GM-CSF and uPA are required for Porphyromonas gingivalis-induced alveolar bone loss in a mouse periodontitis model

Granulocyte-macrophage colony-stimulating factor (GM-CSF) and urokinase-type plasminogen activator (uPA) can contribute to the progression of chronic inflammatory diseases with possible involvement of macrophages. In this study, we investigated the role of both GM-CSF and uPA in Porphyromonas gingivalis-induced experimental periodontitis using GM-CSF-/- and uPA-/- mice. Intra-oral inoculation of wild-type (WT) C57BL/6 mice with P. gingivalis resulted in establishment of the pathogen in plaque and a significant increase in alveolar bone resorption. The infected mice also exhibited a CD11b(+) CD86(+) macrophage infiltrate into the gingival tissue, as well as P. gingivalis-specific pro-inflammatory cytokine and predominantly IgG2b antibody responses. In comparison, intra-oral inoculation of P. gingivalis did not induce bone resorption and there was significantly less P. gingivalis recovered from plaque in GM-CSF-/- and uPA-/- mice. Furthermore, P. gingivalis did not induce a macrophage gingival infiltrate or activate isolated peritoneal macrophages from the gene-deficient mice. Pro-inflammatory P. gingivalis-specific T-cell cytokine responses and serum interferon-gamma (IFN-γ) and IgG2b concentrations were significantly lower in GM-CSF-/- mice. In uPA-/- mice, T-cell responses were lower but serum IFN-γ and IgG2b levels were comparable with WT mice levels. These results suggest that GM-CSF and uPA are both involved in the progression of experimental periodontitis, possibly via a macrophage-dependent mechanism(s).

Identification of gingipain-specific I-A(b) -restricted CD4+ T cells following mucosal colonization with Porphyromonas gingivalis in C57BL/6 mice

Chronic periodontitis is associated with Porphyromonas gingivalis infection. Although virulence factors of P. gingivalis are hypothesized to contribute to the pathogenesis of periodontitis, it is unclear whether the local CD4(+) T-cell-mediated response they elicit prevents or contributes to periodontal bone destruction. We hypothesize that major histocompatibility complex class II I-A(b) -binding peptides existing in Kgp and RgpA are presented to CD4(+) T cells during P. gingivalis oral colonization. The protein sequences of gingipains RgpA and Kgp, and OMP40 and OMP41 of P. gingivalis were scanned using an I-A(b) -binding matrix. From this analysis we identified 53 candidate peptides that had the potential to engage the peptide-binding groove of the I-A(b) molecule of C57BL/6 mice. An ELISpot-based screen revealed those peptide-primed effector/memory CD4(+) T cells that could be re-stimulated in vitro with P. gingivalis or the peptide itself to produce interleukin-17A or interferon-γ. Two immunodominant peptides, Kgp467-477 (pKgp) and RgpA1054-1064 /Kgp1074-1084 (pR/Kgp) were identified and engineered to be displayed on I-A(b) molecular tetramers. Peptide pR/Kgp is conserved across all sequenced P. gingivalis strains. C57BL/6 mice were orally inoculated with P. gingivalis strain 53977 and cervical lymph node cells were stained with phycoerythrin-conjugated pKgp::I-A(b) and pR/Kgp::I-A(b) tetramers. We found that only pR/Kgp::I-A(b) bound with the desired specificity to gingipain-specific CD4(+) T cells. The pR/Kgp::I-A(b) tetramer complex will allow the identification of effector/memory CD4(+) T cells specific for two virulence factors of P. gingivalis strains associated with periodontal disease.

Disruption of gingipain oligomerization into non-covalent cell-surface attached complexes

RgpA and Kgp gingipains are non-covalent complexes of endoprotease catalytic and hemagglutinin-adhesin domains on the surface of Porphyromonas gingivalis. A motif conserved in each domain has been suggested to function as an oligomerization motif. We tested this hypothesis by mutating motif residues to hexahistidine or insertion of hexahistidine tag to disrupt the motif within the Kgp catalytic domain. All modifications led to the secretion of entire Kgp activity into the growth media, predominantly in a form without functional His-tag. This confirmed the role of the conserved motif in correct posttranslational proteolytic processing and assembly of the multidomain complexes.

Synergistic virulence of Porphyromonas gingivalis and Treponema denticola in a murine periodontitis model

Chronic periodontitis is characterized by the destruction of the tissues supporting the teeth and has been associated with the presence of a subgingival polymicrobial biofilm containing Porphyromonas gingivalis and Treponema denticola. We have investigated the potential synergistic virulence of P. gingivalis and T. denticola using a murine experimental model of periodontitis. An inoculation regime of four intra-oral doses of 1 × 10(10) P. gingivalis cells induced significant periodontal bone loss compared with loss in sham-inoculated mice, whereas doses of 1 × 10(9) cells or lower did not induce bone loss. Inoculation with T. denticola with up to eight doses of 1 × 10(10) cells failed to induce bone loss in this model. However, four doses of a co-inoculum of a 1 : 1 ratio of P. gingivalis and T. denticola at 5 × 10(8) or 1 × 10(9) total bacterial cells induced the same level of bone loss as four doses of 1 × 10(10) P. gingivalis cells. Co-inoculation induced strong P. gingivalis-specific T-cell proliferative and interferon-γ-dominant cytokine responses, and induced a strong T. denticola-specific interferon-γ dominant cytokine response. Only at the higher co-inoculum dose of 1 × 10(10) total cells was a T. denticola-specific T-cell proliferative response observed. These data show that P. gingivalis and T. denticola act synergistically to stimulate the host immune response and to induce alveolar bone loss in a murine experimental periodontitis model.

HGP44 induces protection against Porphyromonas gingivalis-Induced alveolar bone loss in mice

The protective effect of DNA vaccines expressing the Arg-gingipain A domain against bone loss induced by Porphyromonas gingivalis infection was investigated in a murine model. phgp44, which expresses the 44-kDa adhesion/hemagglutinin domain of Arg-gingipain A, prevented P. gingivalis-induced alveolar bone loss. The results indicate that phgp44 could be a candidate antigen for a vaccine against P. gingivalis infection.

Feasibility and therapeutic strategies of vaccines against Porphyromonas gingivalis

Periodontitis is a chronic infectious disease that is highly prevalent worldwide and is characterized by inflammation of the gums, and loss of connective tissue and bone support. The Gram-negative anerobic bacterium Porphyromonas gingivalis is generally accepted as the main etiological agent for chronic periodontitis. The objective of this paper is to elucidate the feasibility of achieving protection against periodontitis though immunization against P. gingivalis. Until now, animal studies have showed no complete protection against P. gingivalis. However, current knowledge about P. gingivalis structures could be applicable for further research to develop a successful licensed vaccine and alternative therapeutic strategies. This review reveals that a multicomponent vaccine against P. gingivalis, which includes structures shared among P. gingivalis serotypes, will be feasible to induce broad and complete protection.