Biomedical subjects

Daniel H D Gray

Publications and source records attributed to Daniel H D Gray.

8 recordsLinked to original sources

PubMed2006

Developmental kinetics, turnover, and stimulatory capacity of thymic epithelial cells.

Despite the importance of thymic stromal cells to T-cell development, relatively little is known about their biology. Here, we use single-cell analysis of stromal cells to analyze extensive changes in the number and composition of thymic stroma throughout life, revealing a surprisingly dynamic population. Phenotypic progression of thymic epithelial subsets was assessed at high resolution in young mice to provide a developmental framework. The cellular and molecular requirements of adult epithelium were studied, using various mutant mice to demonstrate new cross talk checkpoints dependent on RelB in the cortex and CD40 in the medulla. With the use of Ki67 and BrdU labeling, the turnover of thymic epithelium was found to be rapid, but then diminished on thymic involution. The various defects in stromal turnover and composition that accompanied involution were rapidly reversed following sex steroid ablation. Unexpectedly, mature cortical and medullary epithelium showed a potent capacity to stimulate naive T cells, comparable to that of thymic dendritic cells. Overall, these studies show that the thymic stroma is a surprisingly dynamic population and may have a more direct role in negative selection than previously thought.

Aging↗

PubMed2005

Effects of castration on thymocyte development in two different models of thymic involution.

Age-associated thymic involution is accompanied by decreased thymic output. This adversely affects general immune competence and T cell recovery following cytoreductive treatments such as chemotherapy. A causal link between increasing sex steroids and age-related thymic atrophy is well established. Although castration has been demonstrated to regenerate the atrophied thymus, little is known about how this is initiated or the kinetics of thymocyte regeneration. The present study shows that although castration impacts globally across thymocyte development in middle-aged mice, the regenerative effects are initiated in the immature triple-negative compartment and early T lineage progenitors (ETP). Specifically, there was a reduction in number of ETP with age, which was restored following castration. There was, however, no change in ETP reconstitution potential in ETP at this age or following castration. Furthermore, in a chemotherapy-induced model of thymic involution, we demonstrate castration enhances intrathymic proliferation and promotes differentiation through the triple-negative program. Clinically, reversible sex steroid ablation is achieved hormonally, and thus presents a means of ameliorating immune inadequacies, for example, following chemotherapy for bone marrow transplantation. By improving our understanding of the kinetics of thymic recovery, this study will allow more appropriate timing of therapy to achieve maximal reconstitution, especially in the elderly.

Aging↗

PubMed2005

Controlling the thymic microenvironment.

T-cell development in the thymus is a stepwise process, mediated by a variety of stromal cells in different regions of the organ. Although the cellular composition of the thymic microenvironment has been known for over a decade, the molecular cues that govern its formation are only beginning to be understood. Stromal-derived chemokines attract T-cell precursors to the thymus and direct maturing thymocytes to appropriate niches for their further development. Reciprocal signals from developing T cells provide crosstalk that is essential for establishment and maintenance of the thymic microenvironment. Elucidation of the molecular players involved and their context within the organ is the challenge for the field today. This knowledge could then be translated to clinical restoration of thymic function and T-cell reconstitution.

Animals↗

PubMed2005

Genetic lesions in T-cell tolerance and thresholds for autoimmunity.

The cause of common organ-specific autoimmune diseases is poorly understood because of genetic and cellular complexity in humans and animals. Recent advances in the understanding of the mechanisms of the defects underlying autoimmune disease in autoimmune polyendocrinopathy syndrome type 1 and non-obese diabetic mice suggest that failures in central tolerance play a key role in predisposition towards organ-specific autoimmunity. The lessons from such rare monogenic autoimmune disorders and well-characterized polygenic traits demonstrate how subtle quantitative trait loci can result in large changes in the susceptibility to autoimmunity. These data allow us to propose a model relating efficiency of thymic deletion to T-cell tolerance and susceptibility to autoimmunity.

Animals↗

PubMed2004

Gene dosage--limiting role of Aire in thymic expression, clonal deletion, and organ-specific autoimmunity.

Inactivation of the autoimmune regulator (Aire) gene causes a rare recessive disorder, autoimmune polyendocrine syndrome 1 (APS1), but it is not known if Aire-dependent tolerance mechanisms are susceptible to the quantitative genetic changes thought to underlie more common autoimmune diseases. In mice with a targeted mutation, complete loss of Aire abolished expression of an insulin promoter transgene in thymic epithelium, but had no effect in pancreatic islets or the testes. Loss of one copy of Aire diminished thymic expression of the endogenous insulin gene and the transgene, resulting in a 300% increase in islet-reactive CD4 T cells escaping thymic deletion in T cell receptor transgenic mice, and dramatically increased progression to diabetes. Thymic deletion induced by antigen under control of the thyroglobulin promoter was abolished in Aire homozygotes and less efficient in heterozygotes, providing an explanation for thyroid autoimmunity in APS1. In contrast, Aire deficiency had no effect on thymic deletion to antigen controlled by a systemic H-2K promoter. The sensitivity of Aire-dependent thymic deletion to small reductions in function makes this pathway a prime candidate for more subtle autoimmune quantitative trait loci, and suggests that methods to increase Aire activity would be a potent strategy to lower the incidence of organ-specific autoimmunity.

Animals↗

PubMed2004

CCR7 signals are essential for cortex-medulla migration of developing thymocytes.

Upon TCR-mediated positive selection, developing thymocytes relocate within the thymus from the cortex to the medulla for further differentiation and selection. However, it is unknown how this cortex-medulla migration of thymocytes is controlled and how it controls T cell development. Here we show that in mice deficient for CCR7 or its ligands mature single-positive thymocytes are arrested in the cortex and do not accumulate in the medulla. These mutant mice are defective in forming the medullary region of the thymus. Thymic export of T cells in these mice is compromised during the neonatal period but not in adulthood. Thymocytes in these mice show no defects in maturation, survival, and negative selection to ubiquitous antigens. TCR engagement of immature cortical thymocytes elevates the cell surface expression of CCR7. These results indicate that CCR7 signals are essential for the migration of positively selected thymocytes from the cortex to the medulla. CCR7-dependent cortex-medulla migration of thymocytes plays a crucial role in medulla formation and neonatal T cell export but is not essential for maturation, survival, negative selection, and adult export of thymocytes.

Animals↗

PubMed2004

Generalized resistance to thymic deletion in the NOD mouse; a polygenic trait characterized by defective induction of Bim.

The cause of common polygenic autoimmune diseases is not understood because of genetic and cellular complexity. Here, we pinpoint the action of a subset of autoimmune susceptibility loci in the NOD mouse strain linked to D1mit181, D2mit490, D7mit101, and D15mit229, which cause a generalized resistance to thymic deletion in vivo that applies equally to Aire-induced organ-specific gene products in the thymic medulla and to systemic antigens expressed at high levels throughout the thymus and affects CD4(+), CD4(+)8(+), and CD4(+)25(+) thymocytes. Resistance to thymic deletion does not reflect a general deficit in TCR signaling to calcineurin- or ERK-induced genes, imbalance in constitutive regulators of apoptosis, nor excessive signaling to prosurvival genes but is distinguished by failure to induce the proapoptotic gene and protein, Bim, during in vivo encounter with high-avidity autoantigen. These findings establish defects in thymic deletion and Bim induction as a key mechanism in the pathogenesis of autoimmunity.

Animals↗

PubMed2002

Role for CCR7 ligands in the emigration of newly generated T lymphocytes from the neonatal thymus.

Most T lymphocytes are generated within the thymus. It is unclear, however, how newly generated T cells relocate out of the thymus to the circulation. The present study shows that a CC chemokine CCL19 attracts mature T cells out of the fetal thymus organ culture. Another CC chemokine CCL21, which shares CCR7 with CCL19 but has a unique C-terminal extension containing positively charged amino acids, failed to show involvement in thymic emigration. Neonatal appearance of circulating T cells was defective in CCL19-neutralized mice as well as in CCR7-deficient mice but not in CCL21-neutralized mice. In the thymus, CCL19 is predominantly localized in the medulla including endothelial venules. These results indicate a CCL19- and CCR7-dependent pathway of thymic emigration, which represents a major pathway of neonatal T cell export.

Animals↗