Browsing by Author "Jacobs, Peter"

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    Clinically silent renal tumour producing erythropoietin
    (Health and Medical Publishing Group, 2003) Wood, Lucille; du Toit, Andrew; Jacobs, Peter; Swanepoel, Charles
    Asymptomatic patients may be referred for a haematology opinion when the routine blood count reveals elevation in haemoglobin level, haematocrit or red cell count.1 There is an all too cavalier approach to this abnormality, which is not only an independent risk factor for arterial or venous thromboembolic disease2 but may signal unsuspected underlying cardiac or pulmonary pathology.3 Infrequently these findings may draw attention to an otherwise silent myeloproliferative syndrome in the form of primary proliferative polycythaemia or polycythaemia rubra vera of old.4 Occasionally, and of major clinical importance, is inappropriate erythropoietin production by tumours, including kidney tumours.
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    Interactions between the haematopoietic stem cell and the myeloid microenvironment in aplastic anaemia
    (1993) Novitzky, Nicolas; Jacobs, Peter
    In patients with aplastic anaemia that respond to immunosuppressive therapy, quantitative, morphological and functional haematologic derangement have been reported. To explain these findings, abnormalities in the marrow stroma or the stem cell have been postulated. To define the relative contribution of each of the latter, the integrity of the bone marrow from sixteen patients that responded to anti-lymphocyte globulin and high dose methyl prednisolone was compared to normal individuals. Bone marrow mononuclear cells were divided into two fractions. From the first, stroma was cultured in aMEM containing 12.5% of both horse and foetal calf serum and 10-5 M hydrocortisone at 37° C in 5% CO2 in 90% humidity. The medium was changed weekly. Upon confluence, these stromal layers were studied morphologically and with cytospin preparations stained with Sudan black, 0 red oil, alkaline and acid phosphatases. The remainder was monocyte and lymphocyte depleted, CD 34+ progenitors were selected with paramagnetic beads and the population morphologically and immunophenotypically defined. To determine the functional status, control or patient CD 34+ progenitors, were suspended for two hours on normal or aplastic stroma for adherence to take place. The non-adhesive fraction was decanted by standardised washing and cultured for fourteen days in the presence of PHA-conditioned medium in the CFU-gm assay. Strama-adherent progenitors were covered with 0.3% agar and cultured for five days. Aggregates with more than twenty cells were scored (CFU-bl). The remaining CD 34+ cells were cultured in the mixed colony assay with combinations of recombinant cytokines belonging to the G protein super-family and the tyrosine kinase group in dose response studies. Light density cells from patients with treated aplasia contained significantly fewer CD 34+ cells than those present in the control suspensions (mean 0.65%, SD 0.35% vs 1.62%, SD 1.4%; p= 0.002). Normal and aplastic stroma became confluent at three and four weeks. There was no difference on the morphology or the cytochemical stains between the two groups. Functionally, aplastic bone marrow stroma supported CFU-bl formation no differently from normal layers. However, CD 34+ precursors from the patients cultured on control stroma resulted in significantly fewer CFU-bl (p= 0.0002,) and CFU-gm (p= 0.0009). This work provides original evidence supporting the reduced clonogenicity of the corresponding populations of CFU-bl from patients with aplasia is unrelated to attachment to the stroma, but intrinsic to the CD 34+ cells. Moreover, this study shows for the first time that exposure of these progenitors to growth factors belonging to the G protein and tyrosine kinase receptor families have defective responses, correctable only at supra physiological concentrations, while effects on combinations containing c-kit ligand, appear preserved. Following immunosuppressive therapy, the bone marrow is repopulated by a hypoproliferative progenitor cell population which responds suboptimally to physiological cytokine stimulation. This suggests that abnormal interactions between receptors and their ligands or alterations in the signal transduction for cell division by the cytokines belonging to the G superfamily lead to suboptimal growth.
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    The iron-binding proteins of iron-absorbing rat intestinal mucosa
    (1983) Johnson, Glynis; Purvis, Langley R; Jacobs, Peter
    Iron deficiency anaemia is perhaps the most widespread nutritional deficiency disease; as result, the topic of iron absorption has received intensive investigation over a relatively long period of time. Most of the investigative thrust has come from clinical medicine and allied fields, with some associated biochemical investigation. Evidence from the latter has pointed towards the involvement of iron-binding proteins especially ferritin and transferrin in the absorptive process. While the biochemical literature on these two proteins, particularly transferrin, is vast, their roles in iron absorption are obscure. This study was undertaken, therefore, as an investigation into these proteins, their quantitation and role in iron absorption. The physiology of absorption was studied by injection of radiolabelled ferrous ascorbate into isolated intestinal loops and the determination of mucosal, blood and carcass uptake.
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    The platelet laminin receptor : discovery of a 67kDA receptor for laminin on the membranes of human platelets : characterisation and isolation
    (1995) Holland, Errol Anthony; Jacobs, Peter; Jamieson, Graham A
    Previous work on the binding of resting platelets to the basement membrane glycoprotein, laminin, has identified the Ic/IIa integrin c01aplex (CD49f/CD29), also known as VLA-6, as the receptor. There exists however, another protein with a molecular weight of 67kDa, that mediates this function on other cells. It is abundantly expressed on the membranes of breast cancer cells, where it plays a key role in both the localisation at, and penetration of vascular beds, by metastases. The objectives of this study were: * The development of a micro-titre assay similar to those used in previous studies, standardised and calibrated to characterize the adhesion of unstimulated normal human platelets to laminin-coated surfaces. * To determine the effect on adhesion of platelet activation, enzymatic surface-glycoprotein removal, antibodies to specific receptors and interaction with other adhesive proteins known to bind to platelet membranes. * To establish the in vivo relevance of the experimental findings, by the assay of adhesion of glycoprotein IIb/IIIa-deficient platelets of two patients with Glanzmann's Thrombasthenia. These studies serve d to distinguish specific binding sites for laminin from the known surface receptors of platelets. The methodology used to isolate laminin receptors from the membranes of breast carcinoma cells was then applied to platelet concentrates. Membranes were obtained by centrifuging the ultrasonic lysate of a unit of platelets. These were solubilized and passed over a laminin-Sepharose column. The bound components were eluted and identified by means of SDS-gel electrophoresis, after which a concentrate was tested for laminin binding by means of dot-blot methodology. The principle contribution of this work is the finding of a 67kDa receptor for laminin on the surface membranes of platelets. The combination of the various approaches applied to characterise the adhesion of platelets to laminin, show that this is a specific, Mg²⁺-dependent process, inhibited by Ca²⁺ and not enhanced by platelet activation. Adhesion was decreased by proteolysis with trypsin and chymotrypsin, showing that the adhesion is mediated by a surface glycoprotein. Proteolysis with the Serratia marcescens metalloprotease, which cleaves off glycoprotein lb, did not affect adhesion, proving that this well-known receptor for platelet adhesion is not involved in the adhesion. The receptors GPIV and glycocalicin were also excluded, as the presence of antibodies to these receptors had no effect. Prior incubation with fibrinogen or von Willebrand factor, which binds to specific receptors on the platelet membrane, inhibited adhesion, most likely due to spatial interference with the receptor site for laminin. The presence of the tetrapeptide recognised by the membrane receptors for many adhesive proteins, RGDS, at concentrations of up to 1mM, had no effect. The platelets of the two subjects with Glanzmann's Thrombasthenia adhered normally, definitively ruling out the involvement of GPIIb/IIIa, which is absent from these platelets. The isolation process recovered a membrane component from the laminin-Sepharose column with an elution pattern identical to that for the well characterised 67kDa receptor for laminin on the surface of breast carcinoma cells. They have the same molecular weights in both the reduced (67kDa) and non-reduced (53kDa) states. Blot identification demonstrated laminin binding by the eluate. In the last part of the work, collaborative studies using more sophisticated methodology have confirmed that platelet receptors for laminin play a role in their adhesion to living tissue. Anti-laminin Fab antibodies significantly decreased the adhesion when whole blood was perfused over isolated rabbit aortic segments. That these receptors are identical to the 67kDa receptor of breast carcinoma cells was shown by the specific, high affinity binding of antibodies directed at the carcinoma receptors to the surface of platelets when examined by flow cytometry. In addition, they inhibit platelet adhesion by 50-60% in the micro-titre assay. It is proposed that both the VLA-6 and the 67kDa receptors are required for platelet adhesion to laminin, possibly as a two-stage process, similar to the systems for adhesion to von Willebrand factor, where binding is initially to GPIb, followed by binding to GPIIb/IIIa. The possible relevance of this receptor in the pathophysiology of the metastatic process is discussed.
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    A stroke service model developed in the private sector
    (2011) Kow, Lynette K R; Kies, Brian; Jacobs, Peter; Wallis, Lee
    This dissertation seeks primarily to enlighten the medical fraternity about the development of a stroke service at Constantiaberg Medi-Clinic and, additionally, how this has been implemented. The objective is to try to improve the outcome of patients presenting with various types and levels of neurological deficits as a consequence of cerebrovascular accidents.