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Published on: November 28, 2015
Enterococcus faecalis sustained infection induces macrophage pro-resolution polarization
David Polak1, Alin Yaya1,2, Dan Henry Levy3
1Department of Periodontology, Jerusalem, Israel.
Aim:
To investigate macrophage function in the presence of sustained infection with Enterococcus faecalis, a prevalent root canal resident in asymptomatic apical periodontitis.
Methodology:
The human monocyte cell line (THP-1) was differentiated into macrophages by exposure to phorbol myristate acetate (PMA), and the cultures were inoculated with E. faecalis for up to 48 h. At three time-points 90 min, 24 and 48 h after inoculation, the macrophages and their supernatants were examined. Assays included macrophage phagocytosis rate and vitality, bacterial survival, reactive oxygen species (ROS) production, mitochondrial activity, cytokine production and the expression of pro/anti-inflammatory M1/M2 markers. Also, periapical tissue from apicectomy samples of human endodontically treated teeth were collected for histological and immunofluorescent analysis. Statistical differences were analysed with RM ANOVA.
Results:
E. faecalis were phagocytized, and subsequently, most of the macrophages underwent apoptosis and necrosis. The small population of macrophages that remained vital after 48 h post-inoculation harboured surviving bacteria. Despite a reduction in the number of macrophages over time, the mitochondrial activity of the surviving macrophages remained constant and external ROS decreased, whereas internal ROS increased. During the infection, a shift to a M2 macrophage population at 48 h post-infection was observed; the results were similar to those obtained in periapical human tissue biopsies (p < .05).
Conclusions:
The study portrays a continuous non-resolved infection with E. faecalis and activation of macrophages that are polarized to the M2 pro-resolution phenotype.
Insights
Enterococcus faecalis infection causes macrophage death, but survivors harbor bacteria and shift to a pro-resolution M2 phenotype, indicating unresolved infection in apical periodontitis.
Area of Science:
- Oral microbiology
- Immunology
- Endodontics
Background:
- Enterococcus faecalis is a common bacterium in persistent root canal infections.
- Asymptomatic apical periodontitis often involves chronic inflammation and bacterial presence.
Purpose of the Study:
- To examine macrophage responses during sustained Enterococcus faecalis infection.
- To understand macrophage polarization and function in the context of apical periodontitis.
Main Methods:
- THP-1 macrophages were infected with E. faecalis.
- Assessed phagocytosis, bacterial survival, ROS production, mitochondrial activity, and M1/M2 marker expression.
- Analyzed periapical tissue samples from human biopsies.
Main Results:
- E. faecalis induced macrophage apoptosis and necrosis.
- Surviving macrophages harbored bacteria, maintained mitochondrial activity, and showed increased internal ROS.
- A polarization towards M2 macrophages occurred, mirroring findings in human periapical tissues.
Conclusions:
- Sustained E. faecalis infection leads to macrophage death and a shift to an M2 pro-resolution phenotype.
- This suggests a non-resolved infectious process in apical periodontitis.
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