Innate Immune Transcriptomic Evaluation of PBMC Isolated from Sheep after Infection with E. ruminantium Welgevonden Strain

Heartwater is a tick-borne non-infectious fatal disease of wild and domestic ruminants caused by the bacterium Ehrlichia ruminantium, transmitted by Amblyomma ticks. Although there is evidence that a cell mediated immune response plays a role in protection against heartwater infection, an effective vaccine for this disease is lacking. Therefore, a systems biology oriented approach focusing on the innate immune response activated upon heartwater infection was investigated to aid vaccine development. In this study heartwater naïve sheep were infected and challenged by allowing heartwater infected ticks to feed on them. Transcriptome sequencing was performed on peripheral blood mononuclear cells (PBMC) collected before infection, after infection and challenge, and during the febrile stage of the disease. Blood was also collected daily for E. ruminantium pCS20 detection (pCS20 qPCR). The pCS20 assay could only detect the pathogen in the blood one day before and during the febrile stage of infection and confirmed that the sheep were infected. Transcripts that are associated with innate activating pathways were identified to be up-regulated after initial infection and the subsequent challenge. These included toll-like receptor (TLR), nod-like receptor (NLR), chemokine, cytosolic and cytokine-cytokine interaction receptor pathways. In particular, both TRL4 and TLR9 were activated together with DNA detection pathways, suggesting that vaccine formulations may be improved if CpG motifs and lipopolysaccharides (LPS) are included. This suggests that innate immune activation, perhaps using adjuvants, could be an important component for consideration during future subunit vaccine development.