• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 172
  • 134
  • 49
  • 18
  • 14
  • 4
  • 3
  • 3
  • 3
  • 2
  • 2
  • 2
  • 2
  • 1
  • 1
  • Tagged with
  • 469
  • 196
  • 136
  • 73
  • 60
  • 54
  • 48
  • 37
  • 37
  • 31
  • 30
  • 29
  • 29
  • 27
  • 25
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Role of von Willebrand factor in shear induced platelet accumulation in a microfluidic device

Casa, Lauren D. C. 08 June 2015 (has links)
Thrombus formation under high fluid shear rates at the site of atherosclerotic plaque rupture leads to myocardial infarction and stroke. At high shear rates, thrombus is formed by platelets adhering via the glycoprotein von Willebrand factor (vWF). To investigate the relative contributions of vWF and platelets in high shear thrombosis, the present work developed a microfluidic thrombosis assay to meet low blood volume requirements and fluid shear conditions (3500-6000 s-1). Microfluidic conditions were selected to mimic the high shear environment of a diseased coronary artery, with the long-term objective of developing a clinically relevant assay for the assessment of thrombosis risk and treatment efficacy. The microfluidic design also addressed the requirement for volumetric thrombus formation rather than only surface platelet adhesion. As part of the design of the microfluidic assay, the effect of flow pulsatility on high shear thrombosis was investigated. It was found that steady wall shear rate matched to the mean pulsatile wall shear rate reproduced bulk thrombus formation characteristics of occlusion time, lag time, and thrombus growth rate, allowing subsequent experiments and future device design to utilize steady flow. The microfluidic assay was implemented to study the roles of vWF and platelets to thrombus formation using blood analogs produced from whole human blood diluted with normal saline at 90% and 99%. Hematocrit was restored to normal in all cases with the addition of red blood cells, and vWF and platelets were selectively restored to normal levels. Results showed that 90% dilutions with only vWF restored to normal levels occluded in 6/7 subject tested. The addition of platelets accelerated thrombus formation, but blood analogs with only platelets restored to normal levels occluded in only 2/5 subjects, indicating that vWF is more contributory in high shear occlusive thrombosis. At 99% dilutions, large thrombus formed with the addition of both platelets and vWF but was unstable and did not fully occlude the channel, indicating the possible requirement of an additional stabilizing factor(s) in occlusive thrombosis. Results of this study may lead to the development of improved anti-thrombotic treatments and improve patient care by providing a potential assay to evaluate treatment effectiveness and predict thrombosis risk.
2

The relationship of in vitro platelet activation to artificial surface induced thrombosis

Goodman, Steven Lee. January 1984 (has links)
Thesis (M.S.)--University of Wisconsin--Madison, 1984. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 78-87).
3

Role of the cytoskeleton in platelet structure and function activation, aggregation, and use as a model system /

Loftus, Joseph C. January 1984 (has links)
Thesis (Ph. D.)--University of Wisconsin--Madison, 1984. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.
4

Platelet size

Behrens, Wieland Eberhard von January 1972 (has links)
Offprint in back pocket / 248 leaves : / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (M.D. 1973) from the Dept. of Medicine, University of Adelaide
5

Human platelet antigen frequencies in the South African blood donor population determined by polymerase chain reaction with sequence-specific primers

Foxcroft, Zyta Krystyna 19 May 2008 (has links)
Platelets play an integral part in the blood clotting process. The normal platelet count ranges from 150 to 400 x 103/μl. To date, twenty-four platelet-specific antigens have been defined. Human Platelet Antigens (HPA) 1-5 and –15 belong to diallelic systems and antibodies formed in response to immunization against these antigens, following transfusion or transplacental haemorrhage, have been responsible for life-threatening conditions in which the platelet counts of patients are markedly decreased. This is due to the destruction of platelets by platelet antigen - specific antibodies in Neonatal Alloimmune Thrombocytopenia and Post-Transfusion Purpura and in some instances, Platelet Refractoriness. In these clinical situations, transfusions of platelets from random donors do not result in post-transfusion platelet increments. Ideally, a database of blood donors who have been HPA typed should be established. This database can then be used to search for HPA – compatible donors and matched platelet donations can be made available to these patients. The aims of this study were primarily to determine the HPA frequencies in the South African blood donor population and establish a register of HPA-typed donors. Secondly, the established frequencies would be compared to those of other world populations. Anticoagulated blood samples from one hundred and fifty donors from each of the four main South African population groups were obtained for typing of HPA 1-5 and –15 by the PCR-SSP method in order to determine their gene and genotype frequencies and establish a platelet donor database. Two methods of analyses were used to determine statistical similarities and differences between the South African population and a number of world populations (X2) and the degree of genetic distance between them (FST). Phylogenetic trees and Principal Components plots were constructed to illustrate relationships between populations. The HPA gene and genotype frequencies of the South African blood donor population have been determined. An accurate, rapid method of HPA typing has been validated and effective HPA matched platelet transfusions are now possible for the first time in South Africa. The gene frequencies of the White population have been found to be similar to those from European populations and the Bantu-speaking population frequencies compared favourably with those of other African populations. The population group of mixed ethnicity (Coloured) was shown to have unique frequencies and were not similar to any of those populations chosen for comparison except with the other populations in South Africa. / Dr. R. L. Crookes Prof. T.L. Coetzer Prof. M. Dutton
6

Surface chemical studies of human platelets

Chiu, Basil January 1983 (has links)
The purpose of this project is to investigate the surface properties of platelet discocytes, echinocytes and spherocytes. Normal "non-sticky" discoid shaped platelets (discocytes) can be transformed by ADP into irregularly shaped echinocytes which are "sticky" and aggregate easily in media containing Ca⁺⁺ and fibrinogen. A model is examined here in which an echinocyte attains its "sticky" properties by evagination of a surface-connected canalicular system. Platelets also evaginate this canalicular system upon hypotonic shock, in which case the platelets swell up to form spherocytes. By comparing the properties of the different geometric forms of platelets insight into the nature of "stickiness" was sought. The surface areas of the discocyte and spherocyte measured microscopically were found to be 16.4 and 36.7x10⁻⁸ cm² respectively while that of the echinocyte was estimated to be 23.7x10⁻⁸ cm² using surface chemical analysis. Electron microscopic examination showed that the canalicular system may not be totally evaginated in the echinocyte. Although it was found that the spherocyte could still be agglutinated passively by ristocetin it had completely lost its ability to aggregate. Microelectrophoretic studies revealed 8 and 6 fold increases in the density of Ca⁺⁺ and Mg⁺⁺ binding sites respectively on the echinocyte surface relative to the discocyte. The spherocyte on the other hand had lost most of its Ca binding sites. Electrokinetic analysis of live, fixed and neuraminidase or alkaline phosphatase treated platelets showed major differences in charge as well as amino, sialic acid and phosphate group densities among the discocyte, echinocyte and spherocyte. The evaginated canalicular membrane surfaces of the latter two were also different. SDS-PAGE of platelets radiolabelled via lactoperoxidase iodination, periodate-borohydride tritiation or neuraminidase/galactose oxidase-borohydride tritiation failed to show any difference in the gel patterns between the three platelet forms. No new glycoprotein species appeared during the transformations. The presence of fibrinogen interferes in a concentration related manner with lactoperoxidase iodination of GP-III on the echinocyte surface. An overall picture is presented here showing differences between the surface properties of platelet discocytes, echinocytes and spherocytes. The accumulated evidence suggests that changes in the whole platelet surface occur during activation and the model of a cloistered "sticky" membrane may be an oversimplification. / Medicine, Faculty of / Pathology and Laboratory Medicine, Department of / Graduate
7

Prevention of bacterial growth in platelet products via inclusion of iron chelators

Ng-Muk-Yuen, Jennifer Diane 05 1900 (has links)
Bacterial infection is a leading cause of morbidity and mortality arising from platelet transfusions (1, 2). Storage of platelet products at room temperature (20 to 24ºC) provides ideal conditions for bacterial proliferation (1, 3-6). Furthermore, platelets are stored in plasma containing bioavailable iron that bacteria require to survive (7). Thus we hypothesize that the inclusion of iron chelators will bind and remove iron, thereby inhibiting bacterial growth in both culture medium and platelet concentrates. Additionally, we hypothesize that residual red blood cells (RBCs) in platelet units may contribute bioavailable iron that promotes bacterial growth. To test these hypotheses, we first assessed growth of Staphylococcus epidermidis in culture medium after treatment with the iron chelators deferoxamine (DFO) or phytic acid. DFO significantly inhibited bacterial growth in a dose dependent manner (p < 0.009). Conversely, phytate only inhibited bacterial growth at concentrations ≥ 100 mM (p < 0.001); at ≤ 5 mM, phytate supplied S. epidermidis with additional nutrients and significantly promoted growth (p < 0.001). Subsequently, we monitored the change in RBCs over time. Hemolysis, methemoglobin, and iron levels all significantly increased over the 7-day storage period (p < 0.001) releasing bioavailable iron. Indeed, we found that S. epidermidis growth in iron-poor medium drastically increased with the addition of RBCs, thus supporting our second hypothesis. Surprisingly, the inclusion of DFO in minimal medium did not demonstrate a bacteriostatic effect in the presence of RBCs. The inhibitory effect of DFO was likely overcome by iron released from the elevated methemoglobin levels arising from the direct interaction of DFO with hemoglobin. Previous studies demonstrate that methemoglobin releases iron more quickly than normal hemoglobin (8). Lastly, we evaluated the effect of DFO on microbial growth in platelet concentrates using the BacT/ALERT system. The presence of DFO significantly inhibited S. epidermidis growth in buffy coat platelets in a dose dependent manner (p < 0.001). With these findings, the inclusion of iron chelators is a promising approach to preventing transfusion-transmitted bacterial infection and providing patients with a safer platelet product.
8

Prevention of bacterial growth in platelet products via inclusion of iron chelators

Ng-Muk-Yuen, Jennifer Diane 05 1900 (has links)
Bacterial infection is a leading cause of morbidity and mortality arising from platelet transfusions (1, 2). Storage of platelet products at room temperature (20 to 24ºC) provides ideal conditions for bacterial proliferation (1, 3-6). Furthermore, platelets are stored in plasma containing bioavailable iron that bacteria require to survive (7). Thus we hypothesize that the inclusion of iron chelators will bind and remove iron, thereby inhibiting bacterial growth in both culture medium and platelet concentrates. Additionally, we hypothesize that residual red blood cells (RBCs) in platelet units may contribute bioavailable iron that promotes bacterial growth. To test these hypotheses, we first assessed growth of Staphylococcus epidermidis in culture medium after treatment with the iron chelators deferoxamine (DFO) or phytic acid. DFO significantly inhibited bacterial growth in a dose dependent manner (p < 0.009). Conversely, phytate only inhibited bacterial growth at concentrations ≥ 100 mM (p < 0.001); at ≤ 5 mM, phytate supplied S. epidermidis with additional nutrients and significantly promoted growth (p < 0.001). Subsequently, we monitored the change in RBCs over time. Hemolysis, methemoglobin, and iron levels all significantly increased over the 7-day storage period (p < 0.001) releasing bioavailable iron. Indeed, we found that S. epidermidis growth in iron-poor medium drastically increased with the addition of RBCs, thus supporting our second hypothesis. Surprisingly, the inclusion of DFO in minimal medium did not demonstrate a bacteriostatic effect in the presence of RBCs. The inhibitory effect of DFO was likely overcome by iron released from the elevated methemoglobin levels arising from the direct interaction of DFO with hemoglobin. Previous studies demonstrate that methemoglobin releases iron more quickly than normal hemoglobin (8). Lastly, we evaluated the effect of DFO on microbial growth in platelet concentrates using the BacT/ALERT system. The presence of DFO significantly inhibited S. epidermidis growth in buffy coat platelets in a dose dependent manner (p < 0.001). With these findings, the inclusion of iron chelators is a promising approach to preventing transfusion-transmitted bacterial infection and providing patients with a safer platelet product.
9

Growth and Biofilm Formation of Bacteria Isolated from Contaminated Platelet Units

Hamza, Ali 09 May 2012 (has links)
Bacterial contamination of platelet concentrates (PCs) poses the major transfusion-associated infectious risk. Coagulase negative staphylococci (CoNS), the predominant platelet contaminants, are recognized as one of the leading causes of hospital-acquired infections due to their ability to form biofilms (surface-attached aggregates). In this study, 29 CoNS strains were characterized for their growth and biofilm formation abilities in media and PCs. Twenty-five strains were aerobic including Staphylococcus epidermidis, S. capitis, and S. chromogenes, while four were identified as the anaerobe S. saccharolyticus. Biofilm-associated icaA and icaD genes were amplified from eight strains. Interestingly, only six of those strains were biofilm-positive. Sequencing of S. capitis icaD revealed no mutations that could explain differences in biofilm phenotypes. Growth of CoNS in PCs varied significantly between strains. This study provides preliminary evidence that slow-growing biofilm-positive S. epidermidis are more likely to be missed during platelet culture, highlighting the need for improved screening methods.
10

Construction, expression and antigenic characterisation of recombinant human platelet antigen-1 (HPA-1)

Anani Sarab, Gholamreza January 2010 (has links)
Previously it has been shown that sequences containing both Trp<sup>25</sup> and Leu<sup>33</sup> are the most effective at inducing Th cell proliferation in HLA-DRB3*0101 positive women, alloimmunised with anti-HPA-1a.  The Leu<sup>33</sup>/Pro<sup>33</sup> polymorphism is embedded in the N-terminal plexin/semaphorin/integrin (PSI) domain of GPIIIa.  In the present study, amino acids 1-62 of the GPIIIa (Leu<sup>33</sup> or Pro<sup>33</sup>) PSI domain were cloned into the vector pGEX-6p-1.  The recombinant proteins were expressed and tested by ELISA, Luminex and Absorption Assays.  The presence of the HPA-1a/-1b epitope was confirmed by the ability of PSI-Leu<sup>33</sup>/-Pro<sup>33</sup> recombinant fragments to specifically capture its corresponding HPA-1 antibody.  Cells from a human B cell line (HHKB), homozygous for HLA-DRB3*0101, were pulsed with the recombinant PSI domain fragment of GPIIIa expressing the HPA-1a antigen.  MHC class II/peptide complexes were isolated from the pulsed cells using an immunoaffinity column.  A nested set of naturally processed and presented HPA-1a derived peptides, each containing the residues Trp<sup>25</sup> – Leu<sup>33</sup> core epitope was identified.  For the first time a naturally processed and presented HPA-1a peptide that spans the HPA-1a polymorphism has been identified, bound to the class II molecule encoded by HLA-DRB3*0101.  The efficient processing and presentation of this peptide, which includes the putative dominant Th epitope, is likely to be an important contributory factor in the immunogenicity of HPA-1a.  Such peptides may also provide the basis for novel treatments to tolerise the corresponding Th response in HPA-1b1b women at risk of NAIT with an HPA-1a-positive fetus.

Page generated in 0.081 seconds