We demonstrate that exposure to the AB5 subtilase cytotoxin (SubAB) induces the unfolded protein response (UPR) in human peripheral blood mononuclear cells, concomitant with a proinflammatory response across distinct cell subsets. Notably, SubAB selectively induces type-I interferon (IFN) expression in plasmacytoid dendritic cells, acting synergistically with Toll-like receptor 7 stimulation. The induction of type-I IFN in response to SubAB relies on stimulator of interferon genes (STING) activation, coupled with protein synthesis inhibition mediated by protein kinase R-like endoplasmic reticulum kinase (PERK) and phosphorylation of the eukaryotic translation initiation factor 2 subunit-alpha. By impeding mRNA translation through the integrated stress response, SubAB precipitates the downregulation of the negative innate signaling feedback regulator Tax1-binding protein 1. This downregulation is necessary to unleash TANK-binding kinase 1 signaling associated with STING activation. These findings shed light on how UPR-inducing conditions may regulate the immune system during infection or pathogenesis.