Tonic type I interferon signaling optimizes the antiviral function of plasmacytoid dendritic cells [Multiome]

Plasmacytoid dendritic cells (pDCs) mount powerful type I interferon (IFN-I) responses against viruses and virus-derived nucleic acids. Only a small fraction of pDCs produces high levels of IFN-I, yet neither the molecular basis nor the purpose of this functional heterogeneity are known. We report that naive murine pDCs comprise three transcriptionally (but not epigenetically) distinct subsets. This heterogeneity is generated by tonic IFN-I signaling elicited in part by the cGAS/STING and TLR9 pathways. A small "IFN-I-naive" subset (pDC-A) was expanded in STING deficiency or after transient IFN-I receptor blockade, but was abolished by exogenous IFN-I. pDC-A showed strong cytokine responses yet were susceptible to infection with vesicular stomatitis virus (VSV). Conversely, the majority of pDCs comprised the "IFN-I-primed" subsets (pDC-B/C) that showed lower IFN-I responses but were resistant to VSV. Thus, tonic IFN-I signaling decreases the cytokine-producing capacity of pDCs but increases their virus resistance, achieving the optimal functional balance for antiviral responses.