The NLRP3 inflammasome is essential for IL-1β production in response to Enterohemorrhagic Escherichia coli (EHEC). To determine the mechanism of NLRP3 inflammasome activation by EHEC, we screened EHEC mutants lacking various virulence genes and found that none of them are essential for inflammasome activation. However, lysosomal acidification following infection was found to be essential for IL-1β production implying that bacterial lysis and its products such as nucleic acids play a role. Consistent with this, pretreating macrophages with RNase A specifically reduced EHEC-induced IL-1β response. Also, EHEC RNA was found to be co-localizing with NLRP3 in the cytosol, revealing a potential mechanism for NLRP3 activation. Interestingly, treating cells with RNase H, which degrades RNA of RNA:DNA hybrids, also markedly reduced IL-1β activation indicating that RNA:DNA hybrids formed as replication and transcription intermediates in bacteria also play a role in NLRP3 activation. Supporting this idea, synthetic EHEC RNA:DNA hybrids potently induced IL-1β production in a NLRP3-dependent manner. Importantly, an E. coli rnhA mutant incapable of producing RNase H induced greater than wild type levels of IL-1β and complementing this mutant with rnhA reduced IL-1β to wild type levels. Altogether these findings identify bacterial RNA:DNA hybrids as novel NLRP3 activators and demonstrate that multiple nucleic acid species such as RNA and RNA:DNA hybrid activate NLRP3 in bacterial infections.
- Copyright © 2013 by The American Association of Immunologists, Inc.