Doctoral Degrees (Medical Microbiology)

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Browsing Doctoral Degrees (Medical Microbiology) by Subject "Dissertations -- Medicine"

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    The relevance of apoptosis in the pathogenesis of human immunodeficiency virus-1 disease
    (Stellenbosch : Stellenbosch University, 2004-12) Cotton, Mark F.; Bouic, Patrick J. D.; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Pathology. Medical Microbiology.
    ENGLISH ABSTRACT: A simple and rapid scatter-based flow cytometric assay was developed to detect apoptosis in CD4+ and CD8+ T cells from a mixed population of cells. The assay was suitable for children. Apoptotic PBMCs were confirmed by morphologic assessment in clinical samples ex vivo and after overnight culture. The scatter-based assay was validated in a number of ways. Firstly, PBMCs were irradiated with 500 rads and cultured overnight to induce apoptosis. Thereafter, PBMCs were labeled with a CD4 MAb. CD4+ cells were sorted into apoptotic and viable populations by scatter characteristics (diminished forward and increased side scatter). Morphology was assessed by fluorescence microscopy. The majority of cells with apoptotic scatter characteristics had apoptotic morphology (chromatin condensation) (80.6%). Ninety-two percent of cells from the viable region had normal morphology. CD4+ T cell apoptosis measured by scatter was then correlated with the TdT assay for DNA fragmentation. Lastly, CD4+ T cell apoptosis by scatter and annexin V uptake were also shown to correlate. In the latter experiments, PBMC morphology and cell death by trypan blue uptake were studied simultaneously and confirmed the two flow cytometric assays. Apoptosis of CD4+ and CD8+ T cells has been shown in PBMCs from HIV infected adults analyzed after overnight culture. Since cell death may be an artifact of in vitro culture, and because there is little information on apoptosis in paediatric HIV disease, I undertook a cross-sectional analysis in PBMCs analyzed immediately ex vivo from HIV infected children and adults. Patients were studied in Denver, CO, USA. PBMCs from 21 children, 4 adolescents and 9 adults and seronegative age-matched controls were stained for CD4 and CD8 surface markers. Apoptotic cells were detected in a newly characterized flow cytometric assay by diminished forward and increased side scatter. For the scatter assay, PBMCs had been labeled initially by an indirect method involving an intermediary incubation in the presence of biotinylated MAbs at 37°C for 30 minutes prior to incubating with streptavidin-FITC at 4°C for 20 minutes. Thereafter, the intermediary incubation step was removed and PBMCs were incubated with PE-conjugated CD4+ and CD8+ MAbs. Both CD4+ and CD8+ T cell apoptosis appeared enhanced in the indirect method. The significant differences were abolished after subtraction of data from simultaneously studied time-matched controls. CD4+ and CD8+ T cell apoptosis were significantly higher in HIV-infected study subjects than in simultaneously studied seronegative controls. PBMCs were assayed immediately ex vivo and after overnight culture after stimulation by an anti-TCR MAb as well as spontaneously. There was a direct correlation between CD4+ and CD8+ T cell apoptosis and CD4+ T cell depletion. A significant correlation was also shown between apoptosis immediately ex vivo and after overnight culture. I then studied apoptosis in a South African population comprising 18 symptomatic children and 4 seroreverters. CD4+ and CD8+ T cell apoptosis were significantly higher in symptomatic HIV-1-infected children than in seroreverters and seronegative controls. CD4+ T cell apoptosis correlated with depletion of CD4+ T cell percentage in symptomatic HIV-1-infected children. I also noted elevated CD4+ T cell apoptosis in patients recovering from intercurrent disease in comparison to those who were either acutely ill or relatively asymptomatic outpatient attendees. Lastly, I compared CD4+ and CD8+ T cell apoptosis in cohorts from Denver, CO and Tygerberg Children’s Hospital, South Africa. I selected only patients with moderate or severe HIV infection from both centers. South African patients were significantly younger, more malnourished, had higher gamma globulin levels and were less likely to receive ART. CD8+ T cell apoptosis was higher in North American patients suggesting a possible impairment in CD8+ activity in the South African study subjects.
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    Sarcomeric modifiers of hypertrophy in hypertrophic cardiomyopathy (HCM)
    (Stellenbosch : Stellenbosch University, 2013-03) Bloem, Liezl Margaretha; Moolman-Smook, J. C.; Van der Merwe, L.; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Biomedical Sciences.
    ENGLISH ABSTRACT: Left ventricular hypertrophy (LVH) is an independent predictor of cardiovascular morbidity and allcause mortality. Significantly, it is considered a modifiable cardiovascular risk factor as its regression increases overall survival and reduces the frequency of adverse cardiac events. A clear understanding of LVH pathogenesis is thus imperative to facilitate improved risk stratification and therapeutic intervention. Hypertrophic cardiomyopathy (HCM), an inherited cardiac disorder, is a model disease for elucidating the molecular mechanisms underlying LVH development. LVH, in the absence of increased external loading conditions, is its quintessential clinical feature, resulting from mutations in genes encoding sarcomeric proteins. The LVH phenotype in HCM exhibits marked variability even amongst family members who carry the same disease-causing mutation. Phenotypic expression is thus determined by the causal mutation and additional determinants including the environment, epigenetics and modifier genes. Thus far, factors investigated as potential hypertrophy modifiers in HCM have been relatively removed from the primary stimulus for LVH; and the few studies that have been replicated yielded inconsistent results. We hypothesized that the factors that closely interact with the primary stimulus of faulty sarcomeric functioning, have a greater capacity to modulate it, and ultimately the LVH phenotype in HCM. Plausible candidate modifiers would include factors relating to the structure or function of the sarcomere, including known HCM-causal genes; and the enzymes that function in sarcomere-based energetics. Indeed, the literature highlights the relevance of sarcomeric proteins, Ca2+-handling and myocardial energetics in the development of LVH in HCM. This study, therefore, set out to evaluate the hypertrophy-modifying capacity of such factors by means of family-based genetic association testing in 27 South African HCM families in which one of three unique HCM-causing founder mutations segregates. Moreover, the single and combined effects of 76 variants within 26 candidate genes encoding sarcomeric or sarcomere-associated proteins were investigated. The study identified a modifying role in the development of hypertrophy in HCM for each of the candidate genes investigated with the exception of the metabolic protein-encoding gene, PRKAG1. More specifically, single variant association analyses identified a modifying role for variants within the genes MYH7, TPM1 and MYL2, which encode proteins of the sarcomere, as well as the genes CPT1B, CKM, ALDOA and PRKAB2, which encode metabolic proteins. Haplotype-based association analyses identified combined modifying effects for variants within the genes ACTC, TPM1, MYL2, MYL3 and MYBPC3, which encode proteins of the sarcomere, as well as the genes CD36, PDK4, CKM, PFKM, PPARA, PPARG, PGC1A, PRKAA2, PRKAG2 and PRKAG3, which encode metabolic proteins. Moreover, a number of variants and haplotypes showed statistically significant differences in effect amongst the three HCM founder mutation groups. The HCM-modifier genes identified were prioritised for future studies according to the number of significant results obtained for the four tests of association performed. The genes TPM1 and MYBPC3, which encode sarcomeric proteins, as well as the genes PFKM and PRKAG2, which encode metabolic proteins, were identified as stronger candidates for future studies as they delivered multiple significant results for various statistical tests. This study makes a novel contribution to the field of hypertrophy research as it tested the hypothesis that structural or energy-related factors located within the sarcomere may act as modifiers of cardiac hypertrophy in HCM, and succeeded in identifying a modifying role for many of the candidate genes selected. The significant results include substantial single and within-genecontext variant effects; and identified sizeable variation in the risk of developing LVH owing to the compound effect of the modifier and the individual founder mutations. Collectively, these findings enhance the current understanding of genotype/phenotype correlations and may, as consequence, improve patient risk stratification and choice of treatment. Moreover, these findings emphasize the potential for modulation of disease by further elucidation of some of the avenues identified.