Interleukin 6 promoter polymorphisms in normal Han Chinese population: frequencies and effects on inflammatory markers.

BACKGROUND: Interleukin 6 (IL-6) is a cytokine involved in different physiologic and pathophysiologic processes, and circulating levels of IL-6 differ greatly between individuals, but the results have not always been concordant among diverse populations. The aim of present study was to determine the prevalence of the 3 polymorphisms (-174G/C, -597G/A, and -634C/G) in the IL-6 gene promoter region and their effects on inflammatory markers in normal Han Chinese population. METHODS: A total of 232 subjects (143 men and 89 women; mean age, 51.37 ± 17.63 years; range, 22-88 years) of unrelated healthy Han Chinese in Jinangsu area (south of China) were enrolled. Genotyping of the 3 polymorphisms were performed by polymerase chain reaction and restriction fragment length polymorphism combined with gel electrophoresis and then confirmed by direct sequencing. RESULTS: Among the 232 individuals studied, 231 carried the GG wild type of -174G/C; only 1 carried the GC genotype. For -597G/A polymorphism, individuals all carried the GG wild type; the GA or AA genotypes were not detected. The frequencies of -634C/G genotypes CC, CG, and GG were found to be 59.48%, 37.07%, and 3.45%, respectively, the derived allele frequencies for the C and G alleles were 78.02% and 21.98%. There were no significant differences in age, sex, body mass index, or lipids parameters between the -634 CC and CG+GG genotypes. However, individuals with CC genotype showed lower levels of high-sensitivity C-reactive protein and IL-6 than those with CG+GG genotype. CONCLUSIONS: IL-6 -174G/C and -597G/A are rare, but -634C/G is common in Han Chinese population, and the -634G allele is associated with circulating levels of IL-6 and C-reactive protein.