Medullary Stromal Cells Research Articles

A novel cytokine-responsive cell surface glycoprotein defines a subset of medullary thymic epithelium in situ.

A hamster mAb (10.1.1), raised against long term cultures of uncloned thymic stromal cells, selectively labeled a subpopulation of medullary stromal cells in situ. By ultrastructural and phenotypic criteria, the stromal cells labeled by this mAb were judged to be epithelial. Although some of the 10.1.1+ epithelial cells were reticular, others were globular and some were associated with structures resembling Hassal's bodies. Ultrastructural immunohistochemistry suggested that 10.1.1 labeling of some of the epithelial cells was preferentially associated at areas of epithelial cell contact with adjacent thymocytes. Reactivity of thymic stromal cells with this antibody was developmentally regulated. A few scattered 10.1.1+ cells were observed at day 14 of gestation, and there were progressive increases in both the extent and intensity of 10.1.1 labeling evident through birth. One thymic stromal cell line, Z210.1, exhibited low levels of constitutive reactivity with this antibody. Exposure to IL-1 resulted in enhanced 10.1.1 reactivity of this cell line, with little, if any, additional response to TNF-alpha or IFN-gamma. Under the same conditions, ICAM-1 expression by this cell line was elevated in response to IL-1, TNF-alpha, or INF-gamma. Immunoprecipitation of detergent lysates prepared from Z210.1.7 cells exposed to IL-1 24 h before cell surface iodination identified a cell surface protein with a molecular mass of about 92 kDa under nonreducing conditions and about 95 kDa under reducing conditions. Digestion of 10.1.1 immunoprecipitates with N-glyconase resulted in a small (5 kDa) reduction in molecular mass. The molecule recognized by the 10.1.1 mAb was distinct from ICAM-1, which possessed a molecular mass of 100 kDa (nonreduced) and 110 kDa (reduced), and also displayed a smaller N-glyconase-resistant molecular mass (65 to 85 kDa).

Thymic irradiation inhibits the rapid recovery of TH1 but not TH2-Like functions of CD4 + T cells after total lymphoid irradiation

Four to six weeks after total lymphoid irradiation (TL1), there is a selective deficit in the CD4 + T cells which secrete IL-2, proliferate in the MLR, and induce GVHD (Th1-like functions). A similar deficit in CD4 + T cells which secrete IL-4 and help antibody responses (Th2-like functions) is not observed. In the present study, shielding of the thymus with lead during TLI increased the Th1-like functions of CD4 + cells. Mice without thymus shields showed a marked selective reduction in the medullary stromal cells identified with the monoclonal antibody, MD1, and the severe reduction was prevented with thymus shields. Thus, shielding the thymus prevents the depletion of thymic medullary stromal cells and allows for a rapid recovery of Th1-like functions in the mouse spleen after TLI. Th2-like functions recover rapidly after TLI whether or not the thymus is irradiated.

Total lymphoid irradiation leads to transient depletion of the mouse thymic medulla and persistent abnormalities among medullary stromal cells.

Mice given multiple doses of sublethal irradiation to both the thymus and the peripheral lymphoid tissues showed major transient, and some persistent disruptions in general thymic architecture and in thymic stromal components. At 2 wk after total lymphoid irradiation (TLI), the thymus lacked identifiable medullary regions by immunohistochemical analyses. Medullary stromal cells expression MHC Ag or a medullary epithelial cell Ag, as well as medullary macrophages, were undetectable. Instead, the processes of cortical epithelial cells were observed throughout the entire thymus. Strikingly, thymocyte subsets with mature phenotypes (CD4+CD8- and CD4-CD8+) were present in the apparent absence of a medulla. This early, gross effect was rapidly reversed such that by 1 to 2 mo after TLI, medullary areas with MHC Ag-positive cells were evident. However, abnormalities in a subset of medullary stromal cells appeared to be more persistent. Medullary epithelial cells, identified by the MD1 mAb, were greatly reduced in number and abnormally organized for at least 4 mo after TLI. In addition, macrophages containing endogenous peroxidase activity, normally abundant in medullary regions, were undetectable at all times examined after TLI. Therefore, this irradiation regimen induced both transient and long term effects in the thymus, primarily in medullary regions. These results suggest that TLI may be used as an experimental tool for studying the impact of selective depletion of medullary stromal cells on the development of specific T cell functions.

Repopulation of the mouse thymus after sublethal fission neutron irradiation. II. Sequential changes in the thymic microenvironment.

The stromal cells of the thymus of sham-irradiated and sublethal fission neutron-irradiated CBA/H mice were analyzed with immunohistology, using monoclonal antibodies directed to I-A and H-2K antigens as well as specific determinants for cortical and medullary stromal elements. In the control thymuses, I-A expression in the thymus shows a reticular staining pattern in the cortex and a confluent staining pattern in the medulla. In contrast, H-2K expression is mainly confluently located in the medulla. Whole body irradiation with 2.5 Gy fission neutrons reduces within 24 hr the cortex to a rim of vacuolized "nurse cell-like" epithelial cells, largely depleted of lymphoid cells. The localization of I-A antigens changes in the cortex and I-A determinants are no longer associated with or localized on epithelial reticular cells. Medullary stromal cells, however, are more or less unaffected. A high rate of phagocytosis is observed during the first 3 days after irradiation. About 5 days after irradiation, the thymus becomes highly vascularized and lymphoid cells repopulate the cortex. The repopulation of the thymic cortex coincides with the appearance of a bright H-2K expression in the cortex which is associated with both stromal cells as well as lymphoid blasts. During the regeneration of the thymus, the thymic stromal architecture is restored before the expression of cell surface-associated reticular MHC staining patterns. The observed sequential changes in the thymic microenvironment are related to the lymphoid repopulation of the thymus.