Assessment of interleukin-18 gene polymorphism and serum levels in cutaneous lichen planus.

BACKGROUND: Lichen planus (LP) is a chronic inflammatory disease with uncertain etiology. Interleukin-18 (IL-18) is an interferon gamma (INFγ) inducing agent. It is a pro-inflammatory cytokine that was found to play a role in the pathogenesis of some autoimmune disorders. MATERIAL AND METHODS: This study included 50 patients with classic cutaneous lichen planus (CLP) and 50 healthy volunteers serving as controls. Venous blood samples were withdrawn from the study subjects under complete aseptic precautions. Blood samples were examined for single nucleotide polymorphisms (SNPs) of IL-18 gene at promoter -137(G/C) and -656 (G/T) using polymerase chain reaction (PCR) and IL-18 level was assessed using enzyme linked immunosorbent assay (ELISA). RESULTS: The mean level of IL-18 was significantly higher in CLP patients (31.63 ± 4.90) compared to control subjects (13.95 ± 6.82). Significantly high levels of IL-18 were found among patients with diabetes, hypertension (p < 0.01 in both). HCV positive patients and patients with both OLP and CLP also expressed higher levels of IL-18. Genotypic and allelic distribution at position -137(G/C) showed that the genotype GG was present at significantly higher frequency in cases (58%) compared to controls (28.0%). On the other hand the CC genotype at position -137 was significantly higher in the controls (28%) as compared to CLP cases (6%). Polymorphism of IL-18 at position -656(G/T) showed no significant difference between cases and controls. No significant difference could be detected in IL-18 level between different genotypic variants at position -137(G/C) and -656(G/T). CONCLUSION: IL-18 may play important role in pathogenesis of LP. Elevated IL-18 levels could be part of the pro-inflammatory autoimmune process in LP. The presence of OLP, HCV, diabetes and hypertension is associated with higher production of IL-18. IL-18 promotor region -137(G/C) polymorphism might be a factor that increase the risk of development of lichen planus in Egyptian patients.