Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Microbiology and Immunology

Supervisor

Sung Ouk Kim

Abstract

Loss of immunoregulation in the intestine results in inflammation, such as is observed in the chronic, relapsing, inflammatory bowel diseases (IBD), Crohn's disease and ulcerative colitis. However, our understanding of this process remains incomplete. The cytokine granulocyte-colony stimulating factor (G-CSF) is an important stimulator of granulopoiesis in steady-state and during inflammation, but has also been shown to have anti-inflammatory effects and is a potential therapeutic for IBD. In addition, certain strains of bacteria, termed probiotics, have been postulated to have anti-inflammatory effects in the intestine. The mechanisms by which these strains of bacteria elicit anti-inflammatory effects are not fully understood.

In this thesis, I show that G-CSF plays an important anti-inflammatory role in the response to the probiotic bacterial strain Lactobacillus rhamnosus GR-1 (GR-1) and within the intestinal immune system. Macrophages treated with GR-1 produce high amounts of G-CSF, but low amounts of tumor necrosis factor (TNF)α and interleukin (IL)-12. G-CSF produced by GR-1-treated macrophages inhibits the activation of c-Jun N-terminal Kinase as well as the production of TNFα and IL-12 by macrophages and dendritic cells (DCs), respectively. Human intestinal lamina propria mononuclear cells (LPMCs) released high levels of G-CSF when cultured ex vivo, which was reduced in LPMCs of IBD patients. Non-IBD LPMCs produced higher G-CSF after stimulation with GR-1 than with E. coli, while IBD LPMCs showed the opposite pattern. The release of G-CSF by mouse intestinal tissue samples was dependent upon MyD88 signaling, but independent of the intestinal microflora. G-CSFR-/- intestinal tissues express higher levels of the cytokines IL-12, IL-23, and TNFalpha, suggesting that G-CSF inhibits inflammatory cytokine production in the gut. G-CSFR-/- mice show increased weight loss and intestinal tissue damage in an acute colitis model induced by dextran sulfate sodium (DSS), and developed a pseudomembranous structure associated with clusters of bacteria over regions of severely damaged colon. Increased levels of intestinal IL-17 are seen in DSS-treated G-CSFR-/- mice, indicating that G-CSF may play a role in regulating the production of IL-17 in the intestine. Overall, I have shown that the immunomodulatory properties of G-CSF are important in intestinal immunoregulation, the effects of probiotics, and IBD.

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