Plasmacytoid dendritic cells (pDCs) are a unique subset of dendritic cells that circulate in the blood and peripheral organs and rapidly secrete large amounts of type I interferons (IFNs) following activation. They are activated in the presence of either viral or self nucleic acids, which are detected by the endosomal toll-like receptors 7 or 9 (TLR7 or TLR9), two pattern recognition receptors selectively expressed by pDCs. Prior to activation, pDCs display a plasma cell-like morphology and express low levels of MHC class II and co-stimulatory molecules. Following activation, they acquire a more characteristic dendritic cell-like morphology and upregulate MHC class II and co-stimulatory molecules, allowing them to prime naïve CD4+ T cells, albeit relatively poorly in mice. In addition to secreting high levels of type I IFNs, pDCs can also secrete pro-inflammatory cytokines and chemokines including IL-6, IL-12, CCL3, CCL4, CXCL8 and CXCL10. In mice, pDCs are commonly identified as Lin-CD11c+B220/CD45R+BST-2/CD317+Ly-6C+CD11b- cells that also express Siglec-H and SIRP alpha/CD172a. In humans, pDCs are typically identified as Lin-CD11clowCD123/IL-3 R alpha+BDCA-2/CD303+BDCA-4/Neuropilin-1+ cells. Both mouse and human pDCs express high levels of E2-2, a master transcription factor required for pDC development and homeostasis, along with Spi-B and IRF8, two additional transcription factors required for pDC development.
Human and Mouse Dendritic Cell Subsets Poster