Date on Master's Thesis/Doctoral Dissertation

8-2017

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Microbiology and Immunology

Degree Program

Microbiology and Immunology, PhD

Committee Chair

Uriarte, Silvia M.

Committee Co-Chair (if applicable)

Alard, Pascale

Committee Member

Lamont, Richard J.

Committee Member

Miller, Richard D.

Committee Member

Graham, James E.

Abstract

Periodontal disease is among the most common of inflammatory conditions and is caused by bacterial and host derived factors. The presence of bacteria drives the recruitment of neutrophils, professional phagocytes, to migrate to specific oral sites where they produce potent antimicrobials to kill their target. However, this inflammation and production of antimicrobials must be strictly regulated to minimize collateral host tissue damage. Human neutrophils recognized the oral pathogen Filifactor alocis through Toll-like receptor (TLR) 2 and upon binding, activated both p38 MAPK and ERK signaling pathways, known to be involved in neutrophil cell migration and degranulation. F. alocis also stimulated secretory vesicle and specific granule exocytosis and enhanced chemokinetic and chemotactic migration to interleukin (IL)-8, a key chemoattractant found in the oral cavity (Chapter 2). Once these challenged neutrophils have arrived at their targeted site, they will employ oxidative-mediated killing mechanisms, operating intracellularly in the bacterial-containing phagosome, and extracellularly, in the extracellular space. Neutrophils effectively perform phagocytosis to internalize F. alocis into their phagosomal compartment, however minimal intracellular respiratory burst response is produced. In addition, F. alocis-challenged neutrophils produced minimal superoxide release, however the bacterial challenge primed neutrophils for an enhanced respiratory burst response. F. alocis survived neutrophil oxygen-dependent intracellular and extracellular killing mechanisms up to 4 h post-infection (Chapter 3). Activated neutrophils can also undergo neutrophil extracellular trap (NET) formation as a means to trap and potentially kill targets. NETs have been described to be formed in the oral cavity in response to oral biofilms. F. alocis failed to induce NETs from neutrophils, which may indicate this bacterium is unique to the oral cavity, as other oral bacteria Streptococcus gordonii and Peptoanaerobacter stomatis induce NETs. However, F. alocis can manipulate neutrophils and reduce their NET formation capacities to known pharmacological (PMA) and bacterial (S. gordonii) inducers (Chapter 4). Overall, our results are the first to show how F. alocis effectively evades human neutrophil killing mechanisms and manipulates some of their functional responses. These results provide information about the pathogenic potential of F. alocis which would help delineate the role of this emerging pathogen in the development of periodontal disease.

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