Background: Systemic lupus erythematosus (SLE) is a systemic autoimmune disease characterized by activation of T and polyclonal B lymphocytes. IL-18 was originally identified as a factor which enhances IFN-γ production and is a potent inducer of the inflammatory mediators by T cells, causing severe inflammatory disorders in SLE. Objectives: This study aimed to evaluate the association of plasma interlukine-18 (IL-18) concentration and severity of lupus nephritis (LN) and disease activity in SLE patients. Patients and Methods: In this cross-sectional study, 113 patients with SLE and 50 healthy individuals were examined. Serum level of IL-18 was measured. The severity and activity of the disease was determined by Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) score. The severity of kidney involvement was studied by renal biopsy, serum creatinine and 24 hours urine protein level. Results: The mean level of serum IL-18 was significantly higher in the patients than controls (577.67 ± 649.95 versus 60.48 ± 19.53 pg/ml; P < 0.001). In SLE patients with active disease level of serum IL-18 was significantly higher than chronic disease (622.77 ± 716.54 versus 182 ± 184.37 pg/ml; P < 0.001). The serum level of IL-18 was significantly higher in stage IV (P < 0.001) and V (P < 0.001) of patients with LN, than other stages. Conclusions: The current study showed that the serum IL-18 is significantly higher in the patients than controls and it significantly correlated with sever renal involvement and disease activity in SLE patients.

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