Modulation of cystic fibrosis lung disease by variants in interleukin-8

Abstract

Cystic fibrosis pulmonary disease is characterized by excessive and prolonged inflammation. CF Pulmonary disease severity exhibits considerable variation that, to some extent, appears to be due to the presence of modifier genes. Several components of the inflammatory response are known to have altered regulation in the CF lung. Genetic variants in 52 inflammatory genes were tested for associations with lung disease indices in a CF patient population (n=737) homozygous for the DeltaF508 cystic fibrosis transmembrane conductance regulator mutation. Variants in three inflammatory genes showed significant genotypic associations with CF lung disease severity, including IL8 and previously reported TGFbeta1 (P< or =0.05). When analyzed by gender, it was apparent that IL8 variant associations were predominantly due to males. The IL8 variants were tested in an additional CF population (n=385) and the association in males verified (P< or =0.01). The IL8 variants were in strong linkage disequilibrium with each other (R2> or =0.82), while variants in neighboring genes CXCL6, RASSF6 and PF4V1 did not associate (P> or =0.26) and were in weaker LD with each other and with the IL8 variants (0.01< or =R2< or =0.49). Studies revealed differential expression between the IL8 promoter variant alleles (P<0.001). These results suggest that IL8 variants modify CF lung disease severity and have functional consequences.

Figure 1

The surveyed IL8 genomic region (240 kb). Markers in the three genes most proximal to IL8 were tested for an association with pulmonary disease severity. Arrows indicate direction of gene transcription. Solid black bars denote haplotype blocks as defined by the Haplotype Map Project.

Figure 2

pCEP-2 cells transfected with IL8 promoter-luciferase constructs (rs4073A or rs4073T) were treated with a pro-inflammatory cytokine mix. (a) Luciferase expression at 6, 12, and 24 hours post-treatment. Treatment with the cytokine mix induced a significant increase in luciferase expression for both constructs, (b) Values represent relative luciferase activity of the rs4073T allele to the rs4073A allele (*p=0.08 p=, **p=0.01, all others p<0.0001).