Isolation of mouse thymic dendritic cell precursors.

Dendritic cells (DC) are efficient antigen-presenting cells. Their ability to present antigens via MHC class I and MHC class II molecules to T cells allows them not only to initiate an immune response to exogenous pathogens but also to induce immune tolerance to self-antigens. Thymic DC play important roles in the establishment of central immune tolerance by presenting self-antigens to developing thymocytes and subsequently deleting the self-reactive thymocytes and inducing naturally occurring regulatory T cells. DC in the thymus are comprised of plasmacytoid DC (pDC) and conventional DC (cDC) populations. The cDC can be divided into two populations based on the expression of CD8 alpha and Sirp alpha: CD8 alpha(+)Sirp alpha(l) degrees (approximately 70%) and CD8 alpha(l) degrees Sirp alpha(+) (approximately 30%). The CD8 alpha(+)Sirp alpha(l) degrees cDC are generated in the thymus by the earliest intrathymic oligo-potent progenitors that are also precursors for T-lineage cells and natural killer cells (NK cells). Whereas the CD8 alpha(l) degrees Sirp alpha(+)cDC and pDC are migratory DC and originate mainly from peripheral blood. The ability to isolate and purify the earliest intrathymic precursors allows us to generate thymic cDC in culture or in vivo upon intrathymic or intravenous injections. These experimental systems are crucial for studying the development and functions of thymic DC.