To understand the roles of thymic stromal cells in T-lymphocyte development, we semiquantitatively analysed rat thymi recovering from irradiation (6 Gy), using a transmission electron microscope. The most striking findings were that the percentage of subcapsular epithelial cells significantly increased in the cortex on day 3 after irradiation compared with the control; the percentage of intermediate epithelial cells significantly increased in the cortex on days 3 and 5 after irradiation and in the medulla on days 5 and 7 compared with the control; the interdigitating cells disappeared from the medulla by day 7 after irradiation and reappeared on day 9. The present data thus reveal that during recovery after irradiation (6 Gy), marked changes occur in the relative proportions of different epithelial cell subtypes in the cortex and medulla of the rat thymus. In addition, the percentages of macrophages and interdigitating cells also changed during the recovery. These changes, which may be associated with the abrupt proliferation of thymocytes after irradiation, should shed light on the significance of stromal cells in the T cell development.
We exposed rats to a heavy, but sublethal, dose of X-radiation that was calculated as the maximum that left them alive. Immediately after irradiation the rats lost body and thymus weight. The number of thymocytes decreased and the structure of the thymus was destroyed. The thymus weights then increased rapidly for a few days from day 7 followed by a slower increase. Immunohistochemically, the recovery of major histocompatibility complex (MHC) class II-positive cells in the thymus was slower than that of MHC class I-positive cells. Recovery of MHC Class II-positive and ED1-positive cells in the thymus was slow, especially in the medulla. Thymus structure appeared similar to normal control animals on day 14, although the number of MHC class II-and ED1-positive cells in the medulla was lower than that of controls even 21 days after radiation exposure. The delay in recovery of MHC class II-positive stromal cells might affect the regeneration of thymocyte subpopulations after irradiation.
This article describes the recognition of a special membrane antigen of the rat squamous cell carcinoma (SCC) by a monoclonal antibody (mAb), UB23, and the characterization of the UB23 antigen expression in the implanted primary and metastatic SCC in rat models. The mAb UB23 was raised against the FF6 tumor, a well-differentiated rat SCC, and it recognized the 120- to 130-kD cell surface antigen in FF6 tumor cells. The UB23 antigen was found in frequently observed small ‘basal’ cells but not in keratinocytes, and an increased expression was seen in the cells at the interface with peritumoral stroma in both the implanted primary FF6 tumors and metastases. These results indicated that the UB23 antigen is closely related with the cell differentiation and invasion of FF6 cells, and could be useful for analyzing the mechanism of differentiation, invasion and metastasis of SCC in animal models.
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