Brucella abortus Triggers a cGAS-Independent STING Pathway To Induce Host Protection That Involves Guanylate-Binding Proteins and Inflammasome Activation

Immunity against microbes depends on recognition of pathogen-associated molecular patterns by innate receptors. Signaling pathways triggered by DNA involves TLR9, AIM2, and stimulator of IFN genes (STING). In this study, we observed by microarray analysis that several type I IFN-associated genes, such as IFN-β and guanylate-binding proteins (GBPs), are downregulated in STING knockout (KO) macrophages infected with or transfected with DNA. Additionally, we determined that STING and cyclic GMP-AMP synthase (cGAS) are important to engage the type I IFN pathway, but only STING is required to induce IL-1β secretion, caspase-1 activation, and and expression. Furthermore, we determined that STING but not cGAS is critical for host protection against infection in macrophages and This study provides evidence of a cGAS-independent mechanism of STING-mediated protection against an intracellular bacterial infection. Additionally, infected IFN regulatory factor-1 and IFNAR KO macrophages had reduced and expression and these cells were more permissive to replication compared with wild-type control macrophages. Because GBPs are critical to target vacuolar bacteria, we determined whether GBP2 and GBP affect control in vivo. GBP but not GBP2 KO mice were more susceptible to bacterial infection, and small interfering RNA treated-macrophages showed reduction in IL-1β secretion and caspase-1 activation. Finally, we also demonstrated that DNA colocalizes with AIM2, and AIM2 KO mice are less resistant to infection. In conclusion, these findings suggest that the STING-dependent type I IFN pathway is critical for the GBP-mediated release of DNA into the cytosol and subsequent activation of AIM2.