The role of inflammasomes during chlamydia infection

Chlamydia. trachomatis is the world’s most commonly occurring bacterial sexually transmitted infection, with over 129 million cases diagnosed annually. In women, infection can ascend from the vagina, into the upper reproductive tract where it leads to the development of a range of diseases including, pelvic inflammatory disease, tubal factor infertility, chronic pelvic pain and ectopic pregnancy. Although antibiotics can successfully treat infection, between 50-80% of females are asymptomatic, leading to a delay in treatment and the development of irreversible damage to the female reproductive tract (FRT). We currently have no approved vaccines or immunotherapies for the treatment and prevention of these diseases. A lack of immunotherapies is in part due to our lack of understanding surrounding the contribution of host mediated immune responses involved in protection and clearance of infection vs those that are responsible for the development of host mediated immunopathology. We, therefore, require a further understanding of these immune processes to develop therapies to help prevent the development of or treat these diseases. Inflammasomes are protein complexes of the innate immune system that act as sensors of, and become activated by, endogenous factors produced during cellular damage, stress and/or exposure to numerous noxious stimuli and pathogen components. Upon activation, inflammasomes initiate a cascade of intracellular processes that are intended to limit the damage caused by these noxious stimuli through the cleavage and activation of caspase-1, IL-1β, IL-18 and the induction of a pro-inflammatory cell death pathway termed pyroptosis. Previous studies have found that the inflammasome pathway leads to the clearance of infection but is also involved in the development of pathology. The first objective of my thesis (Chapter 2) was to characterise the expression of inflammasome sensor molecules, and the proinflammatory cytokines activated by these inflammasomes at the different levels of the FRT (vagina, cervix, uterus, oviduct, and ovaries) during Chlamydia infection compared to uninfected mice. To do this female C57BL/7 mice were intravaginally infected with the commonly occurring mouse pathogen Chlamydia. muridarum (C. muridarum) and sacrificed at 3dpi and 14dpi. I show for the first time that inflammasomes are differentially expressed throughout the different levels of the FRT during Chlamydia infection, I highlight that at 3 days post infection (3dpi) the nucleotide-binding oligomerisation domain (NOD)- and leucine-rich repeat (LRR)-containing receptor (NLR) family pyrin domain-containing 3 (NLRP3) inflammasome and the absent in melanoma 2 (AIM2) inflammasome protein expression in absent in the vagina early during infection, however, NLRP3 and AIM2 expression is upregulated colocalised within epithelial secretory crypts in the uterus during infection, moreover, I show that NLRP3 staining is also is present in uninfected mice, but is less intense and does colocalise with AIM2 as seen during infection. Furthermore, I show that AIM2 and NLRP3, protein expression is upregulated in the oviducts during infection. Furthermore, later during infection, at 14dpi, gene expression for wide array of inflammasome sensor molecules was significantly upregulated during infection at every level of the FRT.