Functional characterisation of bovine interleukin 8 promoter haplotypes in vitro

Interleukin 8 (IL-8) is a major mediator of the innate immune response and polymorphisms in this gene are associated with susceptibility to inflammatory disease in humans. The aim of this study was to characterise the promoter region of the bovine IL8 gene towards understanding its regulation and the effect of promoter polymorphisms on gene expression levels. Twenty-nine polymorphic sites were identified across a 2.1 kb upstream promoter region of the IL8 gene including two insertion/deletion polymorphisms. Sequence analysis and SNP genotyping identified two distinct promoter haplotypes (IL8-h1 and IL8-h2), which were present at significantly different frequencies in two divergently selected cattle breeds – Holstein-Friesian and Norwegian Red (IL8-h1 at 48% and 80% respectively). IL8-h1 was functionally less responsive in unstimulated mammary epithelial cells and in response to stimulation with LPS or bovine TNF. Serial deletion analysis and in silico transcription-factor binding site analysis indicated that allele specific binding of the transcriptional repressor Oct-1 may account for the reduced sensitivity of IL8-h1. Our finding of genetic variation in the bovine IL8 promoter that differentially regulates its expression has significant functional implications for IL8 expression in vitro and which may impact on susceptibility to bovine infectious disease and inflammation.

► We uncover 29 novel high number polymorphisms in the promoter region of a key immune gene (IL8) in cattle.
► The polymorphisms form two distinct haplotypes that we demonstrate to be significantly functionally different, both in response to LPS and the endogenous cytokine – TNF.
► We show that divergently selected breeds have significant differences in allele selection that may facilitate future selection for disease resistance, which will benefit agriculture and human health.