Antigenic cross-reactivity among Porphyromonas gingivalis serotypes

A novel approach for purification and selective capture of membrane vesicles of the periodontopathic bacterium, Porphyromonas gingivalis: membrane vesicles bind to magnetic beads coated with epoxy groups in a noncovalent, species-specific manner

Membrane vesicles (MVs) of Porphyromonas gingivalis are regarded as an offensive weapon of the bacterium, leading to tissue deterioration in periodontal disease. Therefore, isolation of highly purified MVs is indispensable to better understand the pathophysiological role of MVs in the progression of periodontitis. MVs are generally isolated by a conventional method based on ultracentrifugation of the bacterial culture supernatant. However, the resulting MVs are often contaminated with co-precipitating bacterial appendages sheared from the live bacteria. Here, we report an intriguing property of P. gingivalis MVs–their ability to bind superparamagnetic beads coated with epoxy groups (SB-Epoxy). Analysis of fractions collected during the purification revealed that all MVs of five tested P. gingivalis stains bound to SB-Epoxy. In contrast, free fimbriae in the crude MV preparation did not bind to the SB-Epoxy. The SB-Epoxy-bound MVs were easily dissociated from the SB-Epoxy using a mild denaturation buffer. These results suggest that the surface chemistry conferred by epoxy on the beads is responsible for the binding, which is mediated by noncovalent bonds. Both the structural integrity and purity of the isolated MVs were confirmed by electron microscopy. The isolated MVs also caused cell detachment from culture dishes at a physiologically relevant concentration. Assays of competitive binding between the SB-Epoxy and mixtures of MVs from five bacterial species demonstrated that only P. gingivalis MVs could be selectively eliminated from the mixtures. We suggest that this novel approach enables efficient purification and selective elimination of P. gingivalis MVs.

Microbial carriage state of peripheral blood dendritic cells (DCs) in chronic periodontitis influences DC differentiation, atherogenic potential

The low-grade oral infection chronic periodontitis (CP) has been implicated in coronary artery disease risk, but the mechanisms are unclear. In this study, a pathophysiological role for blood dendritic cells (DCs) in systemic dissemination of oral mucosal pathogens to atherosclerotic plaques was investigated in humans. The frequency and microbiome of CD19(-)BDCA-1(+)DC-SIGN(+) blood myeloid DCs (mDCs) were analyzed in CP subjects with or without existing acute coronary syndrome and in healthy controls. FACS analysis revealed a significant increase in blood mDCs in the following order: healthy controls < CP < acute coronary syndrome/CP. Analysis of the blood mDC microbiome by 16S rDNA sequencing showed Porphyromonas gingivalis and other species, including (cultivable) Burkholderia cepacia. The mDC carriage rate with P. gingivalis correlated with oral carriage rate and with serologic exposure to P. gingivalis in CP subjects. Intervention (local debridement) to elicit a bacteremia increased the mDC carriage rate and frequency in vivo. In vitro studies established that P. gingivalis enhanced by 28% the differentiation of monocytes into immature mDCs; moreover, mDCs secreted high levels of matrix metalloproteinase-9 and upregulated C1q, heat shock protein 60, heat shock protein 70, CCR2, and CXCL16 transcripts in response to P. gingivalis in a fimbriae-dependent manner. Moreover, the survival of the anaerobe P. gingivalis under aerobic conditions was enhanced when within mDCs. Immunofluorescence analysis of oral mucosa and atherosclerotic plaques demonstrate infiltration with mDCs, colocalized with P. gingivalis. Our results suggest a role for blood mDCs in harboring and disseminating pathogens from oral mucosa to atherosclerosis plaques, which may provide key signals for mDC differentiation and atherogenic conversion.

Antibodies to periodontal pathogens and coronary artery calcification in type 1 diabetic and nondiabetic subjects

BACKGROUND AND OBJECTIVE

The aim of this study was to examine whether serum immunoglobulin G (IgG) levels to Porphyromonas gingivalis and Actinobacillus actinomycetemcomitans are higher in type 1 diabetic patients than in controls and are associated with coronary artery calcification, a measure of atherosclerosis.

MATERIAL AND METHODS

One-hundred and ninety nine type 1 diabetic patients (mean age 38 +/- 4 years) and 201 age- and gender-matched nondiabetic subjects had coronary artery calcification, as measured by electron beam computed tomography. Serum IgG levels to P. gingivalis W50 and to A. actinomycetemcomitans HK1651 whole cells were measured by enzyme-linked immunosorbent assay.

RESULTS

A similar proportion of diabetic patients (29%) and controls (31%, p = 0.7) had elevated serum IgG to periodontal bacteria, defined as being above the median antibody level for both microorganisms. Elevated antibody levels were associated with higher systolic blood pressure (p = 0.02) and an increased odds of coronary artery calcification in all subjects combined (odds ratio = 1.7, p = 0.047) and in diabetic subjects examined separately (odds ratio = 2.01, p = 0.027). Association of serum IgG levels with coronary artery calcification was independent of social class, lipids and antibody levels to other microorganisms, but not systolic blood pressure (odds ratio = 1.4, p = 0.1 on adjustment for blood pressure). There was no association between serum IgG level and vascular endothelial function.

CONCLUSION

Elevated levels of serum IgG to P. gingivalis and A. actinomycetemcomitans are associated with coronary artery atherosclerosis. This may reflect a direct role for periodontal infection or a role for the host response to infection in coronary atherosclerosis, particularly in patients with type 1 diabetes.

Immunoglobulin G Antibodies Against Environmental Moulds in a Norwegian Healthy Population Shows a Bimodal Distribution for Aspergillus versicolor

Immunoglobulin G (IgG) antibodies against moulds related to indoor dampness problems are used as biomarkers to indicate exposure. In the present study, we evaluated the frequency of mould exposure in an adult healthy population by examining levels of mould-specific IgG antibodies in Norwegian blood donors. Using enzyme-linked immunosorbent assay, 106 blood donor sera were analyzed for IgG antibodies to Aspergillus versicolor, Penicillium chrysogenum, Cladosporium herbarum, Stachybotrys chartarum and Fusarium oxysporum. The levels of specific IgG antibodies to P. chrysogenum, C. herbarum and S. chartarum correlated (r = 0.46-0.62). Responses to A. versicolor were considerably stronger than to the other moulds, and another 996 blood donor sera were analyzed for IgG antibodies to this mould. Women had significantly higher levels of specific IgG antibodies to A. versicolor than men. The concentration of A. versicolor-specific IgG antibodies showed a non-Gaussian, bimodal distribution profile, in which 12.5% were defined as positive to exposure. This suggests that significant mould exposure in a healthy population can be calculated from mean + 1SD. Western blotting analyses showed that antibody responses to A. versicolor were largely directed against carbohydrate antigens of unknown saccharides.

Characterization of two outer membrane protein antigens of Porphyromonas gingivalis that are protective in a murine lesion model

Porphyromonas gingivalis is a key periodontal pathogen that has been implicated in the aetiology of chronic adult periodontitis. The aim of this study was to characterize two potential vaccine candidates (PG32 and PG33) identified from a previous genomic sequence analysis. Gene knockout studies suggested that these proteins play an important role in bacterial growth and are transcriptionally linked. Analysis of 14 laboratory and clinical isolates of P. gingivalis found that in all strains, both genes were present with a high level of conservation and that the two proteins were also expressed in vitro. Truncated recombinant PG32 and PG33 proteins were produced in Escherichia coli in an attempt to increase the solubility of the proteins while retaining their native conformation. While most of the truncated proteins remained insoluble, two truncated proteins showed good solubility and high levels of protection in the P. gingivalis murine lesion model and may be considered as potential vaccine candidates for further testing in models of human periodontal disease.

Multiserotype enzyme-linked immunosorbent assay as a diagnostic aid for periodontitis in large-scale studies

Periodontitis is a common chronic oral infection caused by gram-negative bacteria, including Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis. Periodontitis evokes inflammatory host response locally in the periodontium but also systemically. The systemic humoral antibody response against oral pathogens can conveniently be measured by an immunoassay. The aim of the study was to measure serum immunoglobulin G class antibodies against A. actinomycetemcomitans and P. gingivalis by an enzyme-linked immunosorbent assay (ELISA) in which mixtures of several serotypes of the pathogens were used as antigens to avoid biasing of the results in favor of a particular strain. For A. actinomycetemcomitans the antigen consisted of six strains representing serotypes a, b, c, d, and e and one nonserotypeable strain. In the P. gingivalis ELISA, antigens representing serotypes a, b, and c were used. Serum samples from 90 subjects, including 35 samples from patients with diagnosed periodontitis, 10 samples from periodontally healthy controls, and 45 samples from randomly selected apparently healthy volunteers (referred to as "healthy subjects"), were tested. For both pathogens the antibody levels (means +/- standard deviations) of the patients--xpressed as area under the dilution curve--were significantly higher than those for healthy controls or healthy subjects, with values for A. actinomycetemcomitans and P. gingivalis, respectively, as follows: patients, 22.60 +/- 9.94 mm(2) and 26.72 +/- 11.13 mm(2); healthy controls, 9.99 +/- 3.92 mm(2) and 6.90 +/- 3.38 mm(2); and healthy subjects, 16.85 +/- 6.67 mm(2) and 8.51 +/- 4.23 mm(2). The serotype mixture ELISA is suitable for measuring antibodies against periodontal pathogens in large epidemiological studies in order to evaluate the role of periodontitis as a risk factor for other diseases.