Phenotypic Mapping of The Chicken Embryonic Thymic Microenvironment Developing Within an Organ Culture System

The chicken thymic microenvironment, as it developed in an embryonic thymus organ culture system, was phenotypically mapped using a panel of mAb defining both epithelial and nonepithelial stromal cell antigens. We have previously reported that thymocyte proliferation and differentiation will proceed for up to 6–8 days in thymus organ culture, hence demonstrating the functional integrity of the thymic microenvironment in vitro. During this time, the stromal component reflected that of the normal embryo with cortical and medullary epithelial areas readily identifiable by both morphology and surface-antigen expression. An abundance of subcapsular and cortical epithelial antigens was detected in the cultured thymus, particularly those normally expressed by the epithelium lining the capsule, trabeculae, and vascular regions (type epithelium) in the adult and embryonic thymus. Medullary epithelial antigens developed in organ culture, although were present in lower frequency than observed in the age-matched embryonic thymus. MHC class II expression by both epithelial and nonepithelial cells was maintained at high levels throughout the culture period. With increasing time in culture, the ratio of epithelial to nonepithelial cells decreased, concurrent with a decrease in thymocyte frequency and suggestive of a bidirectional interaction between these two cell types. Thus, a functionally intact thymic microenvironment appears to be maintained in embryonic thymus organ culture, a model that is currently being exploited to assess the role of stromal antigens, as defined by our mAb, in the process of thymopoiesis

Thymic-Shared Antigen-1 (TSA-1) A Lymphostromal Cell Membrane Ly-6 Superfamily Molecule with a Putative Role in Cellular Adhesion

The seeding and colonization of the thymus by bone marrow stem cells and the maturation of these cells into mature T lymphocytes are dependent on cell-surface recognition events between different cell lineages within the thymic microenvironment. Positive and negative selection processes within the thymus produce a peripheral T-cell repertoire capable of recognizing peptides derived from foreign antigen bound to self MHC molecules. In addition to the TCR/ MHC-peptide interaction, many other cell-surface molecules act in concert to regulate the kinetics of cellular interactions and intracellular signaling events during thymopoiesis. We have investigated the complexity of the thymic stroma by using monoclonal antibodies to clone cellmembrane molecules of thymic stromal cells. Thymic-shared antigen-1 (TSA-1) is a molecule of interest because it is expressed by both immature thymocytes and stromal cells. We report herein the structural and evolutionary relationships between TSA-1 and molecules of the Ly-6 superfamily (Ly-6SF), and present evidence that TSA-1 functions as a cell-surface receptor by binding a cognate cell target molecule on the surface of a subset of thymocytes

A Study to Develop and Propose a System of Industrial Arts Accounting and Bookkeeping for the Secondary Schools of Fort Worth, Texas

The purpose of the study is to develop and propose a system of industrial arts accounting and bookkeeping for the secondary schools of Fort Worth, Texas, if it is found, through the study, that the instructors of industrial arts in Fort Worth, Texas, need and desire a systematic method of keeping financial records

An optical phase locked loop for semiconductor lasers

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1988.Title as it appeared in MIT Graduate list, June, 1988: An optical phase locked loop.Includes bibliographical references.by Richard L. Boyd.M.S

Characterization of Thymic Nurse-Cell Lymphocytes, Using an Improved Procedure for Nurse-Cell Isolation

Thymic nurse cells (TNC), multicellular complexes consisting of lymphoid cells enclosed within cortical epithelial cells, were isolated from mouse thymus by a modified procedure allowing immunofluorescent labeling and flow cytometric analysis of their lymphoid contents (TNC-L). Collagenase was the only protease used for tissue digestion, to ensure that surface antigen markers remained intact. Zonal unit-gravity elutriation was used to enrich the TNC on the basis of their high sedimentation rate, followed by immunomagnetic bead depletion to remove residual mononuclear cell contaminants and a density separation to remove debris. The TNC-L were then released from inside TNC by a short period of culture. The measured contamination of TNC-L with exogenous thymocytes was around 0.5%. Three-color immunofluorescent labeling revealed that TNC-L included, as well as a maiority of immature CD4+8+3low thymocytes, about 12% of apparently mature CD4+8-3high and CD4-8+3high thymocytes. TNC are located in the cortex, where mature cells are rare; the occurrence of mature phenotype cells within these structures suggests that they represent a microenvironment for the selection and generation of mature T cells

Thymic Medulla Epithelial Cells Acquire Specific Markers by Post-Mitotic Maturation

The development of thymocyte subsets and of the thymic epithelium in SCID and RAG-2-/– mice was monitored after normal bone-marrow-cell transfer. The kinetics of thymic reconstitution and their relationships with cell proliferation were investigated by using bromodeoxyuridine to detect DNA-synthesizing cells among lymphoid cells by 3-color flow cytometry, and in epithelial compartments by staining frozen sections. Thymocytes started to express CD8 and CD4 10 days after transfer, simultaneously with extensive proliferation. The first mature CD4+ single-positive cells were generated, from resting CD4+CD8+ cells after day 15. During this day 10–15 period, many epithelial cells positive for cortexspecific or panepithelial markers were labeled with BrdUrd after pulse-injection. Organized medullary epithelium also developed after day,15, that is, synchronously with the appearance of mature thymocytes, but medullary cells were never found BrdUrd+. These results suggest that, in these models, the reconstitution of the thymic epithelial network proceeds through expansion of preexisting cortical or undifferentiated cells and by later maturation (acquisition of specific markers) of medullary cells. This last process is dependent of the presence of mature thymocytes

An Adult Thymic Stromal-Cell Suspension Model for in Vitro Positive Selection

Presented here is a cell-suspension model for positive selection using thymocytes from αβ-TCR (H-2Db-restricted) transgenic mice specific to the lymphocytic choriomeningitis virus (LCMV) on a nonselecting MHC background (H-2d or TAP-1 –/–), cocultured with freshly isolated adult thymus stromal cells of the selecting MHC type. The thymic stromal cells alone induced positive selection of functional CD4-CD8+ cells whose kinetics and efficiency were enhanced by nominal peptide. Fibroblasts expressing the selecting MHC alone did not induce positive selection; however, together with nonselecting stroma and nominal peptide, there was inefficient positive. These results suggest multiple signaling in positive selection with selection events able to occur on multiple-cell types. The ease with which this model can be manipulated should greatly facilitate the resolution of the mechanisms of positive selection in normal and pathological states