Cutting Edge: TNF-α Mediates Sensitization to ATP and Silica via the NLRP3 Inflammasome in the Absence of Microbial Stimulation

The Nlrp3 inflammasome is critical for the activation of caspase-1 in response to danger signals and particulate matter. However, its role in sterile inflammation remains unclear because prestimulation of phagocytic cells with microbial molecules is required for caspase-1 activation. We show here that exposure of macrophages and dendritic cells to TNF-alpha promotes ATP- or silica-mediated caspase-1 activation and IL-1 beta secretion in the absence of microbial stimulation. The effect of TNF-alpha was abolished in macrophages deficient in TNF receptor I and II, Nlrp3, or ASC, whereas that induced by TLR ligands required MyD88/Trif. In addition to TNF-alpha, IL-1 alpha and IL-1 beta promoted caspase-1 activation via Nlrp3 in response to ATP. Remarkably, macrophages tolerized to TNF-alpha, but not to LPS, retained full sensitivity to ATP stimulation via NIrp3. These results provide a mechanism by which danger signals and particulate matter mediate inflammation via the Nlrp3 inflammasome in the absence of microbial infection. The Journal of Immunology, 2009, 183: 792-796.