Browsing by Author "Young, Caitlyne"
Now showing 1 - 1 of 1
Results Per Page
Sort Options
- ItemInvestigating the host immune response to population-tailored PPE_MPTR peptides(Stellenbosch : Stellenbosch University, 2020-03) Young, Caitlyne; Sampson, Samantha Leigh; Kriel, Nastassja; Loxton, Andre G.; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Biomedical Sciences: Molecular Biology and Human Genetics.ENGLISH ABSTRACT: Tuberculosis (TB), caused by Mycobacterium tuberculosis, is one of the top 10 causes of death worldwide, with more than 95% of deaths occurring in low- and middle-income countries. Eradication of TB disease within these countries requires the development of more effective diagnostic tools, anti-TB drugs and vaccines. The host immune response against M. tuberculosis is largely governed by CD4+ T-cells, making M. tuberculosis-specific antigens that induce strong CD4+ T-cell responses of interest for vaccine studies. The induction of an effective cell-mediated immune response requires activation of CD4+ T-cells following antigen presentation via MHC-II molecules. The human leukocyte antigen (HLA) alleles that encode MHC-II molecules are polymorphic, resulting in thousands of these alleles within a population. The distribution of HLA alleles differs between individuals from different geographical populations; thus, an effective vaccine candidate should include a variety of epitopes that bind numerous HLA alleles. The PPE_MPTR proteins are a sub-family of the PE/PPE proteins, which are encoded by the pe/ppe genes. This family occupies approximately 10% of the M. tuberculosis H37Rv genome, however the precise role of PE/PPE proteins in M. tuberculosis pathogenicity is unclear. Numerous PE/PPE proteins have shown to be highly immunogenic, however little is known regarding the immunogenicity of PPE_MPTR proteins. Previous work in our laboratory made use of a reverse vaccinology workflow which identified 35 PPE_MPTR epitopes predicted to have strong binding affinity for HLA alleles found in African populations. Nineteen epitopes from six PPE_MPTR proteins (PPE_MPTR12, -13, -28, -40, -42 and -62) showed high population coverage in four African populations. Here we present functional assays performed to assess the immunogenicity of the nineteen epitopes in African populations. We also investigated the potential of these epitopes to distinguish between infected vs uninfected and active TB vs LTBI individuals, as determined by cytokine release assays following peptide stimulation. This was complemented by analysing the distribution of functional and activation markers following PPE_MPTR stimulation. The remaining red blood cells were lysed and the distribution of functional states of CD4+ and CD8+ T-cells and B-cells in peripheral blood were analysed using specific antibody staining in conjunction with flow cytometry. PPE_MPTR peptides induced a pro-inflammatory cell-mediated response characterized by detectable concentrations of IL-6, TNF-α and IL-17A. In response to PPE_MPTR peptides, significant differences in cytokine production were observed between individuals of different disease states. The PPE_MPTR peptides were shown to induce the expansion and activation of memory CD4+ and CD8+ T-cells, with CD4+ T-cell populations being the predominant responding population. The results of this study highlight the heterogeneity of the host immune response against M. tuberculosis. The pro-inflammatory cell-mediated immune response and the emergence of circulating memory populations in response to stimulation with selected PPE_MPTR peptides, make these promising vaccine candidates. Future work in which further immunological characterization of these peptides is performed, either alone or in combination, would greatly advance our understanding of the role PPE_MPTR proteins play in the cell-mediated immune response.