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Title: Contribution of the inflammasome-autophagy axis in host defense to enteropathogenic Escherichia coli (EPEC)
Author: Pramanik, N.
ISNI:       0000 0004 5369 2696
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2015
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Enteropathogenic Escherichia coli (EPEC) is a non-invasive, gram-negative bacterium that causes acute and persistent diarrhoea in infants under the age of five. Infantile diarrhoea is the second leading cause of mortality in children recorded by the World Health Organization (WHO). At present the role of innate and adaptive immunity in providing protection or mediating pathology in response to EPEC remains less well studied. Herein, multiple facets of EPEC interaction with the immune system were explored in co-cultures utilising wild-type and bacterial isogenic mutants in murine and human model systems. EPEC-mediated bone-marrow derived dendritic cell (BMDC) activation was investigated. The flagellin moiety and the type three secretion system (T3SS) inhibit DC surface marker and IL-10 expression, thus modulating the innate IL-12/IL-10 axis. The T3SS of Enterohemorrhagic E.coli (EHEC) and Salmonella typhimurium (STM) exerted similar effects on the cytokine milieu, supporting the hypothesis that enteropathogens may promote inflammation by inhibiting IL-10 expression. Infection led to potent Th1 and Th-17 immunity, the latter response was generated in the absence of any detectable IL-23. Evidence suggests a central role for IL-1 signalling in Citrobacter rodentium (murine model for EPEC) infection and inflammation. We investigated EPECmediated inflammasome activation, a protein-complex involved in the release of bioactive IL-1 . The present study is the first to implicate NLRP3 in EPEC-mediated BMDC inflammasome activation. The T3SS was crucial for NLRC4 but not for NLRP3-driven inflammasome assembly. K+ ion influx was identified as an important mediator of EPEC-driven NLRP3 function. EPEC sabotages intestinal epithelial actin cytoskeleton in multiple ways, cellular events that promote disease on-set. Wiskott-Aldrich syndrome (WAS) is a rare immunodeficiency where the WAS protein, an important mediator of actin polymerisation is defunct. The role of actin in EPEC-BMDC crosstalk was studied in WT and WASP-deficient murine and human innate immune cells. WASP deficiency resulted in increased bacterial load, impaired autophagy and deregulated inflammasome activity. Similar effects were also observed in response to infection with the intracytosolic enteropathogen Shigella flexneri. Our observations suggest for the first time that WASP is a pivotal rheostat between bacterial Autophagy and the Inflammasome axis.
Supervisor: Elliott, Mona Bajaj Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available