Abstract Plasmacytoid dendritic cells(pDCs) function as sentinels against viral infection in humans by producingabundant amounts of Type-I and Type-III interferons as well as other cytokines. Detection of viral nucleic acids remains the major initiating factor forinterferon and cytokine production in pDCs. Although the Toll-likereceptor-mediated endosomal pathway of nucleic acid detection has been studiedand documented in great detail, detection of cytoplasmic DNA in human pDCsremains, for the most part, unexplored. Recently, a cytoplasmic pathway of DNArecognition and interferon expression has been discovered in the murine systemand certain human cell lines. This pathway is mediated by the cytoplasmicprotein cGAMP synthetase (cGAS), which initiates Type-I interferon productionvia a cyclic dinucleotide called 2′3′ cyclic GMP-AMP (cGAMP), which in turn,activates the endoplasmic reticulum resident protein Stimulator of InterferonGenes (STING) and leads to cytokine expression. Here, for the first time, wedemonstrate the existence of components of the cGAS/STING pathway present inhuman pDCs. Our data indicate that both cGAS and STING are transcribed and translatedin primary human pDCs. We have also confirmed the functionality of the pathwayby inducing cytokine (IFN-α, IFN-λ, TNF-α, IL-6) production through stimulatingpDCs by exogenous cGAMP. Our study suggests that this cGAS-STING-mediatedcytokine response exists in parallel to the TLR9-mediated DNA recognition andimmune activation in human pDCs.