TNF and type I interferon crosstalk controls the fate and function of plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDCs) are major producers of type I interferon (IFN-I), an important antiviral cytokine, and activity of these cells must be tightly controlled to prevent harmful inflammation and autoimmunity. Evidence exists that one regulatory mechanism is a fate-switching process from an IFN-I-secreting pDC to a professional antigen-presenting conventional dendritic cell (cDC) that lacks IFN-I-secreting capacity. However, this differentiation process is controversial owing to limitations in tracking the fate of individual cells over time. Here we use single-cell omics and functional experiments to show that activated human pDCs can lose their identity as IFN-I-secreting cells and acquire the transcriptional, epigenetic and functional features of cDCs. This pDC fate-switching process is promoted by tumor necrosis factor but blocked by IFN-I. Importantly, it occurs in vivo during human skin inflammatory diseases and injury, and physiologically in elderly people. This work identifies the pDC-to-cDC reprogramming trajectory and unveils a mechanistic framework for harnessing it therapeutically. Plasmacytoid dendritic cells are type 1 interferon (IFN-I)-producing antiviral specialists that have been shown to be able to differentiate into conventional dendritic cells. Here the authors show how this differentiation is controlled by tumor necrosis factor driving type 2 conventional dendritic cell-like reprogramming and IFN-I blocking it, a process that occurs during inflammation, injury and aging.