The adaptor ASC exacerbates lethal Listeria monocytogenes infection by mediating IL‐18 production in an inflammasome‐dependent and ‐independent manner

Abstract

Listeria monocytogenes induces the formation of inflammasomes and subsequent caspase-1 activation, and the adaptor apoptosis-associated speck-like protein containing a CARD (ASC) is crucial for this response. However, the role of ASC in L. monocytogenes infection in vivo is unclear. In this study, we demonstrate that ASC has a detrimental effect on host defense against L. monocytogenes infection at a lethal dose (10 6 CFU), but not at a sublethal dose (10 3 CFU). During lethal L. monocytogenes infection, serum levels of IL-18 and IL-10 were markedly elevated in WT mice, but not in ASC KO mice. IL-18 KO mice were more resistant to lethal L. monocytogenes infection than WT mice and had lower levels of serum IL-10. Furthermore, blockade of IL-10 receptor resulted in a reduction in bacterial counts, suggesting that ASC and IL-18 might exacerbate L. monocytogenes infection through induction of IL-10. We noticed that maturation of IL-18 during lethal infection was partially independent of caspase-1, but was critically dependent on ASC. ASC was required for the elevation of serum neutrophil serine protease activity, which correlated with caspase-1-independent IL-18 maturation and IL-10 production. Collectively, these results suggest that ASC plays a detrimental role in lethal L. monocytogenes infection through IL-18 production in an inflammasome-dependent and -independent manner.Keywords: ASC r Caspase-1 r IL-18 r Inflammasome r Listeria monocytogenes Additional supporting information may be found in the online version of this article at the publisher's web-site IntroductionListeria monocytogenes is a Gram-positive, intracellular parasitic bacterium, which causes foodborne listeriosis in humans Correspondence: Dr. Kohsuke Tsuchiya e-mail: tsuchiya.kohsuke.5w@kyoto-u.ac.jp [1,2]. Listeria monocytogenes invades and multiplies within the cytoplasm of various types of cells, including macrophages, epithelial cells, and hepatocytes [3,4]. Several virulence factors have been reported to support the intracellular parasitism of L. monocytogenes at various steps, including invasion of host cells, escape from endosomal compartments, evasion of autophagy, utilization of cytosolic nutrient sources, and cell-to-cell spread [3,4].C 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu Eur. J. Immunol. 2014. 44: 3696-3707 Innate immunity 3697Listeriolysin O, a 56 kDa protein encoded by the hly gene, is a member of the cholesterol-dependent cytolysin family and plays an essential role in the escape of L. monocytogenes from phagosomes, because mutant strains lacking the hly gene are avirulent and incapable of escaping from phagosomes and of multiplying in host phagocytes [3][4][5][6]. Inflammasomes are multiprotein complexes formed typically in the cytoplasm and serve as platforms for caspase-1 activation [7]. Each inflammasome consists of pro-caspase-1 and a receptor protein that belongs to the nucleotide-binding oligomerization domain like receptor (NLR) family or the HIN-200 family. Among NLR family, CARD domain cont...

Listeria monocytogenes and the Inflammasome: From Cytosolic Bacteriolysis to Tumor Immunotherapy

“…As such, ASC −/− peritoneal macrophages fail to activate Caspase-1 or secrete IL-1β and IL-18 (Ozören et al 2006). Consistent with observations that loss of Caspase-1 has no effect on L. monocytogenes virulence in vivo (Sauer et al 2011a; Tsuchiya et al 2014), loss of ASC results in similar susceptibility to L. monocytogenes (Sauer et al 2011a). Interestingly, recent work by Tsuchiya suggests that ASC deficiency may in some cases result in enhanced host protection during L. monocytogenes infection (Tsuchiya et al 2014).…”

“…Consistent with observations that loss of Caspase-1 has no effect on L. monocytogenes virulence in vivo (Sauer et al 2011a; Tsuchiya et al 2014), loss of ASC results in similar susceptibility to L. monocytogenes (Sauer et al 2011a). Interestingly, recent work by Tsuchiya suggests that ASC deficiency may in some cases result in enhanced host protection during L. monocytogenes infection (Tsuchiya et al 2014). ASC −/− mice are able to withstand a bacterial load of 1×10 6 colony forming units (CFU) of L. monocytogenes , a log higher than the LD 50 for wild-type C57Bl/6 mice, and harbor lower bacteria burdens in their livers.…”

“…While these observations were made in initial reports, the authors also observed decreases in TNFα production, another critical cytokine in innate susceptibility, and suggest that the corresponding lack of TNFα from IL-18 deprived mice is largely what is responsible for susceptibility to infection. More recent studies in both IL-18 −/− and IL-18Rα −/− contradict these earlier results and suggest that IL-18 −/− mice are actually more resistant to L. monocytogenes , particularly at high doses (Lochner et al 2008; Tsuchiya et al 2014). These results are in line with reports that suggest that ASC −/− mice, which also lack IL-18 secretion, are less susceptible to L. monocytogenes (Tsuchiya et al 2014).…”

“…While these initial experiments suggest a critical role for Casapse-1/11 in controlling L. monocytogenes infection, further experiments have failed to find a similar role. Both Sauer et al (2011) and Tsuchiya et al (2014) observed no increased susceptibility to L. monocytogenes in Caspase-1/11 −/− mice at 2 days post infection. Similarly, there was no increased susceptibility to L. monocytogenes in zebrafish lacking Caspase-1 (Vincent et al 2015).…”

“…ASC −/− mice are able to withstand a bacterial load of 1×10 6 colony forming units (CFU) of L. monocytogenes , a log higher than the LD 50 for wild-type C57Bl/6 mice, and harbor lower bacteria burdens in their livers. The investigators report that ASC promotes production of the anti-inflammatory cytokine IL-10, and that protection in ASC deficient mice is likely due to reduced IL-10 production (Tsuchiya et al 2014). Taken together, these results suggest that similar to loss of Caspase-1, loss of ASC does not promote the virulence of L. monocytogenes, and in fact may result in enhanced protection, although this phenotype may be independent of ASC’s role in Caspase-1 activation (Tsuchiya et al 2014).…”