Characterising the transcriptomic response of bovine peripheral blood mononuclear cells to a mycobacterial cell wall fraction

Background: Innate immune stimulants, including mycobacterium cell wall fractions (MCWF), offer an alternative control option to prevent and treat disease in livestock, by appropriately augmenting the innate immune response. However, the functional response to mycobacterium cell wall fractions in cattle is not well defined. In this study we report the transcriptomic response of bovine peripheral blood mononuclear cells to MCWF in the product Amplimune®.

Methods: Amplimune-induced transcriptomic changes in bovine peripheral blood mononuclear cells were determined following an initial pilot study and a later time course experiment. These cells were cultured in vitro for 24 h. In the pilot experiment, cells were stimulated with 0, 2, 5, 12.5 or 31.25 µg/mL Amplimune. In the time course experiment, cells were stimulated with 0 or 31.25 µg/mL Amplimune. In both experiments the total RNA was extracted at 0 h, 6 h and 24 h following stimulation. Ribosomal RNA depleted samples were sequenced, and data analysed to determine differential gene expression profiles. Differential gene expression was further analysed to determine enriched biological processes and pathways and a co-expression network.

Results and conclusion: Amplimune induced dose- and time-dependent gene expression profile changes in bovine peripheral blood mononuclear cells, which were enriched into GO-BP regulation of signalling receptor activity, response to cytokine and inflammatory response. Enriched pathways from KEGG analysis were cytokine-cytokine receptor interaction, IL17 signalling and TNF signalling pathways. Selected genes involved in these processes and pathways included IFNG, IL17A, TNF, IL22 and IL23A. PDE1B, CSF2 and IL36G were identified as the most connected genes in a co-expression network, while the connection between SAA2 and SIGLEC5 was the most important for flow of information within the network. Genes encoding for pro-inflammatory cytokines TNF, IL1B, IL6, IL2, and IL12B, and chemokines CCL3, CCL4 and CCL20 were also upregulated at 6 and 24 h post stimulation, as was the β-defensin gene TAP. These results assist in understanding how mycobacterial cell wall fractions alter immune function and may contribute to our understanding of the immune stimulant response attributed to Amplimune.