Investigating the role of Escherichia coli in perpetuating inflammation in Crohn’s disease

Crohn’s disease (CD) is characterised by chronic intestinal inflammation and dysbiosis. Intestinal dendritic cells (DCs) prime and shape mucosal T cell responses, and a defect in the myeloid compartment in CD implicates them in its pathogenesis. Recent work has linked Escherichia coli with perpetuating inflammation in CD. To investigate how interaction between E. coli and DCs may maintain chronic intestinal inflammation, we characterised colonisation dynamics of a strain of E. coli isolated from a CD patient, NRG857c, in C57BL/6 mice. Mice were treated with streptomycin 24 h before oral infection with NRG857c. After 7 days, infected mice showed faecal shedding at 10⁷ CFU g^-1. NRG857c was recovered from all intestinal tissues, but caecum and colon were most heavily colonised (>10⁶ CFU g^-1). As little is known about DC subsets in the murine caecum, we examined this tissue and show that caecal DC subsets mirror those found in the colon, and that CD103+CD11b+ DCs are absent from the caecal patch. We further show that caecal DCs migrate to the colon-draining MLN in the steady state. This work provides a basis for characterising the immunological consequences of NRG857c colonisation in vivo, and for identifying factors that could contribute to CD pathogenesis.