Department of Veterinary Medicine Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2762
Browse
2 results
Search Results
Item HOST-PATHOGEN INTERACTION DURING CRYPTOCOCCUS NEOFORMANS CNS INFECTION(2024) Chen, Yanli; Shi, Meiqing MS; Veterinary Medical Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Cryptococcus neoformans (C. neoformans) is an opportunistic fungal pathogen widely distributed in the environment globally. C. neoformans infection initiates from the lung through inhaling the spores. While most healthy individuals can clear the fungus or contain the fungus in the granuloma, immunosuppressed patients and a small group of healthy populations fail in controlling the cryptococcal fungal pulmonary infection. In those cases, C. neoformans transmigrates from the lung to the central nervous system (CNS) and causes fatal meningoencephalitis, which accounts for 112,000 deaths each year worldwide. However, we have a very limited understanding of the transmigration of C. neoformans from the bloodstream to the brain in vivo, and the mechanism involved in the clearance of the organism in the brain remains poorly understood. In this study, we first report a novel approach to quantitatively analyze the interactions between C. neoformans and brain endothelial cells in a mouse model using flow cytometry. Using this system, we show that C. neoformans was internalized by brain endothelial cells in vivo and that mice infected with acapsular or heat-killed C. neoformans yeast cells displayed a lower frequency of brain endothelial cells containing the yeast cell compared to mice infected with wild-type or viable yeast cells, respectively. We further demonstrate that brain endothelial cells were invaded by the serotype A strain (H99 strain) at a higher rate compared to the serotype D strain (52D strain). Moreover, we found that clearance of C. neoformans in the brain correlates with accumulation and pro-inflammatory M1 polarization of Ly6Chi mononuclear phagocytes and that these phagocytes play a critical role in the clearance of C. neoformans in the brain. Notably, the accumulation of Ly6Chi mononuclear phagocytes coincides with enhanced secretions of TNF and IFN-γ in the brain. TNF receptor (TNFR) signaling, but not IFN-γ receptor (IFN-γR) signaling, mediates the recruitment of Ly6Chi mononuclear phagocytes to the brain in a cell-intrinsic manner. By contrast, IFN-γ induces M1 polarization of Ly6Chi mononuclear phagocytes. Disruption of TNFR or IFN-γR signaling enhances cryptococcal growth in the brain. Thus, Ly6Chi mononuclear phagocytes act as effector cells for cryptococcal clearance in the brain, involving TNFR as well as IFN-γR signaling. Collectively, our study established that 1) internalization of C. neoformans by brain endothelial cells occurred in vivo and offered a powerful approach to quantitatively analyze fungal migration into the brain; 2) Ly6Chi mononuclear phagocytes accumulate in the brain during brain infection with C. neoformans and function as effector cells for clearance of C. neoformans in the brain involving TNFR signaling and IFN-γ signaling.Item Host Immune Responses to Fungal Pathogens(2022) Strickland, Ashley Brenda; Shi, Meiqing; Veterinary Medical Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Fungal infections are an increasing threat to global public health. Worldwide, more than one billion fungal infections are diagnosed each year and result in 1.5 million deaths annually. This number is expected to rise as advances in medical care for immunocompromised patients continue to be made. Furthermore, limited antifungal treatment options, coupled with the emergence of new and resistant fungal species, is anticipated to exacerbate this issue. For these reasons, it is essential to understand the dynamic interactions between host and fungus that contribute to fungal pathogenesis. The following work examined the role of IL-27 on T cell regulation in the lungs during infection with Aspergillus fumigatus, and in the brain during infection with Cryptococcus neoformans. In contrast to most infection settings demonstrating that IL-27 is anti-inflammatory, we report that this cytokine is proinflammatory in both the lung and the brain during infection with A. fumigatus and C. neoformans respectively. Genetic ablation of IL-27Rα in mice resulted in higher fungal burdens in the lung during Aspergillus infection and in the brain during Cryptococcus infection. These were associated with reduced IFN-γ production, as well as a fewer CD4+ T cells in target organs. In the case of C. neoformans infection, IL-27 signaling enhanced T cell accumulation by promoting T cell proliferation early during infection, and inhibiting T cell death at later time points. These suggest that IL-27 promotes T cell responses required for fungal clearance during infection with A. fumigatus or C. neoformans. In addition, the work presented here also characterized lung resident macrophage responses during infection with C. neoformans. Here, we report that cryptococcal infection induced the accumulation of CD68hi macrophages in the lungs of infected mice. Approximately 10% of these cells were alveolar macrophages, while nearly 90% were interstitial macrophages. Both of these populations were observed to interact with fungi and upregulated their expression of arginase 1. The absence of either macrophage in transgenic mice, or following pharmacological depletion, significantly reduced fungal burdens in the lungs of mice, indicating that these cells enhance fungal growth and may represent attractive targets aimed at limiting the pathogenesis of C. neoformans.