Defining the role of the transcription factor T-bet in the innate immune system in intestinal inflammation.

Mice lacking the transcription factor T-bet in the innate immune system (Tbx21-/- x Rag2-/- Ulcerative Colitis, or TRUC) develop microbiota-dependent inflammatory bowel disease (IBD). The innate immune mechanisms responsible for causing disease are still to be resolved, yet potentially offer novel insights into the pathogenesis of IBD, and how T-bet might influence inflammation in the gut. <br/>In this thesis it was shown that chronic IBD in TRUC mice was dependent on interleukin-17A (IL-17A) producing IL-7R+ CD90+ innate lymphoid cells (ILCs). Depletion of ILCs or IL-17A neutralization cured disease. Cytokines responsible for driving innate IL-17A included IL-23, IL-6 and TL1A. IL-23 and IL-6 played functionally important roles in TRUC disease, since neutralisation reduced innate IL-17A production and attenuated disease. TNFα, predominantly produced by CD11chigh class II+ CD11b+ CD103- dendritic cells (DCs), synergised with IL-23 to drive IL-17A production by ILCs. <br/>Helicobacter typhlonius (HT) was identified as the key colitigenic bacterium driving TRUC disease. Four-five-four ribosomal RNA gene sequencing demonstrated that HT was consistently present in the faeces of all TRUC mice, but absent from a newly-derived colony of disease-free Tbx21-/- x Rag2-/- mice. Inoculation of pure HT cultures was sufficient to reinstate disease into this new colony of healthy mice. <br/>T-bet impacted on colitis in several ways. In the absence of T-bet, ILCs selectively produced IL-17A and were poor producers of interferon-γ. Second, T-bet deficient DCs produced excess TNFα in comparison with T-bet sufficient DCs. Finally, T-bet was a transcriptional repressor of the Il7ra locus. IL-7R was expressed by ILCs and signalling through this receptor was critical for TRUC disease. Selective IL-7R blockade attenuated disease. Together these data provide new insights into TRUC disease and demonstrate at least some of the mechanisms by which T-bet regulates the interplay between mucosal innate immune cells and the intestinal microbiota.

Name dc:type.qualificationname

Doctor of Philosophy

Level dc:type.qualificationlevel

Doctoral Thesis

Grantor dc:publisher.institution

King's College London

Year dc:date.issued

2014

Author dc:creator

• Powell, Nicholas

Advisor dc:contributor.advisor

• Lord, Graham Michael

Language dc:language

eng

Identifier

oai:kclpure.kcl.ac.uk:studenttheses/d78ff348-ac4f-4ef6-b1a9-7e527226bf04

OAI identifier oai:identifier

oai:kclpure.kcl.ac.uk:studenttheses/d78ff348-ac4f-4ef6-b1a9-7e527226bf04