InTechOpen uses cookies to offer you the best online experience. By continuing to use our site, you agree to our Privacy Policy.

Medicine » Dentistry » "Periodontitis - A Useful Reference", book edited by Pachiappan Arjunan, ISBN 978-953-51-3606-4, Print ISBN 978-953-51-3605-7, Published: November 15, 2017 under CC BY 3.0 license. © The Author(s).

Chapter 3

Cellular Response Mechanisms in Porphyromonas gingivalis Infection

By Hazem Khalaf, Eleonor Palm and Torbjörn Bengtsson
DOI: 10.5772/intechopen.69019

Article top


Overview of receptors and intracellular signaling pathways in response to virulence factors of P. gingivalis. See text for details.
Figure 1. Overview of receptors and intracellular signaling pathways in response to virulence factors of P. gingivalis. See text for details.
A novel biochemical link between periodontitis and cardiovascular disease.
Figure 2. A novel biochemical link between periodontitis and cardiovascular disease.
Model showing platelets as a linker between periodontal infection and innate immune response at the vessel wall.
Figure 3. Model showing platelets as a linker between periodontal infection and innate immune response at the vessel wall.

Cellular Response Mechanisms in Porphyromonas gingivalis Infection

Hazem Khalaf, Eleonor Palm and Torbjörn Bengtsson
Show details


The pathogenicity of the periodontal biofilm is highly dependent on a few key species, of which Porphyromonas gingivalis is considered to be one of the most important pathogens. P. gingivalis expresses a broad range of virulence factors, of these cysteine proteases (gingipains) are of special importance both for the bacterial survival/proliferation and for the pathological outcome. Several cell types, for example, epithelial cells, endothelial cells, dendritic cells, osteoblasts, and fibroblasts, reside in the periodontium and are part of the innate host response, as well as platelets, neutrophils, lymphocytes, and monocytes/macrophages. These cells recognize and respond to P. gingivalis and its components through pattern recognition receptors (PRRs), for example, Toll-like receptors and protease-activated receptors. Ligation of PRRs induces downstream-signaling pathways modifying the activity of transcription factors that regulates the expression of genes linked to inflammation. This is followed by the release of inflammatory mediators, for example, cytokines and reactive oxygen species. Periodontal disease is today considered to play a significant role in various systemic conditions such as cardiovascular disease (CVD). The mechanisms by which P. gingivalis and its virulence factors interact with host immune cells and contribute to the pathogenesis of periodontitis and CVD are far from completely understood.

Keywords: host-microbe interaction, immune cells, pathogen recognition receptors, intracellular signaling, inflammatory responses, Porphyromonas gingivalis, gingipains, LPS, cardiovascular disease, treatment

1. Introduction

Evidence suggests that it is the early host-inflammatory and immune responses to the oral microbiota that changes the subgingival environment and favors the emergence of periodontal opportunistic pathogens during the development of periodontitis. Substances released from the dental biofilm, such as lipopolysaccharides, proteolytic enzymes, and other virulence factors, activate the innate immune system and initiate an inflammatory response, which disrupts the host-microbe homeostasis. The activation of immune cells leads to a release of an array of inflammatory mediators, for example, cytokines, chemokines, proteases, reactive oxygen species (ROS), and eicosanoids, which struggle against the bacterial burden. However, the complexity of the microbial biofilm of the subgingival dental plaque and the failure of the acute inflammation to resolve lead to an accumulation of mediators of the innate and adaptive immune systems that collectively promote chronic inflammation and tissue destruction. How host cells discriminate commensal from pathogenic microbial species and why this ability seems to differ between individuals is currently unknown. The variation in individual susceptibility to develop periodontal disease appears to be determined by the magnitude of the inflammatory response to a dysbiotic microbial community and whether only the innate or also the adaptive immune pathways are activated.

2. Porphyromonas gingivalis in periodontitis

There are a number of bacterial species that are associated to periodontitis, based on their detection in periodontal pockets, their pathogenicity, and the immunological responses they evoke [1]. The red complex is a consortium of three periodontal bacterial species, Treponema denticola, Tannarella forsythia, and Porphyromonas gingivalis, which are linked to each other and to diseased sites [2]. The development and progression of periodontitis is believed to be due to a synergistic and dysbiotic polymicrobial community, and the oral biofilm (dental plaque) [3]. A biofilm is a highly structured, three-dimensional matrix with a simple circulatory system. The biofilm provides physical protection and a gradient of oxygen, allowing anaerobic species to grow in the deeper pocket, and aerobic species near the surface. Furthermore, metabolic by-products from one species can be used as nutrients by other species in the biofilm, the so-called cross-feeding [4]. The keystone species hypothesis suggests that some species, like P. gingivalis, exerts a disproportionally large effect in the biofilm. P. gingivalis can turn from a natural low-abundance microorganism residing in the oral cavity to an opportunistic pathogen that interferes with the host immune system and from a normal, symbiotic microbiota, and enables the transition and emergence into a dysbiotic bacterial society that drives the progress of periodontitis [2, 5]. P. gingivalis is a late colonizer usually found in a rather low number in the dental plaque, and interestingly, P. gingivalis is not able to induce periodontitis in germ-free mice, suggesting that P. gingivalis is dependent on the complex microbial community. Through synergistic interactions, the biofilm promotes colonization, nutrition acquisition and subvert, and evades host immune responses [4, 6].

P. gingivalis is a non-motile, proteolytic, and Gram-negative rod that expresses several virulence factors that are related to colonization of oral tissues, periodontal tissue destruction, and evasion of the host responses [7]. P. gingivalis exhibits genotypic and phenotypic diversity, which results in differences in virulence and in the capacity of individual strains to colonize and induce destruction of periodontal tissues. Certain strains may therefore exhibit a higher pathogenic potential than others and may be linked to a more severe form of periodontitis [812]. The asaccharolytic bacterium P. gingivalis grows under anaerobic conditions and acquires metabolic energy by fermenting amino acids. P. gingivalis also uses micronutrients, such as metal ions for anabolic and catabolic purposes, as well as vitamin K. P. gingivalis expresses a broad range of virulence factors, all of which add to enhanced growth and survival in a hostile environment [7]. However, the virulence of P. gingivalis is affected by its surroundings, including other bacterial species in the biofilm and host-derived factors. By altering the gene expression of virulence factors, P. gingivalis can adjust to a more or less virulent phenotype depending on the environment [13].

Fimbriae are hair-like protrusions emanating from the outer cell surface that facilitate the adherence and colonization of the bacterium. Indeed, fimbriae are critical for mediating the initial bacterial interaction with the host tissue. P. gingivalis expresses major and minor fimbriae, encoded by the fimA and mfa1 genes, respectively. Today, six fimA allele types are known (fimA I, Ib, II, III, IV, and V). These variants are more or less associated to periodontitis [14]. P. gingivalis isolated from periodontally healthy persons more often expresses type I, II, or V. Types Ib, II, and IV, on the other hand, are more associated to diseased periodontal pockets [9, 15]. Major fimbriae can attach and bind to host cells, extracellular matrix (ECM), as well as salivary proteins. Major fimbriae can also facilitate binding to other bacteria, both P. gingivalis itself and other species. Minor fimbriae have a role in biofilm formation [14, 16].

As a Gram-negative species, P. gingivalis possesses lipopolysaccharides (LPS). Intriguingly, the lipid A part of P. gingivalis LPS has a structure that is heterogeneous. The number of associated fatty acids coupled to the disaccharide core varies, resulting in penta- or tetra-acylated lipid A moieties that allows interaction with both Toll-like receptors (TLR) 2 and TLR4 [17]. It is the availability of hemin in the microenvironment that defines which lipid A form that P. gingivalis expresses, enabling the bacteria to determine how it interacts with the host to elicit various inflammatory responses [8, 18].

Gingipains are cysteine proteases which probably are the most vital virulence factor expressed by P. gingivalis. Gingipains are membrane-bound, as well as secreted from the bacterium, thus, P. gingivalis can exert all the various gingipain activities at distant sites. P. gingivalis possesses arginine-specific gingipains, Rgp (RgpA and RgpB), encoded by rgpA and rgpB, respectively, and the lysine-specific gingipain, Kgp, encoded by kgp. P. gingivalis expresses numerous proteolytic enzymes, but the gingipains are by far the most important ones, accounting for at least 85% of the total proteolytic activity. Furthermore, they are implicated and play key roles in adherence and colonization of the host, in nutrition acquisition by cleaving host proteins, in neutralization of host defense mechanisms, and in manipulation of the host inflammatory response. In summary, gingipains are vital for bacterial survival and proliferation in vivo [7]. In the process of adherence and colonization, P. gingivalis utilizes fimbrial adhesions, but nevertheless, gingipains are also necessary in these steps. RgpA and Kgp contain hemagglutinin-adhesin domains, which are directly involved in conjugation with other bacterial species, thereby promoting the construction of the bacterial biofilm. These domains also enable binding to ECM, as well as interaction with host cells [1921]. Rgp is also important for processing various P. gingivalis-derived proteins. For instance, Rgp is necessary for the modification of major fimbriae to the mature form [22]. Gingipains are also key mediators in dysregulation of the host immune response [23, 24].

Some P. gingivalis strains possess a capsule. Encapsulated strains are more virulent since they have been shown to be more invasive and more resistant to phagocytosis [2527]. P. gingivalis also releases outer membrane vesicles, small cargos that are shed from the outer bacterial membrane that are loaded with LPS, gingipains and other proteases, fimbriae, and capsule (encapsulated strains). The shedding of outer membrane vesicles occurs at a higher rate during colonization and biofilm formation, enabling immune modulation at sites distant from the actual site of infection [28].

3. Mechanisms of P. gingivalis interaction with host cells

P. gingivalis, as a keystone pathogen, has the ability to interfere with the host in such ways that the growth and survival of the entire biofilm is promoted and enhanced. It is vital for P. gingivalis in a hostile environment to be able to counteract, modify, and manipulate the host immune response in order to survive and evade the various host defense mechanisms. Although it is important to evade the host defense mechanisms, it is also of essential importance to induce inflammation to secure a constant delivery of nutrients to the biofilm through the formation of the nutrient-rich-inflammatory exudate that constitutes the gingival crevicular fluid. P. gingivalis has indeed evolved elaborated strategies to diminish as well as promote inflammation [5]. The complement system, which targets microbes, is itself a target for proteolysis by gingipains. In fact, P. gingivalis can both inhibit and stimulate the complement system [29]. Also, depending on the type of lipid A expressed, P. gingivalis can act as both a TLR4 agonist and an antagonist and regulate the TLR4-dependent immune responses [10, 18]. Realizing all the clever ways of escaping, it may not come as a surprise that P. gingivalis, as an additional function on the repertoire, also is resistant to oxidative killing by phagocytes and can survive phagocytosis by macrophages [26, 30]. Furthermore, P. gingivalis is able to activate the coagulation cascade and the kallikrein/kinin cascade, thereby enhancing inflammation [3133]. P. gingivalis can invade host cells and replicate within the cell [34]. P. gingivalis is also able to protect itself from neutrophil-released reactive oxygen species, leaving the oxidative burst effortless and instead contributing to the destruction of the periodontium [13, 30].

The interactions between the host immune system and the oral microbial flora involve complex cellular and molecular mechanisms. Several cell types, for example, epithelial cells, dendritic cells, osteoblasts, and fibroblasts that reside in the periodontium, are part of the innate host response, as well as platelets, neutrophils, and monocytes/macrophages. Cells of the innate immune system recognize and respond to pathogens (e.g., LPS, fimbriae, DNA, and proteases) through pathogen recognition receptors (PRRs). Important PRRs are TLRs and protease-activated receptors (PARs). Ligation of PRRs induces downstream signaling pathways that modify the activity of transcription factors that regulates the expression of genes linked to inflammation. Early cellular events leading to a phosphorylation cascade of mitogen-activated protein kinase (MAPK) signaling include the activation of Protein kinase C (PKC) by diacylglycerol and calcium. Signals transduced via MAPK pathways lead to the assembly and activation of the transcription factor AP-1. TLR activation results in the recruitment of an adaptor protein, which in many cases involves MyD88, followed by a signaling cascade that phosphorylates, polyubiquitylates, and degrades IκB. This allows the transcription factor NFκB to translocate to the nucleus and induces gene expression (Figure 1). AP-1, NFκB, and other transcription factors cooperatively regulate genes, such as inflammatory mediators and growth factors that are important in many biological processes [35, 36]. This is followed by the release of inflammatory mediators such as CXCL8 and interleukin (IL)-6. The chemokine CXCL8 attracts and recruits neutrophils to the site of infection and promotes monocyte adhesion to the vessel wall. The infiltrating neutrophils, as well as resident cells and macrophages, release cytokines, such as tumor necrosis factor-α (TNF-α), IL-1, and IL-6. These inflammatory mediators will eventually contribute to tissue destruction with alveolar bone loss and a sustained chronic inflammation. In addition, the innate immune system will in turn also activate the adaptive immune system with the involvement of lymphocytes [1, 2, 5].


Figure 1.

Overview of receptors and intracellular signaling pathways in response to virulence factors of P. gingivalis. See text for details.

How host-derived factors such as cytokines, hormones, and reactive oxygen species affect periodontal biofilm formation and bacterial virulence is poorly studied and thus not well understood. A recent study suggests that the host-inflammatory responses affect the physiology of bacteria, for example, by utilizing inflammatory mediators as transcription factors [37]. It thus seems quite reasonable that bacteria have evolved mechanisms to sense their environment and to respond to their surrounding by using inflammatory mediators as regulators to be able to adjust and adapt to a changing environment. Consequently, it is possible that early host-inflammatory and immune responses affect and modulate the composition and function of the oral biofilm and the progression of periodontitis.

TLRs are a family of receptors which are of high importance in the innate immune response in sensing pathogens and other danger-associated signals. LPS and fimbriae originate from P. gingivalis signals mainly through TLR2, which mediates the release of inflammatory mediators like CXCL8 [3840]. P. gingivalis-mediated activation of TLR2 has been demonstrated to stimulate differentiation and formation of osteoclasts [40]. A study showed that TLR2−/− mice more rapidly cleared P. gingivalis infection, had a more efficient phagocytosis of P. gingivalis, and also resisted alveolar bone loss despite being repeatedly infected with P. gingivalis [41]. TLR2 expression has also been found to be upregulated by P. gingivalis [42]. During inflammation, the hemin concentration in the gingival crevicular fluid is high and the tetra-acylated lipid A form is expressed. The tetra-acylated lipid A is acting as a TLR4 antagonist, suppressing TLR4-mediated inflammatory events. The TLR4 antagonist also competitively blocks the binding of TLR4; hence, TLR4 is unable to respond to other bacterial species as well. In addition, since the outer membrane vesicles contain LPS, and can penetrate through the gingival tissue, P. gingivalis can dampen the TLR4 effects for the entire oral microbial community. When the hemin concentration is low, inflammation is promoted by expressing penta-acylated lipid A, which works as a TLR4 agonist [10, 18, 43].

PARs have been found to be activated by proteolytic cleaving by gingipains, leading to increased inflammatory response with the release of inflammatory chemokines [39, 44]. PAR2 activation has been demonstrated to induce alveolar bone loss in rats. Since PAR2 is expressed by the cells in the periodontium, P. gingivalis and its gingipains are able through PAR2 activation to significantly contribute to the release of several pro-inflammatory mediators that cause degradation of the periodontal tissue [45]. Furthermore, P. gingivalis per se has been demonstrated to upregulate the PAR2 expression in gingival fibroblasts [39].

A gradient of CXCL8 is normally established in the healthy periodontal tissue with the highest concentration at the border of the symbiotic dental plaque. This gradient establishes a “wall” of neutrophils, a continuous flow of migrating neutrophils that transit from the vasculature into the periodontium and the gingival crevice. P. gingivalis can interact with CXCL8 and this gradient in several ways [2]. In contact with gingival epithelial cells, P. gingivalis expresses phosphoserine phosphatase SerB, which contributes to CXCL8 inhibition [46]. Gingipains are well known to cleave CXCL8, as well as other cytokines and chemokines, such as IL-6, IL-6 receptor, CXCL10, TNF-α, CD14, IL-4, and IL-12 [23, 24, 44, 4752]. By targeting inflammatory mediators such as CXCL8, the resulting chemokine paralysis leads to inhibited neutrophil recruitment, thereby promoting the growth of the biofilm. Consequently, P. gingivalis undermines innate immunity [2]. Furthermore, CXCL8 is secreted in two different isoforms, as a 72 amino acid (CXCL8-72aa) variant from immune cells and as a 77 amino acid variant (CXCL8-77aa) from non-immune cells such as fibroblasts. CXCL8-72aa is a stronger chemoattractant than CXCL8-77aa, but after cleavage of CXCL8-77aa by gingipains, this is shifted so that the CXCL8-77a has a higher chemotactic potential. This could be a mechanism whereby P. gingivalis, by creating a gradient of gingipains across the periodontal tissue can suppress neutrophilic response in the periodontal pocket where the concentration of gingipains is the highest. At a more distant site, with lower concentrations of gingipains, the chemotactic function of CXCL8-77aa is increased, enhancing the inflammatory response and thereby promoting leaky vessels and a constant delivery of nutrients to the biofilm [47, 53].

4. Host cell responses in the oral cavity

4.1. Gingival epithelial cells

The first line of host defense in the gingiva consists of the epithelial cells forming a physical barrier against mechanical stress, exogenous substances, and pathogenic bacteria. This is achieved through different cell-cell junctions, including tight junction and gap junction. P. gingivalis uses different strategies to survive and persist in the oral cavity, and invasion of epithelium is one tactical approach in its lifestyle. The advantages of intracellular translocation of P. gingivalis into the cells include evasion from immune responses and antibiotics, and accessibility to disseminate to other sites, which collectively leads to persistence and proliferation [4]. The mechanism by which P. gingivalis enters epithelial cells is initiated by fimbriae that bind to α5β1-integrin, followed by the formation of cellular pseudopodia and entry through early endosomes. Intracellular bacteria are then either sorted to late endosomes followed by lysosomes for degradation, or fused with autophagosomes and subsequently degraded in autolysosomes. However, a large number of bacteria are able to escape through recycling pathways for exocytosis and are able to infect new cells, which facilitate deeper penetration into the host tissue [54]. While in other cell types, such as endothelial and smooth muscle cells, P. gingivalis has been reported to reside and persist within autophagosomes, followed by the prevention of lysosomal fusion and formation of autolysosomes [55, 56]. Interestingly, α5β1-integrin on epithelial cells has recently been shown to positively correlate with cells in S phase of the cell cycle, and P. gingivalis persistence may be associated with the ability to preferentially target dividing cells [57]. The virulence of intracellular P. gingivalis is associated with its ability to degrade paxillin and focal adhesion kinase, and may explain the significant periodontal tissue degradation and lack of wound healing and tissue regeneration processes in periodontitis [58, 59].

Epithelial cells also participate in innate immune responses by secreting a variety of cytokines and chemokines, such as TNF, IL-6, and CXCL8 [60]. P. gingivalis suppresses cytokine and chemokine accumulation below basal levels in vitro. These effects are most probably due to the potent enzymatic action of proteinases. Indeed, leukocytes are manipulated by P. gingivalis to express a limited repertoire of inflammatory mediators, while suppressing CXCL8 release, which is termed “local chemokine paralysis” [61]. Interestingly, P. gingivalis significantly increased TGF-β1 expression from gingival epithelial cells. TGF-β1 functions as a growth factor with anti-inflammatory characteristics. Besides TGF-β1, P. gingivalis was observed to induce the expression of a wide array of different growth factors, including Insulin-like growth factor (IGF), Platelet-derived growth factor (PDGF), endothelial growth factor (EGF), and Hepatocyte growth factor (HGF). We have previously shown that P. gingivalis induces high levels of HGF in clinical samples from patients with periodontitis. However, the activity of HGF was significantly reduced in patients compared to healthy controls [62].

4.2. Gingival fibroblasts

Gingival and periodontal ligament fibroblasts are the main cell types found in the connective tissue of the periodontium, and they are exposed to pathogens once the epithelial barrier is breached [2, 63]. Fibroblasts provide a structural tissue framework (stroma) and define the microanatomy of the tissue with the key function to regulate and maintain integrity of the connective tissue. Homeostasis of connective tissues is maintained through the production of ECM and by modifying existing ECM by secreting matrix metalloproteinases (MMPs) that cleave and degrade ECM components [64]. The ability of fibroblasts to secrete as well as respond to growth factors and cytokines/chemokines allows reciprocal communication with adjacent cells that facilitates homeostasis of the tissue. Considering the functions of fibroblasts makes it easy to realize that fibroblasts play a vital role in tissue development, differentiation, and repair. Fibroblasts are also of importance in tissue destruction by the release of MMPs and pro-inflammatory cytokines and chemokines [6365]. PAR1 and TLR2 have been shown to be important in the interaction between gingival fibroblasts and P. gingivalis. Gingival fibroblasts can sense P. gingivalis through PAR1 and TLR2, and the activation of these receptors leads to the secretion of CXCL8 and IL-6, suggesting that fibroblasts could make a substantial contribution to the inflammatory process seen in periodontitis [38, 39, 66]. Furthermore, P. gingivalis is able to modify this response by cleaving fibroblast-derived cytokines through the proteolytic activity of the gingipains and thereby hampering the antimicrobial capacity of the fibroblasts [23, 24, 66].

4.3. Leukocytes

Periodontitis is characterized by interaction between a number of oral pathogens, such as P. gingivalis, and blood leukocytes. Neutrophils and monocytes are well equipped with PRRs, such as TLRs, nuclear-oligomerizing domains ½, and PARs. This arsenal of receptors enables the detection of invading pathogens and production of reactive oxygen species, cytokines, and chemokines. We have shown that P. gingivalis is capable of inducing ROS in isolated neutrophils and in whole blood, and stimulating the release of inflammatory mediators, such as IL-1β and CXCL8 [67]. Both these cytokines are capable of priming neutrophils, endothelial cells, and other vascular cells in an autocrine and paracrine manner. Studies have demonstrated that gingipains hydrolyze pro-inflammatory cytokines, but not growth factor/anti-inflammatory cytokines, which result in aberrant immune cell recruitment to the site of infection, ensuring a continued low-grade infection.

The critical balance of different T-cell subsets has previously been described to play an important role in the inflammatory process underlying periodontitis. The presence of specific antibodies for oral bacteria in patients with periodontitis indicates an involvement of adaptive immune responses [68], of which different T-cell subsets play a detrimental role in the pathogenesis of this inflammatory disease. The T-cell-associated cytokine profile in gingival tissue suggests an engagement of T-helper (Th) 1, Th2, and Th17 cells [6971]. These T-cell subsets are associated with host-derived tissue destruction and bone loss, through, for example, Receptor activator of nuclear factor kappa-B ligand (RANKL) expression. Exaggerated pro-inflammatory responses from T-cells can be controlled by regulatory T-cells (Tregs) that display protective effects through the secretion of anti-inflammatory IL-10 and TGF-β1. Tregs have a central role in maintaining homeostasis by regulating other leukocyte functions and thereby avoiding extensive immune cell activation and its pathological consequences, for example, in periodontitis. Interestingly, we have previously shown that T-cell interaction with P. gingivalis leads to a gingipain-mediated inactivation of IL-2 [72], which may thus downregulate Tregs and support the process of periodontitis. Thus, the inhibition of gingipains and maintenance of a Treg-mediated beneficial homeostasis may be a successful strategy for the prevention and treatment of periodontitis.

5. Periodontitis, systemic inflammation, and cardiovascular disease

Periodontal disease is today considered to play a significant role in various systemic conditions and, in the past decade, the enhanced prevalence of cardiovascular disease (CVD) among patients with periodontitis has received increased attention [73, 74]. Several periodontal bacteria and their agents have been identified in atherosclerotic plaques, for example, P. gingivalis, Fusobacterium nucleatum, T. forsythia, Prevotella intermedia, Aggregatibacter actinomycetecomitans, and T. denticola [7578]. The occurrence of periodontal bacteria in coronary artery plaques was found to be 5-fold greater in patients with severe periodontitis compared to those with medium periodontitis [79], and DNA from periodontal bacteria, including P. gingivalis, was identified in more than 70% of carotid plaque samples [80]. Furthermore, P. gingivalis has been shown to influence the development of abdominal aorta aneurysm, involving the activation of TLRs and MMPs [81]. Several animal experiments have demonstrated that oral and systemic infection with periodontal bacteria induces atherosclerosis [74]. Hokamura and Umemura [82] showed that the administration of P. gingivalis in a mouse model induces arterial intimal hyperplasia associated with upregulation of the calcium-binding protein S100A9.

When the periodontal disease develops, the gingival epithelium becomes ulcerated by proteolytic activity, for example, by P. gingivalis, leading to exposure of the underlying connective tissues and blood capillaries to the bacterial plaque biofilm. At medium periodontitis, the ulcerative area in the oral cavity ranges between 8 and 20 cm2, which means that large amounts of periodontal bacteria and their toxins and metabolic products have a chance, during chewing and oral hygiene activities, to disseminate into the bloodstream and cause transient bacteremias and systemic inflammation [74]. By entering the circulation, the bacteria and/or their components (e.g., proteases, fimbrillin, and LPS) activate platelets and neutrophils, induce ROS production, and trigger inflammatory processes in coronary vessels.

Studies using knockout mice orally infected by P. gingivalis, demonstrate that atherosclerosis, involving the accumulation of macrophages and inflammatory mediators (CD40, IL-1ß, IL-6, and TNF-α) in atherosclerotic lesions, is highly dependent on TLR2 [41, 83]. In correlation, interaction between P. gingivalis and human blood cells, for example, platelets, neutrophils, monocytes, and T-cells, is mainly mediated by TLR2 and has dramatic inflammatory and immunomodulatory effects, including cellular aggregation, oxygen radical production, low-density lipoprotein (LDL) oxidation, and release and degradation of cytokines. Furthermore, P. gingivalis changes the expression of more than thousand genes in vascular smooth muscle cells [84]. For example, P. gingivalis upregulates genes involved in proliferation, for example, the TGFβ1 pathway and production of matrix proteins, but downregulates pro-inflammatory genes, such as those involved in IL-1β, IL-6, and CXCL8 production. P. gingivalis also caused a dramatic increase in the expression of angiopoietin2 (ANGPT2), which is highly correlated with inflammation and atherosclerosis, whereas ANGPT1, inhibitor of inflammation, was downregulated [85, 86]. These effects are mediated via gingipain R, possibly through PAR signaling. Furthermore, the level of another angiogenic factor, vascular endothelial growth factor (VEGF), increases in patients with periodontitis, and periodontal treatment reduces its concentration [87]. These data indicate that P. gingivalis causes a shift from contractile smooth muscle cells to proliferating and matrix-producing smooth muscle cells, which contributes to the growth of the fibrous atherosclerotic plaque, and promotes vascular inflammation and angiogenesis.

P. gingivalis has also been shown to modify LDL and promote phenotypic shift of monocytes to foam cells [75, 77, 88]. Our group has previously found fragmentation of the dominating apoprotein of LDL, apo B-100, by P. gingivalis and its Rgps [88]. Consequently, our findings together with others suggest that P. gingivalis during translocation in circulating blood modifies LDL to an atherogenic form which may represent a link between periodontal disease and atherosclerosis (Figure 2).


Figure 2.

A novel biochemical link between periodontitis and cardiovascular disease.

6. Host cell responses in the circulation and vascular wall

Endothelial cells possess secretory and immunological properties and play therefore important roles in the cardiovascular system. The association of periodontitis with cardiovascular complications includes the induction of endothelial dysfunction, oxidative stress, and systemic inflammation [89]. Furthermore, patients with periodontitis have increased levels of pro-inflammatory mediators, including C-reactive protein (CRP), IL-6, and TNF that may induce endothelial dysfunction [90]. Endothelial dysfunction, which is the initial step in the development and progression of atherosclerosis, is mediated by endotoxins and gingipains of periodontal bacteria. These toxins lead to an impairment of normal endothelial function, including vessel permeability and immune cell adhesion and function [91, 92]. Furthermore, P. gingivalis and other periodontal pathogens induce the expression of endothelin-1, a potent vasoconstrictor released by endothelial cells [93, 94]. Endothelin-1 expression has shown a positive correlation to pro-inflammatory cytokines TNF, IL-6, and IL-1β [95], and a negative correlation to anti-inflammatory mediators, for example, angiopoietin-1 [96, 97].

Platelets are key players in hemostasis and acute thrombosis and are initial actors in the development of atherosclerotic lesions often triggered by endothelial dysfunction [98]. However, they are also involved in the immune system and express a broad repertoire of immune cell features such as TLRs, the immunoglobulin γ-receptor FcγRIIA, complement receptors, inflammatory mediators, as well as microbicidal activities, for example, thrombocidins [99, 100]. Furthermore, platelets bind to and encapsulate bacteria, release ROS and recruit and activate leukocytes and regulate inflammatory processes of the vessel wall [101]. These characteristics make it possible for platelets to recognize and respond to pathogens, such as P. gingivalis, and engage other immune cells for enhanced bacterial clearance and inflammatory response.

Several studies suggest that platelet-leukocyte interaction is an essential underlying inflammatory process in atherosclerosis, and patients with cardiovascular disease have an increased number of neutrophil-platelet aggregates in the blood circulation [102, 103]. In correlation, we have shown that P. gingivalis markedly induces the formation of large aggregates of neutrophils and platelets, associated with ROS production and lipid peroxidation, in whole blood and that this effect is dependent on CD11b/CD18-fibrinogen-GpIIb/IIIa interaction, and Rac2 and Cdc42 activation [104, 105] (Figure 3). In addition, mice challenged with P. gingivalis were found to form platelet-neutrophil aggregates, whereas knockout TLR2−/− mice did not. Human platelets express TLRs (TLR 1, 2, 4, 6, and 9), which could be key molecules linking periodontal infection and CVD. For example, TLR2-mediated platelet activation involving the activation of GpIIb/IIIa and P-selectin contributes to the formation of platelet-leukocyte complexes and ROS production [99].


Figure 3.

Model showing platelets as a linker between periodontal infection and innate immune response at the vessel wall.

Platelets activation by TLR1/2 receptor ligands results in aggregation as well as secretion of inflammatory mediators such as RANTES, macrophage migration inhibitory factor (MIF), and plasminogen activator inhibitor-1 (PAI-1) [105]. Interestingly, these platelet-derived factors are degraded by gingipains from P. gingivalis [105]. Regulated on activation, normal T-cell expressed and secreted (RANTES) is induced by P. gingivalis and its lipopolysaccharides and is thus implicated in periodontitis, where elevated levels have been detected in the gingival crevicular fluid of patients with periodontitis [106]. It has been demonstrated that P. gingivalis, in addition to TLR2, also can trigger platelet activation via PAR receptors. Through the action of Rgp on PARs, P. gingivalis activates platelets by increasing intracellular-free calcium and induces aggregation [105]. In correlation, Lourbakos et al. and McNiol and Israels [107, 108] have demonstrated that gingipains activate PAR1 and PAR4 on platelets leading to aggregation and secretion. We have shown that P. gingivalis triggers platelet aggregation through gingipain interaction with PARs and sensitizes platelets for activation by epinephrine, which may explain the association between periodontitis, stress and CVD [109].

7. Preventive and treatment strategies

Periodontal pathogens reside in biofilms of subgingival dental plaque and form complex polymicrobial communities. The failure of the immune system to resolve bacterial biofilms results in an accumulation of inflammatory mediators that accelerates the disease state toward a chronic inflammatory condition. Bacterial biofilms are difficult to treat, and conventional methods, including mechanical removal and scaling and root planning (SRP), are still being used. These methods are less efficient and new preventive/treatment strategies are needed. A new approach includes the administration of adjunctive antibiotics systemically in combination with SRP. Different antibiotics have been applied, and a combination of metronidazole and amoxicillin was found to be effective at reducing pocket depth and clinical attachment gain compared to SRP alone, reviewed in [110]. Although antibiotic therapy is effective in modern medicine, microorganisms that are resistant to single or multiple antibiotics have emerged. The development of new families of antibiotics has significantly declined, which is associated with high costs and concerns for possible effects on the commensal microbiota and host health [111]. It is evident that new alternative strategies to traditional antibiotic therapy are needed. New approaches to combat bacterial infections include antibodies, vaccines, bacteriophages, probiotics, and antimicrobial peptides (host- and bacteria-derived) [111114]. These strategies of promising candidates to traditional antibiotics deserve more consideration.

8. Concluding remarks

In summary, it is possible that P. gingivalis has a role in pathogenic oral biofilms to undermine important factors of innate immunity, by altering the functions of receptors and their intracellular signaling pathways and the levels of effector molecules, and thereby antagonizing an effective host response. These activities of key periodontal pathogens could contribute to an adaptation and maturation of dysbiotic biofilm communities and promote chronic inflammation and tissue destruction of periodontitis. Increased understanding of the interbacterial interactions that occur in the oral polymicrobial biofilm and its interplay with the host immune system is of uttermost importance for identifying novel targets for the prevention, diagnosis, and treatment of periodontitis and associated systemic disorders.


This work was supported by research grants from the Swedish Research Council (2016-04874), the Swedish Heart-Lung Foundation (20130576), the Knowledge Foundation (20150244, 20150086), and the foundation of Magnus Bergvall (201500823).


1 - Haffajee AD, Socransky SS. Microbial etiological agents of destructive periodontal diseases. Periodontology. 2000. 1994 Jun;5:78–111. PubMed PMID: 9673164. Epub 1994/06/01. eng
2 - Darveau RP. Periodontitis: A polymicrobial disruption of host homeostasis. Nature Review Microbiology. 2010 Jul;8(7):481–490. PubMed PMID: 20514045. Epub 2010/06/02. eng
3 - Sanz M, Quirynen M. Advances in the aetiology of periodontitis. Group A consensus report of the 5th European Workshop in Periodontology. Journal of Clinical Periodontology. 2005;32(Suppl 6):54–56. PubMed PMID: 16128829. Epub 2005/09/01. eng
4 - Sakanaka A, Takeuchi H, Kuboniwa M, Amano A. Dual lifestyle of Porphyromonas gingivalis in biofilm and gingival cells. Microbial Pathogenesis. 2016 May;94:42–47. PubMed PMID: 26456558. Epub 2015/10/13. eng
5 - Hajishengallis G, Darveau RP, Curtis MA. The keystone-pathogen hypothesis. Nature Review Microbiology. 2012 Oct;10(10):717–725. PubMed PMID: 22941505. Pubmed Central PMCID: Pmc3498498. Epub 2012/09/04. eng
6 - Hajishengallis G, Liang S, Payne MA, Hashim A, Jotwani R, Eskan MA, et al. Low-abundance biofilm species orchestrates inflammatory periodontal disease through the commensal microbiota and complement. Cell Host & Microbe. 2011 Nov 17;10(5):497–506. PubMed PMID: 22036469. Pubmed Central PMCID: Pmc3221781. Epub 2011/11/01. eng
7 - Guo Y, Nguyen KA, Potempa J. Dichotomy of gingipains action as virulence factors: From cleaving substrates with the precision of a surgeon’s knife to a meat chopper-like brutal degradation of proteins. Periodontology 2000. 2010 Oct;54(1):15–44. PubMed PMID: 20712631. Pubmed Central PMCID: Pmc2924770. Epub 2010/08/18. eng
8 - Herath TD, Wang Y, Seneviratne CJ, Lu Q, Darveau RP, Wang CY, et al. Porphyromonas gingivalis lipopolysaccharide lipid A heterogeneity differentially modulates the expression of IL-6 and IL-8 in human gingival fibroblasts. Journal of Clinical Periodontology. 2011 Aug;38(8):694–701. PubMed PMID: 21752043. Epub 2011/07/15. eng
9 - Missailidis CG, Umeda JE, Ota-Tsuzuki C, Anzai D, Mayer MP. Distribution of fimA genotypes of Porphyromonas gingivalis in subjects with various periodontal conditions. Oral Microbiology and Immunology. 2004 Aug;19(4):224–229. PubMed PMID: 15209991. Epub 2004/06/24. eng
10 - Herath TD, Darveau RP, Seneviratne CJ, Wang CY, Wang Y, Jin L. Tetra- and penta-acylated lipid A structures of Porphyromonas gingivalis LPS differentially activate TLR4-mediated NF-kappaB signal transduction cascade and immuno-inflammatory response in human gingival fibroblasts. PloS One. 2013;8(3):e58496. PubMed PMID: 23554896. Pubmed Central PMCID: PMC3595299. Epub 2013/04/05. eng
11 - Al-Qutub MN, Braham PH, Karimi-Naser LM, Liu X, Genco CA, Darveau RP. Hemin-dependent modulation of the lipid A structure of Porphyromonas gingivalis lipopolysaccharide. Infection and immunity. 2006 Aug;74(8):4474-4485. PubMed PMID: 16861633. Pubmed Central PMCID: Pmc1539574. Epub 2006/07/25. eng
12 - Amano A, Nakagawa I, Kataoka K, Morisaki I, Hamada S. Distribution of Porphyromonas gingivalis strains with fimA genotypes in periodontitis patients. Journal of Clinical Microbiology. 1999 May;37(5):1426–1430. PubMed PMID: 10203499. Pubmed Central PMCID: PMC84792. Epub 1999/04/16. eng
13 - Hajishengallis G. Porphyromonas gingivalis-host interactions: Open war or intelligent guerilla tactics?. Microbes and infection. 2009 May–Jun;11(6–7):637–645. PubMed PMID: 19348960. Pubmed Central PMCID: PMC2704251. Epub 2009/04/08. eng
14 - Amano A. Molecular interaction of Porphyromonas gingivalis with host cells: Implication for the microbial pathogenesis of periodontal disease. Journal of Periodontology. 2003 Jan;74(1):90–96. PubMed PMID: 12593602. Epub 2003/02/21. eng
15 - Kristoffersen AK, Solli SJ, Nguyen TD, Enersen M. Association of the rgpB gingipain genotype to the major fimbriae (fimA) genotype in clinical isolates of the periodontal pathogen Porphyromonas gingivalis. Journal of Oral Microbiology. 2015;7:29124. PubMed PMID: 26387644. Pubmed Central PMCID: PMC4576663. Epub 2015/09/22. eng
16 - Inaba H, Nakano K, Kato T, Nomura R, Kawai S, Kuboniwa M, et al. Heterogenic virulence and related factors among clinical isolates of Porphyromonas gingivalis with type II fimbriae. Oral Microbiology and Immunology. 2008 Feb;23(1):29–35. PubMed PMID: 18173795. Epub 2008/01/05. eng
17 - Kumada H, Haishima Y, Umemoto T, Tanamoto K. Structural study on the free lipid A isolated from lipopolysaccharide of Porphyromonas gingivalis. Journal of Bacteriology. 1995 Apr;177(8):2098–2106. PubMed PMID: 7721702. Pubmed Central PMCID: Pmc176854. Epub 1995/04/01. eng
18 - Darveau RP, Pham TT, Lemley K, Reife RA, Bainbridge BW, Coats SR, et al. Porphyromonas gingivalis lipopolysaccharide contains multiple lipid A species that functionally interact with both Toll-like receptors 2 and 4. Infection and Immunity. 2004 Sep;72(9):5041–5051. PubMed PMID: 15321997. Pubmed Central PMCID: Pmc517442. Epub 2004/08/24. eng
19 - Chen T, Duncan MJ. Gingipain adhesin domains mediate Porphyromonas gingivalis adherence to epithelial cells. Microbial Pathogenesis. 2004 Apr;36(4):205–209. PubMed PMID: 15001226. Epub 2004/03/06. eng
20 - Pathirana RD, O’Brien-Simpson NM, Veith PD, Riley PF, Reynolds EC. Characterization of proteinase-adhesin complexes of Porphyromonas gingivalis. Microbiology (Reading, England). 2006 Aug;152(Pt 8):2381–2394. PubMed PMID: 16849802. Epub 2006/07/20. eng
21 - Pathirana RD, O’Brien-Simpson NM, Visvanathan K, Hamilton JA, Reynolds EC. The role of the RgpA-Kgp proteinase-adhesin complexes in the adherence of Porphyromonas gingivalis to fibroblasts. Microbiology (Reading, England). 2008 Oct;154(Pt 10):2904–2911. PubMed PMID: 18832297. Epub 2008/10/04. eng
22 - Kadowaki T, Nakayama K, Yoshimura F, Okamoto K, Abe N, Yamamoto K. Arg-gingipain acts as a major processing enzyme for various cell surface proteins in Porphyromonas gingivalis. The Journal of Biological Chemistry. 1998 Oct 30;273(44):29072–29076. PubMed PMID: 9786913. Epub 1998/10/24. eng
23 - Palm E, Khalaf H, Bengtsson T. Suppression of inflammatory responses of human gingival fibroblasts by gingipains from Porphyromonas gingivalis. Molecular Oral Microbiology. 2015 Feb;30(1):74–85. PubMed PMID: 25055828. Epub 2014/07/25. eng
24 - Palm E, Khalaf H, Bengtsson T. Porphyromonas gingivalis downregulates the immune response of fibroblasts. BMC Microbiology. 2013;13:155. PubMed PMID: 23841502. Pubmed Central PMCID: Pmc3717116. Epub 2013/07/12. eng
25 - Irshad M, van der Reijden WA, Crielaard W, Laine ML. In vitro invasion and survival of Porphyromonas gingivalis in gingival fibroblasts; role of the capsule. Archivum immunologiae et therapiae experimentalis. 2012 Dec;60(6):469–476. PubMed PMID: 22949096. Epub 2012/09/06. eng
26 - Singh A, Wyant T, Anaya-Bergman C, Aduse-Opoku J, Brunner J, Laine ML, et al. The capsule of Porphyromonas gingivalis leads to a reduction in the host inflammatory response, evasion of phagocytosis, and increase in virulence. Infection and Immunity. 2011 Nov;79(11):4533–4542. PubMed PMID: 21911459. Pubmed Central PMCID: PMC3257911. Epub 2011/09/14. eng
27 - Vernal R, Leon R, Silva A, van Winkelhoff AJ, Garcia-Sanz JA, Sanz M. Differential cytokine expression by human dendritic cells in response to different Porphyromonas gingivalis capsular serotypes. Journal of Clinical Periodontology. 2009 Oct;36(10):823–829. PubMed PMID: 19682172. Epub 2009/08/18. eng
28 - Gui MJ, Dashper SG, Slakeski N, Chen YY, Reynolds EC. Spheres of influence: Porphyromonas gingivalis outer membrane vesicles. Molecular Oral Microbiology. 2016 Oct;31(5):365–378. PubMed PMID: 26466922. Epub 2015/10/16. eng
29 - Popadiak K, Potempa J, Riesbeck K, Blom AM. Biphasic effect of gingipains from Porphyromonas gingivalis on the human complement system. Journal of Immunology (Baltimore, MD: 1950). 2007 Jun 01;178(11):7242–7250. PubMed PMID: 17513773. Epub 2007/05/22. eng
30 - Mydel P, Takahashi Y, Yumoto H, Sztukowska M, Kubica M, Gibson FC, 3rd, et al. Roles of the host oxidative immune response and bacterial antioxidant rubrerythrin during Porphyromonas gingivalis infection. PLoS Pathogens. 2006 Jul;2(7):e76. PubMed PMID: 16895445. Pubmed Central PMCID: PMC1522038. Epub 2006/08/10. eng
31 - Imamura T, Tanase S, Hamamoto T, Potempa J, Travis J. Activation of blood coagulation factor IX by gingipains R, arginine-specific cysteine proteinases from Porphyromonas gingivalis. The Biochemical Journal. 2001 Jan 15;353(Pt 2):325–331. PubMed PMID: 11139397. Pubmed Central PMCID: PMC1221575. Epub 2001/01/05. eng
32 - Imamura T, Potempa J, Tanase S, Travis J. Activation of blood coagulation factor X by arginine-specific cysteine proteinases (gingipain-Rs) from Porphyromonas gingivalis. The Journal of Biological Chemistry. 1997 Jun 20;272(25):16062–16067. PubMed PMID: 9188512. Epub 1997/06/20. eng
33 - Imamura T, Potempa J, Travis J. Activation of the kallikrein-kinin system and release of new kinins through alternative cleavage of kininogens by microbial and human cell proteinases. Biological Chemistry. 2004 Nov;385(11):989–996. PubMed PMID: 15576318. Epub 2004/12/04. eng
34 - Houalet-Jeanne S, Pellen-Mussi P, Tricot-Doleux S, Apiou J, Bonnaure-Mallet M. Assessment of internalization and viability of Porphyromonas gingivalis in KB epithelial cells by confocal microscopy. Infection and Immunity. 2001 Nov;69(11):7146–7151. PubMed PMID: 11598091. Pubmed Central PMCID: PMC100107. Epub 2001/10/13. eng
35 - Zhao W, Wang L, Zhang M, Wang P, Zhang L, Yuan C, et al. NF-kappaB- and AP-1-mediated DNA looping regulates osteopontin transcription in endotoxin-stimulated murine macrophages. Journal of Immunology. 2011 Mar 01;186(5):3173–3179. PubMed PMID: 21257959. Pubmed Central PMCID: 4227538
36 - DebRoy A, Vogel SM, Soni D, Sundivakkam PC, Malik AB, Tiruppathi C. Cooperative signaling via transcription factors NF-kappaB and AP1/c-Fos mediates endothelial cell STIM1 expression and hyperpermeability in response to endotoxin. Journal of Biological Chemistry. 2014 Aug 29;289(35):24188–24201. PubMed PMID: 25016017. Pubmed Central PMCID: 4148850
37 - Mahdavi J, Royer PJ, Sjolinder HS, Azimi S, Self T, Stoof J, et al. Pro-inflammatory cytokines can act as intracellular modulators of commensal bacterial virulence. Open Biology. 2013 Oct 09;3(10):130048. PubMed PMID: 24107297. Pubmed Central PMCID: PMC3814720. Epub 2013/10/11. eng
38 - Morandini AC, Chaves Souza PP, Ramos-Junior ES, Brozoski DT, Sipert CR, Souza Costa CA, et al. Toll-like receptor 2 knockdown modulates interleukin (IL)-6 and IL-8 but not stromal derived factor-1 (SDF-1/CXCL12) in human periodontal ligament and gingival fibroblasts. Journal of Periodontology. 2013 Apr;84(4):535–544. PubMed PMID: 22680301. Epub 2012/06/12. eng
39 - Palm E, Demirel I, Bengtsson T, Khalaf H. The role of Toll-like and protease-activated receptors in the expression of cytokines by gingival fibroblasts stimulated with the periodontal pathogen Porphyromonas gingivalis. Cytokine. 2015 Dec;76(2):424–432. PubMed PMID: 26318255. Epub 2015/09/01. eng
40 - Hiramine H, Watanabe K, Hamada N, Umemoto T. Porphyromonas gingivalis 67-kDa fimbriae induced cytokine production and osteoclast differentiation utilizing TLR2. FEMS Microbiology Letters. 2003 Dec 05;229(1):49–55. PubMed PMID: 14659542. Epub 2003/12/09. eng
41 - Burns E, Bachrach G, Shapira L, Nussbaum G. Cutting edge: TLR2 is required for the innate response to Porphyromonas gingivalis: Activation leads to bacterial persistence and TLR2 deficiency attenuates induced alveolar bone resorption. Journal of Immunology (Baltimore, MD: 1950). 2006 Dec 15;177(12):8296–8300. PubMed PMID: 17142724. Epub 2006/12/05. eng
42 - Wara-aswapati N, Chayasadom A, Surarit R, Pitiphat W, Boch JA, Nagasawa T, et al. Induction of Toll-like receptor expression by Porphyromonas gingivalis. Journal of Periodontology. 2013 Jul;84(7):1010–1018. PubMed PMID: 23003918. Epub 2012/09/26. eng
43 - Coats SR, Jones JW, Do CT, Braham PH, Bainbridge BW, To TT, et al. Human Toll-like receptor 4 responses to P. gingivalis are regulated by lipid A 1- and 4’-phosphatase activities. Cellular Microbiology. 2009 Nov;11(11):1587–1599. PubMed PMID: 19552698. Pubmed Central PMCID: PMC3074576. Epub 2009/06/26. eng
44 - Uehara A, Naito M, Imamura T, Potempa J, Travis J, Nakayama K, et al. Dual regulation of interleukin-8 production in human oral epithelial cells upon stimulation with gingipains from Porphyromonas gingivalis. Journal of Medical Microbiology. 2008 Apr;57(Pt 4):500–507. PubMed PMID: 18349372. Epub 2008/03/20. eng
45 - Fagundes JA, Monoo LD, Euzebio Alves VT, Pannuti CM, Cortelli SC, Cortelli JR, et al. Porphyromonas gingivalis is associated with protease-activated receptor-2 upregulation in chronic periodontitis. Journal of Periodontology. 2011 Nov;82(11):1596–1601. PubMed PMID: 21513479. Epub 2011/04/26. eng
46 - Bainbridge B, Verma RK, Eastman C, Yehia B, Rivera M, Moffatt C, et al. Role of Porphyromonas gingivalis phosphoserine phosphatase enzyme SerB in inflammation, immune response, and induction of alveolar bone resorption in rats. Infection and Immunity. 2010 Nov;78(11):4560–4569. PubMed PMID: 20805334. Pubmed Central PMCID: PMC2976320. Epub 2010/09/02. eng
47 - Moelants EA, Loozen G, Mortier A, Martens E, Opdenakker G, Mizgalska D, et al. Citrullination and proteolytic processing of chemokines by Porphyromonas gingivalis. Infection and Immunity. 2014 Jun;82(6):2511–2519. PubMed PMID: 24686061. Pubmed Central PMCID: PMC4019151. Epub 2014/04/02. eng
48 - Mikolajczyk-Pawlinska J, Travis J, Potempa J. Modulation of interleukin-8 activity by gingipains from Porphyromonas gingivalis: Implications for pathogenicity of periodontal disease. FEBS Letters. 1998 Dec 04;440(3):282–286. PubMed PMID: 9872387. Epub 1999/01/01. eng
49 - Oleksy A, Banbula A, Bugno M, Travis J, Potempa J. Proteolysis of interleukin-6 receptor (IL-6R) by Porphyromonas gingivalis cysteine proteinases (gingipains) inhibits interleukin-6-mediated cell activation. Microbial Pathogenesis. 2002 Apr;32(4):173–181. PubMed PMID: 12079407. Epub 2002/06/25. eng
50 - Sugawara S, Nemoto E, Tada H, Miyake K, Imamura T, Takada H. Proteolysis of human monocyte CD14 by cysteine proteinases (gingipains) from Porphyromonas gingivalis leading to lipopolysaccharide hyporesponsiveness. Journal of Immunology (Baltimore, MD: 1950). 2000 Jul 01;165(1):411–418. PubMed PMID: 10861079. Epub 2000/06/22. eng
51 - Takayanagi H, Iizuka H, Juji T, Nakagawa T, Yamamoto A, Miyazaki T, et al. Involvement of receptor activator of nuclear factor kappaB ligand/osteoclast differentiation factor in osteoclastogenesis from synoviocytes in rheumatoid arthritis. Arthritis and Rheumatism. 2000 Feb;43(2):259–269. PubMed PMID: 10693864. Epub 2000/02/29. eng
52 - Yun PL, Decarlo AA, Collyer C, Hunter N. Hydrolysis of interleukin-12 by Porphyromonas gingivalis major cysteine proteinases may affect local gamma interferon accumulation and the Th1 or Th2 T-cell phenotype in periodontitis. Infection and Immunity. 2001 Sep;69(9):5650–5660. PubMed PMID: 11500441. Pubmed Central PMCID: PMC98681. Epub 2001/08/14. eng
53 - Dias IH, Marshall L, Lambert PA, Chapple IL, Matthews JB, Griffiths HR. Gingipains from Porphyromonas gingivalis increase the chemotactic and respiratory burst-priming properties of the 77-amino-acid interleukin-8 variant. Infection and Immunity. 2008 Jan;76(1):317–323. PubMed PMID: 18025101. Pubmed Central PMCID: PMC2223636. Epub 2007/11/21. eng
54 - Amano A, Chen C, Honma K, Li C, Settem RP, Sharma A. Genetic characteristics and pathogenic mechanisms of periodontal pathogens. Advances in Dental Research. 2014 May;26(1):15–22. PubMed PMID: 24736700
55 - Dorn BR, Dunn WA, Jr, Progulske-Fox A. Porphyromonas gingivalis traffics to autophagosomes in human coronary artery endothelial cells. Infection and Immunity. 2001 Sep;69(9):5698–5708. PubMed PMID: 11500446. Pubmed Central PMCID: 98686
56 - Ham H, Sreelatha A, Orth K. Manipulation of host membranes by bacterial effectors. Nature Reviews Microbiology. 2011 Jul 18;9(9):635–646. PubMed PMID: 21765451
57 - Al-Taweel FB, Douglas CW, Whawell SA. The periodontal pathogen Porphyromonas gingivalis preferentially interacts with oral epithelial cells in S phase of the cell cycle. Infection and Immunity. 2016 Jul;84(7):1966–1974. PubMed PMID: 27091929. Pubmed Central PMCID: 4936351
58 - Hintermann E, Haake SK, Christen U, Sharabi A, Quaranta V. Discrete proteolysis of focal contact and adherens junction components in Porphyromonas gingivalis-infected oral keratinocytes: A strategy for cell adhesion and migration disabling. Infection and Immunity. 2002 Oct;70(10):5846–5856. PubMed PMID: 12228316. Pubmed Central PMCID: 128337
59 - Kato T, Kawai S, Nakano K, Inaba H, Kuboniwa M, Nakagawa I, et al. Virulence of Porphyromonas gingivalis is altered by substitution of fimbria gene with different genotype. Cellular Microbiology. 2007 Mar;9(3):753–765. PubMed PMID: 17081195
60 - Groeger SE, Meyle J. Epithelial barrier and oral bacterial infection. Periodontology 2000. 2015 Oct;69(1):46–67. PubMed PMID: 26252401
61 - Darveau RP, Belton CM, Reife RA, Lamont RJ. Local chemokine paralysis, a novel pathogenic mechanism for Porphyromonas gingivalis. Infection and Immunity. 1998 Apr;66(4):1660–1665. PubMed PMID: 9529095. Pubmed Central PMCID: 108102. Epub 1998/04/07. eng
62 - Lonn J, Johansson CS, Nakka S, Palm E, Bengtsson T, Nayeri F, et al. High concentration but low activity of hepatocyte growth factor in periodontitis. Journal of Periodontology. 2014 Jan;85(1):113–122. PubMed PMID: 23594192
63 - Morandini AC, Sipert CR, Ramos-Junior ES, Brozoski DT, Santos CF. Periodontal ligament and gingival fibroblasts participate in the production of TGF-beta, interleukin (IL)-8 and IL-10. Brazilian Oral Research. 2011 Mar–Apr;25(2):157–162. PubMed PMID: 21537641. Epub 2011/05/04. eng
64 - Naylor AJ, Filer A, Buckley CD. The role of stromal cells in the persistence of chronic inflammation. Clinical Experimental Immunology. 2013 Jan;171(1):30–35. PubMed PMID: 23199320. Pubmed Central PMCID: Pmc3530092. Epub 2012/12/04. eng
65 - Filer A, Raza K, Salmon M, Buckley CD. Targeting stromal cells in chronic inflammation. Discovery Medicine. 2007 Feb;7(37):20–26. PubMed PMID: 17343801. Pubmed Central PMCID: PMC3160478. Epub 2007/03/09. eng
66 - Palm E, Demirel I, Bengtsson T, Khalaf H. The role of Toll-like and protease-activated receptors and associated intracellular signaling in Porphyromonas gingivalis-infected gingival fibroblasts. APMIS: Acta Pathologica, Microbiologica, et Immunologica Scandinavica. 2017 Feb;125(2):157–169. PubMed PMID: 28120492. Epub 2017/01/26. eng
67 - Jayaprakash K, Demirel I, Khalaf H, Bengtsson T. The role of phagocytosis, oxidative burst and neutrophil extracellular traps in the interaction between neutrophils and the periodontal pathogen Porphyromonas gingivalis. Molecular Oral Microbiology. 2015 Oct;30(5):361–375. PubMed PMID: 25869817
68 - Morozumi T, Nakagawa T, Nomura Y, Sugaya T, Kawanami M, Suzuki F, et al. Salivary pathogen and serum antibody to assess the progression of chronic periodontitis: A 24-mo prospective multicenter cohort study. Journal of Periodontal Research. 2016 Dec;51(6):768–778. PubMed PMID: 26791469
69 - Berglundh T, Liljenberg B, Lindhe J. Some cytokine profiles of T-helper cells in lesions of advanced periodontitis. Journal of Clinical Periodontology. 2002 Aug;29(8):705–709. PubMed PMID: 12390567
70 - Takeichi O, Haber J, Kawai T, Smith DJ, Moro I, Taubman MA. Cytokine profiles of T-lymphocytes from gingival tissues with pathological pocketing. Journal of Dental Research. 2000 Aug;79(8):1548–1555. PubMed PMID: 11023273
71 - Cheng WC, Hughes FJ, Taams LS. The presence, function and regulation of IL-17 and Th17 cells in periodontitis. Journal of Clinical Periodontology. 2014 Jun;41(6):541–549. PubMed PMID: 24735470
72 - Khalaf H, Bengtsson T. Altered T-cell responses by the periodontal pathogen Porphyromonas gingivalis. PLoS One. 2012;7(9):e45192. PubMed PMID: 22984628. Pubmed Central PMCID: 3440346. Epub 2012/09/18. eng
73 - Seymour GJ, Ford PJ, Cullinan MP, Leishman S, Yamazaki K. Relationship between periodontal infections and systemic disease. Clinical Microbiology and Infection. 2007 Oct;13(Suppl 4):3–10. PubMed PMID: 17716290
74 - Inaba H, Amano A. Roles of oral bacteria in cardiovascular diseases--from molecular mechanisms to clinical cases: Implication of periodontal diseases in development of systemic diseases. Journal of Pharmacological Sciences. 2010;113(2):103–109. PubMed PMID: 20501966
75 - Kozarov EV, Dorn BR, Shelburne CE, Dunn WA, Jr, Progulske-Fox A. Human atherosclerotic plaque contains viable invasive Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis. Arteriosclerosis, Thrombosis, and Vascular Biology. 2005 Mar;25(3):e17–18. PubMed PMID: 15662025
76 - Rosenfeld ME, Campbell LA. Pathogens and atherosclerosis: Update on the potential contribution of multiple infectious organisms to the pathogenesis of atherosclerosis. Thrombosis and Haemostasis. 2011 Nov;106(5):858–867. PubMed PMID: 22012133
77 - Wada K, Kamisaki Y. Molecular dissection of Porphyromonas gingivalis-related arteriosclerosis: A novel mechanism of vascular disease. Periodontology 2000. 2010 Oct;54(1):222–234. PubMed PMID: 20712642
78 - Vongpatanasin W. Hydrochlorothiazide is not the most useful nor versatile thiazide diuretic. Current Opinion in Cardiology. 2015 Jul;30(4):361–365. PubMed PMID: 26049382. Pubmed Central PMCID: 4460599
79 - Koo J, Choe HK, Kim HD, Chun SK, Son GH, Kim K. Effect of mefloquine, a gap junction blocker, on circadian period2 gene oscillation in the mouse suprachiasmatic nucleus ex vivo. Endocrinology and Metabolism. 2015 Sep;30(3):361–370. PubMed PMID: 25491783. Pubmed Central PMCID: 4595362
80 - Reszec J, Szkudlarek M, Hermanowicz A, Bernaczyk PS, Mariak Z, Chyczewski L. N-cadherin, beta-catenin and connexin 43 expression in astrocytic tumours of various grades. Histology and Histopathology. 2015 Mar;30(3):361–371. PubMed PMID: 25386667
81 - Suzuki J, Aoyama N, Aoki M, Tada Y, Wakayama K, Akazawa H, et al. High incidence of periodontitis in Japanese patients with abdominal aortic aneurysm. International Heart Journal. 2014;55(3):268–270. PubMed PMID: 24806388
82 - Hokamura K, Umemura K. Roles of oral bacteria in cardiovascular diseases--from molecular mechanisms to clinical cases: Porphyromonas gingivalis is the important role of intimal hyperplasia in the aorta. Journal of Pharmacological Sciences. 2010;113(2):110–114. PubMed PMID: 20501963
83 - Hayashi C, Madrigal AG, Liu X, Ukai T, Goswami S, Gudino CV, et al. Pathogen-mediated inflammatory atherosclerosis is mediated in part via Toll-like receptor 2-induced inflammatory responses. Journal of Innate Immunity. 2010;2(4):334–343. PubMed PMID: 20505314. Pubmed Central PMCID: PMC2895755
84 - Zhang B, Elmabsout AA, Khalaf H, Basic VT, Jayaprakash K, Kruse R, et al. The periodontal pathogen Porphyromonas gingivalis changes the gene expression in vascular smooth muscle cells involving the TGFbeta/Notch signalling pathway and increased cell proliferation. BMC Genomics. 2013 Nov 09;14:770. PubMed PMID: 24209892. Pubmed Central PMCID: 3827841
85 - Zhang B, Khalaf H, Sirsjo A, Bengtsson T. Gingipains from the periodontal pathogen Porphyromonas gingivalis play a significant role in regulation of Angiopoietin1 and Angiopoietin 2 in human aortic smooth muscle cells. Infection and Immunity. 2015 Nov; 83(11):4256-65. PubMed PMID: 26283334
86 - Trollope AF, Golledge J. Angiopoietins, abdominal aortic aneurysm and atherosclerosis. Atherosclerosis. 2011 Feb;214(2):237–243. PubMed PMID: 20832800. Pubmed Central PMCID: 3012744
87 - Padma R, Sreedhara A, Indeevar P, Sarkar I, Kumar CS. Vascular endothelial growth factor levels in gingival crevicular fluid before and after periodontal therapy. Journal of Clinical and Diagnostic Research. 2014 Nov;8(11):ZC75–ZC79. PubMed PMID: 25584323. Pubmed Central PMCID: PMC4290334
88 - Bengtsson T, Karlsson H, Gunnarsson P, Skoglund C, Elison C, Leanderson P, et al. The periodontal pathogen Porphyromonas gingivalis cleaves apoB-100 and increases the expression of apoM in LDL in whole blood leading to cell proliferation. Journal of Internal Medicine. 2008 May;263(5):558–571. PubMed PMID: 18248365
89 - Higashi Y, Goto C, Jitsuiki D, Umemura T, Nishioka K, Hidaka T, et al. Periodontal infection is associated with endothelial dysfunction in healthy subjects and hypertensive patients. Hypertension. 2008 Feb;51(2):446–453. PubMed PMID: 18039979
90 - Bokhari SA, Khan AA, Butt AK, Azhar M, Hanif M, Izhar M, et al. Non-surgical periodontal therapy reduces coronary heart disease risk markers: A randomized controlled trial. Journal of Clinical Periodontology. 2012 Nov;39(11):1065–1074. PubMed PMID: 22966824
91 - Bhagat K, Moss R, Collier J, Vallance P. Endothelial “stunning” following a brief exposure to endotoxin: A mechanism to link infection and infarction? Cardiovascular Research. 1996 Nov;32(5):822–829. PubMed PMID: 8944812
92 - Maekawa T, Takahashi N, Honda T, Yonezawa D, Miyashita H, Okui T, et al. Porphyromonas gingivalis antigens and interleukin-6 stimulate the production of monocyte chemoattractant protein-1 via the upregulation of early growth response-1 transcription in human coronary artery endothelial cells. Journal of Vascular Research. 2010;47(4):346–354. PubMed PMID: 20016208
93 - Awano S, Ansai T, Mochizuki H, Yu W, Tanzawa K, Turner AJ, et al. Sequencing, expression and biochemical characterization of the Porphyromonas gingivalis pepO gene encoding a protein homologous to human endothelin-converting enzyme. FEBS Letters. 1999 Oct 22;460(1):139–144. PubMed PMID: 10571076
94 - Ansai T, Yamamoto E, Awano S, Yu W, Turner AJ, Takehara T. Effects of periodontopathic bacteria on the expression of endothelin-1 in gingival epithelial cells in adult periodontitis. Clinical Science. 2002 Aug;103(Suppl 48):327S–331S. PubMed PMID: 12193115
95 - Rikimaru T, Awano S, Mineoka T, Yoshida A, Ansai T, Takehara T. Relationship between endothelin-1 and interleukin-1beta in inflamed periodontal tissues. Biomedical Research. 2009 Dec;30(6):349–355. PubMed PMID: 20051644
96 - Lester SR, Bain JL, Serio FG, Harrelson BD, Johnson RB. Relationship between gingival angiopoietin-1 concentrations and depth of the adjacent gingival sulcus. Journal of Periodontology. 2009 Sep;80(9):1447–1453. PubMed PMID: 19722795
97 - McCarter SD, Lai PF, Suen RS, Stewart DJ. Regulation of endothelin-1 by angiopoietin-1: Implications for inflammation. Experimental Biology and Medicine. 2006 Jun;231(6):985–991. PubMed PMID: 16741035
98 - Gawaz M. Platelets in the onset of atherosclerosis. Blood Cells, Molecules & Diseases. 2006 Mar–Apr;36(2):206–210. PubMed PMID: 16476558
99 - Blair P, Rex S, Vitseva O, Beaulieu L, Tanriverdi K, Chakrabarti S, et al. Stimulation of Toll-like receptor 2 in human platelets induces a thromboinflammatory response through activation of phosphoinositide 3-kinase. Circulation Research. 2009 Feb 13;104(3):346–354. PubMed PMID: 19106411. Pubmed Central PMCID: 2732983
100 - Kerrigan SW. The expanding field of platelet-bacterial interconnections. Platelets. 2015;26(4):293–301. PubMed PMID: 25734214
101 - Hamzeh-Cognasse H, Damien P, Chabert A, Pozzetto B, Cognasse F, Garraud O. Platelets and infections—Complex interactions with bacteria. Frontiers in Immunology. 2015;6:82. PubMed PMID: 25767472. Pubmed Central PMCID: PMC4341565
102 - Klinger MH, Jelkmann W. Role of blood platelets in infection and inflammation. Journal of Interferon & Cytokine Research: The Official Journal of the International Society for Interferon and Cytokine Research. 2002 Sep;22(9):913–922. PubMed PMID: 12396713
103 - Blair P, Flaumenhaft R. Platelet alpha-granules: Basic biology and clinical correlates. Blood Review. 2009 Jul;23(4):177–189. PubMed PMID: 19450911. Pubmed Central PMCID: 2720568
104 - Borgeson E, Lonn J, Bergstrom I, Brodin VP, Ramstrom S, Nayeri F, et al. Lipoxin A(4) inhibits Porphyromonas gingivalis-induced aggregation and reactive oxygen species production by modulating neutrophil-platelet interaction and CD11b expression. Infection and Immunity. 2011 Apr;79(4):1489–1497. PubMed PMID: 21263017. Pubmed Central PMCID: 3067532
105 - Klarstrom Engstrom K, Khalaf H, Kalvegren H, Bengtsson T. The role of Porphyromonas gingivalis gingipains in platelet activation and innate immune modulation. Molecular Oral Microbiology. 2015 Feb;30(1):62–73. PubMed PMID: 25043711
106 - Gamonal J, Acevedo A, Bascones A, Jorge O, Silva A. Levels of interleukin-1 beta, -8, and -10 and RANTES in gingival crevicular fluid and cell populations in adult periodontitis patients and the effect of periodontal treatment. Journal of Periodontology. 2000 Oct;71(10):1535–1545. PubMed PMID: 11063385
107 - Lourbakos A, Yuan YP, Jenkins AL, Travis J, Andrade-Gordon P, Santulli R, et al. Activation of protease-activated receptors by gingipains from Porphyromonas gingivalis leads to platelet aggregation: A new trait in microbial pathogenicity. Blood. 2001 Jun 15;97(12):3790–3797. PubMed PMID: 11389018
108 - McNicol A, Israels SJ. Mechanisms of oral bacteria-induced platelet activation. Canadian Journal of Physiology and Pharmacology. 2010 May;88(5):510–524. PubMed PMID: 20555421
109 - Nylander M, Lindahl TL, Bengtsson T, Grenegard M. The periodontal pathogen Porphyromonas gingivalis sensitises human blood platelets to epinephrine. Platelets. 2008 Aug;19(5):352–358. PubMed PMID: 18791941
110 - Keestra JA, Grosjean I, Coucke W, Quirynen M, Teughels W. Non-surgical periodontal therapy with systemic antibiotics in patients with untreated aggressive periodontitis: A systematic review and meta-analysis. Journal of Periodontal Research. 2015 Dec;50(6):689–706. PubMed PMID: 25522248
111 - Czaplewski L, Bax R, Clokie M, Dawson M, Fairhead H, Fischetti VA, et al. Alternatives to antibiotics-a pipeline portfolio review. The Lancet Infectious Diseases. 2016 Feb;16(2):239–251. PubMed PMID: 26795692
112 - Bonifait L, Chandad F, Grenier D. Probiotics for oral health: Myth or reality? Journal. 2009 Oct;75(8):585–590. PubMed PMID: 19840501
113 - Cotter PD, Ross RP, Hill C. Bacteriocins—A viable alternative to antibiotics? Nature Reviews Microbiology. 2013 Feb;11(2):95–105. PubMed PMID: 23268227
114 - Khalaf H, Nakka SS, Sanden C, Svard A, Hultenby K, Scherbak N, et al. Antibacterial effects of Lactobacillus and bacteriocin PLNC8 alphabeta on the periodontal pathogen Porphyromonas gingivalis. BMC Microbiology. 2016 Aug 18;16(1):188. PubMed PMID: 27538539. Pubmed Central PMCID: 4990846