Dysregulation of T-Cell Development in Adrenal Glucocorticoid-Deprived Rats

A number of different experimental approaches have been used to elucidate the impact: of basal levels of adrenal gland-derived glucocorticoids (GCs) on T cell development, and thereby T cell-mediated immune responses. However, the relevance of the adrenal GCs to T cell development is still far from clear. This study was undertaken to explore the relevance of basal levels of GCs to T cell differentiation/maturation. Eight days post-adrenalectomy in adult male rats the thymocyte yield, apoptotic and proliferative rate and the relationship amongst major thymocyte subsets, as defined by TCR alpha beta/CD4/CD8 expression, were examined using flow cytometry. Adrenal GC deprivation decreased thymocyte apoptosis and altered the kinetics of T cell differentiation/maturation. In the adrenalectomized rats there was increased thymic hypercellularity and an over-representation of the CD4+CD8+ double positive (DP) TCR alpha beta(low) cells entering selection, as well as increased numbers of their DP TCR alpha beta(-) immediate precursors. These changes were accompanied with under-representation of the postselected DP TCR alpha beta(high) and the most mature CD4-CD8+ and, particularly, CD4+CD8-single positive (SP) TCR alpha beta(high) cells. This data suggests that withdrawal of adrenal GCs produces alterations in the thymocyte selection processes, possibly affecting the diversity of functional T cell repertoire and generation of potentially self-reactive cells as indicated by the reduced proportion and number of CD4-CD8- double negative TCR alpha beta(high) cells. In addition, it indicates that GCs influence the post-selection maturation of thymocytes and plays a regulatory role in controlling the ratio of mature CD4+CD8-/CD4-CD8+ SP TCR alpha beta(high) cells. Exp Biol Med 234:1067-1074, 200