Developmental dissociation of thymic dendritic cell and thymocyte lineagesrevealed in growth factor receptor mutant mice

Thymocytes and thymic dendritic cell (DC) lineages develop simultaneously a nd may originate from a common intrathymic progenitor. Mice deficient for t wo growth factor receptor molecules [c-kit and the common cytokine receptor gamma chain (gamma(c))] lack all thymocytes including T cell progenitors. Despite this lack of pro-T cells, thymic DC compartments were identified in c-kit(-)gamma c(-) mice. Thus, c-kit- and gamma(c)-mediated signals are no t essential to generate thymic DCs. In addition, pro-T cells do not appear to be obligatory progenitors of thymic DCs, because DC development is disso ciated from the generation of thymocytes in these mice. Thymic DCs in c-kit (-)gamma c(-) mice are phenotypically and functionally normal. In contrast to wild-type mice, however, thymic DCs in c-kit(-)gamma c(-) and, notably, in RAG-2-deficient mice are CD8 alpha(neg/low), indicating that CD8 alpha e xpression on thymic DCs is not independent of thymocytes developing beyond the "RAC-block".