Association of the single-nucleotide polymorphism and haplotype of the interleukin 18 gene with atopic dermatitis in Koreans

Background IL-18 is a proinflammatory cytokine that plays an important role for T-helper type 1 (Th 1) and Th2 cytokine in the presence/absence of IL- 12. It has been recently shown that human IL-18 plays a role in atopic dermatitis (AD) by enhancing IL-4 and IL-13 production and by stimulating the synthesis of IgE. Objective We wanted to evaluate the associations of single-nucleotide polymorphism (SNP) and the haplotype in the IL- 18 gene, hence we performed genotyping for the SNPs in the IL- 18 gene in AD patients and normal controls. Method We genotyped three SNPs from the IL- 18 gene for the 1120 case-control samples (646 AD patients and 474 normal controls). We measured the serum IL- 18, IL-4 and IL- 13 concentrations in 74 individuals (25 ADe, 25 AM and 24 controls) by performing ELISA. Result The rs795467 SNP and haplotype T-T-C were significantly associated with AD, and especially between the ADe and normal control groups (P = 0.03 and 0.01). The serum IL- 18 concentration was higher in the AD group than in the normal controls without any correlation with the rs795467 polymorphism. We did not find any correlations between the serum IL- 18 levels and the SCORing atopic dermatitis index, the blood eosinophil counts and the ECP, and there was no correlation between the serum IL- 18 levels and the serum IL-4 and IL- 13 levels. Conclusion We found that the one SNP and the haplotype T-T-C were strongly associated with the allergic type of AD, but not with the non-allergic intrinsic type. These data support the hypothesis that IL- 18 up-regulates IgE production, yet more experiments will be needed to prove the in vivo involvement of Th2 cytokine.