Plasmacytoid dendritic cells in tolerance.

Dendritic cells (DC) are professional antigen-presenting cells (APCs) that modulate the outcome of the immune response toward immunity or tolerance. There are a large variety of DC subsets according to surface phenotype, function, and tissue distribution. Murine plasmacytoid DC (pDC) represent a distinctive DC population and are characterized by the expression of CD11c, B220, Gr-1, CD45RA, Ly49Q, BST2, and siglec-H on the cell surface. PDC act as immunogenic cell sentinels by secreting large amounts of type I interferon (IFN) in the lymph nodes in response to viral stimulation. PDC also act as tolerogenic cells when expressing the inducible tolerogenic enzyme indoleamine 2,3-dioxygenase (IDO), the inducible costimulator ligand (ICOS-L), and/or the programmed death 1 ligand (PD-L1), which mediate regulatory T-cell (Treg) development and suppression of self- and alloreactive cells. The PDC ability to induce Treg development is associated with capture and presentation of antigenic peptides associated with major histocompatibility complex (MHC) class I and II. Here, we provide the tools to study PDC development from bone marrow cultures, their antigen presentation properties, and their interactions with Treg under a tolerogenic setting of sterile inflammation.