Formation of a functional thymus initiated by a postnatal epithelial progenitor cell

The thymus is essential for the generation of self-tolerant effector and regulatory T cells. Intrathymic T-cell development requires an intact stromal microenvironment, of which thymic epithelial cells (TECs) constitute a major part. For instance, cell-autonomous genetic defects of forkhead box N1 (Foxn1) and autoimmune regulator (Aire) in thymic epithelial cells cause primary immunodeficiency and autoimmunity, respectively. During development, the thymic epithelial rudiment gives rise to two major compartments, the cortex and medulla. Cortical TECs positively select T cells, whereas medullary TECs are involved in negative selection of potentially autoreactive T cells. It has long been unclear whether these two morphologically and functionally distinct types of epithelial cells arise from a common bi-potent progenitor cell and whether such progenitors are still present in the postnatal period. Here, using in vivo cell lineage analysis in mice, we demonstrate the presence of a common progenitor of cortical and medullary TECs after birth. To probe the function of postnatal progenitors, a conditional mutant allele of Foxn1 was reverted to wild-type function in single epithelial cells in vivo. This led to the formation of small thymic lobules containing both cortical and medullary areas that supported normal thymopoiesis. Thus, single epithelial progenitor cells can give rise to a complete and functional thymic microenvironment, suggesting that cell-based therapies could be developed for thymus disorders.     

Dose relationships of morning bright white light in seasonal affective disorders (SAD)

Bright white full spectrum light (greater than 2500 lux) can improve depressive symptomatology in a selected group of patients with recurrent autumn and winter depression. This crossover study demonstrates that 0.5-h morning white light is not an effective treatment, whereas 2-h is.     

Dose relationships of morning bright white light in seasonal affective disorders (SAD)

Summary Bright white full spectrum light (>2500 lux) can improve depressive symptomatology in a selected group of patients with recurrent autumn and winter depression. This crossover study demonstrates that 0.5-h morning white light is not an effective treatment, whereas 2-h is.