Elsevier

Journal of Endodontics

Volume 38, Issue 3, March 2012, Pages 346-350
Journal of Endodontics

Basic Research
Bacteria-reactive Immune Response May Induce RANKL-expressing T Cells in the Mouse Periapical Bone Loss Lesion

https://doi.org/10.1016/j.joen.2011.12.029Get rights and content

Abstract

Introduction

The present study investigated whether bacteria infecting the root canal can activate any infiltrating T cells to produce receptor activator of nuclear factor kappa B (NF-κB) ligand (RANKL).

Methods

Using a mouse model of periapical lesion induced by artificial dental pulp exposure, the presence of RANKL-positive T cells and osteoclasts in the periapical lesion was examined by an immunohistochemical approach. The bacteria colonizing the exposed root canal were identified by 16S ribosomal RNA (rRNA) sequence analysis. The isolated endodontic bacteria were further immunized to normal mice, and soluble activator of NF-κB ligand (sRANKL) production by the T cells isolated from the immunized mice was evaluated by ex vivo culture system.

Results

RANKL-positive T cells along with TRAP+ osteoclasts were identified in periapical bone resorption lesions. The gram-negative bacterium Pasteurella pnumotropica, which was most frequently detected from the root canal of exposed pulp, showed remarkably elevated serum immunoglobulin G (IgG)-antibody response in pulp-exposed mice compared with control nontreated mice. Immunization of mice with P. pneumotropica induced not only serum IgG-antibody but also primed bacteria-reactive T cells that produced sRANKL in response to ex vivo exposure to P. pneumotropica.

Conclusions

T cells infiltrating the periapical region express RANKL, and the endodontic bacteria colonizing the root canal appear to induce RANKL expression from bacteria-reactive T cells, suggesting the possible pathogenic engagement of the immune response to endodontic bacteria in the context of developing bone resorptive periapical lesions.

Section snippets

Animals

C57BL/6j mice (8-week-old males) were kept in the Forsyth Animal Facility. The experimental protocols used in this study were approved by the Forsyth Institutional Animal Care and Use Committee.

Induction of Periapical Lesion

Periapical lesions were induced by pulp exposure of the mandibular first molar pulps of mice (n = 5/group) following the protocol published previously (15). Both sides of mandibular first molars were exposed using a ¼-size dental round bur. Three groups of animals receiving pulp exposure were sacrificed

Pulp Exposure Induces Inflammatory Tissue Disruption in Periapical Lesions

On day 3 after pulp exposure, the periodontal ligament space at the apex of teeth was enlarged (Fig. 1B) compared with control healthy tissue (Fig. 1A). Newly formed blood vessels were also observed in the periapical lesion (Fig. 1B), indicating the induction of the primary inflammatory response by pulp exposure. At day 7, remarkable inflammatory cell infiltration was observed in the periapical lesion (Fig. 1C). Furthermore, substantial bone resorption was found at the apical area at day 14 (

Discussion

This study showed that CD3+ T cells produce RANKL in the periapical lesion with resulting pathogenic bone resorption. The infiltration of RANKL-expressing CD3+ T cells in the periapical lesion peaked between days 3 and 7, whereas such infiltration remitted to baseline by day 14 after pulp exposure. The inflammatory cell infiltration in the lesion occurring within the first 3 days after pulp exposure appears to be composed of innate immune cells (Fig. 1B), some of which, probably macrophages,

Conclusion

Specific bacterial invasion into root canals activates an adaptive immune response, which results in the induction of RANKL-producing, bacteria-specific memory T cells, possibly contributing to osteoclast-mediated bone resorption in the periapical lesion.

Acknowledgments

The authors deny any conflicts of interest related to this study.

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  • MicroRNA-335-5p Plays Dual Roles in Periapical Lesions by Complex Regulation Pathways

    2017, Journal of Endodontics
    Citation Excerpt :

    In line with these reports, our results showed secretions of IL-6 and TNF-α were decreased by uPAR siRNA under inflammatory conditions, indicating its proinflammatory role in HPDLF inflammation. RANKL, an important mediator in the activation of osteoclasts, has been reported to be highly associated with alveolar bone resorption in rat periapical lesions (32, 33). Recent studies showed miR-335-5p positively regulates MSC chondrogenesis and osteogenesis, whereas others demonstrated miR-335-5p inhibits both adipogenic and osteogenic differentiation of MSCs and abolishes the in vivo chondro-osseous potential of hMSCs (13, 15, 16, 34).

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Supported by grants DE-18499 and DE-19917 from the National Institute of Dental and Craniofacial Research and Krakow Harvard/Forsyth Endowed Endodontic Research Fund.

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