Browsing by Subject "Microbiology, immunology and cancer biology"

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    B cells, T follicular helpers, and germinal centers as facilitators of chronic Graft-versus-Host disease
    (2014-08) Flynn, Ryan Patrick
    Allogeneic hematopoietic stem cell transplantation is a potential cure for many malignant diseases. However, the possibility of chronic Graft-Versus-Host Disease (GVHD) is a major obstruction to the therapeutic results. Development of novel therapies has been hindered by an incomplete knowledge of the mechanism of disease. This is in part due to a lack of relevant mouse models. Using a new murine model of chronic GVHD we shed light on the mechanism of disease as well as proposed novel therapeutics that could be beneficial for the treatment of chronic GVHD. First, we demonstrate that B cells derived from the donor bone marrow are necessary for the progression of disease and that these B cells had to produce class-switched antibodies. The production of class-switched antibody is dependent on the germinal center reaction. The need for the germinal center is further highlighted by the requirement for the presence of T follicular helper cells. These specialized cells promote the germinal center reaction by providing survival signaling to B cells through the IL-21 cytokine and ICOS and CD40 costimulatory molecules. We further provide evidence that T follicular helper cells and the germinal center reaction are necessary by demonstrating that therapeutic depletion of B cells during active chronic GVHD is unable to prevent the progression of disease. Finally, we demonstrate the importance of B cell signaling following antigen stimulation. Inhibition of the B-cell signaling molecule Syk directly down-stream of B-cell receptor signaling is sufficient to prevent the progression of chronic GVHD. Collectively this work identifies important B-cell survival signals that are necessary for the development of chronic GVHD.
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    Export and role of flavin electron shuttles in Shewanella oneidensis Strain MR-1
    (2014-09) Kotloski, Nicholas Jason
    Our planet is home to microbes with an impressive diversity of metabolic capabilities. For instance, dissimilatory metal reducing bacteria (DMRB) can respire minerals, heavy metals, and electrodes. Electrode respiration is important both for investigating DMRB and biotechnology applications including biosensors, bioenergy, and wastewater treatment. Placing electrodes in wastewater allows for electricity production and oxidation of carbon sources to carbon dioxide. Shewanella oneidensis MR-1, a model DMRB, transfers electrons generated from metabolism across the inner and outer membranes to insoluble external electron acceptors. This feat is accomplished using an electron conduit consisting of multi-heme cytochromes and flavin electron shuttles. The electron conduit in Shewanella evolved to move electrons out of the cell, but in controlled environments, the conduit is functionally reversible, meaning electrons can flow either out of or into the cell. In a process termed electrosynthesis, electrons are transferred from an electrode into a cell to direct metabolism to produce specific metabolites. A useful way to study electrosynthesis in cells is to use three-electrode bioreactors. The working electrode in a bioreactor is poised at an oxidizing or reducing potential and continuously measures electrons entering or leaving the electrode. When electrodes were used to donate electrons to attached Shewanella cells, intracellular ATP was produced. Mutants defective in generating or using proton motive force were unable to produce wild-type levels of ATP. If significant quantities of ATP can be produced by reverse electron flow, it will be a critical step towards fixing carbon dioxide into metabolic precursors and eventually into biofuels.
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    Human immunodeficiency virus evasion of APOBEC3 restriction factors
    (2012-10) Albin, John Squire
    The human immunodeficiency virus accessory protein Vif protects the viral genome from the mutational activity of APOBEC3 subfamily DNA cytosine deaminases by facilitating their proteasomal degradation, thereby preserving viral infectivity. A comprehensive understanding of the components of the Vif-APOBEC3 interaction is therefore important for consideration of the potential for novel antiretroviral approaches aimed at modulating this critical host-pathogen interaction. Here, we establish APOBEC3F among the seven subfamily members as a valid model for the study of the APOBEC3-Vif interaction. By utilizing this model as a starting point, we further define the APOBEC3-Vif interaction sites in each protein and the downstream ubiquitin acceptor sites modified en route to APOBEC3 degradation, in the process deriving broader insights into the nature of the interactions between different APOBEC3 proteins and Vif. In contrast with the diversiform APOBEC3-Vif interactions proposed in the extant literature, we find that the interaction of Vif with different APOBEC3 proteins likely proceeds through a conserved helix-helix interaction. Even if one were to successfully block this interaction for therapeutic purposes, however, the virus may develop accessory mechanisms of APOBEC3 evasion to bypass the intervention. While we find that this can occur, present evidence suggests that such alternatives may be insufficient to circumvent restriction in cells that naturally express multiple APOBEC3 proteins. Thus, it may be possible to potentiate the action of multiple endogenous antiretroviral proteins to counteract human immunodeficiency virus infection by targeting a conserved interaction motif as described herein.