Association of Interleukin-6-572C/G Gene Polymorphism and Serum or Cerebrospinal Fluid Interleukin-6 Level with Enterovirus 71 Encephalitis in Chinese Han Patients with Hand, Foot, and Mouth Disease

Abstract

Interleukin-6 (IL-6), as one of pro-inflammatory cytokines, plays a key role in Enterovirus 71 (EV71) encephalitis. We investigated the association of IL-6-572C/G polymorphism and serum or cerebrospinal fluid (CSF) IL-6 level with EV71 encephalitis in patients with hand, foot, and mouth disease (HFMD). This study was carried out in 59 Chinese Han patients with EV71 encephalitis, 128 EV71-related HFMD without complications, and 232 controls. The IL-6-572C/G polymorphism was detected by polymerase chain reaction-restricted fragment length polymorphism gene analysis. Serum or CSF IL-6 levels were determined using a commercial enzyme-linked immunosorbent assay. The patients with EV71 encephalitis had a higher frequency of IL-6-572GG/GC genotype compared to the patients with EV71-related HFMD without encephalitis complications (40.7 vs. 15.6 %, odds ratio (OR) = 3.70, 95 % confidence interval (CI) = 1.83–7.50, p = 0.001). Similarly, the frequency of IL-6-572 G allele among the patients with EV71 encephalitis was also higher than that of patients with EV71-related HFMD without encephalitis complications (23.7 vs. 8.6 %, OR = 3.31, 95 % CI = 1.80–6.08, p < 0.001). Serum IL-6 levels in G carries (CG + GG) (195.1 ± 11.8 pg/ml) elevated significantly compared to CC homozygotes (167.7 ± 6.7 pg/ml) in EV71-infected patients (p < 0.001), but no significant differences were observed in CSF IL-6 levels among different genotypes in patients with EV71 encephalitis. Furthermore, G carriers (GG + GC) (10.6 ± 1.29 mg/l) had significantly higher blood CRP levels compared to CC homozygotes (9.31 ± 1.93 mg/l) in patients with EV71 encephalitis (p = 0.005). These findings suggested that IL-6-572 G allele was significantly associated with the susceptibility to EV71 encephalitis in Chinese Han patients, and IL-6-572 G allele might elevate the risk to EV71 encephalitis.