Notch signaling regulates the development of a novel type of Thy1-expressing dendritic cell in the thymus.

Dendritic cells (DCs) are specialized antigen-presenting cells (APCs) required for T-cell activation and are classified into several subtypes by phenotypic and functional characteristics. However, it remains unclear if distinct transcription factors control the development of each DC subpopulation. In this report, we demonstrate that Notch signaling controls the development of a novel DC subtype that expresses Thy1 (Thy1(+) DCs). Overstimulation of bone marrow cells with the Notch ligand Delta-like 1 promoted the development of Thy1(+) DCs. Thy1(+) DCs are characterized as CD11c(+) MHC class II(+) NK1.1(-) B220(-) CD8α(+) , and are present in the thymus but not in the spleen and lymph nodes. Thymic Thy1(+) DCs are able to capture exogenous proteins and delete CD4(+) CD8(+) T cells. Transplantation experiments demonstrated that CD44(+) CD25(-) and CD44(+) CD25(+) thymocytes can differentiate into Thy1(+) DCs. Recombination signal binding protein for immunoglobulin kappa J region (RBP-J) deficiency in lineage-negative bone marrow cells, but not CD11c(+) cells, disrupted Thy1(+) DC development in the thymus. Our data indicate that Notch signaling controls the development of a novel type of Thy1-expressing DC in the thymus that possibly controls negative selection, and indicates that there may be highly regulated, differential transcriptional control of DC development. Furthermore, our findings suggest that Notch signaling regulates T-cell development not only by intrinsically inducing T-cell lineage-specific gene programs, but also by regulating negative selection through Thy1(+) DCs.