Browsing PhD e-theses by Subjects
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Characterisation of immune responses to the E5 protein of the human papillomavirus type 16High-risk mucosal human papillomaviruses (HPVs) are major aetiological agents for the development of cervical cancer. Thus, the current goal of cervical cancer treatment is to develop vaccines against HPV s. Such vaccines would either prevent cervical cancer by eliminating HPV infection or be useful for treating established lesions by the destruction of cells displaying HPV proteins. The aim of this thesis was to characterise immune responses to the E5 protein of HPV -16, one of several antigens with possible use in vaccination. To determine whether immune responses to HPV -16 E5 existed and whether they could be correlated with disease severity or with the presence of HPV -16 DNA, both cell mediated (Chapter Two) and humoral (Chapter Three) immunity was investigated in women with and without cervical disease. Cellular responses in a minority of women were inversely correlated with disease severity. However, E5 specific antibodies were negatively correlated with the absence of HPV -16 DNA. Thus, although some immune responses were evident, these were generally limited to a small number of subjects and were not associated with the detection of HPV-16 E5 mRNA or DNA sequence variants. Due to the immune responses in women, E5 was further investigated to determine if the absence of HPV -16 E5 specific immune responses was due to the poor antigenicity of HPV -16. Mice were immunised with synthetic peptides corresponding to full length HPV -16 E5 (Chapter Four). As with the human data, cellular responses and weak antibody responses were detected in mice. Some mice also exhibited cytotoxic T -lymphocyte responses and when E5/major histocompatibility class I (MHC-I) interactions were investigated, a number of peptides showed a high percentage of binding. The E5/MHC-I interactions were further investigated (Chapter Five). The surface expression of MHC-I on cells containing HPV-16 or -18 DNA was found to be lower than on HPV DNA negative cell lines even after stimulation with interferon-gamma. Stimulation with E5 synthetic peptides increased expression of cell surface MHC-I molecules on cell lines negative for HPV DNA. Furthermore, the presence of the E5 gene reduced the expression of the ovalbumin gene in normal human keratinocytes. In conclusion, the data contained within this thesis indicate that HPV-16 E5 CMI is inversely correlated with disease status. It is possible to induce cell mediated responses to HPV -16 E5 and low-titre antibody responses. The presence of HPV16 E5 DNA may impair normal cellular function.
The loss of PI3K C2β is associated with a heightened immune responseThe phosphoinositide 3-kinase (PI3K) enzymes are well known for their regulation of pro-survival signalling cascades that result in increased cell survival and proliferation. However, most of what we understand is based on Class I PI3K enzymes and much less is understood about the Class II enzymes. Loss of PI3K C2α in mice results in embryonic lethality, or severe glomerular injury with increased morbidity. In contrast, PI3K C2β deficient mice display no apparent phenotype and are healthy and viable. Previous work in our laboratory revealed that administration of a sub-nephritogenic dose of nephrotoxic serum led to an augmented immune response resulting in glomerular damage and impaired renal function, which was associated with T-cell infiltration. Elucidating the immunological basis of this sensitivity was the basis of my project. In response to a subcutaneous injection of sheep IgG in complete Freund’s adjuvant, the spleens of PI3K C2β-/- mice showed prominent germinal centre associated cell proliferation that was absent in the controls. Analysis of splenocyte populations revealed that PI3K C2β-/- mice had an increased population of CD4+ T-cells and when cultured in vitro within a total splenocyte population, the increased CD4+ T-cell population was maintained. However, this effect was lost when T-cells were purified and maintained ex vivo. These data suggest that the increased PI3K C2β-/- CD4+ proliferation may be due to additional factors within the total splenocyte population. B-cell populations from the spleens of PI3K C2β-/- mice had higher CD19 expression compared to B-cells from control mice. Elevated levels of CD19 are associated with a reduced activation threshold. In response to stimulation with a sub-optimal dose of LPS and IL-4 PI3K C2β-/- B-cells underwent increased class switch recombination, displayed increased metabolic activity and remained viable for longer than B-cells from control mice. B-cell lysates from PI3K C2β-/- mice also revealed increased levels of phosphorylated MEK1/2. These data indicate that PI3K C2β may serve as a negative regulator of B-cell function and that loss of this PI3K enzyme isoform activity produces a heightened immune response which may lead to a predisposition to associated pathologies.