Abstract
Podoconiosis is a form of non-filarial lymphoedema that causes bilateral swelling of the lower legs, resulting from exposure of bare feet to volcanic clay soils. It is a neglected tropical disease that affects impoverished communities in several low income countries mainly located in sub-Saharan Africa. There is a convincing association between genetic variation in class II Human Leukocyte Antigen (HLA) genes and the development of podoconiosis, raising the hypothesis that podoconiosis is caused by an inflammatory immune response to a currently unknown soil component. This thesis describes my research exploring this hypothesis using a range of approaches to study peripheral blood immune responses in people with podoconiosis and endemic healthy controls.The study was conducted in and around Bahir Dar in Northeast Ethiopia and at the Armauer Hansen Research Institute in Ethiopia in collaboration with Brighton and Sussex Medical School, UK. A rapid ethical appraisal of stakeholder views on research was conducted prior to the start of the study to better understand the socio-cultural context in which the research was to be undertaken and to explore the ethical issues and concerns my research could raise with the study community. Just before the commencement of this study there was a mob attack on researchers from a national research institute during a period of social unrest and political instability. I identified a number of issues related to the consent process, participant recruitment, specimen collection and the factors which led to the violence against researchers that allowed me to appropriately tailor my consent process to the community's needs whilst maintaining the universal principles of biomedical research ethics.
Immunological and molecular studies to characterise the phenotypes and functional responses of innate and adaptive immune cells were undertaken using flow cytometry, in vitro stimulation assays, real time PCR and next generation RNA sequencing. Peripheral blood immunophenotyping of T cells indicated podoconiosis patients had significantly higher surface expression of HLA-DR molecules on both CD4 and CD8 T lymphocytes compared to healthy controls, while CD62L expression was significantly lower. The levels of expression of the activation markers CD40 and CD86 were significantly higher on monocytes and dendritic cell subsets from podoconiosis patients compared to the controls.
Background levels of the inflammatory cytokines tumour necrosis factor-α and interleukin-1β were significantly higher in podoconiosis patients before in vitro stimulation with various minerals known to be abundant in endemic soils, although such differences were not observed between the two study groups in stimulated wells. There was no difference in interferon-γ levels between the two study groups either in mineral-stimulated or background wells. Gene expression data indicated higher levels of transcription of genes encoding activation markers, scavenger receptors and molecules involved in inflammation while lower levels of transcription of genes encoding histones, T cell receptors, and immunoglobulin chains were found in podoconiosis patients compared to healthy controls.
In conclusion, the data provide evidence that podoconiosis is associated with high levels of immune activation and inflammation compared to healthy control subjects with over-expression of genes within the pro-inflammatory axis. These studies are the first to characterise the nature and extent of immune responses in individuals with podoconiosis and contribute to our understanding of the pathways involved in the pathogenesis of the disease. Building on these foundations, further studies are required to identify the soil trigger and define specific pathways that could be targeted for future research into diagnostic and treatment options.
| Date of Award | Apr 2023 |
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| Original language | English |
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| Supervisor | Melanie Newport (Supervisor) & Dr Rawleigh Howe (Supervisor) |