• Immune Dysfunction in the Ts65Dn Mouse Model of Down Syndrome: Potential Role(s) of Reactive Oxygen Species (ROS) and Alterations in IL-7Ralpha Expression

      Lorenzo, Laureanne; Williams, Mark S., Ph.D. (2011)
      Down Syndrome (DS), a genetic disease caused by a triplication of chromosome 21, is characterized by increased markers of oxidative stress. In addition to cognitive defects, DS is characterized by hematologic disorders such as myelodysplastic syndrome, premature thymic involution and increased incidence of infections and leukemia. However, the potential causes of these defects have not been fully elucidated. The goal of this study was to examine hematopoietic stem cell, lymphoid progenitor cell, and mature lymphocyte function in DS using the Ts65Dn mouse model, which contains a segmental triplication of mouse chromosome 16 that is partially syntenic to human chromosome 21. Analysis of hematopoietic progenitor populations showed that Ts65Dn mice possessed fewer functional hematopoietic stem cells (HSC) and a significantly decreased percentage of bone marrow lymphoid progenitors. Increased reactive oxygen species (ROS) and markers of oxidative stress were detected in HSC populations and were associated with a loss of quiescence and increased apoptosis. Bone marrow progenitor, immature thymocyte, and mature lymphocyte populations expressed diminished levels of the IL-7Rα chain, which was associated with decreased proliferation and increased apoptosis. Modulating oxidative stress in vitro suggested that oxidative stress induced by diminished glutathione levels selectively leads to decreased IL-7Rα expression, and inhibits the survival of IL-7Rα expressing hematopoietic progenitors, potentially linking increased ROS and immunopathology. Other possible mechanisms identified in Ts65Dn mice that could induce diminished IL-7Rα expression in DS are increased microRNA expression and inhibition of the Notch pathway. The data suggest that hematopoietic stem cell, lymphoid progenitor cell, and mature lymphocyte defects underlie immune dysfunction in DS and that increased oxidative stress and reduced cytokine signaling may alter hematologic development in Ts65Dn mice. Therefore, the current study may support modulation of redox balance and IL-7Rα expression as possible therapeutic targets to treat immune dysfunction in DS and may provide a starting point for the manipulation of redox balance to modulate the immune response.
    • Regulation of adaptive immune responses by the phagocyte-type NADPH oxidase in T cells and antigen presenting cells

      Shatynski, Kristen Elizabeth; Williams, Mark S., Ph.D. (2012)
      Absence of phagocyte NADPH oxidase (NOX2) activity causes chronic granulomatous disease (CGD), a primary immunodeficiency characterized by recurrent bacterial infections. In contradiction to this innate immune dysfunction, CGD patients or animal models of the disease display improved response to infectious agents such as Helicobacter pylori, influenza virus or Cryptococcus neoformans. These and other data imply an altered adaptive immune response in CGD. In addition to antigen presenting cells (APCs), NOX2 is expressed in T cells, and the goal was to determine if these differences are T cell inherent, or if NOX2-deficient APCs promote T-helper polarization. We hypothesize that NOX2 shapes both adaptive and innate immune responses in a T cell and APC-dependent fashion. In order to study T-helper polarization in vivo, wild type and NOX2-deficient (NOX2<super>(-/-)</super>) mice were immunized with OVA in CFA or Alum. Upon in vitro restimulation, lymph node cells from NOX2<super>(-/-)</super> mice had increased Th1 but decreased Th2 cytokine production. Adoptive transfer of OT-II T cells into wild type or NOX2<super>(-/-)</super> hosts followed by immunization also revealed increased IL-17 and IFN-γ, but decreased IL-4 after restimulation in vitro. NOX2<super>(-/-)</super> APCs (resident peritoneal cells and adherent splenocytes) displayed enhanced proinflammatory cytokine secretion in vitro, and stimulation of OT-II T cells with antigen-pulsed NOX2<super>(-/-)</super> APCs in vitro induced altered cytokine production, suggesting that NOX2 deficiency modifies APC function, resulting in T helper skewing. In addition to APC-induced changes, T cells from NOX2<super>(-/-)</super> mice were inherently skewed. Naïve T cells from NOX2<super>(-/-)</super>mice demonstrated Th1 skewed cytokine secretion as compared to their wild type counterparts, through increased IFN-γ, but decreased IL-4 in response to anti-CD3 and anti-CD28 stimulation. There were also selective decreases in GATA-3 and phosphorylated STAT5, with decreased Il4 gene expression, suggesting a mechanism for decreased Th2 responses. Finally, treatment with antioxidants recapitulated these selective changes in TCR-induced transcription factor activation. These findings indicate that TCR-induced reactive oxygen species generation from NOX2 activation selectively promotes STAT5 phosphorylation and downstream Th2 development in CD4+ T cells. Taken together, these findings suggest NOX2 affects cross talk between the innate and adaptive immune systems, resulting in changes in T helper differentiation.