Mining the Methylome for New Insights into Bovine Tuberculosis.

Bovine tuberculosis (bTB), caused by Mycobacterium bovis, represents a significant issue for the global agriculture industry as well as for human health. Epigenetic modifications can alter the course of the immune response and differentially methylated regions (DMRs) could contribute to the failure of current generation tests to detect all TB-infected cattle. Whole Genome Bisulphite Sequencing (WGBS) was used to profile DNA methylation levels from peripheral blood of cattle naturally infected with M. bovis (positive for the single intradermal comparative tuberculin test (SICTT) and/or the interferon-? release assay (IGRA) compared to negative controls [n=8/group, total of 16 WGBS libraries]. Although overall methylation profiles were similar across the genome, 224 DMRs and 159 Differentially Methylated Promoter Gene (DMPGs) were identified between groups with an excess of hypermethylated sites in bTB+ infected cattle (threshold >15% differential methylation). Genes located within these DMRs included the Interleukin 1 receptor (IL1R1) and MHC related genes (BOLA and BOLA-DQB) which may influence effective immunity. KEGG pathway analysis identified enrichment of genes involved in Calcium and MAPK signalling, as well as metabolism pathways. Analysis of DMRs in a subset of SICTT- cattle (n=4 group) which were IGRA+, and thereby potentially represent a risk for disease recurrence on farms, showed differential methylation of genes including Interleukin 10 Receptor, alpha (IL10RA), Interleukin 17F (IL17F) and host defence peptides (DEFB and BDEF109). This study has identified a number of immune gene loci at which differential methylation could impact on the host immune response and the ability of cattle to clear infection. Differential methylation of immune gene loci is an informative avenue to improve our understanding of the regulation of host immunity as well as the role of methylation on diagnostic test performance.