ETD Collection

Now showing 1 - 4 of 4

Blood group polymorphisms in Southern Africa and innate resistance to plasmodium falciparum
(1992) Field, Stephen Paul
The observation by Haldane in 1949 that the distribution of malaria and certain thalassaemias were similar and that the former disease must be a selective force tor the continued existence of the latter by preservation of the heterozygotes. This theory which later became known as lithe malaria hypothesis" has been applied to other inherited conditions such as G6PD deficiency, membranopathies, certain blood group polymorphisms, other heamoglobinopathies such as sickle cell disease, blood group polymorphisms and more recently HLA phenotypes. It has been shown that the Duffy blood group antigens are the receptors for. Plasmodium vivax and since these antigens are lacking in most black Africans this species of malaria is virtually absent in Africa. It has also been shown that the glycophorins are at least in part the receptors for Pfalciparum. Several variants of the glycophorins exist and the biochemistry and, where known, the molecular mechanisms by which these arise is reviewed. Experimental work is carried out to establish the growth characteristics of Pfalciparum in an in vitro culture system using cells with glycophorin variants on their membranes. Three such variants were compared to normal cells and two (S~s-U-and Dantu) were found to be partially resistant to invasion by Pfalciparum merozoites whereas the third (Henshaw) was found to be no different to controls.
Flow cytometry in diagnostic haematopathology
(1992) Glencross, Deborah Kim
Standardisation, calibration and development of novel flow cytometry techniques
(2014-02-18) Lawrie, Denise
Bead count rate (BCR) monitoring successfully identifies pipetting error during single platform enumeration. Enumeration beads are a stable constant in each patient’s sample and if these can be multitasked to monitor overall flow cytometer operation in a model of continuous quality control (CQC), they could reveal further details of flow cytometer operation and fulfill more quality assurance functions than identify pipetting error alone. Methods The CQC model used manufacturer recommended quality control procedures daily. In addition, methods were developed to monitor flow cytometer fluidics and electronics as well as sample preparation to standardise and extended quality monitoring. Sample-to-sample CQC included monitoring BCR, selected time, optical and fluorescence histograms as well as FPCV and MCN. This model also incorporated diligent monitoring of BCR patterns to detect instrument malfunctions. Post standardisation and implementation of the CQC model, an extended EQA exercise assessed bias between standardised CD4 counting methods and determined a ‘near true’ CD4 count to use as a calibrator. Conclusion The proposed CQC model standardised overall flow cytometer and automated sample preparation systems and, established imprecision reference intervals for each aspect of testing (fluidics <3%, sample preparation 2-4% and protocol and electronics <2%). Further BCR pattern recognition was used to identify instrument malfunctions in real-time and, longitudinally for pro-actively identifying imminent breakdowns. CD4 counts were calibrated to consensus mean ‘near true’ counts on two flow cytometers in the Reference Laboratory.
Establishment of a flow cytometric assay in the setting of renal transplant for T and B cell crossmatching
(2014-02-17) Ramparsad, Narisha
Donor specific crossmatching is performed prior to renal transplantation in order to determine the presence of pre-existing antibodies against donor HLA antigens which can result in hyperacute rejection. Flow cytometric crossmatching is reported in the literature to be a more sensitive and objective method of testing than the complement dependent cytotoxicity (CDC) method that is currently used in the Gauteng Province. A prospective analysis of the flow cytomeric crossmatch (FCXM) assay using the Luminex technology as the reference method was conducted. Forty-three samples were analysed. The T cell crossmatch (using a cutoff value of 2) revealed a sensitivity of 66.7%, a specificity of 83.8%, a positive predictive value (PPV) of 40% and negative predictive value (NPV) of 93.9%. The B cell crossmatch (using a cutoff value of 5) gave a sensitivity of 100%, specificity of 92.7%, and a PPV and NPV of 40 and100%, respectively. In addition, a retrospective analysis of clinical data for all patients transplanted during the period January 2008 to May 2009 was performed. Of a total of 50 patients assessed post transplant, none of the patients showed signs of hyperacute rejection, while twelve percent (12%) of patients revealed signs and symptoms suggestive of acute rejection. The validation of the flow cytometric crossmatch analysis was complex as there is no gold standard reference method. The assay was validated based on the clinical relevance of its high negative predictive value and the absence of hyperacute rejections in the clinical follow up. The rate of acute rejection found in this study is similar to that reported in literature.

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