IFNβ expression is restricted to a subpopulation of splenic pDCs exhibiting a specific immune modulatory transcriptome signature

Type I IFNs are critical in initiating protective antiviral immune responses and plasmacytoid DCs (pDCs) represent a major source of these cytokines. Here we show that only few pDCs are capable to produce IFNβ after virus infection or CpG stimulation. Utilizing IFNβ/YFP reporter mice, we identify these IFNβ-producing cells in the spleen as a CCR9+CD9- pDC subset exclusively localized within the T/B cell zones. IFNβ-producing pDCs exhibit a distinct transcriptome profile with higher expression of genes encoding cytokines and chemokines, facilitating T cell recruitment and activation. These distinctive characteristics of IFNβ-producing pDCs are independent of the type I IFN receptor mediated feedback loop. Furthermore, IFNβ-producing pDCs exhibit enhanced CCR7-dependent migratory properties in vitro and in a peritoneal inflammation model they effectively recruit T cells in vivo. We define “professional type I IFN-producing cells” as a distinct subset of pDCs specialized in coordinating cellular immune responses. IFNβ associated gene expression in ex vivo sorted IFNβ/YFPpos vs. IFNβ/YFPneg splenic pDCs was measured at 6 hr after i.v. injection of CpG 1668 complexed to DOTAP. Two independent experiments were performed using pooled samples of at least 12 mice per experiment.