Cysteine protease of Porphyromonas gingivalis 381 enhances binding of fimbriae to cultured human fibroblasts and matrix proteins

Local and Systemic Effects of Porphyromonas gingivalis Infection

Porphyromonas gingivalis, a gram-negative anaerobe, is a leading etiological agent in periodontitis. This infectious pathogen can induce a dysbiotic, proinflammatory state within the oral cavity by disrupting commensal interactions between the host and oral microbiota. It is advantageous for P. gingivalis to avoid complete host immunosuppression, as inflammation-induced tissue damage provides essential nutrients necessary for robust bacterial proliferation. In this context, P. gingivalis can gain access to the systemic circulation, where it can promote a prothrombotic state. P. gingivalis expresses a number of virulence factors, which aid this pathogen toward infection of a variety of host cells, evasion of detection by the host immune system, subversion of the host immune responses, and activation of several humoral and cellular hemostatic factors.

Porphyromonas gingivalis FimA and Mfa1 fimbriae: Current insights on localization, function, biogenesis, and genotype

In general, the periodontal pathogen Porphyromonas gingivalis expresses distinct FimA and Mfa1 fimbriae. Each of these consists of five FimA–E and five Mfa1–5 proteins encoded by the fim and mfa gene clusters, respectively. The main shaft portion comprises FimA and Mfa1, whereas FimB and Mfa2 are localized on the basal portion and function as anchors and elongation terminators. FimC–E and Mfa3–5 participate in the assembly of an accessory protein complex on the tips of each fimbria. Hence, they serve as ligands for the receptors on host cells and other oral bacterial species. The crystal structures of FimA and Mfa1 fimbrial proteins were recently elucidated and new insights into the localization, function, and biogenesis of these proteins have been reported. Several studies indicated a correlation between P. gingivalis pathogenicity and the fimA genotype but not the mfa1 genotype. We recently revealed polymorphisms of all genes in the fim and mfa gene clusters. Intriguingly, mfa5 occurred in numerous different forms and underwent duplication. Detailed structural and functional knowledge of the fimbrial proteins in the context of the entire filament could facilitate the development of innovative therapeutic strategies for structure-based drug design.

The role of staphopain a in Staphylococcus aureus keratitis

Staphylococcus aureus is a common bacterial isolate from cases of microbial keratitis. The virulence factors that contribute to its pathogenicity during this disease have not been fully resolved. The aim of the current study was to examine the effects of the extracellular protease Staphopain A on corneal virulence. Two strains were used, one Staph 38 that gives a high pathology score during keratitis and a less virulent strain ATCC 8325-4. The effect of inhibition of Staphopain by general or specific protease inhibitors on adhesion of strains to fibronectin-coated glass or PMMA was determined. This was followed by an analysis of the effect of Staphopain A on the ability of the bacteria to adhere to and invade corneal epithelial cells. Finally, the effect of inhibiting Staphopain A on pathogenesis in a mouse model of keratitis was studied. Staphopain A increased the adhesion of strains to fibronectin-coated substrata and inhibition of Staphopain A reduced adhesion. The inhibition of Staphopain A by staphostatin A significantly decreased both association with and invasion into human corneal epithelial cells by 15-fold for strain Saur38. Inhibition of Staphopain A significantly reduced the pathology associated with S. aureus keratitis, reducing the infecting numbers of bacteria from 1.8x10⁵ to <1x10⁴ cells/cornea (p ≤ 0.001), significantly reducing the corneal pathology score (p ≤ 0.038) and reducing the numbers of infiltrating PMNs. This study shows that Staphopain increases adhesion and invasion of corneal cells due to increasing fibronectin binding and its inhibition has a significant impact on pathogenicity of S. aureus during keratitis.

Human pathogens utilize host extracellular matrix proteins laminin and collagen for adhesion and invasion of the host

Laminin (Ln) and collagen are multifunctional glycoproteins that play an important role in cellular morphogenesis, cell signalling, tissue repair and cell migration. These proteins are ubiquitously present in tissues as a part of the basement membrane (BM), constitute a protective layer around blood capillaries and are included in the extracellular matrix (ECM). As a component of BMs, both Lns and collagen(s), thus function as major mechanical containment molecules that protect tissues from pathogens. Invasive pathogens breach the basal lamina and degrade ECM proteins of interstitial spaces and connective tissues using various ECM-degrading proteases or surface-bound plasminogen and matrix metalloproteinases recruited from the host. Most pathogens associated with the respiratory, gastrointestinal, or urogenital tracts, as well as with the central nervous system or the skin, have the capacity to bind and degrade Lns and collagen(s) in order to adhere to and invade host tissues. In this review, we focus on the adaptability of various pathogens to utilize these ECM proteins as enhancers for adhesion to host tissues or as a targets for degradation in order to breach the cellular barriers. The major pathogens discussed are Streptococcus, Staphylococcus, Pseudomonas, Salmonella, Yersinia, Treponema, Mycobacterium, Clostridium, Listeria, Porphyromonas and Haemophilus; Candida, Aspergillus, Pneumocystis, Cryptococcus and Coccidioides; Acanthamoeba, Trypanosoma and Trichomonas; retrovirus and papilloma virus.

Adsorption of components of the plasma kinin-forming system on the surface of Porphyromonas gingivalis involves gingipains as the major docking platforms

Enhanced production of proinflammatory bradykinin-related peptides, the kinins, has been suggested to contribute to the pathogenesis of periodontitis, a common inflammatory disease of human gingival tissues. In this report, we describe a plausible mechanism of activation of the kinin-generating system, also known as the contact system or kininogen-kallikrein-kinin system, by the adsorption of its plasma-derived components such as high-molecular-mass kininogen (HK), prekallikrein (PK), and Hageman factor (FXII) to the cell surface of periodontal pathogen Porphyromonas gingivalis. The adsorption characteristics of mutant strains deficient in selected proteins of the cell envelope suggested that the surface-associated cysteine proteinases, gingipains, bearing hemagglutinin/adhesin domains (RgpA and Kgp) serve as the major platforms for HK and FXII adhesion. These interactions were confirmed by direct binding tests using microplate-immobilized gingipains and biotinylated contact factors. Other bacterial cell surface components such as fimbriae and lipopolysaccharide were also found to contribute to the binding of contact factors, particularly PK. Analysis of kinin release in plasma upon contact with P. gingivalis showed that the bacterial surface-dependent mechanism is complementary to the previously described kinin generation system dependent on HK and PK proteolytic activation by the gingipains. We also found that several P. gingivalis clinical isolates differed in the relative significance of these two mechanisms of kinin production. Taken together, these data show the importance of this specific type of bacterial surface-host homeostatic system interaction in periodontal infections.

The role of the RgpA-Kgp proteinase-adhesin complexes in the adherence of Porphyromonas gingivalis to fibroblasts

Porphyromonas gingivalis strains W50 and ATCC 33277 were shown to bind to cultured human fibroblast (MRC-5) cells using flow cytometry. As the concentration of P. gingivalis strain W50 cells was increased relative to the concentration of MRC-5 cells, the number of W50 cells bound per MRC-5 cell increased, as did the percentage of MRC-5 cells with bacteria bound. However, this relationship was only seen for P. gingivalis strain ATCC 33277 at low cell concentrations: at high bacterial cell concentrations strain ATCC 33277 auto-aggregated and binding to the MRC-5 cells decreased. Strain W50 was therefore chosen to study the role of the surface proteinase-adhesin complexes (RgpA-Kgp complexes) in binding to MRC-5 cells. P. gingivalis W50 cells treated with an inhibitor of the RgpA-Kgp complexes exhibited reduced binding to MRC-5 cells. The purified active and proteinase-inactive RgpA-Kgp complexes competitively inhibited binding of W50 to MRC-5 cells, and isogenic mutants of W50 lacking RgpA/B and Kgp displayed reduced binding. P. gingivalis W50 mutant cells lacking Kgp exhibited the lowest binding to MRC-5 cells, suggesting an important role for this proteinase and its associated adhesins in binding to fibroblasts.

Heterogenic virulence and related factors among clinical isolates of Porphyromonas gingivalis with type II fimbriae

BACKGROUND/AIMS

Porphyromonas gingivalis is a periodontal pathogen whose fimbriae are classified into six genotypes (types I-V and Ib) based on the diversity of the fimA genes encoding the fimbrial subunits. Accumulated evidence suggests that P. gingivalis strains with type II fimbriae are more virulent as compared to those with other types. However, it is unknown if strong virulence is uniformly conserved among clones with type II fimbriae. In the present study, we compared infectious inflammatory changes in clinical isolates of P. gingivalis with type II fimbriae using a mouse abscess model to examine their pathogenic heterogeneity and heterogeneity-related factors.

METHODS

Suspensions of nine different clinical isolates with type II fimbriae were subcutaneously injected into female BALB/c mice and inflammatory parameters, such as serum sialic acid concentration, were compared.

RESULTS

Many of the type II fimbrial isolates caused severe inflammation in the mice, though some were less causative, as was the control strain ATCC 33277 (type I fimbria strain). These results showed that pathogenic heterogeneity exists among P. gingivalis clones with type II fimbriae. Further, the heterogeneity-related factors of P. gingivalis strains were analyzed and the pathogenic potentials showed positive relationships to gingipain activities and invasive efficiency but not to hydrophobicity or autoaggregation. In addition, invasive efficiency was related to the activities of gingipains that were extracellularly secreted.

CONCLUSION

These results suggest that pathogenic heterogeneity has relationships with the invasive and proteolytic activities of P. gingivalis clones with type II fimbriae.

Involvement of minor components associated with the FimA fimbriae of Porphyromonas gingivalis in adhesive functions

The FimA fimbriae of Porphyromonas gingivalis, the causative agent of periodontitis, have been implicated in various aspects of pathogenicity, such as colonization, adhesion and aggregation. In this study, the four open reading frames (ORF1, ORF2, ORF3 and ORF4) downstream of the fimbrilin gene (fimA) in strain ATCC 33277 were examined. ORF2, ORF3 and ORF4 were demonstrated to encode minor components of the fimbriae and were therefore renamed fimC, fimD and fimE, respectively. Immunoblotting analyses revealed that inactivation of either fimC or fimD by an ermF-ermAM insertion, but not inactivation of ORF1, was accompanied by concomitant loss of the products from the downstream genes, raising the possibility that fimC, fimD and fimE constitute a transcription unit. The fimE mutant produced FimC and FimD, but fimbriae purified from it contained neither protein, suggesting that FimE is required for the assembly of FimC and FimD onto the fimbrilin (FimA) fibre. The fimC, fimD and fimE mutants lost autoaggregation abilities. Fimbriae purified from these three mutants showed attenuated binding activities to glyceraldehyde-3-phosphate dehydrogenase of Streptococcus oralis and to two extracellular matrix proteins, fibronectin and type I collagen. These results suggest that FimE, as well as FimC and FimD, play critical roles in the adhesive activities of the mature FimA fimbriae in P. gingivalis.

Morphometric, histomorphometric, and microcomputed tomographic analysis of periodontal inflammatory lesions in a murine model

BACKGROUND

Porphyromonas gingivalis is recognized as one of the major periodontal pathogens in chronic periodontitis, a common infectious disease characterized by inflammation and destruction of periodontal tissues. Several animal models with P. gingivalis have been used in periodontitis studies. Additionally, multiple approaches have also been applied to measuring alveolar bone loss in periodontitis models, including histomorphometry, morphometry, and radiography. The aims of this study were to assess periodontal inflammatory lesions after P. gingivalis-induced periodontitis and use this model to compare three approaches for assessing alveolar bone loss.

METHODS

Twelve-week-old male C57BL/6 mice were divided into two groups: 48 P. gingivalis-infected and 52 untreated control mice. Periodontitis was induced by wrapping P. gingivalis-soaked ligatures around the left maxillary second molar and changing the ligatures every other day. Mice were euthanized on days 0, 3, 7, and 10 after ligature placement, for a total of 12 experimental and 13 control mice per time point. Epithelial downgrowth, inflammation, and osteoclast activity were evaluated; alveolar bone loss was determined by histomorphometry, morphometry, and microcomputed tomography.

RESULTS

The P. gingivalis-infected group showed significantly increased epithelial downgrowth (P <0.05), inflammation (P <0.05), alveolar bone loss (P <0.05), and osteoclast activity (P <0.05) throughout the experimental period compared to the controls. All three methods yielded efficient evaluation of alveolar bone loss.

CONCLUSIONS

Our results show evidence that the P. gingivalis-soaked ligature-induced murine model mounts an adequate inflammatory response and exhibits periodontal tissue breakdown compatible with other models of periodontal disease. In addition, alveolar bone loss can accurately be quantified using any of the three alveolar bone analyses presented in this article.

Maturation of fimbria precursor protein by exogenous gingipains in Porphyromonas gingivalis gingipain-null mutant

Porphyromonas gingivalis expresses several virulence factors such as fimbriae and proteases, termed gingipains, which are enzymes that process precursor fimbriae proteins. Thus, gingipain-null mutants lack mature fimbriae. Membrane vesicle-depleted supernatants (VDS) containing soluble gingipains were prepared as an exogenous gingipain fraction. Precursor proteins were treated with VDS and a fimbriated gingipain-null mutant was successfully generated. Experiments showed that the wild strain adhered to and invaded epithelial cells at a greater level than the fimbriated gingipain-null mutant, while adhesion/invasion was prevented in the presence of fetal calf serum, which inhibits gingipain activity. The findings of this study suggest that gingipains expose cellular cryptic ligands in a proteolytic manner and promote fimbriae binding to epithelial cells.

Flow cytometric analysis of adherence of Porphyromonas gingivalis to oral epithelial cells

By using fluorescence microscopy, fluorescently labeled Porphyromonas gingivalis W50 was shown to adhere to oral epithelial (KB) cells as discrete cells or small cell aggregates, whereas P. gingivalis ATCC 33277 bound as large cell aggregates. Flow cytometric analysis showed that for P. gingivalis W50 there was a logarithmic relationship between the bacterial cell ratio (BCR), that is the number of bacterial cells to KB cells, and the percentage of KB cells with W50 cells attached. This percentage of KB cells with W50 attached reached a plateau of approximately 84% cells at a BCR of 500:1. In contrast, a quadratic relationship was observed between BCR and the percentage of KB cells with P. gingivalis ATCC 33277 attached, reaching a maximum of 47% at a BCR of 100:1 but decreasing to 7% at a BCR of 1,000:1. The lower binding of ATCC 33277 at high cell concentrations was attributed to autoaggregation. P. gingivalis W50 cells treated with an inhibitor (Nalpha-p-tosyl-L-lysine chloromethyl ketone [TLCK]) of its RgpA-Kgp proteinase-adhesin complex exhibited significantly reduced binding to KB cells than to untreated cells, suggesting a role for proteinase activity in binding to KB cells. Competitive inhibition with purified proteinase-active and TLCK-inactivated RgpA-Kgp complex significantly decreased the adherence of P. gingivalis W50 cells to KB cells. Furthermore, isogenic mutants of P. gingivalis W50 lacking the kgp gene product, but not the rgpA or rgpB gene products, exhibited significantly decreased adherence to KB cells compared to the wild type.

Characterization of proteinase-adhesin complexes of Porphyromonas gingivalis

Proteinase-adhesin complexes of Porphyromonas gingivalis wild-type and RgpA and Kgp mutants were extracted using a Triton X-114 procedure and purified using arginine-affinity chromatography. The complexes were then characterized by peptide mass fingerprinting (PMF) and their equilibrium binding constants, immunogenicity and ability to induce protection as vaccines in the murine lesion model determined. The Triton X-114 procedure resulted in consistently higher yield and specific activity of the wild-type (wt) complex compared with that produced by the previously published sonication method. PMF and N-terminal sequencing of the purified wt complex showed that it consisted of the previously identified Arg-specific proteinase RgpA(cat), the Lys-specific proteinase Kgp(cat) and adhesin domains RgpA A1, RgpA A2, RgpA A3, Kgp A1 and Kgp A2. However, analysis of the 30 kDa band in the wt complex, previously suggested to be RgpA A4, indicated that this band contained C-terminally truncated Kgp A1 (which has an identical N-terminus to RgpA A4) as well as the HagA A1* adhesin. Analysis of the Triton X-114 extracted complexes from the P. gingivalis isogenic mutants kgp (RgpA complex) and rgpA (Kgp complex) suggested that the Kgp complex consisted of Kgp(cat), Kgp A1 and Kgp A2/HagA A2 and that the RgpA complex consisted of RgpA(cat), RgpA A1, HagA A1*, RgpA A2 and RgpA A3. Each of the complexes was found to have equilibrium binding constants (K(D)) in the nanomolar range for fibrinogen, fibronectin, haemoglobin, collagen type V and laminin. However, the Triton-wt complex exhibited significantly lower K(D) values for binding to each host protein compared with the sonication-wt complex, or the Triton-RgpA complex and Triton-Kgp complex. Furthermore, the Triton-wt complex induced a stronger antibody response to the A1 adhesins and tended to be more effective in providing protection in the mouse lesion model compared with the sonication-wt complex.

Glyceraldehyde-3-phosphate dehydrogenase of Streptococcus oralis functions as a coadhesin for Porphyromonas gingivalis major fimbriae

Cohesive interactions between Porphyromonas gingivalis and plaque-forming bacteria, such as Streptococcus oralis, are considered to play an important role in the colonization of P. gingivalis in periodontal sites. Although P. gingivalis fimbriae have been reported to mediate coaggregation with S. oralis, the S. oralis molecule involved has not been identified. We identified the coadhesin of S. oralis ATCC 9811 and purified it by affinity column chromatography. We found that the molecular mass of the purified protein was approximately 40 kDa. Dot blot and Western blot assays showed binding of the 40-kDa protein to P. gingivalis fimbriae. Further, turbidimetric assays showed that the coadhesin inhibited coaggregation between P. gingivalis and S. oralis in a dose-dependent manner. Analyses of the amino-terminal sequences of the protein and its lysyl endopeptidase-cleaved fragments revealed that the coadhesin was identical to glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Next, we cloned the gene that encodes S. oralis GAPDH and found that the sequence had a high degree of homology with the sequences of GAPDHs of various bacteria, including Streptococcus gordonii and Fusobacterium nucleatum. To confirm the contribution of S. oralis GAPDH to the interaction with P. gingivalis, a recombinant GAPDH protein was generated in Escherichia coli; this protein bound to P. gingivalis fimbriae and had an inhibitory effect on coaggregation. These results suggest that S. oralis GAPDH functions as a coadhesin for P. gingivalis fimbriae. In addition, considering the high degree of homology of the GAPDHs of various bacteria, those of other plaque-forming bacteria also may contribute to the colonization of P. gingivalis.

Gingipain adhesin domains mediate Porphyromonas gingivalis adherence to epithelial cells

Porphyromonas gingivalis, a Gram-negative oral anaerobe, interacts with epithelium lining the gingival sulcus. Continuing our studies on the role of gingipain cysteine proteinases in P. gingivalis adherence to epithelial cells, we showed that antibody raised to the recombinant adhesin domain of arg-gingipain A blocked bacterial attachment, providing new additional evidence that P. gingivalis adherence to epithelial cells is mediated by gingipain adhesin peptides.

Cys32 and His105 Are the Critical Residues for the Calcium-dependent Cysteine Proteolytic Activity of CvaB, an ATP-binding Cassette Transporter

CvaB, a member of the ATP-binding cassette transporter superfamily, is the central membrane transporter of the colicin V secretion system in Escherichia coli. Cys32 and His105 in the N-terminal domain of CvaB were identified as critical residues for both colicin V secretion and cysteine proteolytic activity. By inhibiting degradation with N-ethylmaleimide and a mixture of protease inhibitors, a stable wild-type N-terminal domain (which showed cysteine protease activity when activated) was purified. Such protease activity was Ca2+- and concentration-dependent and could be inhibited by antipain, N-ethylmaleimide, EDTA, and EGTA. At low concentrations, the Ca2+ analogs Tb3+ and La3+ (but not Fe3+) significantly enhanced proteolytic activity, suggesting that the size of the cations is important for activity. Together with comparisons of the sequences of members of the cysteine protease family, these results indicate that Cys32 and His105 are the critical residues in the CvaB N-terminal domain for the calcium-dependent cysteine protease activity and secretion of colicin V.

Virulence factors of Porphyromonas gingivalis are modified by polyphenol oxidase and asparaginase

Porphyromonas gingivalis is a well-adapted pathogen of the periodontal pocket distinguished by its wide array of proteolytic activities and its ability to adhere to multiple substrata in the oral cavity. Microbial proteins with binding functions (such as adhesins and enzymes) very often contain critical tyrosine residues, supported by one or more asparagines in the binding cleft. This study investigates the reduction in adhesiveness and in proteolytic activity after treating P. gingivalis with the tyrosine- and asparagine-targeting enzymes polyphenol oxidase (PPO) and asparaginase (ASG). Cysteine protease activity was reduced by pretreatment with both enzymes, while the trypsin-like activity was affected only by PPO. Adhesion to buccal epithelial cells, laminin and fibronectin as well as hemagglutination was reduced by one or both of the enzymes. PPO, but not ASG, reduced the coaggregation of P. gingivalis with Actinomyces naeslundii. Treatment with these enzymes might provide an alternative to traditional antimicrobial strategies.

Complete genome sequence of the oral pathogenic Bacterium porphyromonas gingivalis strain W83

The complete 2,343,479-bp genome sequence of the gram-negative, pathogenic oral bacterium Porphyromonas gingivalis strain W83, a major contributor to periodontal disease, was determined. Whole-genome comparative analysis with other available complete genome sequences confirms the close relationship between the Cytophaga-Flavobacteria-Bacteroides (CFB) phylum and the green-sulfur bacteria. Within the CFB phyla, the genomes most similar to that of P. gingivalis are those of Bacteroides thetaiotaomicron and B. fragilis. Outside of the CFB phyla the most similar genome to P. gingivalis is that of Chlorobium tepidum, supporting the previous phylogenetic studies that indicated that the Chlorobia and CFB phyla are related, albeit distantly. Genome analysis of strain W83 reveals a range of pathways and virulence determinants that relate to the novel biology of this oral pathogen. Among these determinants are at least six putative hemagglutinin-like genes and 36 previously unidentified peptidases. Genome analysis also reveals that P. gingivalis can metabolize a range of amino acids and generate a number of metabolic end products that are toxic to the human host or human gingival tissue and contribute to the development of periodontal disease.

Epithelial cell surface sites involved in the polyvalent adherence of Porphyromonas gingivalis: a convincing role for neuraminic acid and glucuronic acid

We investigated the target structures of the epithelial cells responsible for the attachment of Porphyromonas gingivalis by immunocytofluorimetry, enzyme-linked immunosorbent assay, and confocal microscopy. Integrins (beta1, beta3, and alphaV) and E-cadherin played no significant role. Carbohydrates (such as alpha-D-methylglucoside, L-fucose, D- and L-mannose, N-acetylglucosamine, and N-acetylgalactosamine) had little inhibitory effect on bacterial binding. Enzymatic treatments of the epithelial membranes and sugar competition studies showed that N-acetylneuraminic acid and glucuronic acid were involved in binding.

Molecular interaction of Porphyromonas gingivalis with host cells: implication for the microbial pathogenesis of periodontal disease

Porphyromonas gingivalis is a predominant periodontal pathogen, which expresses a number of potential virulence factors involved in the pathogenesis of periodontitis. Among them, fimbriae are a critical factor to mediate the bacterial interaction with host tissues, which promotes the bacterial adhesion to and invasion of the targeted sites. Fimbriae are capable of binding to human salivary components, commensal bacteria, and a variety of host cells including macrophages, epithelial cells, and fibroblasts. Human extracellular matrix (ECM) proteins such as vitronectin and fibronectin play important roles in cellular signal transduction via binding to receptor integrins. Fimbriae showed significant binding affinity to ECM proteins and clearly inhibited the molecular interactions between vitronectin/fibronectin and their receptor alphavbeta3 and alpha5beta1 integrins overexpressed on Chinese hamster ovary (CHO) cell strain. P. gingivalis fimbriae are likely to interrupt the cellular signaling via ECM proteins/integrins in periodontal regions. Fimbriae are also thought to be critically important in invasive events of the organism to host cells. The fimA genes, encoding FimA (a subunit of fimbriae), of P. gingivalis strains are classified into 5 types, I to V. Recent clinical investigations demonstrated the close relationship between the organisms with type II fimA and periodontitis development. Recombinant FimA (rFimA) proteins of types I to V were generated to compare their adhesion/invasion abilities to human gingival fibroblasts (HGF) and a human epithelial cell line (HEp-2 cells), respectively. There were no significant differences in the adhesion ability of microspheres (MS) coated with these rFimAs to HGF; however, the adhesion of type II rFimA-MS to HEp-2 cells was significantly greater than that of other rFimA types. It was also observed that the type II rFimA-MS markedly invaded the epithelial cells and accumulated around the nuclei. Collectively, these findings suggest that fimbriae of P. gingivalis, especially type II, are involved in the initiation and progression of human periodontitis.

Functional differences among FimA variants of Porphyromonas gingivalis and their effects on adhesion to and invasion of human epithelial cells

Fimbriae of Porphyromonas gingivalis, a periodontopathogen, play an important role in its adhesion to and invasion of host cells. The fimA genes encoding fimbrillin (FimA), a subunit protein of fimbriae, have been classified into five types, types I to V, based on nucleotide sequences. We previously reported that P. gingivalis with type II fimA was strongly associated with adult periodontitis. In the present study, we compared the abilities of recombinant FimA (rFimA) types I to V to adhere to and invade human gingival fibroblasts (HGF) and a human epithelial cell line (HEp-2 cells) by using rFimA-conjugated microspheres (rFimA-MS). There were no significant differences in the abilities of the rFimA-MS to adhere to HGF; however, the adhesion of type II rFimA-MS to HEp-2 cells was significantly greater than those of other types of rFimA-MS. We also observed that type II rFimA-MS invaded epithelial cells and accumulated around the nuclei. These adhesion and invasion characteristics were eliminated by the addition of antibodies to type II rFimA and alpha5beta1-integrin. In contrast, Arg-Gly-Asp-Ser peptide and a synthetic peptide of proline-rich protein C had negligible inhibitory effects. Furthermore, P. gingivalis strain HW24D1 with type II fimA adhered to cells and invaded them more than strains with other fimA genotypes. These results suggest that type II FimA can bind to epithelial cells most efficiently through specific host receptors.

Fimbriae of Porphyromonas gingivalis induce opsonic antibodies that significantly enhance phagocytosis and killing by human polymorphonuclear leukocytes

Porphyromonas gingivalis has been strongly implicated in the pathogenesis of human periodontitis. Fimbriae mediate adherence and colonization of the oral cavity by this organism and may, therefore, have potential for use as antigen in an anti-P. gingivalis vaccine. The purpose of our study was to determine whether P. gingivalis fimbriae have opsonic target sites and whether they are accessible on the cell surfaces and cross-reactive among P. gingivalis fimbrial types and serotypes. Rabbits were immunized with a vaccine. The antiserum reacted with a 43-kDa fimbrillin monomer and a 43-kDa component in whole-cell sonicates of P. gingivalis 33277, but it showed only very weak reactivity in the 43-kDa region of Western blots of a whole-cell sonicate of strain DPG3, a mutant that does not express functional fimbriae. The antibody enhanced chemiluminescence approximately six-fold relative to preimmune serum values and significantly enhanced phagocytosis and killing of P. gingivalis 33277 by human polymorphonuclear leukocytes. Peak opsonic activity was observed at week 6 followed by a plateau that remained until week 16. The fimbria-deficient mutant DPG3 did not bind antifimbrial antibody and was not opsonized, whereas strain 381, the parent of the mutant, was opsonized. The specific antibody bound to and opsonized P. gingivalis strains 33277 and 381 (fimbria type I) but not W50, A7A-1-28, 9-14K-1 or FAY-19M-1 (fimbrial types II-V). Specific antibody bound to strain 2561 (fimbrial type I) but, as assessed by chemiluminescence, did not opsonize it. While fimbriae have opsonic target sites that are accessible on P. gingivalis cell surfaces, the relevant opsonic target sites do not appear to be shared across serotypes or fimbrial types. Thus, a vaccine containing, as antigen, fimbrial protein from a single P. gingivalis strain would likely be ineffective against infections by P. gingivalis strains expressing other fimbrial types.

Porphyromonas gingivalis gingipain-R enhances interleukin-8 but decreases gamma interferon-inducible protein 10 production by human gingival fibroblasts in response to T-cell contact

Proteases produced by Porphyromonas gingivalis, an oral pathogen, are considered important virulence factors and may affect the responses of cells equipped with proteinase-activated receptors. The aim of this study was to investigate the effect of the arginine-specific cysteine protease gingipain-R produced by P. gingivalis on chemokine production by human gingival fibroblasts (HGF) and the effect of gingipain-R treatment on the subsequent contact-dependent activation of HGF by T cells. HGF incubated in the presence of purified 47-kDa gingipain-R showed increased levels of interleukin-8 (IL-8) mRNA. Cyclooxygenase-2 (COX-2) mRNA was also induced. Further exposure of HGF to activated T cells resulted in the dose- and time-dependent enhancement of IL-8 transcription and release. T-cell membrane-bound tumor necrosis factor (TNF) was the ligand inducing IL-8 production by HGF, since TNF neutralization abrogated HGF responses to T-cell contact. The enhanced IL-8 release was due, at least in part, to prostaglandin-E(2) production, which was mostly blocked by indomethacin. Gingipain-R proteolytic activity was required since heat inactivation, specific synthetic protease inhibitors, and the natural substrate competitor histatin 5 abrogated its effects. The enhanced production of IL-8 in response to T-cell contact was specific since monocyte chemotactic protein-1 (MCP-1) production was unaffected while interferon-gamma-inducible protein-10 (IP-10) was inhibited. The sum of these activities may result in the recruitment of differential cell types to sites of inflammation since IL-8 preferentially recruits neutrophils and IP-10 attracts activated T cells and may be relevant to the pathogenesis of periodontitis.

Adhesion of Porphyromonas gingivalis strains to cultured epithelial cells from patients with a history of chronic adult periodontitis or from patients less susceptible to periodontitis

BACKGROUND

The present study aimed to explain the interindividual variation in periodontitis susceptibility by differences in the initial adhesion rate of Porphyromonas gingivalis to the pocket epithelium of these individuals, and/or by inter-P. gingivalis strain differences in association capacity (adhesion and internalization).

METHODS

Adhesion assays were performed on epithelial monolayers (cultured in vitro from pocket epithelium belonging to patients who were less or more susceptible to chronic adult periodontitis) using 11 genetically different clinical strains of P. gingivalis.

RESULTS

Both the disease category (less susceptible versus susceptible) and the interstrain variation were found to have a significant effect (both P <0.05) on the initial bacterial association. The chronic adult periodontitis group showed significantly more association of P. gingivalis when compared to less susceptible patients (4.2 x 10(6) versus 3.5 x 10(6)). Also, the interstrain variation was significant, with strains Pg 4 and 5 representing the least and best associating bacteria (1.8 x 10(6) colony forming units for Pg 4, 9 x 10(6) for Pg 5).

CONCLUSIONS

These results indicate that periodontitis susceptibility is influenced by both the interindividual differences in pocket epithelium (allowing more adhesion of P. gingivalis) or by the strain type by which the patient is infected (intra-species differences in adhesion capacity).

Porphyromonas gingivalis gingipains and adhesion to epithelial cells

Porphyromonas gingivalis is one of the principal organisms associated with adult periodontitis. Bacterial surface proteins such as fimbriae and gingipain hemagglutinin domains have been implicated as adhesins that actuate colonization of epithelium lining the gingival sulcus. We investigated the genetics of P. gingivalis adhesion to monolayers of epithelial cells using wild-type and gingipain mutant strains. These experiments suggested that arginine-specific gingipain (Rgp) catalytic activity modulated adhesion. From the data obtained with rgp mutants, we constructed a working hypothesis predicting that attachment and detachment of P. gingivalis to epithelial cells were mediated by gingipain adhesin and Rgp catalytic domains, respectively. A membrane-based epithelial cell binding assay, used to locate adhesins in extracellular fractions of wild-type and mutant strains, recognized gingipain peptides as adhesins rather than fimbriae. We developed a capture assay that demonstrated the binding of gingipain adhesin peptides to oral epithelial cells. The adherence of fimbrillin to epithelial cells was detected after heat denaturation of cell fractions. The prediction that Rgp catalytic activities mediated detachment was substantiated when the high level of attachment of an rgp mutant was reduced in the presence of wild-type cell fractions that contained gingipain catalytic activities.

Subgingival colonization by Porphyromonas gingivalis

Porphyromonas gingivalis, a gram-negative anaerobe, is a major causative agent in the initiation and progression of severe forms of periodontal disease. In order to cause periodontal disease, P. gingivalis must colonize the subgingival region, a process that involves several distinct steps and multiple gene products. The organism must first navigate within the oral fluids in order to reach the hard or soft tissues of the mouth. Retention and growth of bacteria on these surfaces is facilitated by a repertoire of adhesins including fimbriae, hemagglutinins and proteinases. Once established subgingivally, P. gingivalis cells participate in intercellular communication networks with other oral prokaryotic cells and with eukaryotic cells. The establishment of these multiple interactive interfaces can lead to biofilm formation, invasion of root dentin and internalization within gingival epithelial cells. The resulting bacterial and host cellular locations, products and fate contribute to the success of P. gingivalis in colonizing the periodontal region.

Induction of experimental periodontitis in mice with Porphyromonas gingivalis-adhered ligatures

BACKGROUND

Little information is available on the colonization of periodontopathic bacteria and alveolar bone loss in a mouse system, because of the difficulty in establishing bacteria in the oral cavity. The aim of this study was to establish experimental periodontitis in mice by applying a Porphyromonas gingivalis-adhered ligature onto the molars.

METHODS

Specific pathogen-free C3H/HeN mice were divided into 3 groups: 80 infected, 80 sham-infected, and 48 non-treated control mice. Sterile silk ligatures were preincubated with and without P. gingivalis 381 in vitro and then physically tied on the right maxillary first molar of infected and sham-infected mice, respectively. Ten mice from the infected and sham-infected groups and 6 from the control group were sacrificed at 2-week intervals for up to 15 weeks after infection.

RESULTS

Plaque samples were collected at the time of sacrifice and alveolar bone loss was examined. The results indicated that P. gingivalis was recovered from the plaque samples in 95% of the infected mice after 1 week and then gradually dropped to 58% after 15 weeks of infection, whereas P. gingivalis was not isolated in either sham-infected or control mice throughout the experimental period. The infected mice showed significant P. gingivalis-induced bone loss at the sites where the ligature was tied weeks 13 to 15. A linear regression analysis revealed a significant positive correlation between the number of P. gingivalis recovered and alveolar bone loss at 15 weeks after infection (P <0.01).

CONCLUSIONS

The use of a P. gingivalis-adhered ligature supported a long-lasting infection of P. gingivalis in mice, resulting in P. gingivalis-induced alveolar bone breakdown.

Characterization of the relA gene of Porphyromonas gingivalis

Based upon the nucleotide sequence of the relA gene from Escherichia coli, a gene fragment corresponding to the homologous gene from the pathogenic oral bacterium Porphyromonas gingivalis 381 was isolated by PCR and utilized to construct a relA mutant. The mutant, KS7, was defective in ribosome-mediated ppGpp formation and also in the stringent response.

Pleiotropic pigmentation mutants of Porphyromonas gingivalis

Porphyromonas gingivalis is a Gram-negative, black pigmented oral anaerobe associated with adult periodontitis. The adherence of the bacterium to junctional epithelial cells is the first step in infection and colonization. The molecular mechanisms and genetics of colonization are, as yet, not well understood, although it has been demonstrated that P. gingivalis fimbriae are involved in adhesion. In addition, cell surface cysteine proteinases may play a role either directly as adhesins or indirectly through their involvement in the biogenesis of fimbriae. A link has been established between cysteine proteinase-hemagglutinating activity and colongy pigmentation on blood agar. In this study a P. gingivalis ATCC 33277 transposon library was screened for white mutants. Pleiotropic mutants were identified with altered pigmentation, proteinase, hemagglutinin and haemolytic activities. Although the mutants fell into two classes based on the above phenotypes, by electron microscopy both classes showed increased fimbriation and decreased vesicle formation. Sequencing of genomic DNA flanking the transposon insertions revealed that one class of mutants carried disruptions in the gene encoding Lys-gingipain (kgp) and the other in a gene homologous to a glycosyl transferase. Potential roles for these genes in pigmentation, fimbriation, vesicle formation and attachment to epithelial cells are discussed.

Oral flora and pathogenic organisms

Oral microbial flora consist of numerous bacterial taxa, ranging from aerobes through fastidious anaerobes, and fungi, viruses, and protozoa. Many of these bacteria are unique to the oral cavity. The organisms exist in a complex interrelationship that is regulated and maintained by physical and metabolic microbial interactions, and by environmental factors, such as saliva and diet. Many of these organisms are relatively harmless, although others are significant pathogens, producing local and systemic diseases in healthy and compromised individuals.

Inhibitory effects of protamines on proteolytic and adhesive activities of Porphyromonas gingivalis

Protamines (salmine prepared from sperm DNA of salmon and clupeine from herring sperm), which are basic peptides rich in arginine, were found to inhibit the proteolytic activity of arginine-specific cysteine protease (RC-protease) from Porphyromonas gingivalis. Lineweaver-Burk plot analysis revealed that the protamines competitively inhibited proteolytic activity with cleavage of benzoyl-L-arginine-p-nitroanilide, a synthetic substrate of RC-protease. Furthermore, the protamines were capable of binding strongly to P. gingivalis fimbriae and inhibited fimbrial interaction with immobilized fibronectin. These results clearly show that protamines are potent inhibitors of the proteolytic and adhesive activities of P. gingivalis.

Specific interactions between Porphyromonas gingivalis fimbriae and human extracellular matrix proteins

The interactions of the extracellular matrix (ECM) proteins (laminin, elastin, fibronectin, type I collagen, thrombospondin and vitronectin) with the fimbriae of Porphyromonas gingivalis were analyzed based on surface plasmon resonance (SPR) spectroscopy using a biomolecular interaction analyzing system (BIAcore). The BIAcore profiles demonstrated that fimbriae specifically bound to all of the ECM proteins with significant association constants (Ka). Vitronectin showed the highest affinity to fimbriae (Ka = 3.79 x 10(6) M-1), while the affinity of laminin was lowest (Ka = 2.15 x 10(6) M-1). A synthetic peptide which is a potent inhibitor of fimbrial binding to salivary proteins was not significantly effective on the fimbrial interactions with the ECM proteins. Using polystyrene microtiter plates revealed that P. gingivalis fimbriae bound markedly to immobilized fibronectin and type I collagen, while the interaction of fimbriae with the other ECM proteins was not clearly demonstrated. These results suggest that interactions between fimbriae and the ECM proteins occur with specific affinities which are not mediated by mechanisms identical to those of salivary proteins. It was also shown that SPR spectroscopy is a useful method to analyze these specific interactions.

Localization of HArep-containing genes on the chromosome of Porphyromonas gingivalis W83

We have mapped a group of virulence genes of Porphyromonas gingivalis to a single large fragment of the genome. These genes (rgpA, kgp, and hagA) all contain a consensus repeat sequence (HArep). rgpA and kgp encode cysteine proteases with Arg-X and Lys-X specificity, respectively, and hagA encodes a hemagglutinin. Genomic DNA fragments separated by pulse-field gel electrophoresis were blotted and probed in order to localize the genes to a 0.25-Mb NheI fragment of the P. gingivalis W83 genome. Further hybridization analyses with single- and double-restriction digestion allowed us to generate a physical map of the fragment and determine the precise locations of the protease and hemagglutinin genes. In addition, we found an insertion-like sequence, IS195, near the ends of the 0. 25-Mb NheI fragment. A similarly sized fragment carrying HArep sequences was also demonstrated in the P. gingivalis W12 and W50 genomes.

Effect of cysteine protease of Porphyromonas gingivalis on adhesion molecules in gingival epithelial cells

We examined the effect of cysteine protease of Porphyromonas gingivalis (P. gingivalis) on cell adhesion molecules including intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) and very late antigen-4 (VLA-4) of human gingival epithelial cells. The cells were incubated for 48 hr with or without P. gingivalis protease. Their cell adhesion molecule expression levels were increased at 12 hr, but decreased at 18-48 hr. This result suggests that protease degrades cell adhesion molecules. After the stimulation with protease for 12 hr, P. gingivalis fimbrial binding to a monolayer of the cells was effectively inhibited by the addition of the cell adhesion molecules, suggesting the fimbrial binding to the cells occurred through cell surface adhesion molecules.

Targeted disruption of fibronectin-integrin interactions in human gingival fibroblasts by the RI protease of Porphyromonas gingivalis W50

Cell surface integrins mediate interactions between cells and their extracellular matrix and are frequently exploited by a range of bacterial pathogens to facilitate adherence and/or invasion. In this study we examined the effects of Porphyromonas gingivalis proteases on human gingival fibroblast (HGF) integrins and their fibronectin matrix. Culture supernatant from the virulent strain W50 caused considerably greater loss of the beta1 integrin subunit from HGF in vitro than did that of the beige-pigmented strain W50/BE1. Prior treatment of the W50 culture supernatant with the protease inhibitor Nalpha-p-tosyl-L-lysine chloromethyl ketone (TLCK) blocked its effects on cultured cells, indicating that this process is proteolytically mediated. Purified arginine-specific proteases from P. gingivalis W50 were able to mimic the effects of the whole-culture supernatant on loss of beta1 integrin expression. However purified RI, an alpha/beta heterodimer in which the catalytic chain is associated with an adhesin chain, was 12 times more active than RIA, the catalytic monomer, in causing loss of the alpha5beta1 integrin (fibronectin receptor) from HGF. No effect was observed on the alphaVbeta3 integrin (vitronectin receptor). The sites of action of RI and RIA were investigated in cells exposed to proteases pretreated with TLCK to inactivate the catalytic component. Use of both monoclonal antibody 1A1, which recognizes only the adhesin chain of RI, and a rabbit antibody against P. gingivalis whole cells indicated localization of RI on the fibroblasts in a clear, linear pattern typical of that seen with fibronectin and alpha5beta1 integrin. Exact colocalization of RI with fibronectin and its alpha5beta1 receptor was confirmed by double labeling and multiple-exposure photomicroscopy. In contrast, RIA bound to fibroblasts in a weak, patchy manner, showing only fine linear or granular staining. It is concluded that the adhesin component of RI targets the P. gingivalis arginine-protease to sites of fibronectin deposition on HGF, contributing to the rapid loss of both fibronectin and its main alpha5beta1 integrin receptor. Given the importance of integrin-ligand interactions in fibroblast function, their targeted disruption by RI may represent a novel mechanism of damage in periodontal disease.

Life below the gum line: pathogenic mechanisms of Porphyromonas gingivalis

Porphyromonas gingivalis, a gram-negative anaerobe, is a major etiological agent in the initiation and progression of severe forms of periodontal disease. An opportunistic pathogen, P. gingivalis can also exist in commensal harmony with the host, with disease episodes ensuing from a shift in the ecological balance within the complex periodontal microenvironment. Colonization of the subgingival region is facilitated by the ability to adhere to available substrates such as adsorbed salivary molecules, matrix proteins, epithelial cells, and bacteria that are already established as a biofilm on tooth and epithelial surfaces. Binding to all of these substrates may be mediated by various regions of P. gingivalis fimbrillin, the structural subunit of the major fimbriae. P. gingivalis is an asaccharolytic organism, with a requirement for hemin (as a source of iron) and peptides for growth. At least three hemagglutinins and five proteinases are produced to satisfy these requirements. The hemagglutinin and proteinase genes contain extensive regions of highly conserved sequences, with posttranslational processing of proteinase gene products contributing to the formation of multimeric surface protein-adhesin complexes. Many of the virulence properties of P. gingivalis appear to be consequent to its adaptations to obtain hemin and peptides. Thus, hemagglutinins participate in adherence interactions with host cells, while proteinases contribute to inactivation of the effector molecules of the immune response and to tissue destruction. In addition to direct assault on the periodontal tissues, P. gingivalis can modulate eucaryotic cell signal transduction pathways, directing its uptake by gingival epithelial cells. Within this privileged site, P. gingivalis can replicate and impinge upon components of the innate host defense. Although a variety of surface molecules stimulate production of cytokines and other participants in the immune response, P. gingivalis may also undertake a stealth role whereby pivotal immune mediators are selectively inactivated. In keeping with its strict metabolic requirements, regulation of gene expression in P. gingivalis can be controlled at the transcriptional level. Finally, although periodontal disease is localized to the tissues surrounding the tooth, evidence is accumulating that infection with P. gingivalis may predispose to more serious systemic conditions such as cardiovascular disease and to delivery of preterm infants.

Contact-dependent protein secretion in Porphyromonas gingivalis

Porphyromonas gingivalis can induce its uptake by host epithelial cells; however, the nature and role of the P. gingivalis molecules involved in this invasion process have yet to be determined. In this study, modulation of secreted P. gingivalis proteins following association with gingival epithelial cells was investigated. Western immunoblot analysis showed that contact with epithelial cells or epithelial cell growth media induces P. gingivalis 33277 to secrete several proteins with molecular masses between 35 and 95 kDa. Secretion of the Arg-gingipain and Lys-gingipain proteases was repressed under these conditions. The contact-induced secreted protein profile was altered in Arg-gingipain-deficient and Lys-gingipain-deficient mutants, indicating a possible role for these proteases in the secretion pathway. The P. gingivalis contact-dependent protein secretion pathway differs to some extent from type III protein secretion pathways in enteric pathogens, as a gene homologous to the invA family genes was not detected in P. gingivalis. The secreted proteins of P. gingivalis may play a role in the interactions of the organism with host cells.

Surface structure, hydrophobicity, phagocytosis, and adherence to matrix proteins of Bacillus cereus cells with and without the crystalline surface protein layer

Nonopsonic phagocytosis of Bacillus cereus by human polymorphonuclear leukocytes (PMNs) with particular attention to bacterial surface properties and structure was studied. Two reference strains (ATCC 14579(T) and ATCC 4342) and two clinical isolates (OH599 and OH600) from periodontal and endodontic infections were assessed for adherence to matrix proteins, such as type I collagen, fibronectin, laminin, and fibrinogen. One-day-old cultures of strains OH599 and OH600 were readily ingested by PMNs in the absence of opsonins, while cells from 6-day-old cultures were resistant. Both young and old cultures of the reference strains of B. cereus were resistant to PMN ingestion. Preincubation of PMNs with the phagocytosis-resistant strains of B. cereus did not affect the phagocytosis of the sensitive strain. Negatively stained cells of OH599 and OH600 studied by electron microscopy had a crystalline protein layer on the cell surface. In thin-sectioned cells of older cultures (3 to 6 days old), the S-layer was observed to peel off from the cells. No S-layer was detected on the reference strains. Extraction of cells with detergent followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a major 97-kDa protein from the strains OH599 and OH600 but only a weak 97-kDa band from the reference strain ATCC 4342. One-day-old cultures of the clinical strains (hydrophobicity, 5.9 to 6.0%) showed strong binding to type I collagen, laminin, and fibronectin. In contrast, reference strains (hydrophobicity, -1.0 to 4.2%) as well as 6-day-old cultures of clinical strains (hydrophobicity, 19.0 to 53.0%) bound in only low numbers to the proteins. Gold-labelled biotinylated fibronectin was localized on the S-layer on the cell surface as well as on fragments of S-layer peeling off the cells of a 6-day-old culture of B. cereus OH599. Lactose, fibronectin, laminin, and antibodies against the S-protein reduced binding to laminin but not to fibronectin. Heating the cells at 84 degreesC totally abolished binding to both proteins. Benzamidine, a noncompetitive serine protease inhibitor, strongly inhibited binding to fibronectin whereas binding to laminin was increased. Overall, the results indicate that changes in the surface structure, evidently involving the S-layer, during growth of the clinical strains of B. cereus cause a shift from susceptibility to PMN ingestion and strong binding to matrix and basement membrane proteins. Furthermore, it seems that binding to laminin is mediated by the S-protein while binding to fibronectin is dependent on active protease evidently attached to the S-layer.

Proteases of Porphyromonas gingivalis: what don't they do?

The gram-negative anaerobic bacterium Porphyromonas gingivalis has been strongly associated with the causation of human periodontal diseases. One distinguishing property of these organisms that has been implicated in periodontal destruction is the expression of potent protease activity. Recent biochemical and genetic approaches have clearly demonstrated that at least five distinct proteases are elaborated by these organisms. The utilization of monospecific mutants defective in individual proteases has demonstrated that protease activity is important in virulence but also has suggested the complexity of the functions of the enzymes in the physiology of these microorganisms. This review summarizes current progress in assessing the role of these enzymes in periodontal inflammation and discusses some unresolved issues relevant to the significance of P. gingivalis proteases in virulence.

Porphyromonas gingivalis fimbriae use beta2 integrin (CD11/CD18) on mouse peritoneal macrophages as a cellular receptor, and the CD18 beta chain plays a functional role in fimbrial signaling

In this study, we demonstrate that Porphyromonas gingivalis fimbriae use molecules of beta2 integrin (CD11/CD18) on mouse peritoneal macrophages as cellular receptors and also show that the beta chain (CD18) may play a functional role in signalling for the fimbria-induced expression of interleukin-1beta (IL-1beta) and tumor necrosis factor alpha (TNF-alpha) genes in the cells. Using a binding assay with 125I-labeled fimbriae, we observed that fimbrial binding to the macrophages was inhibited by treatment with CD11a, CD11b, CD11c, or CD18 antibody but not by that with CD29 antibody. Western blot assays showed that the fimbriae bound to molecules of beta2 integrin (CD11/CD18) on the macrophages. Furthermore, Northern blot analyses showed that the fimbria-induced expression of IL-1beta and TNF-alpha genes in the cells was inhibited strongly by CD18 antibody treatment and slightly by CD11a, CD11b, or CD11c antibody treatment. Interestingly, intracellular adhesion molecule 1 (ICAM-1), a ligand of CD11/CD18, inhibited fimbrial binding to the cells in a dose-dependent manner. In addition, ICAM-1 clearly inhibited the fimbria-induced expression of IL-1beta and TNF-alpha genes in the cells. However, such inhibitory action was not observed with laminin treatment. These results suggest the importance of beta2 integrin (CD11/CD18) as a cellular receptor of P. gingivalis fimbriae in the initiation stage of the pathogenic mechanism of the organism in periodontal disease.

A peptide domain on gingipain R which confers immunity against Porphyromonas gingivalis infection in mice

The cysteine proteinases referred to as gingipains R (gingipain R1 and gingipain R2) and gingipain K produced by Porphyromonas gingivalis are virulence factors of this periodontal pathogen which likely act by interrupting host defense mechanisms and by participating in the penetration and destruction of host connective tissue. To examine the effect of immunization with gingipains R on the ability of P. gingivalis to colonize and invade in the mouse chamber model, BALB/c mice were immunized intraperitoneally with the 95-kDa gingipain R1, the 50-kDa gingipain R2, or multiple antigenic peptide (MAP)-conjugated gingipain R-derived peptides and then challenged with P. gingivalis. Immunization of mice with the 95-kDa gingipain R1, the 50-kDa gingipain R2, or a peptide derived from the N-terminal sequence of the catalytic domain of gingipains R (peptide A) followed by challenge with P. gingivalis A7436 resulted in protection from P. gingivalis invasion. In contrast, immunization with peptides corresponding to either a sequence encompassing the catalytic cysteine residue of gingipains R (peptide B) or an identical sequence within the catalytic domains of gingipain R1 and gingipain K (peptide C), followed by challenge with P. gingivalis, did not protect animals, nor did immunization with a peptide corresponding to sequences within the adhesion/hemagglutinin domain of gingipain R1 (peptide D) which have been shown to be directly involved in the hemagglutinin activity of gingipain R1. However, the immunoglobulin G (IgG) titer obtained following immunization with peptide D was comparable to that obtained following immunization with the N-terminal peptide (peptide A). Competitive enzyme-linked immunosorbent assays, using either the 95-kDa gingipain R1 or gingipain K as the competing soluble antigen, indicated that 42 and 53% of the antibodies induced by immunization with heat-killed bacteria recognize gingipain R1 and gingipain K, respectively; however, even at very high concentrations, the 50-kDa gingipain R2 did not hinder IgG binding to P. gingivalis. These results indicate that antibodies directed to the amino-terminal region of the catalytic domain of gingipains R are capable of inducing a protective immune response against P. gingivalis infection in the mouse chamber model.