Cutting Edge: TLR Signaling Licenses IRAK1 for Rapid Activation of the NLRP3 Inflammasome

Activation of the NLRP3 inflammasome by diverse stimuli requires a priming signal from TLRs and an activation signal from purinergic receptors or pore-forming toxins. In this study, we demonstrate, through detailed analysis of NLRP3 activation in macrophages deficient in key downstream TLR signaling molecules, that MyD88 is required for an immediate early phase, whereas Toll/IL-1R domain-containing adapter inducing IFN-beta is required for a subsequent intermediate phase of post-translational NLRP3 activation. Both IL-1R-associated kinase (IRAK) 1 and IRAK4 are critical for rapid activation of NLRP3 through the MyD88 pathway, but only IRAK1 is partially required in the Toll/IL-1R domain-containing adapter inducing IFN-beta pathway. IRAK1 and IRAK4 are also required for rapid activation of NLRP3 by Listeria monocytogenes, as deletion of IRAK1 or IRAK4 led to defective inflammasome activation. These findings define the pathways that lead to rapid NLRP3 activation and identify IRAK1 as a critical mediator of a transcription-independent, inflammasome-dependent early warning response to pathogenic infection.