Year: 2015
Type: dissertation
Abstract: Chronic periodontitis is an inflammatory disease of the supporting tissues of teeth that is characterised by bone resorption and if left untreated can result in eventual tooth loss.The subgingival plaque bacteria Porphyromonas gingivalis, Treponema denticola and Tannerella forsythia have been closely associated with chronic periodontitis.T cell immunity during periodontal infections has been well-documented, mainly involving the adaptive immunity which includes Th1 and Th2 responses.A small number of clinical studies have reported the presence of IL-17 and Th17-related cytokines in the gingival crevicular fluid and diseased tissues of periodontitis patients.However, the roles of innate T cells and Th17-related responses in disease progression is unclear.This study shows that NKT cells play a role in pro-inflammatory cytokine production, contributing to P. gingivalis-induced bone loss in the mouse periodontitis model.Inflammation and bone resorption was reduced in the absence of NKT cells or CD1d, the corresponding activating receptor for the TCR of NKT cells.As NKT cell responses were likely to be associated with glycolipid antigens, a major glycolipid of P. gingivalis was isolated, Pg-GL1, which was found to induce NKT cell and B cell activation.Results from knock-out mice studies suggested that NKT activation by Pg-GL1 occurs through a mixed requirement for TCR/CD1d-engagement and additional cytokines.Furthermore, Pg-GL1 was shown to induce the secretion of IL-1β, IL-6, IL-12(p40), IL-17, and G-CSF, cytokines that have been associated with inducing Th17-responses and, as contributing factors during periodontal inflammation and bone resorption.Similar to P. gingivalis, three major glycolipids (termed Tf-GL1, Tf-GL2, Tf-GL3) of T. forsythia were found to highly activate NKT cells and B cells.Alkaline treatment of T. forsythia glycolipids revealed that Tf-GL2 was alkali-resistant, while Tf-GL1 and Tf-GL3 were susceptible and their deacylated forms showed the presence of complex carbohydrates.Mass spectrometry analysis revealed a wide structural variation in the carbohydrate head-group and acyl chain lengths.Base-labile Tf-GL1 and Tf-GL3 were identified to be diacylgylcerolipids while base-resistant Tf-GL2 was proposed to be a glycosphingolipid.The structure of the third glycolipid, Tf-GL3, was predicted to be highly complex and thus may have contributed to its lower antigenicity compared with Tf-GL1 and Tf-This thesis not only represents a testimony of my growth as a researcher, but also a symbol of gratitude to those who have helped me achieve to where I am now.My time spent at the Melbourne Dental School in the last decade has been a rewarding journey, where there were countless opportunities to explore my interest for research in Microbiology and Immunology.I am entirely grateful for the staff and students at the Melbourne Dental School who have become friends and family over these years.My deepest appreciation goes to my supervisor, A/Prof Neil O'Brien-Simpson.Since the first day, he has been very patient as he showed me the ins and outs of how things are conducted in the lab.With Neil's guidance in planning and conducting experiments, I have been well-trained to an extent that we can complete each other's procedures without the need for much instruction.I have also been very fortunate to be allowed freedom in developing my own research ideas, but also having Neil as a support when I stumble.I would also like to extend my gratitude to my co-supervisor, Dr Katrina Walsh, who was first to show me the tricks and technicalities to using our temperamental flow cytometer, which has thankfully survived through my entire PhD course!Many thanks for being a sounding-board and staying until late to FACS sort those precious NKT cells.Also to my other cosupervisor, Dr Jason Lenzo, who had already started imparting useful techniques (murine peritoneal washes) even before he joined the Dental School.Despite arriving in the later part of my PhD course, Jason has been really helpful in providing great advice in tackling complex problems systematically and continually reminding me that I am proficient in my work.His jovial personality makes working together during those 16-h long γδ T cell experiments easier and he even stayed around until late in the night to make sure I clean up and go home.In addition, I would like to thank
Author: Shao Bing Fong
Language: English
Subfield: Periodontics
Field: Dentistry
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W2581884396