In vivo relevance of polymorphic Interleukin 8 promoter haplotype for the systemic immune response to LPS in Holstein-Friesian calves

Abstract

Interleukin 8, also known as CXC chemokine ligand 8 (CXCL8), is a critical chemokine in the recruitment of leukocytes to sites of infection and is a potent mediator of inflammation. We previously discovered 29 polymorphic sites in the promoter region of the bovine Interleukin 8 gene, which segregate into two distinct haplotypes, denoted IL8-h1 and IL8-h2. Population genetic analysis of these two haplotypes showed significant inter-breed differences in haplotype frequency, which is suggestive of selection acting at this locus. Furthermore functional characterisation identified that IL8-h2 was more active in mammary epithelial cells stimulated with the bacterial endotoxin, LPS. However, the in vivo relevance of these functional differences in the IL8 gene has not been ascertained. Therefore, in the current study, we tested the hypothesis that IL8 haplotype would result in variation in the systemic immune response to LPS challenge in Holstein-Friesian (HF) calves. A Taqman assay was designed to genotype both Jersey and HF calves, from which 20 healthy HF calves (representing IL8-h1 and IL8-h2) from the same farm were subjected to LPS stimulation via jugular venepuncture (100ng/kg). Systemic immune profiling was subsequently performed up to 216h post-challenge. Haematological analysis showed perturbations in leukocyte populations of cells but only the lymphocyte response was significantly different between IL8-h1 and IL8-h2. IL8 expression levels were significantly different between haplogroups, at both the gene expression and protein levels (P<0.05). Circulating neutrophils were subsequently purified from each haplogroup to measure potential haplotype specific effects on neutrophil migration and bacterial killing but no significant differences were detected, which is likely due to the low circulating levels of IL8. We conclude that IL8 haplotype significantly affects IL8 expression profile in response to bacterial endotoxin in vivo, and the significant increase in IL8 in IL8-h2 calves supports our earlier findings in vitro. Genetic variation at the IL8 locus therefore explains a proportion of the inter-breed and inter-individual variation in immunity between neonatal calves which is likely to influence their resistance to infection.