Abstract
Outer membrane vesicles (OMVs) are proteoliposomes blebbed from the surface of Gram-negative bacteria. Chronic periodontitis is associated with an increase in subgingival plaque of Gram-negative bacteria, Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia. In this study, we investigated the immune-modulatory effects of P. gingivalis, T. denticola, and T. forsythia OMVs on monocytes and differentiated macrophages. All of the bacterial OMVs were phagocytosed by monocytes, M(naïve) and M(IFNγ) macrophages in a dose-dependent manner. They also induced NF-κB activation and increased TNFα, IL-8, and IL-1β cytokine secretion. P. gingivalis OMVs were also found to induce anti-inflammatory IL-10 secretion. Although unprimed monocytes and macrophages were resistant to OMV-induced cell death, lipopolysaccharide or OMV priming resulted in a significantly reduced cell viability. P. gingivalis, T. denticola, and T. forsythia OMVs all activated inflammasome complexes, as monitored by IL-1β secretion and ASC speck formation. ASC was critical for OMV-induced inflammasome formation, while AIM2−/− and Caspase-1−/− cells had significantly reduced inflammasome formation and NLRP3−/− cells exhibited a slight reduction. OMVs were also found to provide both priming and activation of the inflammasome complex. High-resolution microscopy and flow cytometry showed that P. gingivalis OMVs primed and activated macrophage inflammasomes in vivo with 80% of macrophages exhibiting inflammasome complex formation. In conclusion, periodontal pathogen OMVs were found to have significant immunomodulatory effects upon monocytes and macrophages and should therefore influence pro-inflammatory host responses associated with disease.
Highlights
Chronic periodontitis is an inflammatory disease of the periodontal tissues associated with an increase in Gram-negative bacteria within the subgingival plaque biofilm; in particular, proportional increases in the pathogenic species Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia [1,2,3]
To investigate early Outer membrane vesicles (OMVs) interactions with THP-1 monocytes, M, and differentiated M (IFNγ) macrophages, OMVs from P. gingivalis, T. denticola, and T. forsythia were labeled with lipid fluorescent dye PKH26 and binding determined by flow cytometry
Periodontal bacteria OMVs were found to bind to monocytes, phorbol 12-myristate 13-acetate (PMA)-treated M(naïve), and cytokine-treated M(IFNγ) macrophages in a dose-dependent manner (Figure 1)
Summary
Chronic periodontitis is an inflammatory disease of the periodontal tissues associated with an increase in Gram-negative bacteria within the subgingival plaque biofilm; in particular, proportional increases in the pathogenic species Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia [1,2,3]. OMVs Activate Macrophage Inflammasome membrane vesicles (OMVs), are released from the subgingival plaque into the subjacent connective tissue where they induce a pro-inflammatory host response [4]. Inflammasome activation triggers a form of inflammatory cell death, termed pyroptosis, which promotes the rapid release of cytosolic contents (including IL-1β) primarily due to Caspase1-induced pores in the cell membrane [25], other caspases are known to perform this role [26]. Inflammasome components Caspase-1, NLRP3, and AIM2 have been shown to be upregulated in the gingival tissue of periodontitis patients, suggesting that macrophage inflammasome activation may play a significant role in periodontal immune responses [31]
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