Activation of serum complement by polysaccharide-containing antigens of Porphyromonas gingivalis

Cardiovascular disease and the role of oral bacteria

In terms of the pathogenesis of cardiovascular disease (CVD) the focus has traditionally been on dyslipidemia. Over the decades our understanding of the pathogenesis of CVD has increased, and infections, including those caused by oral bacteria, are more likely involved in CVD progression than previously thought. While many studies have now shown an association between periodontal disease and CVD, the mechanisms underpinning this relationship remain unclear. This review gives a brief overview of the host-bacterial interactions in periodontal disease and virulence factors of oral bacteria before discussing the proposed mechanisms by which oral bacterial may facilitate the progression of CVD.

Cytokine profiling of macrophages exposed to Porphyromonas gingivalis, its lipopolysaccharide, or its FimA protein

To characterize the roles of Porphyromonas gingivalis and its components in the disease processes, we investigated the cytokine profile induced by live P. gingivalis, its lipopolysaccharides (LPS), and its major fimbrial protein, fimbrillin (FimA). Using cytokine antibody arrays, we found that P. gingivalis LPS and FimA induced a similar profile of cytokine expression when exposed to mouse peritoneal macrophages but that this profile differed significantly in response to live P. gingivalis. In vitro, mouse peritoneal macrophages were stimulated to produce interleukin-6 (IL-6), granulocyte colony-stimulating factor, and lymphotactin by live P. gingivalis, but not by P. gingivalis LPS or FimA, while RANTES, gamma interferon, IL-17, vascular cell adhesion molecule 1 (VCAM-1), and vascular endothelial growth factor were induced by P. gingivalis LPS or FimA, but not by live P. gingivalis. In vivo, IL-6 mRNA was strongly induced only by live P. gingivalis while monocyte chemoattractant protein 1 mRNA was strongly induced only by P. gingivalis LPS and FimA in mouse calvarial scalp, further confirming the differences of cytokine profile induced in vitro. Cytokine antibody arrays using toll-like receptor 2 (TLR2)- and TLR4-deficient macrophages revealed that most of the cytokines induced by P. gingivalis LPS or FimA signal through TLR2, while most of cytokines induced by live P. gingivalis signal through both TLR2 and TLR4. Interestingly, the activation of TLR2 by live P. gingivalis inhibited the release of RANTES, VCAM-1, and IL-1alpha from mouse peritoneal macrophages. A tumor necrosis factor alpha enzyme-linked immunosorbent assay further confirmed that P. gingivalis LPS and FimA activate mouse peritoneal macrophages via TLR2. These results indicate that host immune cells sense live P. gingivalis and its components differently, which translates into the expression of different inflammatory cytokine profiles.

Adhesion of Porphyromonas gingivalis serotypes to pocket epithelium

BACKGROUND

Porphyromonas gingivalis, a key pathogen in periodontitis, is able to adhere to and invade the pocket epithelium. Different capsular antigens of P. gingivalis have been identified (K-serotyping). These P. gingivalis capsular types show differences in adhesion capacity to human cell lines or to cells cultured on a feeder layer or stromal equivalent.

METHODS

The adhesion capacity of different P. gingivalis serotypes (6 capsular types and non-encapsulated strains) was compared on in vitro cultured epithelial monolayers from periodontal pockets of patients with periodontitis. The degree of adherence of P. gingivalis was evaluated by both culture and fluorescence microscopy.

RESULTS

Non-encapsulated strains adhered significantly more than their capsulated variants. Capsule type 4 (K-4) adhered slightly better than the remaining K-types.

CONCLUSION

This study indicates that the presence and type of capsule have a significant influence on the initial adhesion of P. gingivalis to human periodontal pocket epithelial cells.

Salivary biochemistry in Buffalo: the legacy of Michael J. Levine

The author pays tribute to the contributions of Michael J. Levine to the field of salivary biochemistry.

Antigenic cross-reactivity among Porphyromonas gingivalis serotypes

The goal of our research program is to develop a Porphyromonas gingivalis vaccine. Vaccine development requires identification of antigenic components shared by the many clonal types of P. gingivalis. The purpose of the present study was to evaluate the extent and nature of antigenic cross-reactivity among serotypes of P. gingivalis and to identify shared antigenic components. Strains selected to represent serotypes A-D were 33277, A7A1-28 W50 and 381, respectively. Using intact cells, antibodies were raised in rabbits. Titers were assessed by enzyme-linked immunosorbent assay (ELISA) using intact cells as antigen, Western blots were prepared and biologic activity was measured as opsonization (chemiluminescence expressed as mV) and enhancement of phagocytosis and killing by polymorphonuclear leukocytes. Extensive cross-reactivity that varied greatly among serotypes was observed by ELISA. The Western blots showed an even greater extent of cross-reactivity, with shared protein components at approximately 140, 130, 37, 32 and 28 kDa and a shared variable molecular mass smear considered to be lipopolysaccharide and other carbohydrate. Additional protein components at 110, 85, 35 and 20 kDa appeared to be shared by some but not all serotypes. In the functional assays, strains 33277 and 381 were equally well opsonized by anti-33277 and anti-381 (500-650 mV) but opsonized to a much lesser extent by anti-A7A1-28 and anti-W50 (roughly 125 mV and 350 mV respectively). A7A1-28 and W50 were opsonized by all four immune sera almost equally but to a much lower extent (roughly 400 mV and 250 mV respectively). Enhancement of phagocytosis and killing in the presence of active complement mirrored opsonization with the exception that 381 was reasonably well opsonized by anti-A7A1-28 (400 mV) and anti-W50 (350 mV), but poorly killed. The protein components at 140, 130, 37 and 28 kDa shared by all of the four serotypes appear to have potential as vaccine candidate antigens.

Dextran sodium sulphate-induced colitis activity varies with mouse strain but develops in lipopolysaccharide-unresponsive mice

Bacteria and their products have been implicated in the pathogenesis of chronic Inflammatory Bowel disease. The aim of this study was to investigate the potential role of lipopolysaccharides (LPS) in the development of intestinal injury by comparing the effects of the dextran sodium sulphate (DSS)-induced model of colitis in LPS-sensitive and -insensitive mice. Experimental colitis was induced in LPS-sensitive mice (C3H/He) and their LPS-insensitive congenic strain (C3H/HeJ). Colitis was assessed clinically using a disease activity index (derived from the three main clinical signs; diarrhoea, rectal bleeding and weight loss) and by histological scoring of the diseased colon. The clinical signs and disease activity index did not differ between the LPS-sensitive and -insensitive costrains. Similarly, histological scores did not differ significantly for either C3H strain at any time point during exposure to DSS. However, there were differences in the inflammatory response when different strains were compared (C3H vs CBA): the effects of DSS in C3H mice were immediate, more severe and mainly involved the caecum and ascending colon. These findings suggest that LPS from colonic bacteria do not play a primary role in the initiation of DSS-induced colitis and demonstrate clear differences in the responsiveness of different mouse strains to DSS.

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.

Characterization of inhibitory effects of suspected periodontopathogens on osteogenesis in vitro

By using an in vitro bone-forming culture system, the chick periosteal osteogenesis (CPO) model, the direct effects on osteogenesis of sonicated extracts derived from oral bacteria were examined. Both extracts from bacterial species having strong associations with periodontal diseases (Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans, and Prevotella intermedia, hereinafter referred to as suspected periodontopathogens) and extracts from species not correlated with periodontal disease (Streptococcus sanguis, Veillonella atypica, and Prevotella denticola, hereinafter referred to as nonpathogenic bacteria) were tested. All bacterial cultures were grown under standard anaerobic culture conditions. Sonicated bacterial extracts were prepared from the bacterial pellet. These were added in various proportions to the CPO cultures. Parameters of osteogenesis, including alkaline phosphatase activity, calcium and P(i) accumulation, and collagen synthesis, were measured in 6-day-old cultures. Compared with controls grown in the absence of bacterial products, osteogenesis was inhibited significantly in cultures treated with extracts derived from the suspected periodontopathogens. No osteogenic inhibition was observed in cultures treated with extracts from the nonpathogenic bacteria. These results suggest that the ability to inhibit osteogenesis in vitro may be a pathogenic property shared by a limited group of species. Further characterization of the P. gingivalis extracts revealed that both proteinaceous and nonproteinaceous products, including lipopolysaccharide, were able to inhibit osteogenesis. P. gingivalis extract-mediated inhibition of osteogenesis in CPO cultures was blocked by indomethacin, implicating prostaglandins in the regulation of the bacterial effects. The bacterial extracts had either reversible or irreversible inhibitory effects on osteogenesis when added after differentiation or before/during differentiation of bone cells, respectively.

Antibody responses of Porphyromonas gingivalis infected gingivitis and periodontitis subjects

Porphyromonas gingivalis demonstrates a strong association with adult periodontitis although some individuals with the infection do not experience attachment loss. Therefore differences in the immune response to this organism may be of importance to the outcome of the disease.

OBJECTIVE

The aim of this study was to determine whether P. gingivalis positive subjects with and without periodontal breakdown, reacted differently to P. gingivalis antigens as assessed by the pattern of serum antibody reactivity.

MATERIALS AND METHODS

Two highly defined groups of subjects were chosen for this study. Both demonstrated P. gingivalis in their plaque and both had responded to P. gingivalis as shown by the presence of serum antibodies. The two groups differed only in their apparent clinical susceptibility to periodontal breakdown. Western blots of P. gingivalis membrane antigens were probed with sera from the two groups to determine their reactivity to specific antigens.

RESULTS

Analysis of the immunoblots showed that there were no differences in either the total numbers of bands, or bands recognized by the majority of subjects in the gingivitis and adult periodontitis groups. There were however, four bands recognized by the majority of the gingivitis group and not by the majority of the adult periodontitis group, there being a significant difference (P = 0.03) in the recognition of the 91.4-kDa antigen band. A further five antigens of lower molecular weight were seen by the majority of the adult periodontitis group and not by the majority of the gingivitis group. When sera were tested against purified P. gingivalis LPS, the results indicated that the five antigens seen by the majority of the adult periodontitis group had molecular weights which were in the range exhibited by the LPS antigens.

CONCLUSION

These results suggest that gingivitis and adult periodontitis subjects with P. gingivalis infection, may recognize different P. gingivalis antigens.

Pathogenic strategies of the oral anaerobe, Porphyromonas gingivalis

Adult periodontitis is a chronic inflammatory disease that affects over 49 million people in the USA alone. Porphyromonas (formerly Bacteroides) gingivalis, a Gram-negative anaerobe, has a diverse repertoire of virulence factors that may be involved in the induction or progression of periodontitis.

Resistance of a Tn4351-generated polysaccharide mutant of Porphyromonas gingivalis to polymorphonuclear leukocyte killing

In this study, we describe the development of an efficient transpositional mutagenesis system for Porphyromonas gingivalis using the Bacteroides fragilis transposon Tn4351. Using this system, we have isolated and characterized a Tn4351-generated mutant of P. gingivalis A7436, designated MSM-1, which exhibits enhanced resistance to polymorphonuclear leukocyte (PMN) phagocytosis and killing. P. gingivalis MSM-1 was initially selected based on its colony morphology; MSM-1 appeared as a mucoid, beige-pigmented colony. Analysis of P. gingivalis MSM-1 by electron microscopy and staining with ruthenium red revealed the presence of a thick ruthenium red-staining layer that was twice the thickness of this layer observed in the parent strain. P. gingivalis MSM-1 was found to be more hydrophilic than strain A7436 by hydrocarbon partitioning. Analysis of phenol-water extracts prepared from P. gingivalis A7436 and MSM-1 by Western (immunoblot) analysis and immunodiffusion with hyperimmune sera raised against A7436 and MSM-1 revealed the loss of a high-molecular-weight anionic polysaccharide component in extracts prepared from MSM-1. P. gingivalis MSM-1 was also found to be more resistant to PMN phagocytosis and intracellular killing than the parent strain, as assessed in a fluorochrome phagocytosis microassay. These differences were statistically significant (P < 0.05) when comparing PMN phagocytosis in nonimmune serum and intracellular killing in nonimmune and immune sera. P. gingivalis MSM-1 was also more resistant to killing by crude granule extracts from PMNs than was P. gingivalis A7436. These results indicate that the increased evasion of PMN phagocytosis and killing exhibited by P. gingivalis MSM-1 may result from alterations in polysaccharide-containing antigens.