Binding of Porphyromonas gingivalis gingipains to human CD4(+) T cells preferentially down-regulates surface CD2 and CD4 with little affect on co-stimulatory molecule expression

Association between Porphyromonas Gingivalis and systemic diseases: Focus on T cells-mediated adaptive immunity

The association between periodontal disease and systemic disease has become a research hotspot. Porphyromonas gingivalis (P. gingivalis), a crucial periodontal pathogen, affects the development of systemic diseases. The pathogenicity of P. gingivalis is largely linked to interference with the host's immunity. This review aims to discover the role of P. gingivalis in the modulation of the host's adaptive immune system through a large number of virulence factors and the manipulation of cellular immunological responses (mainly mediated by T cells). These factors may affect the cause of large numbers of systemic diseases, such as atherosclerosis, hypertension, adverse pregnancy outcomes, inflammatory bowel disease, diabetes mellitus, non-alcoholic fatty liver disease, rheumatoid arthritis, and Alzheimer's disease. The point of view of adaptive immunity may provide a new idea for treating periodontitis and related systemic diseases.

The Effects of Porphyromonas gingivalis on Atherosclerosis-Related Cells

Atherosclerosis (AS), one of the most common types of cardiovascular disease, has initially been attributed to the accumulation of fats and fibrous materials. However, more and more researchers regarded it as a chronic inflammatory disease nowadays. Infective disease, such as periodontitis, is related to the risk of atherosclerosis. Porphyromonas gingivalis (P. gingivalis), one of the most common bacteria in stomatology, is usually discovered in atherosclerotic plaque in patients. Furthermore, it was reported that P. gingivalis can promote the progression of atherosclerosis. Elucidating the underlying mechanisms of P. gingivalis in atherosclerosis attracted attention, which is thought to be crucial to the therapy of atherosclerosis. Nevertheless, the pathogenesis of atherosclerosis is much complicated, and many kinds of cells participate in it. By summarizing existing studies, we find that P. gingivalis can influence the function of many cells in atherosclerosis. It can induce the dysfunction of endothelium, promote the formation of foam cells as well as the proliferation and calcification of vascular smooth muscle cells, and lead to the imbalance of regulatory T cells (Tregs) and T helper (Th) cells, ultimately promoting the occurrence and development of atherosclerosis. This article summarizes the specific mechanism of atherosclerosis caused by P. gingivalis. It sorts out the interaction between P. gingivalis and AS-related cells, which provides a new perspective for us to prevent or slow down the occurrence and development of AS by inhibiting periodontal pathogens.

Host cell-surface proteins as substrates of gingipains, the main proteases of Porphyromonas gingivalis

Gingipains are extracellular cysteine proteases of the oral pathogen Porphyromonas gingivalis and are its most potent virulence factors. They can degrade a great variety of host proteins, thereby helping the bacterium to evade the host immune response, deregulate signaling pathways, trigger anoikis and, finally, cause tissue destruction. Host cell-surface proteins targeted by gingipains are the main focus of this review and span three groups of substrates: immune-regulatory proteins, signaling pathways regulators and adhesion molecules. The analysis of published data revealed that gingipains predominantly inactivate their substrates by cleaving them at one or more sites, or through complete degradation. Sometimes, gingipains were even found to initially shed their membrane substrates, but this was mostly just the first step in the degradation of cell-surface proteins.

Vaccination with recombinant RgpA peptide protects against Porphyromonas gingivalis-induced bone loss

OBJECTIVE

Following Porphyromonas gingivalis infection in mice, the efficacy of vaccination by recombinant and native RgpA in modulating the early local anti-inflammatory and immune responses and periodontal bone loss were examined.

MATERIAL AND METHODS

Using the subcutaneous chamber model, exudates were analyzed for cytokines after treatment with native RgpA and adjuvant (test), or adjuvant and saline alone (controls). Mice were also immunized with recombinant RgpA after being orally infected with P. gingivalis. After 6 wk, serum was examined for anti-P. gingivalis IgG1 and IgG2a titers and for alveolar bone resorption.

RESULTS

Immunization with native RgpA shifted the immune response toward an anti-inflammatory response as demonstrated by decreased proinflammatory cytokine IL-1β production and greater anti-inflammatory cytokine IL-4 in chamber exudates. Systemically, immunization with recombinant RgpA peptide prevented alveolar bone loss by 50%, similar to immunization with heat-killed whole bacteria. Furthermore, recombinant RgpA shifted the humoral response toward high IgG1 and low IgG2a titers, representing an in vivo anti-inflammatory response.

CONCLUSIONS

The present study demonstrates the potential of RgpA to shift the early local immune response toward an anti-inflammatory response while vaccination with recRgpA protected against P. gingivalis-induced periodontitis.

Gingipains: Critical Factors in the Development of Aspiration Pneumonia Caused by Porphyromonas gingivalis

Aspiration pneumonia is a life-threatening infectious disease often caused by oral anaerobic and periodontal pathogens such as Porphyromonas gingivalis. This organism produces proteolytic enzymes, known as gingipains, which manipulate innate immune responses and promote chronic inflammation. Here, we challenged mice with P. gingivalis W83 and examined the role of gingipains in bronchopneumonia, lung abscess formation, and inflammatory responses. Although gingipains were not required for P. gingivalis colonization and survival in the lungs, they were essential for manifestation of clinical symptoms and infection-related mortality. Pathologies caused by wild-type (WT) P. gingivalis W83, including hemorrhage, necrosis, and neutrophil infiltration, were absent from lungs infected with gingipain-null isogenic strains or WT bacteria preincubated with gingipain-specific inhibitors. Damage to lung tissue correlated with systemic inflammatory responses, as manifested by elevated levels of TNF, IL-6, IL-17, and C-reactive protein. These effects were unequivocally dependent on gingipain activity. Gingipain activity was also implicated in the observed increase in IL-17 in lung tissues. Furthermore, gingipains increased platelet counts in the blood and activated platelets in the lungs. Arginine-specific gingipains made a greater contribution to P. gingivalis-related morbidity and mortality than lysine-specific gingipains. Thus, inhibition of gingipain may be a useful adjunct treatment for P. gingivalis-mediated aspiration pneumonia.

The role of RgpA in the pathogenicity of Porphyromonas gingivalis in the murine periodontitis model

AIM

To investigate the in vivo role of gingipains in Porphyromonas gingivalis' virulence, and suggest a possible host mechanisms through which the bacteria cause alveolar bone loss.

MATERIALS AND METHODS

Mice were orally infected with P. gingivalis wild type, or the gingipains mutants (RgpA⁻, Kgp⁻, RgpA⁻/Kgp⁻). Mice were analysed for alveolar bone loss using micro-computed tomography. The molecular effects of the proteases were evaluated using the subcutaneous chamber model. Mice were infected with P. gingivalis wild type or mutants. Exudates were analysed for cytokine and leukocytes levels, in vivo phagocytosis, P. gingivalis survival and serum anti-P. gingivalis IgG titres.

RESULTS

Only RgpA-expressing bacteria induced significantly alveolar bone loss, and suppressed phagocytosis resulting in increased survival of P. gingivalis in the chamber exudates. In addition, RgpA-expressing bacteria induced higher levels of leukocytes and cytokines 2 h post-infection, and reduced levels of serum anti-P. gingivalis IgG titres 7 days post-infection.

CONCLUSIONS

Our findings showed that elimination of RgpA from P. gingivalis diminished inflammation, but augmented phagocytosis and antibody titres, coincidental with reduced alveolar bone loss. These findings support the hypothesis that RgpA is a critical virulence factor in the pathogenesis of experimental periodontitis in mice.

Suppression of inflammatory gene expression in T cells by Porphyromonas gingivalis is mediated by targeting MAPK signaling

There is increasing awareness of the effects of Porphyromonas gingivalis on host immune responses. Degradation of cytokines and chemokines by cysteine proteinases has previously been reported. However, the precise mechanisms by which P. gingivalis is able to alter intracellular signaling, and thus proliferation and inflammation, have not been described. We have previously reported suppression of activator protein-1 (AP-1) and degradation of IL-2 by proteinases from P. gingivalis. In the present study, we have analyzed the effects of P. gingivalis on Jurkat T-cell signal transduction and subsequent IL-2 and CXCL8 expression. We found that CXCL8, but not IL-2, gene expression levels were significantly suppressed by viable P. gingivalis. Analysis of intracellular signaling revealed an inhibitory effect of P. gingivalis on c-Jun and c-Fos, but not NFκB (p50 and p65), NFAT or STAT5 expression. This inhibitory effect was not due to suppression of mitogen-activated protein kinase (MAPK) (p38, erk and JNK) gene expression, but was rather due to prevention of protein kinase C (PKC) and p38 phosphorylation, as demonstrated by western blot analysis. Furthermore, SOCS1 and SOCS3 expression levels decreased following treatment of Jurkat T cells with viable P. gingivalis. The results indicate that P. gingivalis is able to suppress inflammatory gene expression by targeting the activity of MAPK pathways in T cells, which was confirmed by using specific inhibitors of NF-κB, PKC, ERK, p38 and JNK.

Alzheimer's Disease: APP, Gamma Secretase, APOE, CLU, CR1, PICALM, ABCA7, BIN1, CD2AP, CD33, EPHA1, and MS4A2, and Their Relationships with Herpes Simplex, C. Pneumoniae, Other Suspect Pathogens, and the Immune System

Alzheimer's disease susceptibility genes, APP and gamma-secretase, are involved in the herpes simplex life cycle, and that of other suspect pathogens (C. pneumoniae, H. pylori, C. neoformans, B. burgdorferri, P. gingivalis) or immune defence. Such pathogens promote beta-amyloid deposition and tau phosphorylation and may thus be causative agents, whose effects are conditioned by genes. The antimicrobial effects of beta-amyloid, the localisation of APP/gamma-secretase in immunocompetent dendritic cells, and gamma secretase cleavage of numerous pathogen receptors suggest that this network is concerned with pathogen disposal, effects which may be abrogated by the presence of beta-amyloid autoantibodies in the elderly. These autoantibodies, as well as those to nerve growth factor and tau, also observed in Alzheimer's disease, may well be antibodies to pathogens, due to homology between human autoantigens and pathogen proteins. NGF or tau antibodies promote beta-amyloid deposition, neurofibrillary tangles, or cholinergic neuronal loss, and, with other autoantibodies, such as anti-ATPase, are potential agents of destruction, whose formation is dictated by sequence homology between pathogen and human proteins, and thus by pathogen strain and human genes. Pathogen elimination in the ageing population and removal of culpable autoantibodies might reduce the incidence and offer hope for a cure in this affliction.

The gingipains: scissors and glue of the periodontal pathogen, Porphyromonas gingivalis

The anaerobic bacterium, Porphyromonas gingivalis, is associated with chronic periodontal disease (periodontitis or gum disease). The disease is not only the leading cause of tooth loss in the developed world, but is associated with a number of systemic diseases, such as cardiovascular disease and diabetes. The most potent virulence factors of this bacterium are the gingipains, three cysteine proteases that bind and cleave a wide range of host proteins. This article summarizes current knowledge of the structure and function of the enzymes, with a particular focus on what remains to be elucidated regarding the structure and function of the nonenzymatic adhesin domains of the high-molecular-weight forms of the proteases.

Blockade of protease-activated receptors on T cells correlates with altered proteolysis of CD27 by gingipains of Porphyromonas gingivalis

Cysteine proteinases, termed gingipains, of Porphyromonas gingivalis are able to inactivate a broad range of host proteins involved in cellular responses and have been implicated as key virulence factors in the onset and progression of adult periodontitis. In the present study, the high molecular weight Arg-gingipain, RgpA, produced a time- and concentration-dependent hydrolysis of the tumour necrosis factor (TNF)-alpha receptor family member CD27 on resting T cells. As a consequence of CD27 degradation, a reduction in CD27-ligation dependent co-stimulatory CD40L expression was observed. Concomitantly, RgpA activated the protease-activated receptors (PAR)-1, PAR-2 and PAR-4 and induced CD69 and CD25 expression on T cells, thereby demonstrating T cell activation. The Lys-gingipain Kgp demonstrated a low capacity to degrade CD27 but the ability to affect CD27 expression and biological activity was increased when T cells were pretreated with blocking peptide against PAR-2. CD70, the ligand for CD27 induced on activated B cells, was significantly reduced by RgpA treatment and weakly affected by Kgp. These findings suggest that while RgpA can activate T cells through PARs, the parallel action of direct hydrolysis of membrane CD27 as well as CD70 indicates a potential down-regulatory effect through inhibition of CD27/CD70-mediated cell activation in periodontitis.

Influence of Combinations of Bacteria on the Levels of Prostaglandin E2, Interleukin-1β, and Granulocyte Elastase in Gingival Crevicular Fluid and on the Severity of Periodontal Disease

BACKGROUND

The aim of this study was to investigate the simultaneous presence of periodontal microbiota on inflammatory markers in gingival crevicular fluid from individuals with periodontal diseases.

METHODS

A total of 82 individuals with periodontal disease (mean age: 54.3 +/- 3.0 years) and 31 periodontally healthy individuals (mean age: 53.2 +/- 3.0 years) were randomly chosen and underwent clinical oral examinations in 2003 with the determination of the dental plaque index (PI), gingival index (GI), and periodontal probing depth (PD). The simultaneous presence of polymerase chain reaction (PCR)-assessed periodontal bacteria, levels of prostaglandin E(2) (PGE(2)), granulocyte elastase, interleukin 1-beta (IL-1beta), and total protein concentration were determined from the pockets. Marginal bone height percent was measured on x-rays. Analysis of variance and chi(2) tests were used to analyze the results.

RESULTS

In sites with Tannerella forsythensis, levels of PGE(2) (pg/site), granulocyte elastase (monoclonal antibodies (mAbs)/site), and total protein (mg/ml) were significantly higher than in sites without T. forsythensis (P <0.05, P <0.01, and P <0.05, respectively). Those with periodontal disease with simultaneous presence of T. forsythensis and Porphyromonas gingivalis, or T. forsythensis and Prevotella nigrescens, showed significantly higher PI and GI, deeper PD, more loss of attachment, and more release of PGE(2) and granulocyte elastase than did periodontitis patients without these bacteria.

CONCLUSION

The simultaneous presence of T. forsythensis and P. gingivalis, or T. forsythensis and P. nigrescens, seemed to promote the release of subgingival inflammatory mediators and seemed to be associated with more severe periodontal disease.