Early differentiation of thymic dendritic cells in the absence of glucocorticoids

The possible role of glucocorticoids (GCs) in the maturation of thymic dend ritic cells (DCs) during early ontogeny was analyzed in the progeny of adre nalectomized pregnant rats (Adx foetuses). This experimental model ensured the lack of GCs until establishment of foetal hypothalamus-pituitary gland- adrenal (HPA) axis, and showed profound modifications of the development of thymus gland. In the absence of maternal GCs, there was a high percentage of DCs, many of them exhibiting a mature phenotype, in the 15-16 day-old Ad x foetal thymus, which sharply decreased to reach control values on foetal day 17. On the other hand, the absolute number of DCs of Sham foetal rats i ncreased throughout ontogeny, whereas the high numbers found in 15-16 day-o ld Adx foetuses significantly diminished in the following days. This proces s was closely correlated with the thymocyte life span, previously demonstra ted, and the early appearance of DCs in the spleen. Our results demonstrate that like for other cell components of rat thymus, DC maturation is accele rated in an early foetal microenvironment devoid of glucocorticoids. (C) 19 99 Elsevier Science B.V. All rights reserved.