Streptococcus pyogenes, the Group A Streptococcus (GAS), is the most common cause of bacterial pharyngitis in children and adults. Host innate and adaptive immune responses mediate defence against streptococcal pharyngitis and are also central to the clinical manifestation of the disease. The ability of GAS to invade the host and establish infection likely involves subversion of host immune defences, however the signalling pathways and immune responses elicited during streptococcal pharyngitis,

more »

... particularly by epithelial cells, are currently not well understood. This thesis focuses on characterising the inflammatory responses of primary human tonsil epithelial (TEpi) cells during intracellular infection with two distinct GAS strains; the laboratory-adapted M6 strain JRS4 and the M1T1 clinical isolate 5448. M1T1 is a globally-disseminated GAS clone that is the most commonly isolated serotype (approximately 20% of all isolates) in high income countries (1). This thesis aims to investigate innate immune responses triggered and/or subverted by these different GAS strains in order to uncover why the M1T1 strain is such a successful pathogen. The pharyngeal and tonsil epithelia are important components of innate immune defence against GAS infection. They primarily act as a physical barrier, but also secrete antimicrobial peptides and cytokines/chemokines that have direct antimicrobial effects and/or signal to immune cells. Previous studies have investigated epithelial immune responses to GAS infection by utilising a number of different cell types, largely immortalised and nonpharyngeal-derived cell lines such as HEp-2 and HaCaT cells, which may not respond in the same manner as pharyngeal cells to GAS infection. Nonetheless, several studies that have used tonsil explant tissue or pharyngeal-derived cell lines appear to be congruent with studies that have used nonpharyngeal cell lines to examine a number of immune mediators secreted in response to GAS infection. Next generation Illumina RNA sequencing was employed to characterise the inflammatory gene expression profile of JRS4-and 5448-infected TEpi cells during early intracellular infection, as reported in Chapter 4. I found that, whilst infection with either GAS strain induced the mRNA expression of a similar array of host inflammatory genes, the transcriptional response to 5448infection was of a much higher magnitude compared to JRS4-infection. Sequential window acquisition of all theoretical fragment ion mass spectra (SWATH-MS) was also employed to characterise changes in the host proteome during early GAS infection, and proteins that significantly changed in abundance during 5448-infection consisted mainly of those involved in metabolic and trafficking pathways, as well as transcriptional regulation. CONTRIBUTIONS BY OTHERS TO THE THESIS Mark Walker -Conception and design of the project; analysis and interpretation of research data; drafting significant parts of the work. Timothy Barnett -Conception and design of the project; analysis and interpretation of research data; drafting significant parts of the work. Matthew Sweet -Conception and design of the project; drafting significant parts of the work.