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. Author manuscript; available in PMC: 2016 May 1.
Published in final edited form as: J Endod. 2015 Jan 30;41(5):646–651. doi: 10.1016/j.joen.2014.12.008

Intermittent Administration of Parathyroid Hormone Ameliorates Periapical Lesions in Mice

Masato Otawa *,†, Ryuichiro Tanoue *,‡, Hirofumi Kido †, Yoshihiko Sawa §, Junro Yamashita *
PMCID: PMC4410053  NIHMSID: NIHMS651297  PMID: 25649296

Abstract

Introduction

Intermittent administration of parathyroid hormone (PTH) promotes oral osseous wound healing and protects against ligature-induced alveolar bone loss. However, its therapeutic value on periapical periodontitis is unknown. The goal of this study was to determine the effect of intermittent PTH administration on the progression of periapical periodontitis.

Methods

Seven lymphotoxin alpha deficient mice received pulp exposures of mandibular first and second molars. Exposed pulp in the right mandible was covered with plaque-contaminated fibrin, while exposed pulp in the left mandible was left open. After four weeks, the periapical tissues were examined to determine the effect of plaque-contaminated fibrin to induce periapical lesions. Fourteen mice received pulp exposure covered with plaque-contaminated fibrin. PTH (40μg/kg/day) was administered intermittently to half of the mice for three weeks beginning one week after pulp exposure. The remaining half received saline injections as vehicle control. At sacrifice, mandibles and tibiae were harvested and processed for histological examination. Evaluation of neutrophils and blood vessels was performed after staining with immunofluorescence and periradicular bone was histomorphometrically analyzed.

Results

The exposed pulp covered with plaque-contaminated fibrin resulted in significantly larger periapical lesions compared to control. Intermittent PTH administration reduced the size of periapical lesions significantly. Significantly less neutrophil infiltration around the root apex was found in PTH-treated animals compared to control.

Conclusions

PTH treatment suppressed periapical inflammation by reducing neutrophil infiltration and protected against tissue destruction by periapical periodontitis.

Keywords: Periapical periodontitis, neutrophil infiltration, parathyroid hormone, lymphotoxin alpha

Introduction

Parathyroid hormone (PTH) increases bone mass when administered intermittently. Teriparatide, a recombinant form of human PTH (1-34), is used for the treatment of osteoporosis. While the mechanisms for the bone anabolic action of intermittent PTH are unclear, it is known to activate both osteoblasts and osteoclasts in favor of osteoblastic bone formation over osteoclastic resorption, resulting in an increase in total bone mass (1). PTH is effective in promoting fracture healing (2, 3). Such an enhanced osseous healing by PTH is seen in craniofacial bones as well where PTH administration promotes bone fill and growth in tooth extraction sockets (4, 5). Barros et.al. reported that intermittent PTH administration protected ligature-induced bone loss in a rat model of periodontitis (6). In that study the numbers of inflammatory cells were significantly reduced in the PTH-treated group compared to control. Likewise, we have discovered that intermittent PTH administration promotes tooth extraction socket healing in rodents (7, 8). PTH-promoted tooth extraction wound healing was accompanied with decreased inflammatory cell infiltration. These findings imply that intermittent PTH administration may have protective effects against inflammation-induced bone loss in the oral cavity.

Periapical periodontitis is an inflammatory disease resulting from root canal infections by mainly anaerobic microorganisms (9-11). Such microorganisms, their endotoxin and enzymes together, stimulate periapical tissues and alert the host defense mechanism (12, 13). Neutrophils play a crucial role in orchestrating the host defense system starting from the early phase of periapical infection. Neutrophils are phagocytes which fight against microorganisms but also cause host tissue breakdown due to their release of pro-inflammatory cytokines, chemokines and proteinases (14, 15). Therefore, suppression of the intensity of inflammatory responses in periapical tissues which is orchestrated by neutrophils would lead to reduced damage in the host tissues. In this study, we hypothesized that intermittent administration of PTH protects against tissue damage caused by apical periodontitis. Using lymphotoxin alpha (LTA) deficient mice, which exhibit defects in secondary lymphoid structures and therefore in adaptive immune responses (16), periapical periodontitis was induced and the effect of PTH administration on the disease progression of periapical periodontitis was determined.

Materials and Methods

Experimental Design

A breeding pair of mice homozygous mutant for LTA (B6.129S2-Ltatm1Dch/J) was obtained from Jackson Laboratory (Bar Harbor, ME). Twenty-one offspring at the age of 8 weeks were used. Seven mice were subjected to pulp exposure of the mandibular molars to assess the effect of plaque contamination and confirm the development of periapical lesions (Supplement A). Fourteen mice were subjected to pulp exposure with plaque contamination to induce periapical lesions. Subsequently, daily injections of either PTH or saline were performed for 3 weeks to evaluate the therapeutic value of PTH treatment on periapical lesions (Supplement B). The experimental protocol was approved and all animals were treated in accordance with the guidelines of the University Committee on Use and Care of Animals.

Mouse Model of Periapical Lesions

Mice were subjected to ligature placement (5/0 Silk) around each of the maxillary second molars five days before pulp exposure (17). On the day of pulp exposure, the ligatures were removed and one ligature was placed in a tube with 1.0 mL of saline and vortexed, while the other was either used as a backup or discarded. Half of the plaque/saline-mixed solution (0.5 mL) was transferred to another tube and centrifuged. The pelleted plaque was mixed with 10μL of fibrinogen solution (Sigma-Aldrich, St. Louis, MO) and placed on ice until use. The pulp exposure of the mandibular first and second molars were conducted with a dental handpiece and 1/4 round bur in seven mice. The exposed pulp in the left mandible was left open to the oral environment. The exposed dental pulp in the right mandible was covered with 2 μL of the plaque/fibrinogen mixture followed by 5 μL of thrombin (Sigma-Aldrich). Mice were euthanized four weeks after pulp exposure to assess the effect of plaque-contaminated fibrin on the development of periapical lesions.

Injections and Euthanasia

Fourteen mice received pulp exposure covered with plaque-contaminated fibrin as described above to induce periapical lesions. Daily subcutaneous injections of either PTH (1-34) (40μg/kg/day, Bachem, Torrance, CA) or equivalent volume of 0.9% saline as vehicle control (VC) for 3 weeks were performed starting one week after pulp exposure. The PTH dose of 40μg/kg/day is a commonly used subcutaneous dose to study bone anabolism by PTH in vivo (18, 19). Mice were euthanized with CO2 asphyxiation. The mandible and tibiae were harvested and fixed in 4% paraformaldehyde.

Histology

The mandibles and tibiae were decalcified in 10%ethylenediaminetertraacetic acid solution. The mandibles were processed for cryo-sectioning at 10 μm. The tibiae were paraffin-embedded and sectioned at 4 μm. Hematoxylin and eosin (HE) staining and tartrate-resistant acid phosphatase (TRAP) staining were performed on the mandibles and tibiae to identify periapical lesions, bone area, and osteoclasts. A commercial kit (Sigma-Aldrich) was used for TRAP staining following an adapted protocol (20). Immunofluorescent staining to visualize neutrophils and blood vessels was performed in the mandibular frozen sections. The sections were rehydrated, blocked with 10% serum, and incubated with primary antibodies overnight at 4°C. Primary antibodies used include anti-Ly6G (Abcam, Cambridge, MA) and anti-CD31 (Abcam). Following incubation, fluorescent-conjugated secondary antibody (AlexaFluor-594, Invitrogen, Carlsbad, CA) was applied. DAPI was used for nuclei visualization.

Histomorphometric Analysis

Stained sections were photomicrographed and histomorphometrically analyzed using Image-Pro Premier (Media Cybernetics, Bethesda, MD). The distance from the apex to the surrounding bone was measured at 7 different points at 10 degrees apart (Fig. 1A). The average distance was used to estimate the size of the periapical lesion. Bone quality around the root apex was analyzed to study the periapical pathosis in the local environment. The area of interest (AOI) was defined as an area within 0.4 mm of the bone surface facing the apex (Fig. 1B). Within this AOI, bone area/tissue area (BA/TA), the numbers of bone fragments, and osteoclast numbers per linear bone perimeter (Oc.N/BS) were measured. Neutrophils were assessed by measuring the distribution of Ly6G(+) cells, around the apex. The AOI for this measurement was defined as a semicircle with a radius of 0.6 mm below the apex (Fig. 1C). CD31(+) cells were histomorphometrically examined to understand the blood vessel formation in the lesions. BA/TA and Oc.N/BS were also determined in the proximal tibiae.

Figure 1. Exposed pulp covered with plaque-contaminated fibrin induced large periapical lesions.

Figure 1

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(A) Distance between the root apex and the surface of periradicular bone was measured at seven points and results averaged. The average was used as a representative distance to estimate the size of the lesion. (B) The bone tissue within 0.4 mm of the bone surface was defined as the area of Interest (AOI) for the measurements of the numbers of bone fragments, BA/TA, and Oc.N/BS. (C) The periapical soft tissue area in a semicircle with a radius of 0.6mm was defined as the AOI for the assessment of inflammatory cells and neutrophils. (D,E) Representative photomicrographs of HE-stained sections of periapical lesions (original magnification, x100). Arrowheads indicate inflammatory cell infiltration. (F) Tissue areas occupied by inflammatory cells were measured. Significantly larger inflammatory cell area was noted in the plaque-contaminated fibrin group than control. (G) Size of periapical lesions were assessed by measuring the distance between the apex and bone surface. Significantly larger periapical lesions were found in the plaque-contaminated fibrin group than control. (H) Ly6G(+) cells, which represent neutrophils, were assessed next to the apex. Significantly more neutrophils were observed in the plaque-contaminated fibrin group than control. (N=7/group; Paired t-test; *p<0.05, **p<0.01)

Statistical Analysis

Paired sample t-test was performed to assess the effect of the plaque-contaminated fibrin on the development of periapical lesions. Independent t-test was used to determine the effect of PTH treatment on periapical lesions. All statistical analysis was carried out with SYSTAT (Systat, Chicago, IL, USA). An α-level of 0.05 was used. Results are presented as mean ± SD.

Results

Plaque Contamination Induced Severe Periapical Lesions

The effect of plaque contamination of exposed pulp on the development of periapical lesions was determined. Inflammatory cell area was used as a surrogate for inflammatory cell numbers since cell aggregation was intensive. When exposed pulp was covered with plaque-contaminated fibrin, increased inflammatory cell area (Fig. 1D-F) and significantly larger periapical lesions (Fig. 1G) were noted compared to control in which the exposed pulp was left open. Immunohistochemical detections of Ly6G(+) cells revealed that significantly more neutrophil aggregation to the apex was observed in the plaque-contaminated group than control (Fig. 1H).

PTH Treatment Suppressed Tissue Destruction and Neutrophil Infiltration

The effect of PTH treatment on periapical lesions was assessed on the teeth with plaque-contaminated pulp. Figure 2A&B shows the HE-stained sections of periapical lesions. Significantly less inflammatory cell area was noted in in the PTH-treated animals than vehicle control (VC) (Fig. 2C). The average size of periapical lesions was found significantly smaller in the PTH-treated animals vs. VC (Fig. 2D). Significantly denser periradicular bone was noted in the PTH-treated animals than VC (Fig. 2E). Consistently, the numbers of bone fragments in the AOI was significantly less in the PTH-treated animals than VC (4.8±5.0* vs. 20.3±16.6). There were no differences in osteoclast numbers per linear perimeters between PTH and VC animals (Fig.2F). Figure 2G&H shows TRAP-stained sections of periapical lesions. Osteoclasts were mostly observed on the bone surfaces facing the root apex in both treatment groups.

Figure 2. PTH treatment protected periapical tissues from destruction.

Figure 2

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(A, B) Representative photomicrographs of HE-stained sections of periapical lesions (original magnification, x100). VC: Vehicle control (Saline) treatment, PTH: PTH treatment. Arrow heads indicate inflammatory cell infiltration. (C) The inflammatory cell area was significantly smaller in PTH-treated animals vs. control. (D) Size of periapical lesions were assessed by measuring the distance between the apex and bone surface. Significantly smaller periapical lesions were found in the PTH than VC group. (E) Periradicular bone was significantly denser in the PTH group compared to VC. (F) The numbers of osteoclasts per linear bone perimeters were measured. There was no difference between PTH-treated animals vs. control. (G, H) Representative photomicrographs of TRAP-stained sections of periapical lesions (original magnifications, x100). (N=7/group; Student t-test; *p<0.05, **p<0.01)

To better understand periapical pathosis, neutrophils were stained for Ly6G. As shown in Fig. 3A&B, intense Ly6G(+) cell aggregation was observed next to the root apex in the VC animals, while minimal Ly6G(+) cells were noted in the PTH-treated animals. Neutrophil (Ly6G(+) cell) area was significantly smaller in the PTH-treated animals than VC (Fig. 3E). Blood vessels were abundant around the periapical lesions but not inside the lesions (Fig. 3C&D). The numbers and areas of blood vessels were quantitated in the tissue area surrounding the lesion (0.05 mm band width). Significantly fewer blood vessels were noted in the PTH group than VC (Fig. 3F). Consistently, the total blood vessel area was significantly less in the PTH group vs. VC (Fig. 3G).

Figure 3. PTH treatment resulted in reduced neutrophil infiltration and blood vessels.

Figure 3

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(A, B) Representative immunofluorescent photomicrographs of Ly6G-stained sections of periapical lesions (bottom). DAPI staining was used for nuclei visualization (top) (original magnification, x200). VC: Vehicle control (Saline) treatment, PTH: PTH treatment. Dotted line indicates the tooth root near the apex. Arrow heads indicate inflammatory cell infiltration. Significantly smaller neutrophil area was found in the PTH-treated group than VC (E). (C, D) Representative immunofluorescent photomicrographs of CD31-stained sections of periapical lesions (bottom). DAPI staining was used for nuclei visualization (top) (original magnification, x200). No blood vessels were observed within the lesions. The numbers and areas of blood vessels around the lesions were significantly less in the PTH-treated group than VC (F, G). (N=7/group; Student t-test; *p<0.05, ***p<0.001)

PTH Treatment Increased Bone Mass in Long Bone

The effect of intermittent PTH administration on the skeleton of LTA deficient mice was examined in the proximal tibiae. PTH treatment significantly increased bone area compared to VC (Fig. 4A-C). Significantly larger osteoclast numbers per bone perimeters were noted in the PTH-treated animals compared to control (Fig. 4D).

Figure 4. PTH treatment increased bone area in long bones of LTA deficient mice.

Figure 4

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(A, B) Representative photomicrographs of HE-stained sections of proximal tibiae (original magnification, x40). VC: Vehicle control (Saline) treatment, PTH: PTH treatment. PTH treatment for 3 weeks significantly increased bone mass in the proximal tibia (C) with significantly more osteoclasts compared to VC (D). (N=7/group, student t-test, ***p<0.001)

Discussion

The most striking and clinically relevant finding is that PTH treatment protected periradicular tissues from destruction caused by periapical periodontitis. It was further found that neutrophil aggregation next to the root apex was greatly limited by PTH treatment compared to control, indicating reduced inflammation in the PTH-treated animals. These findings may suggest that intermittent PTH administration augments host innate immune responses. A link between PTH and immune function has been suggested since immune cells such as T and B lymphocytes and leukocytes express PTH receptors (21, 22) . In fact, neutrophils from patients with hyperparathyroidism exhibit defects in chemotaxis, migration, and phagocytosis (23-25) and these defects are rescued when parathyroidectomy is performed (26). Thus, the concept that PTH is a negative modifier of the host immune system has been established (27, 28). Contrary to this concept, our finding is that PTH may be a positive modifier in the immune system. The discrepancy may lie in a difference in systemic PTH levels. The above studies discuss PTH effects in the context of hyperparathyroidism in which systemic PTH levels are continuously elevated. In this study, PTH was administered intermittently and the peak of systemic PTH levels was for a moment a day. Thus, the curve of systemic PTH levels in our study would be quite different from those in patients with hyperparathyroidism. Barros et al. investigated the effect of intermittent PTH administration on bone loss induced by ligature-induced periodontitis and found that intermittent PTH protected against periodontitis-associated bone loss (6). Bashutski et al. reported that intermittent PTH administration resulted in significantly less attachment loss compared to control after periodontal surgery (29). Kuroshima et al. studied the effect of intermittent PTH administration in oral osseous wound healing and found that intermittent PTH rescued bisphosphonate-associated impaired wound healing in rats (7). These studies support our finding that intermittent PTH protected against tissue destruction caused by periapical periodontitis. It is known that the effect of PTH on the skeleton is a double edged sword; it is catabolic when administered continuously as seen in hyperparathyroidism, while it is anabolic when administered intermittently. We speculate that it is possible that the impact of PTH on the immune system could also be different depending on the administration regimen.

The bone anabolic effect of PTH was observed in LTA deficient mice, indicating that LTA is dispensable for PTH bone anabolic actions. PTH augmented bone mass with a significant increase in osteoclast numbers (Oc.N/BS) in tibiae. This indicates that PTH stimulated both bone formation and resorption in favor of formation. Different from tibiae, however, Oc.N/BS was similar in the periapical tissues between the PTH-treated and control animals. This is likely due to the induced severe periapical inflammation in VC. Since significantly more periapical bone resorption was noted in VC than PTH-treated animals, more osteoclasts were involved in VC, hence, increased osteoclast numbers in VC which resulted in no differences in periapical Oc.N/BS between the PTH-treated and control animals.

Conventionally, the dental pulp is exposed and left open to induce periapical lesions (30) or inoculated with specific pathogens such as Actinomyces viscosus, to secure the development of periapical lesions (31, 32). Although the specific anaerobic bacteria inoculation is an excellent method, it requires culturing specific bacteria. We set out to establish a simple and natural yet secure method to induce periapical lesions. In this study we covered exposed dental pulp with plaque-contaminated fibrin. Silk ligatures were used to isolate plaque. Plaque buildup begins soon after ligature placement. Although younger plaque is composed of mainly aerobic species, anaerobic species increases as plaque matures into biofilm. A study that analyzed the composition of bacteria species in silk ligatures placed in mouse molars shows a time-dependent accumulation of anaerobic bacteria (17). A peak of an accumulation of anaerobic bacteria in a ligature is at 5 days after ligature placement. Hence, in the current study silk ligatures were set on molars for 5 days pre-surgery to establish biofilm in which aerobic and obligatory anaerobic bacteria co-exist. In this study, significantly larger periapical lesions were observed in the plaque-contaminated fibrin group compared to the simple pulp exposure group. Thus, confirming that our method is useful to study periapical lesions.

It was considered in this study that simple pulp exposure alone would also trigger the development of periapical periodontitis (33). To confirm this, the average distance between the apex and the surrounding alveolar bone was assessed on the intact third molars and then compared to that on the pulp-exposed molars without plaque contamination. We found a trend that simple pulp exposure resulted in mild periapical bone destruction but the degree of the destruction did not reach a statistical difference when compared to the apical tissues of the intact molars (Supplement C). This finding indicates that simple pulp exposure may not be a predictable method to induce periapical periodontitis in LTA deficient mice. The method used in this study, pulp exposure with bacterial inoculation, proved to be a better protocol to study periapical periodontitis in these specific mice.

In a preliminary study, PTH effects on periapical periodontitis were investigated in wild type mice. Daily PTH treatment for 3 weeks significantly suppressed disease progression (supplement D). It is generally known that activated PMNs are involved in acute inflammation which results from innate immune responses to bacterial infection, while lymphocytes play a role in chronic inflammation. Recent literature, however, indicates that not only neutrophils but also great numbers of lymphocytes participate innate immunity (34). To focus on PTH effects on neutrophil dominant inflammation, in this study, LTA deficient mice were utilized. LTA deficient mice are fertile, devoid of lymph nodes and exhibit defects in adaptive immune responses (35). Accordingly, the influence of lymphocytes on periapical inflammation is miniscule and inflammatory cell infiltration observed next to the root apex is neutrophil dominant. Therefore, our result is consistent with previous findings that intermittent PTH administration suppressed neutrophil infiltration in acute inflammation (7).

Since periapical periodontitis is caused by chiefly anaerobic bacteria and bacterial products such as endotoxin and enzymes in contaminated root canals, no cure was expected by PTH treatment. However, the findings of this study suggest that intermittent PTH administration can be considered to promote periapical tissue healing adjunct to conventional endodontic treatment. In summary, this work indicates that intermittent administration of PTH protects against tissue destruction by periapical periodontitis. Reduced neutrophil infiltration is partially responsible for this protective effect of PTH treatment.

Highlights.

  • We examined the therapeutic value of PTH treatment on periapical periodontitis

  • Pulp exposure covered with plaque-mixed fibrin induced severe periapical lesions

  • Daily administration of PTH protected against periapical tissue destruction caused by infection

  • Daily administration of PTH suppressed neutrophil infiltration around the root apex

Acknowledgments

This work was supported by the NIH/NIDCR R01DE023538-01 (J.Y.)

Footnotes

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

References

  • 1.Dobnig H, Turner RT. The effects of programmed administration of human parathyroid hormone fragment (1-34) on bone histomorphometry and serum chemistry in rats. Endocrinology. 1997;138:4607–12. doi: 10.1210/endo.138.11.5505. [DOI] [PubMed] [Google Scholar]
  • 2.Peichl P, Holzer LA, Maier R, et al. Parathyroid hormone 1-84 accelerates fracture-healing in pubic bones of elderly osteoporotic women. J Bone Joint Surg Am. 2011;93:1583–7. doi: 10.2106/JBJS.J.01379. [DOI] [PubMed] [Google Scholar]
  • 3.Nakajima A, Shimoji N, Shiomi K, et al. Mechanisms for the enhancement of fracture healing in rats treated with intermittent low-dose human parathyroid hormone (1-34) J Bone Miner Res. 2002;17:2038–47. doi: 10.1359/jbmr.2002.17.11.2038. [DOI] [PubMed] [Google Scholar]
  • 4.Kuroshima S, Mecano RB, Tanoue R, et al. Distinctive tooth-extraction socket healing: bisphosphonate versus parathyroid hormone therapy. J Periodontol. 2014;85:24–33. doi: 10.1902/jop.2013.130094. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 5.Kuroshima S, Al-Salihi Z, Yamashita J. Parathyroid hormone related to bone regeneration in grafted and nongrafted tooth extraction sockets in rats. Implant Dent. 2013;22:71–6. doi: 10.1097/ID.0b013e318278f94d. [DOI] [PubMed] [Google Scholar]
  • 6.Barros SP, Silva MA, Somerman MJ, et al. Parathyroid hormone protects against periodontitis-associated bone loss. J Dent Res. 2003;82:791–5. doi: 10.1177/154405910308201006. [DOI] [PubMed] [Google Scholar]
  • 7.Kuroshima S, Entezami P, McCauley LK, et al. Early effects of parathyroid hormone on bisphosphonate/steroid-associated compromised osseous wound healing. Osteoporos Int. 2014;25:1141–50. doi: 10.1007/s00198-013-2570-8. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 8.Kuroshima S, Kovacic BL, Kozloff KM, et al. Intra-oral PTH administration promotes tooth extraction socket healing. J Dent Res. 2013;92:553–9. doi: 10.1177/0022034513487558. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 9.Baumgartner JC, Falkler WA., Jr. Bacteria in the apical 5 mm of infected root canals. J Endod. 1991;17:380–3. doi: 10.1016/s0099-2399(06)81989-8. [DOI] [PubMed] [Google Scholar]
  • 10.Matsuo T, Shirakami T, Ozaki K, et al. An immunohistological study of the localization of bacteria invading root pulpal walls of teeth with periapical lesions. J Endod. 2003;29:194–200. doi: 10.1097/00004770-200303000-00008. [DOI] [PubMed] [Google Scholar]
  • 11.Chu FC, Tsang CS, Chow TW, et al. Identification of cultivable microorganisms from primary endodontic infections with exposed and unexposed pulp space. J Endod. 2005;31:424–9. doi: 10.1097/01.don.0000148149.27636.9c. [DOI] [PubMed] [Google Scholar]
  • 12.Marton IJ, Kiss C. Overlapping protective and destructive regulatory pathways in apical periodontitis. J Endod. 2014;40:155–63. doi: 10.1016/j.joen.2013.10.036. [DOI] [PubMed] [Google Scholar]
  • 13.Hahn CL, Liewehr FR. Update on the adaptive immune responses of the dental pulp. J Endod. 2007;33:773–81. doi: 10.1016/j.joen.2007.01.002. [DOI] [PubMed] [Google Scholar]
  • 14.AlShwaimi E, Purcell P, Kawai T, et al. Regulatory T cells in mouse periapical lesions. J Endod. 2009;35:1229–33. doi: 10.1016/j.joen.2009.06.006. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 15.Taichman NS, McArthur WP, Tsai CC, et al. Conference on inflammation. Polymorphonuclear leukocytic-bacterial interaction as a pathogenetic mechanism in periodontal disease. J Endod. 1977;3:292–300. doi: 10.1016/s0099-2399(77)80033-2. [DOI] [PubMed] [Google Scholar]
  • 16.Mounzer RH, Svendsen OS, Baluk P, et al. Lymphotoxin-alpha contributes to lymphangiogenesis. Blood. 2010;116:2173–82. doi: 10.1182/blood-2009-12-256065. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 17.Abe T, Hajishengallis G. Optimization of the ligature-induced periodontitis model in mice. J Immunol Methods. 2013;394:49–54. doi: 10.1016/j.jim.2013.05.002. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 18.Iida-Klein A, Zhou H, Lu SS, et al. Anabolic action of parathyroid hormone is skeletal site specific at the tissue and cellular levels in mice. J Bone Miner Res. 2002;17:808–16. doi: 10.1359/jbmr.2002.17.5.808. [DOI] [PubMed] [Google Scholar]
  • 19.Samadfam R, Xia Q, Miao D, et al. Exogenous PTH and endogenous 1,25-dihydroxyvitamin D are complementary in inducing an anabolic effect on bone. J Bone Miner Res. 2008;23:1257–66. doi: 10.1359/jbmr.080318. [DOI] [PubMed] [Google Scholar]
  • 20.Yamashita J, Datta NS, Chun YH, et al. Role of Bcl2 in osteoclastogenesis and PTH anabolic actions in bone. J Bone Miner Res. 2008;23:621–32. doi: 10.1359/JBMR.071211. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 21.Perry HM, 3rd, Chappel JC, Bellorin-Font E, et al. Parathyroid hormone receptors in circulating human mononuclear leukocytes. J Biol Chem. 1984;259:5531–5. [PubMed] [Google Scholar]
  • 22.Yamamoto I, Potts JT, Jr., Segre GV. Circulating bovine lymphocytes contain receptors for parathyroid hormone. J Clin Invest. 1983;71:404–7. doi: 10.1172/JCI110784. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 23.Doherty CC, LaBelle P, Collins JF, et al. Effect of parathyroid hormone on random migration of human polymorphonuclear leukocytes. Am J Nephrol. 1988;8:212–9. doi: 10.1159/000167585. [DOI] [PubMed] [Google Scholar]
  • 24.Alexiewicz JM, Smogorzewski M, Fadda GZ, et al. Impaired phagocytosis in dialysis patients: studies on mechanisms. Am J Nephrol. 1991;11:102–11. doi: 10.1159/000168284. [DOI] [PubMed] [Google Scholar]
  • 25.Tuma SN, Martin RR, Mallette LE, et al. Augmented polymorphonuclear chemiluminescence in patients with secondary hyperparathyroidism. J Lab Clin Med. 1981;97:291–8. [PubMed] [Google Scholar]
  • 26.Khan F, Khan AJ, Papagaroufalis C, et al. Reversible defect of neutrophil chemotaxis and random migration in primary hyperparathyroidism. J Clin Endocrinol Metab. 1979;48:582–4. doi: 10.1210/jcem-48-4-582. [DOI] [PubMed] [Google Scholar]
  • 27.Kaneko T, Osono E, Hayama N, et al. T-cell activation modified by parathyroid hormone (PTH) in patients with end-stage renal disease. Clin Nephrol. 1997;48:353–8. [PubMed] [Google Scholar]
  • 28.Alexiewicz JM, Klinger M, Pitts TO, et al. Parathyroid hormone inhibits B cell proliferation: implications in chronic renal failure. J Am Soc Nephrol. 1990;1:236–44. doi: 10.1681/ASN.V13236. [DOI] [PubMed] [Google Scholar]
  • 29.Bashutski JD, Eber RM, Kinney JS, et al. Teriparatide and osseous regeneration in the oral cavity. N Engl J Med. 2010;363:2396–405. doi: 10.1056/NEJMoa1005361. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 30.von Stechow D, Balto K, Stashenko P, et al. Three-dimensional quantitation of periradicular bone destruction by micro-computed tomography. J Endod. 2003;29:252–6. doi: 10.1097/00004770-200304000-00005. [DOI] [PubMed] [Google Scholar]
  • 31.AlShwaimi E, Berggreen E, Furusho H, et al. IL-17 receptor A signaling is protective in infection-stimulated periapical bone destruction. J Immunol. 2013;191:1785–91. doi: 10.4049/jimmunol.1202194. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 32.Fukada SY, Silva TA, Saconato IF, et al. iNOS-derived nitric oxide modulates infection-stimulated bone loss. J Dent Res. 2008;87:1155–9. doi: 10.1177/154405910808701207. [DOI] [PubMed] [Google Scholar]
  • 33.McAbee J, Li Q, Yu H, et al. Sexual dimorphism in periapical inflammation and bone loss from mitogen-activated protein kinase phosphatase-1 deficient mice. J Endod. 2012;38:1097–100. doi: 10.1016/j.joen.2012.04.016. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 34.Wagner C, Kotsougiani D, Pioch M, et al. T lymphocytes in acute bacterial infection: increased prevalence of CD11b(+) cells in the peripheral blood and recruitment to the infected site. Immunology. 2008;125:503–9. doi: 10.1111/j.1365-2567.2008.02863.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 35.Banks TA, Rouse BT, Kerley MK, et al. Lymphotoxin-alpha-deficient mice. Effects on secondary lymphoid organ development and humoral immune responsiveness. J Immunol. 1995;155:1685–93. [PubMed] [Google Scholar]

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