RENEWAL OF THYMOCYTE PROGENITORS AND EMIGRATION OF THYMOCYTES DURING AVIAN DEVELOPMENT

The avian thymus is colonized by three waves of hemopoietic progenitor s during embryogenesis, An in vivo thymus reconstitution assay based o n intrathymic injection of irradiated chicks showed that cells of para -aortic foci were able to differentiate into T lymphocytes, confirming their putative role in the first wave of thymus colonization. This as say was also used to detect and to characterize T cell progenitors fro m the bone marrow which are involved in the second and third wave of t hymus colonization. In the bone marrow, progenitors that differentiate d into T cells were found in a subpopulation that expressed the molecu les HEMCAM, c-kit and c128, Engraftment of thymus lobes into thymectom ized young chick recipients showed that T cell progenitors are replace d in the thymus by subsequent waves of progenitors after hatching, Fin ally, analysis of thymocyte differentiation suggested that gamma delta and alpha beta T cells migrate from the thymus to the periphery in al ternating waves. (C) 1998 Elsevier Science Ltd. All rights reserved.