<p>Thymus atrophy is highly inducible by stress and prolonged thymus atrophy can contribute to T cell deficiency or inhibit immune recovery after acute peripheral T cell depletion. Little is known regarding the mechanisms driving thymic involution or thymic reconstitution after acute stress. Leptin deficiency in mice results in chronic thymic atrophy, suppressed cell-mediated immunity, and decreased numbers of total lymphocytes, suggesting a role for leptin in regulating thymopoiesis and overall immune homeostasis. Exogenous leptin administration during stress has been shown to protect against thymic damage, yet the mechanisms governing these thymostimulatory effects are currently undefined. Studies herein define the impact of endotoxin-induced thymic damage in the stromal and lymphoid compartment of the thymus and systemic glucocorticoid and cytokine responses in the animal. We report here the novel finding that leptin receptor expression is restricted to medullary thymic epithelial cells in the normal thymus. Using a model of endotoxin-induced acute thymic involution and recovery, we have demonstrated a role for the metabolic hormone leptin in protection of medullary thymic epithelial cells from acute endotoxin-induced damage. We also demonstrated that systemic leptin treatment decreased endotoxin-induced apoptosis of double positive thymocytes and promoted proliferation of double negative thymocytes in vivo through a leptin receptor isoform b-specific mechanism. Leptin treatment increased thymic expression of IL-7, an important soluble thymocyte growth factor produced by medullary thymic epithelial cells. We also found leptin to inhibit systemic glucocorticoid and pro-inflammatory cytokine responses. Using leptin-deficient and leptin receptor-deficient mice in our stress model, we found that endotoxin-induced thymic atrophy was exacerbated in the absence of leptin, despite an inability to mount a proper pro-inflammatory cytokine response. Together, these data support a model in which leptin can function to protect the thymus gland from stress-induced acute damage in part by reduction of systemic corticosteroid and pro-inflammatory cytokine responses, and intrathymically through a mechanism orchestrated by medullary thymic epithelial cells and their soluble mediators (e.g. IL-7). Taken together, these studies suggest a physiological role for leptin signaling in the thymus for maintaining healthy thymic epithelium and promoting thymopoiesis, which is revealed when thymus homeostasis is perturbed by stress.</p> / Dissertation

Studying lymphocyte development using mass cytometry Abstract Development of mature lymphocytes, a white blood cell subtype, is crucial for the correct function of the human immune system. Currently, developmental pathways of lymphocytes can be studied using high-throughput single-cell measurements. In particular, mass cytometry enables the study of immunologically relevant pheno- typic and functional markers on a vast scale. In this work I present my individual contribution to tviblindi, a powerful software tool for analysis of cytometric data aimed at uncovering developmental trajectories. tviblindi is a package written in R, Python and C++. It provides a means to integrate prior knowledge with data analyses grounded in graph theory and algebraic topology. tviblindi is accessible to biological researchers without background in computer science or mathematics. It is an addition to the expanding field of trajectory inference in single-cell data. Furthermore, I review current knowledge of T-cell development and conduct a tviblindi analysis thereof using human thymus and peripheral blood datasets and evaluate the results. 1

Studying lymphocyte development using mass cytometry Abstract Development of mature lymphocytes, a white blood cell subtype, is crucial for the correct function of the human immune system. Currently, developmental pathways of lymphocytes can be studied using high-throughput single-cell measurements. In particular, mass cytometry enables the study of immunologically relevant pheno- typic and functional markers on a vast scale. In this work I present my individual contribution to tviblindi, a powerful software tool for analysis of cytometric data aimed at uncovering developmental trajectories. tviblindi is a package written in R, Python and C++. It provides a means to integrate prior knowledge with data analyses grounded in graph theory and algebraic topology. tviblindi is accessible to biological researchers without background in computer science or mathematics. It is an addition to the expanding field of trajectory inference in single-cell data. Furthermore, I review current knowledge of T-cell development and conduct a tviblindi analysis thereof using human thymus and peripheral blood datasets and evaluate the results. 1