[Clinical significance of serum IL-18 determination in rheumatoid arthritis]

Interleukin (IL)-18 is a novel cytokine expressing at inflammatory lesion. In this study, to evaluate the clinical significance of IL-18 determination, we have examined serum IL-18, inflammation markers, sFas, and sFas-ligand concentrations in patients with rheumatoid arthritis(RA). Serum was obtained from 56 RA patients aged 35-74 years, 16 osteoarthritis (OA) patients aged 36-78 years and 178 healthy subjects aged 20-72 years and IL-18 was measured by ELISA. Serum IL-18 concentrations in RA (240.1 +/- 15.6 pg/ml, mean +/- SE) were significantly higher than OA (151.8 +/- 12.7 pg/ml, p < 0.005) and healthy controls(141.5 +/- 26.1 pg/ml, p < 0.001). Serum IL-18 levels were significantly increased in II to IV stages of RA (stage II; 218.6 +/- 31.2 pg/ml, stage III; 258.7 +/- 38.4 pg/ml, stage IV; 231.6 +/- 13.1 pg/ml) than those in OA. Furthermore, a positive correlation was observed between serum IL-18 concentration and serum Fas level in patients with RA (r = 0.472), whereas there was no significant correlation between serum IL-18 and sFas-ligand or other inflammatory markers (CRP, RF, CA-RF, IL-6, and IL-8). The present study showed that serum IL-18 level increased in RA, but it is unknown how IL-18 is involved in the pathogenesis of RA. Further study will be necessary to clarify the role of IL-18 in RA.