Investigations into resistance and susceptibility to Johne's Disease in Red Deer

Abstract

Johne’s disease (JD), caused by the pathogen Mycobacterium avium subspecies paratuberculosis (MAP), is a chronic inflammatory bowel disease of ruminants that is characterised in its clinical stage by progressive weight loss/wasting and profuse diarrhea. Immune responses to MAP infection are initially characterised by a Th1 T cell response that subsequently decreases over disease progression. Detection of MAP occurs via pathogen recognition receptors (PRR) including NOD2 and the toll like receptors (TLR). Mutations in NOD2 have been identified as a susceptibility factor to JD. To cause infection MAP has a documented role in manipulating its environment including gene expression profiles. The aims of this project was to map the NOD2 gene for mutations associated with resistance or susceptibility to JD in red deer (Cervus elaphus), and to investigate the gene expression profiles of deer of demonstrated resistance and susceptibility for informative factors in disease progression. Foundational work, carried out at AgResearch Invermay investigating the heritability of resistance/susceptibility to JD in red deer, included artificially infecting 18 4 month old fawns with MAP. These deer then had mesenteric lymph node biopsies at weeks 4, 12, and 49 of the infection trial. Messenger RNA (mRNA) was extracted from the biopsied tissue from 6 animals chosen to represent the polarised extremes of resistance and susceptibility, purified, and reverse transcribed to produce cDNA that was used for qPCR of immune related genes. Blood collected via vascular venepuncture at the week 49 time point was used for mRNA extraction for reverse transcribing to investigate the CARD15 sequence. The primary finding from the CARD15 sequence evaluation identified one non-synonymous mutation named 1816 and five synonymous mutations. Using histopathology data from the 14 deer, (the CARD15 sequence was obtained from), as a measure of disease severity indicated that this mutation does not affect resistance or susceptibility. Profiling of multiple immune related genes indicated likely disease severity phenotypes, including heightened IFNβ related genes at week 4 being associated with resistance as well as heightened NLRP3 expression. Expression of immune genes throughout this infection trial has led to some insightful factors, including IFNs and NLRP3, influencing susceptibility and resistance to JD in red deer.