Association of Serum Interleukin-6 Concentration with a Functional IL6 −6331T>C Polymorphism

Background: Interleukin-6 (IL-6) concentrations vary substantially among individuals. This study aimed to identify novel genetic markers to explain these differences. Methods: We sequenced a region 6-kb upstream of the IL6 [interleukin 6 (interferon, beta 2)] transcription start site in a search for functional variants and detected 3 common variants: −6331T>C, −6101A>T, and −5617/−5616C/A>T/G. IL6 −6331T>C (C allele frequency, 0.20; 95% confidence interval, 0.16–0.24) showed strong negative linkage disequilibrium with −174G>C (D′ = −0.97) and was studied further in 309 individuals who underwent coronary artery bypass grafting. Results: Patients with the TT genotype had higher IL-6 concentrations 6 h after surgery than those with the CC genotype (mean, 199.4 ng/L vs 114.9 ng/L; P = 0.02). A similar association was seen in a cohort of 173 patients who underwent intensive periodontal therapy: Individuals with the CC genotype had significantly lower IL-6 concentrations 24 h after therapy than TT patients (mean, 0.78 ng/L vs 5.00 ng/L; P < 0.0001). A similar trend was observed in 203 healthy individuals from northern Europe (1.29 ng/L for the TT genotype vs 0.89 ng/L for the CC genotype; P = 0.07). Reporter assays that used a sequence flanking the −6331 single-nucleotide polymorphism spliced upstream to the IL-6 minimal promoter driving luciferase gene expression demonstrated a 1.3-fold increase in promoter activity (P < 0.01) for constructs containing −6331T. Electrophoretic mobility shift assays revealed enhanced binding of transcription factor Oct-1 to the T allele. Conclusions: IL6 −6331T is associated with increased IL-6 concentrations in an acute inflammatory state via a mechanism involving binding of the Oct-1 transcription factor. This finding may help resolve conflicting studies based on the IL6 −174G>C variant.