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Involvement of T helper type 17 and regulatory T cell activity in Citrobacter rodentium invasion and inflammatory damage

Citrobacter rodentium is a murine pathogen that transiently colonizes the lumen of the large intestine. C. rodentium induces colitis, but the relative importance and temporal induction of the T helper type 17 (Th17) and regulatory T cell (Treg) pathways in protection from the infection and inflammation have not been assessed. Our aim was to investigate the key immunological signalling events associated with successful clearance of C. rodentium. Mice were challenged with luminescent‐tagged C. rodentium and killed at days 3 (early infection), 10 (peak infection) and 21 (late infection) post‐infection. Bioluminescent imaging and bacterial culture determined levels of C. rodentium. Distal colon mRNA expression of interleukin (IL)‐17, IL‐6, IL‐1β, tumour necrosis factor (TNF)‐α, forkhead box P3 (FoxP3) and ghrelin were assessed using real‐time polymerase chain reaction. Results were compared with age‐matched non‐infected mice. Low levels of C. rodentium were found at day 3, high levels at day 10, with clearance from the majority of the mice by day 21. In the distal colon, there was up‐regulation of TNF‐α and FoxP3 throughout the study and increases in IL‐6 and IL‐17 during the peak and late stages of infection. Ghrelin expression was increased at the peak and late stages of infection. This study has characterized changes to the T helper cell pathways, following the course of C. rodentium infection in mice. There were significant immunological changes, with up‐regulation of the Th17 and Treg pathways in the distal colon and an increase in ghrelin expression compared with non‐infected control mice. These changes may play a role in the pathology and clearance of C. rodentium.