Semiquantitative morphological analysis of stromal cells in the irradiatedand recovering rat thymus

To understand the roles of thymic stromal cells in T-lymphocyte development , we semiquantitatively analysed rat thymi recovering from irradiation (6 G y), using a transmission electron microscope, The most striking findings we re that the percentage of subcapsular epithelial cells significantly increa sed 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 da ta thus reveal that during recovery after irradiation (6 Gy), marked change s occur in the relative proportions of different epithelial cell subtypes i n the cortex and medulla of the rat thymus. In addition, the percentages of macrophages and interdigitating cells also changed during the recovery. Th ese changes, which may be associated with the abrupt proliferation of thymo cytes after irradiation, should shed light on the significance of stromal c ells in the T cell development.