in 66 patients with rheumatoid arth ritis (RA) and 24 healthy controls. We examined a possible association betw een the serum levels of these peptides and RA activity according to the Mal lya and Mace scoring system and Ritchie's index. We also evaluated the corr elation between the serum levels of IL-6, LIF CNTF and sIL-6R and, duration of the disease and calculated sIL-6R/IL-6 ratio in RA. patients and in the control group. IL-G and sIL-6R were detectable in all 66 patients with RA and 24 normal individuals. LIF was also found in the serum of all patients with RA and in 16 (66.7%) normal individuals. In contrast CNTF was measurab le only in 15 (22.7%) patients with RA. and 24 (33.3%) normal individuals. The highest IL-6 and sIL-6R levels were found in the patients with Stages 3 and 4 of RA activity and the lowest in the control group. In contrast ther e were no statistically significant diferences between the LIF and CNTF lev els in RA patients and normal individuals. We found positive correlation be tween IL-6 acid sIL-6R concentrations and Ritchie's index and a lack of suc h correlation with LIF and CNTF. IL-6 serum level correlated positively wit h the disease duration, but sIL-6R, LIF and CNTF did not. Serum sIL-6R/IL-6 ratio was significantly lower in RA patients than in healthy controls. In conclusion, an increase in the serum levels of IL-6 and sIL-6R, but not LIF and CNTF concentrations, may be useful markers for RA activity.