The effect of the interleukin-6 c/g-174 polymorphism and circulating interleukin-6 on fibrinogen plasma levels

BACKGROUND AND OBJECTIVES: C-reactive protein (C-RP) levels correlate with fibrinogen values and are predictive of coronary artery disease. Interleukin-6 (IL-6) strongly regulates the production of C-RP. A polymorphism (C/G-174) within the IL-6 gene has been shown to affect IL-6 gene expression and plasma concentrations. DESIGN AND METHODS: In 598 asymptomatic employees of a hospital in Southern Italy, we investigated the association between IL-6 C/G-174 gene variants and plasma fibrinogen levels. RESULTS: Subjects with IL-6 plasma levels >2.0 pg/mL had a higher body mass index (BMI) (24.5+/-1.2) than subjects with IL-6 levels below this cut-off value (23.7+/-1.2; p =0.005). No association was found with sex, cigarette smoking, or alcohol consumption (p always>0.05). When the whole sample was analyzed according to the IL-6 C/G-174 polymorphism, there was no difference with respect to age, sex, alcohol consumption, cigarette smoking, total cholesterol, triglycerides, and body mass index. Median plasma fibrinogen levels, as well as carriers of plasma levels of IL-6 >2.0 pg/mL and C-RP >0.33 mg/L, were similar among subjects with different IL-6 genotypes. Similarly, no difference was observed when only carriers of plasma levels of IL-6 >2.0 pg/mL were analyzed, whereas in those with C-RP >0.33 mg/L IL-6 GG carriers had significantly lower plasma fibrinogen levels. INTERPRETATION AND CONCLUSIONS: The investigation of the IL-6 C/G-174 polymorphism does not seem to be a useful tool for predicting raised plasma fibrinogen levels.