ABSTRACT
Three major subsets constitute the dendritic cells (DCs) pool in the thymus. They play key roles in self-antigen-specific thymocyte deletion and in the development of immunoregulatory T cells. Resident SIRPa- conventional DCs (cDCs, CD11c+ PDCA1lo ) are derived from intrathymic progenitors, whereas migratory SIRPa+ cDCs and plasmacytoid DCs (pDCs, CD11c+ PDCA1+ ) originate from extrathymic sites. Here, we describe the organization and the shaping of cDC populations at the steady state and under stress conditions in wild-type and mutant mice (CD3eKO, IL7RaKO, and Flt3LKO). In neonates, the thymus is mainly composed of SIRPa- -resident cDCs, whereas both cDC subsets are present in equal proportions in the adult. Upon thymus colonization, migratory SIRPa+ cDCs gain expression of phenotypic markers in a microenvironment dependent way. Here, we show that both processes are deeply impacted by mutations affecting T cell development. Under stress conditions such as sublethal irradiation, intrathymic resident SIRPa- cDCs are the first to regenerate the thymic cDC pool. Upon bone marrow transplantation, migratory SIRPa+ cDCs become the main source of thymic cDCs. These successive waves of regeneration eventually lead to a balance between resident and migratory DCs within the newly colonized thymus. These findings highlight an unrevealed division of labor between resident and migratory subsets for the organization/establishment of the thymic cDC compartment.
