Effects of Helicobacter pylori induced neutrophil subtype differentiation on chemotaxis and phagosome maturation
Creators: name: Prichard, Allan Scot
Publisher: name: University of Iowa
Year: 2022
Subjects: Gastric Cancer
Helicobacter pylori
Neutrophil
Phagosome
Subtype differentiation
public abstract
Migration

description: Helicobacter pylori is gastric pathogen that colonizes 50% of the global population and evokes a histological gastritis that often remains asymptomatic. This infection is characterized by a neutrophil dominant inflammatory response with increased cell density resulting in increased disease severity. Often persisting for the life of the individual, this pathogenic infection can induce peptic ulcer disease, gastric adenocarcinoma, and even mucosa-associated lymphoid tissue (MALT) lymphoma. Remarkably, the neutrophil dominant immune response fails to resolve infection instead resulting in accumulation of heavily infected cells. Our lab discovered that H. pylori infection prevents neutrophil antimicrobial killing mechanisms by regulating cell respiratory burst, however the mechanisms by which this is achieved, and resultant accumulation of cells is unknown.
description: We demonstrate within this thesis that H. pylori infection causes defective PMN migration, possibly explaining enhanced accumulation of these cells at sites of infection. Our data reveal failed uropod retraction in a 2D model, which is characterized by aberrant actin structures and mis-localized myosin machinery. This uropod retraction phenotype resembled the effects of myosin machinery inhibitors, however, analysis of myosin phosphorylation by immunoblotting showed that his aspect of the myosin activation cycle significantly increased during infection. Interestingly, adhesion of infected PMNs and subcellular localization of the integrin CD11b/CD18 were unchanged. Furthermore, H. pylori the gastric epithelial virulence effectors tested were dispensable to defective chemotaxis even though we determined that this is an active process that is not recapitulated by formalin-killed bacteria. Thus, as migration is an essential neutrophil function, our phenotype indicates that infected neutrophils exhibit altered cell function.
description: The next aim of my thesis was to determine the effects of H. pylori on another essential function, phagosome maturation. PMN phagosome maturation during infection results in bacterial killing and degradation through delivery of cytotoxic peptides, enzymes, and reactive oxygen species (ROS) to these compartments. As H. pylori displays intracellular persistence, we examined phagocytosis and phagosome maturation during this infection. This revealed failed phagosome maturation through inhibited granule-phagosome fusion, yet, interestingly, granule exocytosis was globally enhanced after 24 hours of infection. Infection was further characterized by CEACAM recruitment to the forming phagosome, in addition to phagosome accumulation of the autophagy protein LC3B. Taken together, the data in this thesis support a model of altered PMN function that results in failed bacterial clearance and infection persistence despite a robust cellular response.