Activation of macrophages in the mucosa and muscularis of jejunum in horses undergoing abdominal surgery for strangulating small intestinal obstructions

Introduction: Postoperative ileus (POI) is the functional inhibition of propulsive intestinal motility following abdominal surgery. Rodent and human-based studies have demonstrated manipulation-induced activation of intestinal muscularis macrophages (MM) in the pathophysiology. LPS translocation from the gut lumen is also an activator of MMs. Few equine studies have focussed on pathogenesis. The aim of this study was to evaluate gene expression in intestine from horses undergoing abdominal surgery for colic to determine whether there was evidence of intestinal macrophage activation.
Material and methods: The normal population of macrophages in equine intestine was determined using CD163 as an immunohistochemical marker. RNA-seq analysis of LPS stimulated equine bone marrow-derived macrophages (eqBMDMs) was used to inform the selection of genes for qPCR analysis of equine intestinal tissue. Mucosal and muscularis tissue was collected from resection margins removed from horses undergoing abdominal surgery (n=12) and subsequently analysed by qPCR.
Results: Macrophages were present in all layers of the equine intestine. Transcriptomic analysis revealed an increased expression of TNF-α, IDO1, IL-1βand IL-6 in eqBMDMs. Analysis of resection margins showed evidence of increased expression of IL-1β, IL-6 and TNF-α in the mucosa and muscularis when compared to control tissue.
Conclusion: These preliminary data support the hypothesis that intestinal surgery results in the activation of the intestinal macrophage population. Further work is required to elucidate whether the risk of developing POI is related to the magnitude of macrophage activation during surgery.
Z.M.L’s PhD was funded by the Horserace Betting Levy Board