Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Microbiology and Immunology

Supervisor

Dr. Sung Ouk Kim

Abstract

The pleiotropic cytokine granulocyte-colony stimulatory factor (G-CSF) is mainly required for the generation of neutrophils, but its role in macrophage generation has also been reported. In addition, G-CSF is effective for the down-regulation of inflammatory cytokines and ameliorating gut disorders, such as colitis. However, the G-CSF function in macrophage generation and gut immunity remains unclear. The first focus of this thesis was to assess the role of G-CSF in macrophage generation and its contribution to gut immunity. G-CSF was found to promote the generation of Gr-1high/F4/80+ macrophages in macrophage (M)-CSF-treated bone marrow cells, most likely through suppressing cell death. Gr-1high macrophages showed anti- inflammatory/regulatory macrophage (M2)-like cytokine and surface marker profiles. G-CSF receptor deficient (G-CSFR-/-) mice harbored less gut macrophages, but had a similar number of neutrophils in the gut. In addition, adoptive transfer of G-CSF- treated bone marrow-derived macrophages (G-BMDM) showed a dominant gut- homing phenotype. G-CSFR-/- mice were also more susceptible to dextran sulfate sodium (DSS)-induced colitis than wild-type mice and adoptive transfer of G-BMDM protected these mice from DSS-induced colitis. The second focus of this thesis was to explore the signaling mechanism(s) controlling the preferential G-CSF production over inflammatory cytokines in probiotic bacteria-exposed BMDM. Lactobacillus rhamnosus GR-1 (GR-1) renders several immunomodulatory effects, at least in part, through preferentially inducing G-CSF in macrophages. However, the mechanism(s) by which GR-1 induces preferential G-CSF production in macrophages is still unknown. Among 84 genes tested, G-CSF was the cytokine induced at highest levels in GR-1-treated BMDM, but the induction of inflammatory cytokines, such as TNF-α, was minimal. The signaling pathway of GR-1-preferential G-CSF production was TLR2-, NF-κB-, ERKs- and PI3K/Akt-dependent. A secreted protein-like molecule(s) was found to be responsible for GR-1-preferential G-CSF production.

Collectively, these results demonstrated the immune regulatory function of G-CSF on macrophages in gut immunity and a potential mechanism of action of certain probiotics.