IL6-174-SNP and P gingivalis independently modulate IL-6 expression in periodontitis

Objectives: The aim of this study was to investigate the role of IL-6 promoter -174 polymorphism and the presence of P. gingivalis in the determination of the tissue levels of IL-6 in chronic periodontitis and the possible correlations with clinical parameters of disease.

Methods: The IL6 promoter -174G/C SNP was analyzed by restriction fragment length polymorphism in 62 chronic periodontitis (CP) patients and 29 control subjects. Additionally, the Pg presence and the levels of IL-6 mRNA expression in gingival tissues were determined by RealTime-PCR.

Results: The C allele was found to be more prevalent in CP patients, and a trend towards a higher IL-6 expression in C allele carriers was verified, despite the lack of statistical significance. Conversely, the Pg presence was significantly associated with higher IL-6 levels, and also with increased probing depth, clinical attachment loss and bleeding on probing. When the genotype influence was evaluated in Pg negative subjects, it was observed that GC and CC carriers presented an increased expression of IL-6 than GG group, and also a tendency to present a higher clinical attachment loss. On the other hand, in Pg positive subjects, the IL-6 expression and the clinical parameters were found to be similar in all genotypes. Interestingly, our data demonstrate there is not a synergic effect in Pg detection and the IL6-174 SNP, except for a trend towards an increased bleeding on probing on GC/CC positive to Pg. Nevertheless, both Pg and IL6-174 SNP can independently result in elevated IL-6 levels.

Conclusions: Our results suggest that the IL-6 promoter -174 SNP seems to be functional in chronic periodontitis and also demonstrate that other predisposal factors as P. gingivalis can result in an intense IL-6 expression even in the absence of such polymorphism.