Elevation of plasma interleukin-18 concentration is correlated with disease activity in systemic lupus erythematosus

Background. Previous studies have indicated that the autoimmune phenomenon might be caused by an imbalance of T-helper cell (Th) cytokines. Methods. We investigated the plasma concentrations of a novel pro-inflammatory Th1 cytokine, interleukin (IL)-18, and its inducer, IL-12, in patients with systemic lupus erythematosus (SLE) and correlated them with the SLE disease activity index (SLEDAI). Plasma IL-18 and IL-12 concentrations of 40 SLE patients and 18 sex- and age-matched control subjects were measured by enzyme-linked immunosorbent assay. Results. Plasma IL-18 and IL-12 concentrations were significantly higher in SLE patients than in control subjects [median (interquarfile range): IL-18, 320.0 pg/ml (164.4-475.6 pg/ml) vs 130.1 pg/ml (57.8-202.4 pg/ml), P < 0.001; IL-12, 143.3 pg/ml (39.4-247.2 pg/ml) vs 84.7 pg/ml (29.3-140.1 pg/ml), P < 0.001]. Increases in IL-18 concentration correlated positively and significantly with SLEDAI score (r = 0.449. P = 0.004). Conclusion. The novel cytokine IL-18 might play a crucial role in triggering the inflammatory processes in SLE.