Boughan, P.K.; (2007) Innate immune defence to Helicobacter pylori. Doctoral thesis , University of London.

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Abstract

Helicobacter pylori exhibits tropism for the human stomach causing a spectrum of complications ranging from gastritis to gastric cancer in susceptible individuals. The mechanism(s) that allow the bacteria to persist and cause disease are unfolding. p-defensins are a family of endogenous, epithelial anti-microbial peptides that engage in host defense most prominently at mucosal surfaces. We and others have previously shown that human p-defensin (hBD)-2 and -3 are potent bactericidal agents against H. pylori. At present the identity of signalling pathways involved in host-bacterial cross talk leading to modulation of host antimicrobial immunity are unknown. The present study firstly investigated the potential role of bacterial virulence factors in mediating human p-defensin gene expression during H. pylori infection. AGS gastric epithelial cells were infected with cytotoxic H. pylori strains (60190, 84-183) and isogenic mutant strains (cagA-, cagE-, vacA- and CagPAl-). Human p-defensin (hBD2 & -3) gene expression quantified by RT-PCR and p-defensin transcriptional regulation was followed by transient transfection studies utilising hBD2 and -3 promoter luciferase constructs. We found hBD2 induction was dependent upon an intact cagPAI and minimal involvement was observed for the bacterial virulence factors CagA and VacA in modulating P-defensin expression. We sought to investigate the bacterial component responsible for instigating epithelial innate immune responses. Through the use of siRNA for NODI we determined a role for NODI-dependent NF-kB activation in mediating hBD2 but not hBD3 expression. Experiments utilising specific inhibitors of the MAP Kinase pathways directed us to delineate the role of each pathway in modulating p-defensin expression by the activation of stably transfected conditional MAP Kinase mutants. These studies revealed critical involvement of ERK pathway in the regulation of hBD3 but not hBD2 gene expression. Signalling upstream of ERK was explored and revealed EGFR as the host receptor responsible for detection and initiation of hBD3 gene and peptide production. Our studies demonstrated a crucial role for NODI in H. /Ty/ort-mediated hBD2 but not hBD3 expression and implicate EGFR transactivation in mediating hBD3 but not hBD2 expression, thus indicating two distinct regulatory mechanisms at play during innate immune host response to H. pylori infection.

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