Objective: Respiratory syncytial virus (RSV) infects nearly all children under two years of age. It is not understood why some develop serious bronchiolitis. Whether there is a genetic component is not known. The nature of the association between RSV bronchiolitis and subsequent wheezing remains unknown. interleukin-8 (IL-8) is a potent neutrophil chemokine and activator, which plays a role in virus-induced wheezing diseases. The purpose of this study was to assess the genetic association between the IL-8 gene promoter -251A/T polymorphism and RSV bronchiolitis and post-bronchiolitis wheezing in children.
Methods: Totally 320 children who were hospitalized for bronchiolitis together with positive immunofluorescence for RSV were recruited in this study from Jan. 2002 to Jan. 2004. A group of 272 healthy children were enrolled as controls. The age of these children ranged from 1 to 12 months. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) was used to identify the polymorphism at position-251 of the IL-8 promoter in RSV bronchiolitis and control groups. The total IL-8 and IgE concentrations in serum samples were measured by enzyme-linked immunosorbent assay (ELISA). The patients with RSV bronchiolitis were followed up in order to analyze the occurrence of wheezing post-bronchiolitis.
Results: (1) Both A allele and T allele were detected at -251 of the IL-8 promoter; the prevalence of the A allele in RSV bronchiolitis group was 45.6%, as compared with 37.7% in normal group. The prevalence of IL-8-251A allele was significantly different between the two groups (P < 0.05). (2) For genotypes T/T, A/T, A/A in RSV bronchiolitis, level of serum IL-8 were (17 +/- 6) ng/L, (21 +/- 7) ng/L, (24 +/- 9) ng/L, respectively, the difference was significant among the three genotypes (P < 0.01). (3) The prevalence of the A allele in the group who wheezed after the episode of RSV bronchiolitis was 54.6%, as compared with 35.8% in the group who had bronchiolitis but did not go on to wheeze. The prevalence of IL-8-251A allele was significantly different between the two groups (P < 0.05).
Conclusion: Polymorphism of IL-8 promoter-251A/T was associated with susceptibility to RSV bronchiolitis in children. The association of IL-8-251A with severe RSV bronchiolitis is most marked in the children who go on to wheeze.