Localization and density of myeloid leucocytes in the periodontal ligament of normal rat molars

Effect of local hIL-10 gene therapy on experimental periodontitis in ovariectomized rats

OBJECTIVE

To investigate the effect of local hIL-10 gene therapy on experimental periodontitis in rats and to elucidate the mechanism underlying this effect.

MATERIAL AND METHODS

Experimental periodontitis was induced in ovariectomized (OVX) rats using a silk ligature. We then injected 5 μg of hIL-10 plasmid with 5 μl of liposomes or 5 μg of vector plasmid with 5 μl of liposomes into the palatal side of the gingival mucosa of the upper left second molar once every two days. The rats were killed 48 hours after the seventh injection. The body weight; bone mineral density of the whole body, pelvis and spine; resorption of the alveolar bone; and number of cytokine-positive cells were measured to determine the effects of hIL-10 on the periodontal tissue.

RESULTS

hIL-10 was expressed in periodontal tissues after local gene delivery. The expressed hIL-10 protein inhibited alveolar bone resorption and downregulated IL-1β, IL-6, TNF-α, RANKL and MMP-8 in the periodontal ligament in the root furcation region.

CONCLUSIONS

Local hIL-10 gene transfer suppressed alveolar bone resorption in OVX rats, and this effect was probably associated with the decline in the expression of pro-inflammatory cytokines in the periodontal tissues.

Epithelial and PGP9.5-immunoreactive cells of Malassez epithelium in the periodontal ligament of cats: a transmission electron microscopic study

OBJECTIVE

The aim of the study was to investigate the ultrastructural features of Malassez epithelium (ME) containing protein gene product 9.5 (PGP9.5)-immunoreactive (IR) cells in the cat periodontal ligament (PDL).

MATERIAL AND METHODS

Specimens from the teeth and tooth-supporting tissues of four mature cats of both sexes, 18 to 24 months of age, were used. The fixed jaws were decalcified in EDTA. Frozen sagittal sections 20 µm thick were immunostained for PGP9.5, and the ME, containing IR cells in the PDL, were evaluated under a transmission electron microscope.

RESULTS

Several epithelial cells and PGP9.5 IR cells formed clusters and were enveloped by a basal lamina and separated from the surrounding connective tissue. A large nucleus and scanty cytoplasm were observed in most of the ME cells, which contained abundant keratin filaments and mitochondria. Caveolae-like structures and vesicles were found in the periphery of the ME. The small cytoplasmic processes of some of the epithelial cells extended toward the surrounding connective tissues. The cytoplasmic matrix of one type of cell comprising the ME showed immunoreactivity for anti-PGP9.5 antibody. The IR cell in the cell clusters was connected to adjacent epithelial cells and extended cytoplasmic processes toward the adjacent epithelial cells. The IR cell contained keratin filaments and abundant densely cored vesicles approximately 100-250 nm in diameter.

CONCLUSIONS

The findings of the study suggest endocytotic capabilities of the epithelial cells and neuroendocrine functions of the IR cells. It is possible that the two different cell types react to extrinsic stimuli and interact with cells comprising the clusters and cords in the PDL. These ultrastructural evidences may imply functional heterogeneity of the ME in the PDL.

Inulin induces dendritic cells apoptosis through the caspase-dependent pathway and mitochondrial dysfunction

Dendritic cells are professional antigen-presenting cells that are responsible for initiating of the immune response. However, there are no reports on how the polysaccharides in an oral biofilm affect the viability of dendritic cells. Inulin, a fructooligossacharide, is one component of oral biofilm fructan that is used as an energy source by oral bacteria. In this study, we found that murine bone marrow derived dendritic cells were induced to undergo apoptosis after being treated with inulin in a dose-dependent manner, as determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), annexinV/propidium iodide (PI), and Hoechest staining methods. Inulin activated the apoptotic pathway, including caspase-9 and caspase-3, decreased the level of B-cell lymphoma 2 (Bcl-2) expression, increased the expression of the Bcl-2-associated X protein (Bax) protein and induced poly(ADP-ribose) polymerase (PARP) cleavage. These observations suggest that inulin induces the apoptosis of dendritic cells by altering the Bcl-2/Bax ratio through the caspase dependant pathway. These results indicated that high concentrations of inulin can cause apoptic cell death in murine bone marrow-derived dendritic cells.

Reactions of periodontal ligament epithelial cell clusters and OX6-immunopositive cells to experimental tooth movement and periodontitis

BACKGROUND AND OBJECTIVE

The aim of this study was to investigate reactions of periodontal ligament epithelial cell clusters and major histocompatibility complex class II (OX6)-immunopositive cells to simultaneously induced tooth movement and periodontitis employing Waldo's method.

MATERIAL AND METHODS

Elastic gums were inserted between the right upper first and second molars of rats. Animals were killed by intracardiac perfusion on days 1, 3, 7 and 14 after the experimental procedures, and maxillary molars were decalcified and processed for OCT compound. Cytokeratin and OX6 antibodies to detect epithelial and immunocompetent cells were used for double-fluorescence immunohistochemistry. Immunostained sections of rat upper molar regions were examined with a fluorescence microscope.

RESULTS

Large periodontal ligament epithelial cell clusters appeared and became contiguous with each other, and OX6-immunopositive cells surrounded the clusters over time in the periodontal ligament near the gum insertion site. In the periodontal ligament distant from the gum insertion site, epithelial cell clusters and OX6-immunopositive cells were scattered. After 14 d, thickened epithelium and elongated rete pegs were found close to large epithelial cell clusters in the periodontal ligament near the gum insertion site.

CONCLUSION

These findings suggest proliferation and/or aggregation of periodontal ligament epithelial cells, and interaction between OX6-immunopositive cells and the periodontal ligament epithelial cells, in response to tooth movement and periodontal inflammation. This method may be a useful experimental model to elucidate the relationship between rete pegs and periodontal ligament epithelial cell clusters in inflammatory conditions.

Immunocompetent cells and cytokine expression in the rat periodontal ligament at the initial stage of orthodontic tooth movement

OBJECTIVE

The aim of the present study is to investigate the involvement of immunocompetent cells, pro-inflammatory cytokines and HSP, to evaluate a change of periodontal ligament during the initial stage of orthodontic tooth movement.

DESIGN

In the present study, we investigated the distributional density of immunocompetent cells, the localisation of cytokines, and the expression levels of their mRNA in the periodontal ligament during the initial stage of orthodontic tooth movement, using immunohistochemistry and real-time PCR.

RESULTS

Orthodontic tooth movement led to significant recruitment of OX6(+) cells and ED1(+) cells in the rat PDL. Double-immunofluorescence staining showed that some ED1(+) cells expressed pro-inflammatory factors of IL-1β and TNF-α in the PDL during orthodontic tooth movement. Real-time PCR analysis revealed that the expression levels of IL-1β (Il1b) and TNF-α (Tnf) mRNA gradually increased following its decrease after 1h of orthodontic tooth movement. These findings suggest that ED1(+) cells are involved in the expression of TNF-α and IL-1β and the subsequent regulation of bone resorption on pressure side. HSP27 (Hspb1) mRNA levels were significantly increased as compared with the control at 1h of the initial stage of treatment.

CONCLUSION

ED1(+) cells involved in the expression of TNF-α and IL-1β may play an important role in the initial reaction of the PDL and in the induction of the osteoclastic bone resorption during orthodontic tooth movement.

Distribution of epithelial cells and their relationship to immunocompetent cells in rat molars: a confocal and transmission electron microscope study

This study sought to investigate the distribution of cytokeratin (CK)-immunopositive cells and their relationship to immunocompetent ED1- and OX6-immunopositive cells in rat periodontium by immunohistochemistry and electron microscopy. CK-immunopositive cells were generally distributed along the surface of the tooth root. They could also be found between root dentin and cementum, in the perivascular space, and close to or in the alveolar bone lacunae. ED1-immunopositive cells exhibited a compact shape with small processes and were widely distributed in the periodontium. Few sections demonstrated an intimate relationship between the CK- and ED1-immunopositive cells close to the cementum, in the perivascular space, and close to or in the alveolar bone. Numerous OX6-immunopositive cells with long branching processes were widely distributed in the periodontal ligament, surrounding and holding CK-immunopositive cells in the cell clusters, close to the cementum. Transmission electron microscopy revealed OX6-immunopositive cells that extended their cytoplasmic processes, which contained vesicles and occasionally lysosomes in between the epithelial cells. This study demonstrates the close relationship between the epithelial cells and the immunocompetent cells in a rat periodontium, indicating a functional interrelationship. It is possible that in a non-inflammatory periodontium, the epithelial cells act not independently, but through interaction with immunocompetent cells.

Characteristics of resident dendritic cells in various regions of rat periodontal ligament

In the periodontal ligament (PDL) of normal rat molars, a considerable number of dendritic cells (DCs) are distributed as resident immunocompetent cells. We have hypothesized that the resident type of DCs can alter their morphology and phenotype to adapt to the microenvironment of the PDL. Thus, we have compared the characteristics of DCs in various regions of rat PDL by immunoelectron microscopy and gene expression analysis by means of reverse transcription/polymerase chain reaction. DCs in the periapical region show immature characteristics, i.e., small round profiles and few organelles. In the mesial region, which is the most stable area in the PDL, the density of DCs is the highest. DCs in the furcal region show the characteristics of activated antigen-presenting cells, i.e., CD86(high) expression, electron-dense lysosomes, and cell-to-cell contacts with lymphocytes. When the PDL is bacterially challenged by pulp exposure, the number of CD86+ DCs and contacts with lymphocytes increase in the furcal region. Gene expression analysis for the furcal region has also shown the up-regulation of the major histocompatibility complex class II alpha-chain, CD83, CD86, and the antigen-presenting cell-lectin-like receptor A1. Thus, we have demonstrated heterogeneity in resident DCs. This may be associated with the difference in DCs regarding their state of maturation/activation, which may further reflect microenvironmental differences such as the amount of external antigens.

Immunoexpression of the HLA-DR class II molecule in cells from inflamed dental pulp

BACKGROUND

Despite that the role of inflammatory cells in chronic inflammatory reactions of pulpal origin (CIRPOs) has been extensively studied, function of the HLA-DR+ cells (HLA-DR+ Cs) is poorly understood. The aim of this study was to quantify their number and clarify their role in these lesions.

METHODS

We studied 11 CIRPOs immunostained with an anti-HLA-DR class II monoclonal antibody and the number and location of the HLA-DR+ Cs quantified. CIRPOs were divided in periapical granulomas (PGs), epithelized granulomas (EGs) and periapical cysts (PCs).

RESULTS

HLA-DR+ Cs were observed within epithelium, inflammatory infiltrate and close to blood vessels. In PGs, they account for 19-256 cells/mm2, in EGs they were 20-494 cells/mm2 and in PCs quantification numbered 39-316 cells/mm2.

CONCLUSIONS

Our results suggest that HLA-DR+ Cs present antigens to lymphocytes, collaborating in initiation, regulation, development and perpetuation of CIRPOs. Also, these results suggest that these cells have an active role during initiation of epithelial proliferation in PGs and that they are partially responsible for cystic transformation from EGs to periapical cysts. They may also play an active role in bone resorption.