Listeria monocytogenes-Infected Human Peripheral Blood Mononuclear Cells Produce IL-1β, Depending on Listeriolysin O and NLRP3

Abstract

Different NOD-like receptors, including NLRP1, NLRP3, and NLRC4, as well as the recently identified HIN-200 protein, AIM2, form multiprotein complexes called inflammasomes, which mediate caspase-1–dependent processing of pro-IL-1β. Listeria monocytogenes is an intracellular pathogen that is actively phagocytosed by monocytes/macrophages and subsequently escapes from the phagosome into the host cell cytosol, depending on its pore-forming toxin listeriolysin O (LLO). In this study, we demonstrate that human PBMCs produced mature IL-1β when infected with wild-type L. monocytogenes or when treated with purified LLO. L. monocytogenes mutants lacking LLO or expressing a noncytolytic LLO as well as the avirulent Listeria innocua induced strongly impaired IL-1β production. RNA interference and inhibitor experiments in human PBMCs as well as experiments in Nlrp3 and Rip2 knockout bone marrow-derived macrophages demonstrated that the Listeria-induced IL-1β release was dependent on ASC, caspase-1, and NLRP3, whereas NOD2, Rip2, NLRP1, NLRP6, NLRP12, NLRC4, and AIM2 appeared to be dispensable. We found that L. monocytogenes-induced IL-1β production was largely dependent on phagosomal acidification and cathepsin B release, whereas purified LLO activated an IL-1β production independently of these mechanisms. Our results indicate that L. monocytogenes-infected human PBMCs produced IL-1β, largely depending on an LLO-mediated phagosomal rupture and cathepsin B release, which is sensed by Nlrp3. In addition, an LLO-dependent but cathepsin B-independent NLRP3 activation might contribute to some extent to the IL-1β production in L. monocytogenes-infected cells.

Aggregatibacter actinomycetemcomitans targets NLRP3 and NLRP6 inflammasome expression in human mononuclear leukocytes

“…These results are in agreement with the up-regulation of NLRP3 [26] and down-regulation of ASC [26,54] in myelomonocytic Monomac-6 or monocytic THP1 cells, by the major periodontal pathogen Porphyromonas gingivalis. Similar findings were are also demonstrated in another experimental system, in which Listeria monocytogenes is shown to up-regulate NLRP3, but down-regulate NLRP6 and ASC expression in human peripheral blood mononuclear cells [55]. In contrast, in gingival epithelial cells P. gingivalis down-regulates NLRP3 expression, but it does not affect ASC [56], denoting that inflammasome responses to a given species may as well be cell-type specific.…”

Listeria monocytogenes engineered to activate the Nlrc4 inflammasome are severely attenuated and are poor inducers of protective immunity

“…Maintenance of its intracellular replication niche is essential to L. monocytogenes virulence as strains that fail to compartmentalize LLO activity to the phagosome are cytotoxic and highly attenuated (16). Nevertheless, there have been numerous reports that L. monocytogenes infection leads to activation of multiple inflammasomes in vitro, including the Nlrp3, Nlrc4, and AIM2 inflammasomes (17)(18)(19)(20)(21)(22)(23). Although these responses can be detected in vitro, the role of inflammasome activation and pyroptosis during in vivo infections is not appreciated.…”

Caspases as the Key Effectors of Inflammatory Responses Against Bacterial Infection

“…Accumulating evidence indicates that NLRP3 inflammasomes play a significant role in the recognition of and response to bacterial infection. Although there is no direct evidence for the interaction of bacterial ligands with NLRP3, a variety of pathogenic bacteria including Staphylococcus aureus (Craven et al 2009;Holzinger et al 2012;Kebaier et al 2012;Maher et al 2013;McGilligan et al 2013;Muñoz-Planillo et al 2009), Streptococcus pneumoniae (Hoegen et al 2011;McNeela et al 2010;Witzenrath et al 2011) and Listeria monocytogenes (Meixenberger et al 2010) have been Arch. Immunol.…”