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

Abstract

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. 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. 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. 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.