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Browsing by Author "Orme, Ian, advisor"

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    Analysis of T cell subsets induced in response to Mycobacterium tuberculosis infection
    (Colorado State University. Libraries, 2009) Henao-Tamayo, Marcela I., author; Orme, Ian, advisor
    Tuberculosis, an ancient disease, still kills more people each year than does any other bacterial infection. The global epidemic of tuberculosis (TB) results in eight million new tuberculosis cases per year and two million deaths; 98% of these occur in developing countries. At present the only available vaccine against tuberculosis, M. bovis Bacillus Calmette-Guerin (BCG), has proven unreliable and only minimally protects against pulmonary tuberculosis in adults. The reasons why the BCG vaccine is not fully protective are still very unclear, and even though novel vaccines are being developed, there is not a clear understanding of what kind of immune response they should elicit in order to provide maximum protection. The overall aim of these studies, therefore, was to investigate the T cell subsets generated by M. tuberculosis [including clinical strains] as well as further analysis of those generated by BCG, in order to explore their role in protection against M. tuberculosis infection.
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    Pathogenesis of experimental tuberculosis in guinea pigs
    (Colorado State University. Libraries, 2010) Sivagiri Palanisamy, Gopinath, author; Basaraba, Randall J., advisor; Orme, Ian, advisor; Mason, Gary L., committee member; Bowen, Richard Arnold, committee member
    Tuberculosis is an important infectious disease of humans that can be modeled in a number of small laboratory animal species. In humans and guinea pigs, infection with the causative agent Mycobacterium tuberculosis, incites a chronic inflammatory response in the lung (pulmonary) and other (extra-pulmonary) tissues and organs of the body. Granulomatous inflammation can become organized into a distinct inflammatory mass referred to as a granuloma. Granuloma formation is thought to represent a favorable host response that functions to contain the infection, thus preventing spread within or between susceptible hosts. If infected cells within the granuloma die, intracellular bacteria are released and become entrapped in an extra-cellular microenvironment where they persist for long periods of time protected from drug therapy and the host immune response. The mechanism responsible for granuloma cell death (necrosis) is unknown but is important to understand as it represents a unique microenvironment for drug-tolerant bacilli to persist. One potential mediator of granuloma necrosis is the generation of cell and tissue damaging oxygen free radicals, also known as reactive oxygen species (ROS), a hypothesis tested in these studies. We used the guinea pig model of human tuberculosis to test what influence bacterial strain had on the development of pulmonary and extra-pulmonary granuloma necrosis. Our studies showed that the virulence of clinical isolates of M. tuberculosis was reflected in more severe and widely disseminated disease in experimentally infected guinea pigs and was a better predictor of virulence than the bacterial burden determined by culture. These data provide supporting evidence that the extent of lesion necrosis correlated with the severity of disease and is an important determinant in the clinical outcome of tuberculosis. We concluded that both host and pathogen factors contribute to the pathogenesis of lesion necrosis during M. tuberculosis infection. To determine the host factors that contribute to the pathogenesis of lesion necrosis, we focused on the role ROS generation has in the pathogenesis of lesion necrosis in experimental tuberculosis and explored whether this adverse response could be controlled therapeutically or through vaccination of guinea pigs with M. bovis BCG prior to virulent challenge. We found that depletion of host antioxidant defenses was a major determinant in the imbalance between the generation of ROS and host antioxidant capacity in this tuberculosis model. Moreover, we attributed the decreased expression of key antioxidant proteins to a defect in the function of a critical antioxidant transcription factor, nuclear factor-erythroid 2-related factor 2 (Nrf2). We were able to partially restore Nrf2-mediated antioxidant defenses therapeutically in M. tuberculosis infected guinea pigs with the antioxidant drug N-acetylcysteine. We also established that low density lipoproteins were among the host macromolecules that are oxidized during the chronic inflammatory response typical of tuberculosis. Oxidized low density lipoproteins (OxLDL), known to be rich in cholesterol, accumulated in macrophages during infection and elevation of OxLDL levels was accompanied by increased expression of the OxLDL scavenger receptors CD36 and LOX-1. The significance of these data are that through the use of the guinea pig tuberculosis model, we have uncovered a previously unrecognized mechanism by which the host and pathogen interact to create a unique microenvironment that allows difficult to treat M. tuberculosis to persist. The characterization of these host-pathogen interactions may lead to the development of novel adjunct therapies aimed at preventing the adverse effect of M. tuberculosis infection in humans.
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    The evaluation of clinical isolates of Mycobacterium tuberculosis in the murine and guinea pig infection models
    (Colorado State University. Libraries, 2011) Caraway, Megan L., author; Orme, Ian, advisor; Lenaerts, Anne, committee member; Callan, Robert, committee member
    Globally the tuberculosis epidemic continues unabated, affecting over nine million people a year, with more than half a million of these cases being resistant to multiple drugs. Multiple drug resistant tuberculosis (MDR-TB) is becoming a growing problem to the world's population. Despite this growing problem, very little research is being focused on MDR-TB. One basic question not yet addressed is how drug resistance affects virulence levels. A hypothesis, originating from classical studies of Mitchison, is that drug resistance results in a lower virulence level. Using the murine and guinea pig models of infection, I studied the ability of multiple isogenic pairs of Mycobacterium tuberculosis to grow in these particular animal models, in order to determine if acquired drug resistance increased or decreased the virulence of the drug resistant strain. In the murine model there was no discernable relationship between the drug resistance of a given strain and its virulence. Instead, isogenic drug resistant strains exhibited a range of virulence. Interestingly, the opposite was seen in the guinea pig infection model. In this model, it was observed that the drug resistant strain of the isogenic pair caused less severe disease and pathology. Drug resistance is not the only cause for concern in the ever continuing tuberculosis epidemic. Many strains that are associated with outbreaks around the world are being classified as either high or low transmission strains. High transmission strains are thought to be associated with increased rates of infections and higher virulence, the latter driving the former. Low transmission strains are the opposite; while they have been known to cause disease the numbers of cases where these strains have been identified appear to be fewer. I examined the virulence and pathogenicity of two strains selected for apparent high versus low transmission patterns, recently seen in a tuberculosis outbreak within the Chinese community of San Francisco, CA, USA that were typed as being W - Beijing strains. My studies did not support the hypothesis that high transmission strains have a higher virulence level.