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Activation of the Nlrp3 Inflammasome by Streptococcus pyogenes Requires Streptolysin O and NF-B Activation but Proceeds Independently of TLR Signaling and P2X7 Receptor¹

Department of Pathology and Comprehensive Cancer Center, University of Michigan Medical School, Ann Arbor, MI 48109

Macrophages play a crucial role in the innate immune response against the human pathogen Streptococcus pyogenes, yet the innate immune response against the bacterium is poorly characterized. In the present study, we show that caspase-1 activation and IL-1β secretion were induced by live, but not killed, S. pyogenes, and required expression of the pore-forming toxin streptolysin O. Using macrophages deficient in inflammasome components, we found that both NLR family pyrin domain-containing 3 (Nlrp3) and apoptosis-associated speck-like protein (Asc) were crucial for caspase-1 activation and IL-1β secretion, but dispensable for pro-IL-1β induction, in response to S. pyogenes infection. Conversely, macrophages deficient in the essential TLR adaptors Myd88 and Trif showed normal activation of caspase-1, but impaired induction of pro-IL-1β and secretion of IL-1β. Notably, activation of caspase-1 by TLR2 and TLR4 ligands in the presence of streptolysin O required Myd88/Trif, whereas that induced by S. pyogenes was blocked by inhibition of NF-B. Unlike activation of the Nlrp3 inflammasome by TLR ligands, the induction of caspase-1 activation by S. pyogenes did not require exogenous ATP or the P2X7R. In vivo experiments revealed that Nlrp3 was critical for the production of IL-1β but was not important for survival in a mouse model of S. pyogenes peritoneal infection. These results indicate that caspase-1 activation in response to S. pyogenes infection requires NF-B and the virulence factor streptolysin O, but proceeds independently of P2X7R and TLR signaling.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ This work was supported by National Institutes of Health Grants AI063331 and AI064748. J.H. was supported by the Heisenberg Program of the Deutsche Forschungsgemeinschaft, L.F. by a Fellowship from the Arthritis Foundation, and T.R. by a Fellowship from the Swiss National Science Foundation.

² J.H. and L.F. contributed equally to the present work.

³ Address correspondence and reprint requests to Dr. Gabriel Núñez, Department of Pathology, University of Michigan Medical School, 4215 CCGC, 1500 E. Medical Center Drive, Ann Arbor, Michigan 48109. E-mail address: bclx{at}umich.edu

⁴ Abbreviations used in this paper: NLR, Nod-like receptor; Asc, apoptosis-associated speck-like protein; KO, knockout; Nlrp3, NLR family pyrin domain-containing 3; Nlrc4, NLR family CARD domain-containing 4; SLO, streptolysin O; SP, Streptococcus pyogenes; WT, wild type.

⁵ The online version of this article contains supplemental material.