IL-18 Gene rs187238 and rs1946518 Polymorphisms and Expression in Gingival Tissue in Patients with Periodontitis

Periodontitis is a chronic disease with disturbed balance between the immune and inflammatory response of the host to bacteria. Many studies have shown that proinflammatory cytokines play a significant role in the pathogenesis of periodontal disease. In this study, we examined the association between the IL-18 gene rs187238 and rs1946518 polymorphisms and periodontitis in non-smoking and smoking patients. This study enrolled 200 patients with periodontitis (130 non-smokers and 70 smokers) and 156 control subjects (124 non-smokers and 32 smokers). There were no statistically significant differences in the distribution of the rs187238 and rs1946518 IL-18 genotypes and alleles between patients with periodontitis and control subjects, between smoking patients with periodontitis and smoking control subjects, and between non-smoking patients with periodontitis and non-smoking control subjects. There were no statistically significant differences in clinical parameters in relation to the IL18 rs187238 genotypes. In patients with the IL18 rs1946518 GG genotype, we observed increased values of bleeding on probing (BoP) and periodontal probing depth (PPD), compared to subjects with the TT genotype. In patients with periodontitis, we observed statistically significant decreased expression of the IL-18 gene in comparison with healthy subjects (0.231 ± 0.163 vs. 0.663 ± 0.197, p = 0.0008). In addition, the IL-18 gene expression in gingival tissue in patients with periodontitis correlated positively with the number of remaining teeth. The results of our study suggest that the IL-18 rs187238 and rs1946518 polymorphisms are not significant risk indicators of periodontitis in our population. However, in patients with the IL18 rs1946518 GG genotype, we observed increased values of BoP and PPD, compared to subjects with the TT genotype. In addition, in gingival tissue of patients with periodontitis, we have detected decreased expression of IL-18. The gingival expression of IL-18 in patients with periodontitis correlated positively with number of remaining teeth. The above results suggest that IL-18, in addition to its pro-inflammatory effects in periodontal disease, may also exhibit protective properties.