A novel approach for detecting an immunodominant antigen of Porphyromonas gingivalis in diagnosis of adult periodontitis

OC-STAMP promotes osteoclast fusion for pathogenic bone resorption in periodontitis via up-regulation of permissive fusogen CD9

Cell fusion-mediated formation of multinuclear osteoclasts (OCs) plays a key role in bone resorption. It is reported that 2 unique OC-specific fusogens [ i.e., OC-stimulatory transmembrane protein (OC-STAMP) and dendritic cell-specific transmembrane protein (DC-STAMP)], and permissive fusogen CD9, are involved in OC fusion. In contrast to DC-STAMP-knockout (KO) mice, which show the osteopetrotic phenotype, OC-STAMP-KO mice show no difference in systemic bone mineral density. Nonetheless, according to the ligature-induced periodontitis model, significantly lower level of bone resorption was found in OC-STAMP-KO mice compared to WT mice. Anti-OC-STAMP-neutralizing mAb down-modulated in vitro: 1) the emergence of large multinuclear tartrate-resistant acid phosphatase-positive cells, 2) pit formation, and 3) mRNA and protein expression of CD9, but not DC-STAMP, in receptor activator of NF-κB ligand (RANKL)-stimulated OC precursor cells (OCps). While anti-DC-STAMP-mAb also down-regulated RANKL-induced osteoclastogenesis in vitro, it had no effect on CD9 expression. In our mouse model, systemic administration of anti-OC-STAMP-mAb suppressed the expression of CD9 mRNA, but not DC-STAMP mRNA, in periodontal tissue, along with diminished alveolar bone loss and reduced emergence of CD9⁺ OCps and tartrate-resistant acid phosphatase-positive multinuclear OCs. The present study demonstrated that OC-STAMP partners CD9 to promote periodontal bone destruction by up-regulation of fusion during osteoclastogenesis, suggesting that anti-OC-STAMP-mAb may lead to the development of a novel therapeutic regimen for periodontitis.-Ishii, T., Ruiz-Torruella, M., Ikeda, A., Shindo, S., Movila, A., Mawardi, H., Albassam, A., Kayal, R. A., Al-Dharrab, A. A., Egashira, K., Wisitrasameewong, W., Yamamoto, K., Mira, A. I., Sueishi, K., Han, X., Taubman, M. A., Miyamoto, T., Kawai, T. OC-STAMP promotes osteoclast fusion for pathogenic bone resorption in periodontitis via up-regulation of permissive fusogen CD9.

DC-STAMP Is an Osteoclast Fusogen Engaged in Periodontal Bone Resorption

Dendritic cell-specific transmembrane protein (DC-STAMP) plays a key role in the induction of osteoclast (OC) cell fusion, as well as DC-mediated immune regulation. While DC-STAMP gene expression is upregulated in the gingival tissue with periodontitis, its pathophysiological roles in periodontitis remain unclear. To evaluate the effects of DC-STAMP in periodontitis, anti-DC-STAMP-monoclonal antibody (mAb) was tested in a mouse model of ligature-induced periodontitis ( n = 6-7/group) where Pasteurella pneumotropica ( Pp)-reactive immune response activated T cells to produce receptor activator of nuclear factor kappa-B ligand (RANKL), which, in turn, promotes the periodontal bone loss via upregulation of osteoclastogenesis. DC-STAMP was expressed on the cell surface of mature multinuclear OCs, as well as immature mononuclear OCs, in primary cultures of RANKL-stimulated bone marrow cells. Anti-DC-STAMP-mAb suppressed the emergence of large, but not small, multinuclear OCs, suggesting that DC-STAMP is engaged in the late stage of cell fusion. Anti-DC-STAMP-mAb also inhibited pit formation caused by RANKL-stimulated bone marrow cells. Attachment of ligature to a second maxillary molar induced DC-STAMP messenger RNA and protein, along with elevated tartrate-resistant acid phosphatase-positive (TRAP+) OCs and alveolar bone loss. As we expected, systemic administration of anti-DC-STAMP-mAb downregulated the ligature-induced alveolar bone loss. Importantly, local injection of anti-DC-STAMP-mAb also suppressed alveolar bone loss and reduced the total number of multinucleated TRAP+ cells in mice that received ligature attachment. Attachment of ligature induced significantly elevated tumor necrosis factor-α, interleukin-1β, and RANKL in the gingival tissue compared with the control site without ligature ( P < 0.05), which was unaffected by local injection with either anti-DC-STAMP-mAb or control-mAb. Neither in vivo anti- Pp IgG antibody nor in vitro anti- Pp T-cell response and resultant production of RANKL was affected by anti-DC-STAMP-mAb. This study illustrated the roles of DC-STAMP in promoting local OC cell fusion without affecting adaptive immune responses to oral bacteria. Therefore, it is plausible that a novel therapeutic regimen targeting DC-STAMP could suppress periodontal bone loss.

Implant Dentistry: Monitoring of Bacteria Along the Transmucosal Passage of the Healing Screw in Absence of Functional Load

PURPOSE

To assess the changes in bacterial profile along the transmucosal path of healing screws placed immediately after insertion of two-piece endosseus implants during the 4-month osseointegration phase, in absence of functional load.

MATERIALS AND METHODS

Two site-specific samples were collected at the peri-implant mucosa of the healing screws of 80 two-piece implants, for a total of 640 samples. Implants placement was performed following a single protocol with flapless technique, in order to limit bacterial contamination of the surgical site. Identical healing screws (5 mm diameter/4 mm height) were used for each of the 80 implants. During the 4 months of the study, the patients followed a standard oral care regimen with no special hygiene maneuvers at the collection sites.

RESULTS

The present research documents that during the 4-month period prior to application of function load the bacterial profile of all sites exhibited a clear prevalence of cocci at the interface between implant neck and osteoalveolar crest margin.

CONCLUSIONS

A potentially pathogenic bacterial flora developed only along the peri-implant transmucosal path.

Macrophage Migration Inhibitory Factor (MIF) Supports Homing of Osteoclast Precursors to Peripheral Osteolytic Lesions

By binding to its chemokine receptor CXCR4 on osteoclast precursor cells (OCPs), it is well known that stromal cell-derived factor-1 (SDF-1) promotes the chemotactic recruitment of circulating OCPs to the homeostatic bone remodeling site. However, the engagement of circulating OCPs in pathogenic bone resorption remains to be elucidated. The present study investigated a possible chemoattractant role of macrophage migration inhibitory factor (MIF), another ligand for C-X-C chemokine receptor type 4 (CXCR4), in the recruitment of circulating OCPs to the bone lytic lesion. To accomplish this, we used Csf1r-eGFP-knock-in (KI) mice to establish an animal model of polymethylmethacrylate (PMMA) particle-induced calvarial osteolysis. In the circulating Csf1r-eGFP+ cells of healthy Csf1r-eGFP-KI mice, Csf1r+/CD11b+ cells showed a greater degree of RANKL-induced osteoclastogenesis compared to a subset of Csf1r+/RANK+ cells in vitro. Therefore, Csf1r-eGFP+/CD11b+ cells were targeted as functionally relevant OCPs in the present study. Although expression of the two cognate receptors for MIF, CXCR2 and CXCR4, was elevated on Csf1r+/CD11b+ cells, transmigration of OCPs toward recombinant MIF in vitro was facilitated by ligation with CXCR4, but not CXCR2. Meanwhile, the level of PMMA-induced bone resorption in calvaria was markedly greater in wild-type (WT) mice compared to that detected in MIF-knockout (KO) mice. Interestingly, in contrast to the elevated MIF, diminished SDF-1 was detected in a particle-induced bone lytic lesion of WT mice in conjunction with an increased number of infiltrating CXCR4+ OCPs. However, such diminished SDF-1 was not found in the PMMA-injected calvaria of MIF-KO mice. Furthermore, stimulation of osteoblasts with MIF in vitro suppressed their production of SDF-1, suggesting that MIF can downmodulate SDF-1 production in bone tissue. Systemically administered anti-MIF neutralizing monoclonal antibody (mAb) inhibited the homing of CXCR4+ OCPs, as well as bone resorption, in the PMMA-injected calvaria, while increasing locally produced SDF-1. Collectively, these data suggest that locally produced MIF in the inflammatory bone lytic site is engaged in the chemoattraction of circulating CXCR4+ OCPs. © 2016 American Society for Bone and Mineral Research.

Aggregatibacter actinomycetemcomitans Omp29 is associated with bacterial entry to gingival epithelial cells by F-actin rearrangement

The onset and progressive pathogenesis of periodontal disease is thought to be initiated by the entry of Aggregatibacter actinomycetemcomitans (Aa) into periodontal tissue, especially gingival epithelium. Nonetheless, the mechanism underlying such bacterial entry remains to be clarified. Therefore, this study aimed to investigate the possible role of Aa outer membrane protein 29 kD (Omp29), a homologue of E. coli OmpA, in promoting bacterial entry into gingival epithelial cells. To accomplish this, Omp29 expression vector was incorporated in an OmpA-deficient mutant of E. coli. Omp29⁺/OmpA⁻E. coli demonstrated 22-fold higher entry into human gingival epithelial line cells (OBA9) than Omp29⁻/OmpA⁻E. coli. While the entry of Aa and Omp29⁺/OmpA⁻E. coli into OBA9 cells were inhibited by anti-Omp29 antibody, their adherence to OBA9 cells was not inhibited. Stimulation of OBA9 cells with purified Omp29 increased the phosphorylation of focal adhesion kinase (FAK), a pivotal cell-signaling molecule that can up-regulate actin rearrangement. Furthermore, Omp29 increased the formation of F-actin in OBA9 cells. The internalization of Omp29-coated beads and the entry of Aa into OBA9 were partially inhibited by treatment with PI3-kinase inhibitor (Wortmannin) and Rho GTPases inhibitor (EDIN), both known to convey FAK-signaling to actin-rearrangement. These results suggest that Omp29 is associated with the entry of Aa into gingival epithelial cells by up-regulating F-actin rearrangement via the FAK signaling pathway.

Cross-reactive adaptive immune response to oral commensal bacteria results in an induction of receptor activator of nuclear factor-?B ligand (RANKL)-dependent periodontal bone resorption in a mouse model

INTRODUCTION

The present study examined whether induction of an adaptive immune response to orally colonizing non-pathogenic Pasteurella pneumotropica by immunization with the phylogenetically closely related bacterium, Actinobacillus actinomycetemcomitans, can result in periodontal bone loss in mice.

METHODS

BALB/c mice harboring P. pneumotropica (P. pneumotropica(+) mice) in the oral cavity or control P. pneumotropica-free mice were immunized with fixed A. actinomycetemcomitans. The animals were sacrificed on day 30, and the following measurements were carried out: (i) serum immunoglobulin G and gingival T-cell responses to A. actinomycetemcomitans and P. pneumotropica; (ii) periodontal bone loss; and (iii) identification of receptor activator of nuclear factor-kappaB ligand (RANKL) -positive T cells in gingival tissue.

RESULTS

Immunization with A. actinomycetemcomitans induced a significantly elevated serum immunoglobulin G response to the 29-kDa A. actinomycetemcomitans outer membrane protein (Omp29), which showed strong cross-reactivity with P. pneumotropica OmpA compared to results in the control non-immunized mice. The A. actinomycetemcomitans-immunized P. pneumotropica(+) mice developed remarkable periodontal bone loss in a RANKL-dependent manner, as determined by the abrogation of bone loss by treatment with osteoprotegerin-Fc. The T cells isolated from the gingival tissue of A. actinomycetemcomitans-immunized P. pneumotropica(+) mice showed an in vitro proliferative response to both A. actinomycetemcomitans and P. pneumotropica antigen presentation, as well as production of soluble(s)RANKL in the culture supernatant. Double-color confocal microscopy demonstrated that the frequency of RANKL(+) T cells in the gingival tissue of A. actinomycetemcomitans-immunized P. pneumotropica(+) mice was remarkably elevated compared to control mice.

CONCLUSION

The induction of an adaptive immune response to orally colonizing non-pathogenic P. pneumotropica results in RANKL-dependent periodontal bone loss in mice.

Diminished forkhead box P3/CD25 double-positive T regulatory cells are associated with the increased nuclear factor-kappaB ligand (RANKL+) T cells in bone resorption lesion of periodontal disease

Periodontal disease involves multi-bacterial infections accompanied by inflammatory bone resorption lesions. The abundant T and B lymphocyte infiltrates are the major sources of the osteoclast differentiation factor, receptor activator for nuclear factor-kappaB ligand (RANKL) which, in turn, contributes to the development of bone resorption in periodontal disease. In the present study, we found that the concentrations of RANKL and regulatory T cell (T(reg))-associated cytokine, interleukin (IL)-10, in the periodontal tissue homogenates were correlated negatively, whereas RANKL and proinflammatory cytokine, IL-1beta, showed positive correlation. Also, according to the fluorescent-immunohistochemistry, the frequency of forkhead box P3 (FoxP3)/CD25 double-positive cells was diminished strikingly in the bone resorption lesion of periodontal disease compared to healthy gingival tissue, while CD25 or FoxP3 single positive cells were still observed in lesions where abundant RANKL+ lymphocytes were present. Very importantly, few or no expressions of FoxP3 by the RANKL+ lymphocytes were observed in the diseased periodontal tissues. Finally, IL-10 suppressed both soluble RANKL (sRANKL) and membrane RANKL (mRANKL) expression by peripheral blood mononuclear cells (PBMC) activated in vitro in a bacterial antigen-specific manner. Taken together, these results suggested that FoxP3/CD25 double-positive T(reg) cells may play a role in the down-regulation of RANKL expression by activated lymphocytes in periodontal diseased tissues. This leads to the conclusion that the phenomenon of diminished CD25+FoxP3+ T(reg) cells appears to be associated with the increased RANKL+ T cells in the bone resorption lesion of periodontal disease.

B and T lymphocytes are the primary sources of RANKL in the bone resorptive lesion of periodontal disease

Receptor activator of nuclear factor-kappaB (RANKL)-mediated osteoclastogenesis plays a pivotal role in inflammatory bone resorption. The aim of this study was to identify the cellular source of RANKL in the bone resorptive lesions of periodontal disease. The concentrations of soluble RANKL, but not its decoy receptor osteoprotegerin, measured in diseased tissue homogenates were significantly higher in diseased gingival tissues than in healthy tissues. Double-color confocal microscopic analyses demonstrated less than 20% of both B cells and T cells expressing RANKL in healthy gingival tissues. By contrast, in the abundant mononuclear cells composed of 45% T cells, 50% B cells, and 5% monocytes in diseased gingival tissues, more than 50 and 90% of T cells and B cells, respectively, expressed RANKL. RANKL production by nonlymphoid cells was not distinctly identified. Lymphocytes isolated from gingival tissues of patients induced differentiation of mature osteoclast cells in a RANKL-dependent manner in vitro. However, similarly isolated peripheral blood B and T cells did not induce osteoclast differentiation, unless they were activated in vitro to express RANKL; emphasizing the osteoclastogenic potential of activated RANKL-expressing lymphocytes in periodontal disease tissue. These results suggest that activated T and B cells can be the cellular source of RANKL for bone resorption in periodontal diseased gingival tissue.

Expression of major histocompatibility complex class II and CD80 by gingival epithelial cells induces activation of CD4+ T cells in response to bacterial challenge

HLA-DR (major histocompatibility complex [MHC] class II) is often expressed by epithelial cells in gingival tissues with periodontal disease but not by cells in healthy gingival tissues. Confocal microscopic analyses revealed that gingival epithelial cells (GEC) from tissue with periodontal disease express both HLA-DR and B7-1 (CD80) costimulatory molecules. Rat GEC lines were established to elucidate the possible role of MHC class II and B7-1 expression by GEC. Stimulation of a rat GEC line with gamma interferon (IFN-gamma) induced the expression of MHC class II, whereas the cell line constitutively expressed B7-1 costimulatory molecules as determined by reverse transcription-PCR and flow cytometry. Actinobacillus actinomycetemcomitans Omp29-specific CD4(+) Th1 clone cells proliferated in response to pretreatment of GEC with fixed A. actinomycetemcomitans and IFN-gamma. However, the Th1 cells did not respond to pretreatment of GEC with the bacteria alone or IFN-gamma alone. The activation of Th1 clone cells induced by the GEC was inhibited by antibody to MHC class II or by CTLA4 immunoglobulin (CTLA4-Ig). Lymph node T cells did not demonstrate superantigen activity to A. actinomycetemcomitans, although both lymph node T cells and Th1 clone cells were sensitive to superantigen activity of staphylococcal enterotoxin A as cultured in the presence of IFN-gamma-treated GEC. These results suggested that GEC can take up bacterial antigen and consequently process and present the bacterial antigen to CD4(+) T cells by MHC class II in conjunction with B7 costimulation. GEC appeared to play a role in the adaptive immune response by stimulating antigen-specific CD4(+) T cells.

Identification and characterization of bacterial-binding property in the type III repeat domain of fibronectin

To characterize fibronectin binding with Granulicatella adiacens, a causative agent of infective endocarditis, monoclonal antibodies were generated against human fibronectin and selected for their capacity to inhibit the fibronectin binding of the organism. Thermolysin and lysyl-endopeptidase digests of fibronectin were characterized by Western blot. The epitope of inhibitory monoclonal antibody was found in the central portion of fibronectin known as the cell-binding domain, and not in the N-terminal portion known to be the binding region of most microbial species, e.g., Staphylococcus aureus and Streptococcus pyogenes. While these two species could bind to both the N-terminal and central portion, Escherichia coli and G. adiacens bind only to the latter. Excess amounts of free fibronectin in the solution inhibited the bacterial adherence to the N-terminal fibronectin fragment, but not to the central region, thereby suggesting the central region plays a significant role for in vivo bacterial colonization in the presence of high concentrations of soluble fibronectin.

Immunodominance of conformation-dependent B-cell epitopes of protein antigens

Immunodominance of conformational epitopes over linear ones in four proteins was quantified making use of the B-cell hybridoma technology. The proteins were immunized in their native forms into BALB/c mice, and clonal frequencies of B-cell hybridomas that produce antibodies to the native and denatured forms were determined, using ELISA and immunoblotting. All 16 monoclonal antibodies (mAbs) to Porphyromonas gingivalis fimbria were suggested to recognize conformational epitopes expressed by the oligomer. Ten out of 14 mAbs to Serratia marcescens fimbria and 13 of 15 mAbs to hen lysozyme were also specific to their conformational epitopes. In contrast, all 18 mAbs to a surface protein of Streptococcus mutans, termed PAc, reacted to both the native and denatured forms, thereby indicating the immunodominance of linear epitopes in this protein. The results suggest that B-cell epitopes of proteins possessing stable tertiary or quaternary structures are predominantly expressed by the higher-order structures.

T(h)1 transmigration anergy: a new concept of endothelial cell-T cell regulatory interaction

Stimulation of endothelial cells (EC) with IFN-gamma generates selective enhancement of T(h)1 cell transmigration and induction of MHC class II expression on EC. In the present study, we tested whether antigen presentation by EC could influence transmigrating T cells in an in vitro system. Bacterial antigen presentation by EC from primary culture and after cloning induced antigen-specific anergy of transmigrating T(h)1 clone cells in a MHC class II-dependent manner as characterized by non-responsiveness to subsequent antigen presentation and inability to produce IL-2. This T cell transmigration anergy induced by EC was abrogated by anti-rat CD28 mAb, suggesting that lack of B7 co-stimulatory signals by EC might be related to the induction of anergy. While MHC class II expression on primary and cloned EC was observed after IFN-gamma stimulation, these cells never expressed B7. B7-1 gene-transfected endothelial clone cells (ECC/B7-1) were developed to elucidate the influence of B7 co-stimulation by EC. ECC/B7-1 induced proliferation of T(h)1 clone cells, whereas ECC did not induce proliferation in co-culture of T(h)1 clone cells and EC stimulated with IFN-gamma and antigen. In the transmigration assay, ECC/B7-1 did not induce transmigration anergy of T(h)1 clones or T(h)1 lines unless anti-rat B7-1 blocking mAb was added. Therefore, in rats, the T cell anergy induced during transmigration across a layer of EC seemed to be due to antigen presentation in the absence of B7 on the EC. We introduce the concept of transmigration anergy in this manuscript. Thus, EC can play a critical immune regulatory role in the context of antigen presentation by MHC class II to transmigrating T cells.

Selective Diapedesis of Th1 Cells Induced by Endothelial Cell RANTES

Differentiated CD4 T cells can be divided into Th1 and Th2 types based on the cytokines they produce. Differential expression of chemokine receptors on either the Th1-type or the Th2-type cell suggests that Th1-type and Th2-type cells differ not only in cytokine production but also in their migratory capacity. Stimulation of endothelial cells with IFN-γ selectively enhanced transmigration of Th1-type cells, but not Th2-type cells, in a transendothelial migration assay. Enhanced transmigration of Th1-type cells was dependent on the chemokine RANTES produced by endothelial cells, as indicated by the findings that Ab neutralizing RANTES, or Ab to its receptor CCR5, inhibited transmigration. Neutralizing Ab to chemokines macrophage-inflammatory protein-1α or monocyte chemotactic protein-1 did not inhibit Th1 selective migration. Whereas anti-CD18 and anti-CD54 blocked basal levels of Th1-type cell adherence to endothelial cells and also inhibited transmigration, anti-RANTES blocked only transmigration, indicating that RANTES appeared to induce transmigration of adherent T cells. RANTES seemed to promote diapedesis of adherent Th1-type cells by augmenting pseudopod formation in conjunction with actin rearrangement by a pathway that was sensitive to the phosphoinositol 3-kinase inhibitor wortmannin and to the Rho GTP-binding protein inhibitor, epidermal cell differentiation inhibitor. Thus, enhancement of Th1-type selective migration appeared to be responsible for the diapedesis induced by interaction between CCR5 on Th1-type cells and RANTES produced by endothelial cells. Further evidence that CCR5 and RANTES play a modulatory role in Th1-type selective migration derives from the abrogation of this migration by anti-RANTES and anti-CCR5 Abs.

Cloning of the gene encoding the Actinobacillus actinomycetemcomitans serotype b OmpA-like outer membrane protein

The gene encoding an outer membrane protein A (OmpA)-like, heat-modifiable Omp of Actinobacillus actinomycetemcomitans ATCC 43718 (strain Y4, serotype b) was cloned by a PCR cloning procedure. DNA sequence analysis revealed that the gene encodes a protein of 346 amino acid residues with a molecular mass of 36.9 kDa. The protein expressed by the cloned gene reacted with a monoclonal antibody to the previously described 29-kDa Omp (Omp29) of strain Y4. This monoclonal antibody reacted specifically with Omp29 of A. actinomycetemcomitans (serotype b), but not with any Omp of Escherichia coli, including OmpA. This protein exhibited characteristic heat modifiability on sodium dodecyl sulfate-polyacrylamide gels, showing an apparent molecular mass of 29 kDa when unheated and a mass of 34 kDa when heated. The N-terminal amino acid sequence of the protein expressed in E. coli perfectly matched those deduced from the purified Omp29 of strain Y4. The deduced amino acid sequence of the gene coding for Omp29 from serotype b matched completely (except for valine at position 321) that of a recently reported omp34 gene described for A. actinomycetemcomitans serotype c (NCTC 9710). Because of the conserved nature of the gene within these serotypes, we designated the gene described herein from serotype b as omp34.