Single-cell analysis reveals stochastic regulation of type I IFN production by plasmacytoid dendritic cells and identifies host-derived environmental cues as amplifier of type I IFN production

Type I interferon (IFN) is a key driver of immunity to infections and cancer. Plasmacytoid dendritic cells (pDCs) are uniquely equipped to produce large quantities of type I IFN but the mech-anisms that control this process are poorly understood. Here, we developed a droplet-based microfluidic platform and investigated type I IFN production in human pDCs at the single-cell level. We show that type I IFN but not TNF alpha production is limited to a small subpopulation of individually stimulated pDCs and controlled by stochastic gene regulation. Combining single-cell cytokine analysis with single-cell RNA-seq profiling reveals no evidence for a pre-existing subset of type I IFN-producing pDCs. Intriguingly, by modulating the droplet microenvironment, we demonstrate that vigorous pDC population responses are driven by a type I IFN amplification loop. Our study highlights the significance of stochastic gene regulation and suggests strategies to dissect the characteristics of immune responses at the single-cell level. Examination of the transcriptional profiles from single human plasmacytoid dendritic cells that were stimulated with CpG-C