Association of interleukin-18 promoter polymorphisms with WHO pathological classes and serum IL-18 levels in Chinese patients with lupus nephritis.

Accumulating evidence indicates that interleukin (IL)-18 has a central role in the pathogenesis of lupus nephritis (LN). Although two recent studies showed that IL-18 promoter gene polymorphisms might be associated with systemic lupus erythematosus (SLE), to our knowledge, there have not been any reports concerning their association with LN. The aim of our study was to investigate the association of IL-18 promoter polymorphisms with World Health Organization pathological classes and identify their functional correlations. Sequence-specific primer polymerase chain reaction and the restriction fragment length polymorphism method were used to analyse the genotypes of IL-18 promoter polymorphism at the position -607 in 101 unrelated patients with LN, 64 non-renal patients with SLE and 174 ethnically matched healthy controls. Serum IL-18 levels were determined using enzyme-linked immunosorbent assay during the active phase. Immunohistochemical analysis was performed for IL-18 expression on renal biopsies from 72 patients with LN. Our results showed that patients with non-renal SLE had significantly higher frequencies of SNP-607/AA when compared to patients with LN (37.5% vs 18.8%, P < 0.05). LN patients with the AA genotype had significantly lower levels of serum IL-18 than those with the CA or CC genotype (P < 0.01) and also had lower levels of glomerular IL-18 expression than those with the CC genotype (P < 0.05). Significantly, higher frequencies of the SNP-607/AA genotype were observed in LN patients with WHO class III than in those with class IV (34.6% vs 15.6%, P < 0.05). The SNP-607/AA genotype was not observed in patients with LN who progressed to end-stage renal failure that required haemodialysis or renal transplantation. In conclusion, the SNP-607/AA genotype that had lower IL-18 levels might be a genetically protective factor against renal involvement in Chinese patients with SLE and against development of severe nephritis in patients with LN.