Cutting Edge: IFN-β Expression in the Spleen Is Restricted to a Subpopulation of Plasmacytoid Dendritic Cells Exhibiting a Specific Immune Modulatory Transcriptome Signature.

Type I IFNs are critical in initiating protective antiviral immune responses, and plasmacytoid dendritic cells (pDCs) represent a major source of these cytokines. We show that only few pDCs are capable of producing IFN-β after virus infection or CpG stimulation. Using IFNβ/YFP reporter mice, we identify these IFN-β-producing cells in the spleen as a CCR9(+)CD9(-) pDC subset that is localized exclusively within the T/B cell zones. IFN-β-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 IFN-β-producing pDCs are independent of the type I IFNR-mediated feedback loop. Furthermore, IFN-β-producing pDCs exhibit enhanced CCR7-dependent migratory properties in vitro. Additionally, they effectively recruit T cells in vivo in a peritoneal inflammation model. We define "professional type I IFN-producing cells" as a distinct subset of pDCs specialized in coordinating cellular immune responses.