Glucocorticoid-induced apoptosis in the thymus.

Destruction of thymus cells was one of the earliest observed properties of adrenal glucocorticoids. The cells affected are primarily immature, CD4/CD8 double-positive lymphocytes. This process has been clearly shown in vivo and in vitro to be apoptosis, as characterized by cell shrinkage, membrane alterations, nuclear collapse and chromatin fragmentation into oligonucleosomes. Glucocorticoid-induced thymocyte death requires new mRNA and protein synthesis. A beginning has been made in identifying the genes involved in thymocyte apoptosis. A case is made for the death of unselected thymocytes in vivo being regulated by endogenous glucocorticoids.