Lamina propria dendritic cells express activation markers and contact lymphocytes in chronic periodontitis

Osteoinduction and osteoimmunology: Emerging concepts

The recognition and importance of immune cells during bone regeneration, including around bone biomaterials, has led to the development of an entire field termed "osteoimmunology," which focuses on the connection and interplay between the skeletal system and immune cells. Most studies have focused on the "osteogenic" capacity of various types of bone biomaterials, and much less focus has been placed on immune cells despite being the first cell type in contact with implantable devices. Thus, the amount of literature generated to date on this topic makes it challenging to extract needed information. This review article serves as a guide highlighting advancements made in the field of osteoimmunology emphasizing the role of the osteoimmunomodulatory properties of biomaterials and their impact on osteoinduction. First, the various immune cell types involved in bone biomaterial integration are discussed, including the prominent role of osteal macrophages (OsteoMacs) during bone regeneration. Thereafter, key biomaterial properties, including topography, wettability, surface charge, and adsorption of cytokines, growth factors, ions, and other bioactive molecules, are discussed in terms of their impact on immune responses. These findings highlight and recognize the importance of the immune system and osteoimmunology, leading to a shift in the traditional models used to understand and evaluate biomaterials for bone regeneration.

Guided Bone Regeneration Using Barrier Membrane in Dental Applications

Guided bone regeneration (GBR) is a widely used technique in preclinical and clinical studies due to its predictability. Its main purpose is to prevent the migration of soft tissue into the osseous wound space, while allowing osseous cells to migrate to the site. GBR is classified into two main categories: resorbable and non-resorbable membranes. Resorbable membranes do not require a second surgery but tend to have a short resorption period. Conversely, non-resorbable membranes maintain their mechanical strength and prevent collapse. However, they require removal and are susceptible to membrane exposure. GBR is often used with bone substitute graft materials to fill the defect space and protect the bone graft. The membrane can also undergo various modifications, such as surface modification and biological factor loading, to improve barrier functions and bone regeneration. In addition, bone regeneration is largely related to osteoimmunology, a new field that focuses on the interactions between bone and the immune system. Understanding these interactions can help in developing new treatments for bone diseases and injuries. Overall, GBR has the potential to be a powerful tool in promoting bone regeneration. Further research in this area could lead to advancements in the field of bone healing. This review will highlight resorbable and non-resorbable membranes with cellular responses during bone regeneration, provide insights into immunological response during bone remodeling, and discuss antibacterial features.

Comparative analysis of antigen-presenting cells in gingival tissues in healthy and periodontitis patients

AIMS

Microbial flora of dental plaque trigger innate and adaptive immune responses. The function of antigen-presenting cells (APCs) is to bridge the innate and adaptive immune systems. The human immune system contains three main types of APCs: dendritic cells (DC) (Langerhans cells (LCs) and interstitial DCs, IDCs), macrophages and B lymphocytes. In this study, the distribution and density of all APCs in healthy and inflamed human gingival tissue were comparatively analysed.

METHODS

Research was conducted on gingival biopsy specimens obtained from 55 patients and classified in three groups: healthy gingiva (control group, n=10), moderate periodontal disease (PD) (n=21) and severe PD (n=24). For APCs' identification antibodies raised against CD_1a (for LCs), S₁₀₀ protein (for iDCs), CD₆₈ (for macrophages) and CD₂₀ (for B lymphocytes) were used.

RESULTS

Increased density of IDCs, macrophages and B lymphocytes in lamina propria and reduced density of LCs in the gingival epithelium were found in patients with periodontitis. Simultaneously, it was noticed an increased concentration of macrophages and B cells in the gingival epithelium in patients with PD. No statistically significant difference in the distribution and density of APC was found among patients with moderate and advanced periodontitis.

CONCLUSIONS

It was hypothesised that in the periodontitis the role of antigen presentation was largely taken from LCs by the DCs, macrophages and B cells. These APCs are thought to have less protective and tolerogenic potential than LCs and this is a significant reason for alveolar bone destruction in periodontitis.

Exogenous and Endogenous Dendritic Cell-Derived Exosomes: Lessons Learned for Immunotherapy and Disease Pathogenesis

Immune therapeutic exosomes, derived exogenously from dendritic cells (DCs), the 'directors' of the immune response, are receiving favorable safety and tolerance profiles in phase I and II clinical trials for a growing number of inflammatory and neoplastic diseases. DC-derived exosomes (EXO), the focus of this review, can be custom tailored with immunoregulatory or immunostimulatory molecules for specific immune cell targeting. Moreover, the relative stability, small size and rapid uptake of EXO by recipient immune cells offer intriguing options for therapeutic purposes. This necessitates an in-depth understanding of mechanisms of EXO biogenesis, uptake and routing by recipient immune cells, as well as their in vivo biodistribution. Against this backdrop is recognition of endogenous exosomes, secreted by all cells, the molecular content of which is reflective of the metabolic state of these cells. In this regard, exosome biogenesis and secretion is regulated by cell stressors of chronic inflammation and tumorigenesis, including dysbiotic microbes, reactive oxygen species and DNA damage. Such cell stressors can promote premature senescence in young cells through the senescence associated secretory phenotype (SASP). Pathological exosomes of the SASP amplify inflammatory signaling in stressed cells in an autocrine fashion or promote inflammatory signaling to normal neighboring cells in paracrine, without the requirement of cell-to-cell contact. In summary, we review relevant lessons learned from the use of exogenous DC exosomes for immune therapy, as well as the pathogenic potential of endogenous DC exosomes.

The Role of the Immune Microenvironment in Bone Regeneration

Bone is an active tissue, being constantly renewed in healthy individuals with participation of the immune system to a large extent. Any imbalance between the processes of bone formation and bone resorption is linked to various inflammatory bone diseases. The immune system plays an important role in tissue formation and bone resorption. Recently, many studies have demonstrated complex interactions between the immune and skeletal systems. Both of immune cells and cytokines contribute to the regulation of bone homeostasis, and bone cells, including osteoblasts, osteoclasts, osteocytes, also influence the cellular functions of immune cells. These crosstalk mechanisms between the bone and immune system finally emerged, forming a new field of research called osteoimmunology. Therefore, the immune microenvironment is crucial in determining the speed and outcome of bone healing, repair, and regeneration. In this review, we summarise the role of the immune microenvironment in bone regeneration from the aspects of immune cells and immune cytokines. The elucidation of immune mechanisms involved in the process of bone regeneration would provide new therapeutic targets for improving the curative effects of bone injury treatment.

The Current Understanding on Langerhans' Cells and Its Role in Oral Lesions

OBJECTIVE

Description of Langerhans' cells (LCs) as an important antigen-presenting cells responsible for detecting the antigens, recruiting T-cells, and thereby initiating the immune response. An adequate response of the mucosal immune system is essential to protect the mucosa against pathological conditions. Hence, a detailed review was planned about this unique antigen-presenting cell.

METHODS

A literature search of the electronic databases included the MEDLINE, EBSCOHOST, PUBMED, and hand searches of references retrieved were undertaken using the following MeSH terms "Langerhans cells," "LCs in Oral Lichen Planus," "Langerhans cell histiocytosis," "LCs and HIV," "LCs in Periodontitis."

RESULTS

LCs are present suprabasally in the epithelium of oral mucosa and in the epidermis of the skin. The role played by LCs though not fully elucidated, but several research studies indicate that these cells are involved in the pathogenesis of many oral diseases. In this article, the historical perspective, structure, function, origin, and phenotypic expressions of LCs are discussed in detail. The current understanding on the role of LCs in various oral lesions and its immunological characteristics are discussed.

CONCLUSION

LCs act as immune mediator cells, tumor cells, vectors of infected cells, and phagocytic cells. Further studies could bolster the knowledge about the role of Langerhans cells in the immune response of various oral diseases and thereby provide diagnostic tools and help for prognostic evaluation. This review illuminates the pivotal role of Langerhans cells and its immune surveillance as a "Sentinels" of the oral mucosa.

FOXP3+ and CD25+ cells are reduced in patients with stage IV, grade C periodontitis: A comparative clinical study

BACKGROUND AND OBJECTIVE

Some studies suggest that regulatory T cells (Tregs) have suppressive effects on inflammatory osteolysis. The aim of this study was to evaluate Treg immunomarkers in periodontitis-affected tissues from patients with periodontitis and clinically healthy gingiva (control).

MATERIAL AND METHODS

The presence and distribution of positive cells for CD4, CD25 and FOXP3 (Treg immunomarkers) in periodontitis-affected tissues (epithelium and lamina propria) of 30 patients (ten per group) with a diagnosis of stage IV, grade C periodontitis (IV-C), stage III, grade B periodontitis (III-B) and the control were evaluated. A two-way ANOVA followed by Fisher's LSD test was used to demonstrate differences between the groups and immunomarkers; Student's t test was used to demonstrate differences between the epithelium and the lamina propria.

RESULTS

Both IV-C and III-B periodontitis presented a significantly high proportion of immune-stained cells for all immunomarkers when compared to the control group. Notably, CD25+ and FOXP3+ cells were detected in a significantly higher number in III-B than IV-C periodontitis (P < .05).

CONCLUSION

Our results suggest the participation of Tregs on the osteoimmunological mechanisms in IV-C and III-B periodontitis patients, notably contributing to strategies for alveolar bone regeneration in clinical treatment decisions.

(C3) The Oral Epithelial Cell and First Encounters with HIV-1

The oral epithelium is the site of first exposure of HIV-1 to host tissues during oral sex with an infected partner or through breast-feeding by an infected mother. Although the oral epithelium is distinguishable by its apparent resistance, the mucosal surfaces represent a primary target of HIV-1. After oral exposure and swallowing, infection is detected prominently in the gastrointestinal tract, which becomes depleted of CD4+ T-cells. The oral cavity and palatine tonsils appear to resist infection and transfer to susceptible lymphoid cells in the lamina propria by local anti-HIV-1 mechanisms. In some cases, expression of these antiviral mechanisms increases after exposure to HIV-1. During primary exposure and before seroconversion, based on limited in vitro and primate data, a window of opportunity for capture of HIV-1 by the oral epithelium may exist. After seroconversion, the risk of infectious HIV-1 appearing in saliva is negligible. This report considers evidence that oral epithelium has the potential both to enable and to resist infection by HIV-1.

Bone Cells Dynamics during Peri-Implantitis: a Theoretical Analysis

OBJECTIVES

The present manuscript aims a detailed characterization of the bone cells dynamics during physiological bone remodelling and, subsequently, to address the cellular and molecular mechanisms that play a fundamental role in the immune-inflammatory-induced uncoupled bone remodelling observed in peri-implantitis.

RESULTS

An intimate relationship between the immune system and bone is acknowledged to be determinant for bone tissue remodelling and integrity. Due to the close interaction of immune and bone cells, the two systems share a number of surface receptors, cytokines, signalling pathways and transcription factors that are involved in mutual regulatory mechanisms. This physiological equilibrium is disturbed in pathological conditions, as verified in peri-implantitis establishment and development. Activation of the innate and adaptive immune response, challenged by the local bacterial infection, induces the synthesis of high levels of a variety of pro- and anti-inflammatory cytokines that disturb the normal functioning of the bone cells, by uncoupling bone resorption and formation, ending up with a net alveolar bone loss and subsequent implant failure. Most data points to an immune-inflammatory induced osteoclast differentiation and function, as the major underlying mechanism to the uncoupled bone resorption to bone formation. Further, the disturbed functioning of osteoblasts, reflected by the possible expression of a fibro-osteoblastic phenotype, may also play a role.

CONCLUSIONS

Alveolar bone loss is a hallmark of peri-implantitis. A great deal of data is still needed on the cellular and humoral crosstalk in the context of an integrated view of the osteoimmunologic interplay occurring in the peri-implantitis environment subjacent to the bone loss outcome.

Skin aging in patients with acquired immunodeficiency syndrome

To evaluate the histomorphometric skin changes over aging patients with autopsied acquired immunodeficiency syndrome (AIDS). In 29 skin fragments of autopsied elderly (older than 50 years) and nonelderly patients with AIDS, epidermal thickness, the number of layers, the diameter of cells, the percentage of collagen and elastic fibers in the dermis, and the number and morphology of Langerhans cells were assessed. Statistical analysis was performed by SigmaStat 2.03 program. The thickness of the epidermis (92.55 × 158.94 μm), the number of layers (7 × 9 layers), and the diameter of the cells (13.27 × 17.6 μm) were statistically lower among the elderly. The quantity of collagen fibers (9.68 × 14.11%) and elastic fibers (11.89 × 15.31%) was also significantly lower in the elderly. There was a decrease in total (10.61 × 12.38 cel/mm(2)) and an increase in immature Langerhans cells (6.31 × 4.98 cel/mm(2)) in elderly patients with AIDS. The aging of the skin of patients with AIDS is amended in different histomorphometric aspects, the epidermis constituents suffer less pronounced changes in normal aging, and the dermis has more intense changes in elastic fibers and collagen.

Cytokine-mediated bone destruction in rheumatoid arthritis

Bone homeostasis, which involves formation and resorption, is an important process for maintaining adequate bone mass in humans. Rheumatoid arthritis (RA) is an autoimmune disease characterized by inflammation and bone loss, leading to joint destruction and deformity, and is a representative disease of disrupted bone homeostasis. The bone loss and joint destruction are mediated by immunological insults by proinflammatory cytokines and various immune cells. The connection between bone and immunity has been intensely studied and comprises the emerging field of osteoimmunology. Osteoimmunology is an interdisciplinary science investigating the interplay between the skeletal and the immune systems. The main contributors in osteoimmunology are the bone effector cells, such as osteoclasts or osteoblasts, and the immune cells, particularly lymphocytes and monocytes. Physiologically, osteoclasts originate from immune cells, and immune cells regulate osteoblasts and vice versa. Pathological conditions such as RA might affect these interactions, thereby altering bone homeostasis, resulting in the unfavorable outcome of bone destruction. In this review, we describe the osteoclastogenic roles of the proinflammatory cytokines and immune cells that are important in the pathophysiology of RA.

Dendritic cells of the oral mucosa

The oral cavity contains distinct mucosal surfaces, each with its own unique distribution of dendritic cell (DC) subsets. In addition to tissue-specific properties, such organization might confer differential immune outcomes guided by tissue-resident DCs, which translate in the lymph node into an overall immune response. This process is further complicated by continual exposure and colonization of the oral cavity with enormous numbers of diverse microbes, some of which might induce destructive immunity. As a central cell type constantly monitoring changes in oral microbiota and orchestrating T-cell function, oral DCs are of major importance in deciding whether to induce immunity or tolerance. In this review, an overview of the phenotype and distribution of DCs in the oral mucosa is provided. In addition, the role of the various oral DC subsets in inducing immunity vs. tolerance, as well as their involvement in several oral pathologies is discussed.

The Interplay between the bone and the immune system

In the last two decades, numerous scientists have highlighted the interactions between bone and immune cells as well as their overlapping regulatory mechanisms. For example, osteoclasts, the bone-resorbing cells, are derived from the same myeloid precursor cells that give rise to macrophages and myeloid dendritic cells. On the other hand, osteoblasts, the bone-forming cells, regulate hematopoietic stem cell niches from which all blood and immune cells are derived. Furthermore, many of the soluble mediators of immune cells, including cytokines and growth factors, regulate the activities of osteoblasts and osteoclasts. This increased recognition of the complex interactions between the immune system and bone led to the development of the interdisciplinary osteoimmunology field. Research in this field has great potential to provide a better understanding of the pathogenesis of several diseases affecting both the bone and immune systems, thus providing the molecular basis for novel therapeutic strategies. In these review, we reported the latest findings about the reciprocal regulation of bone and immune cells.

Polybacterial challenge effects on cytokine/chemokine production by macrophages and dendritic cells

OBJECTIVE

To investigate the polymicrobial infection of periodontal disease, which elicits inflammatory mediators/cytokines/chemokines in the local gingival tissues, and a polybacterial challenge of antigen-presenting cells, e.g. macrophages and dendritic cells (DCs), at the mucosal surface.

MATERIALS AND METHODS

The cytokine/chemokine profiles of human macrophages and DCs in response to polybacterial challenges were investigated.

RESULTS

Oral Gram-negative bacteria elicited significantly greater IL-8 levels from macrophages, compared to Gram-positive bacteria. Gram-positive bacteria did not show synergism in inducing this chemokine from macrophages. In contrast, pairs of oral Gram-negative bacteria elicited synergistic production of IL-8 by macrophages. Similar results were not observed with TNFα, which only appeared additive with the polybacterial challenge. Selected Gram-negative bacterial pairs synergized in IL-6 production by immature DCs. In mature DCs (mDCs), a Porphyromonas gingivalis/Fusobacterium nucleatum and Porphyromonas intermedia/F. nucleatum polybacterial challenge resulted in significant synergism for IL-6 and TNFα levels. However, only the Pi/Fn combination synergized for IL-12 production and there appeared to be no polybacterial effect on IL-10 production by the mDCs.

CONCLUSIONS

These results indicate that a polybacterial challenge of cells linking innate and adaptive immune responses results in varied response profiles that are dependent upon the characteristics of the microorganisms that are components of the polybacterial complex.

Effects of oral commensal and pathogenic bacteria on human dendritic cells

BACKGROUND/AIMS

The oral cavity harbors a diverse and complex microbial community. Bacteria accumulate on both the hard and soft oral tissues in sessile biofilms and engage the host in an intricate cellular dialog, which normally constrains the bacteria to a state of commensal harmony. Dendritic cells (DCs) are likely to balance tolerance and active immunity to commensal microorganisms as part of chronic inflammatory responses. While the role played by DCs in maintaining intestinal homeostasis has been investigated extensively, relatively little is known about DC responses to oral bacteria.

METHODS

In this study, we pulsed human monocyte-derived immature DCs (iDCs) with cell wall extracts from pathogenic and commensal gram-positive or gram-negative oral bacteria.

RESULTS

Although all bacterial extracts tested induced iDCs to mature and produce cytokines/chemokines including interleukin-12p40, tumor necrosis factor-alpha, and monocyte chemoattractant protein-1 (MCP-1), the most important factor for programming DCs by oral bacteria was whether they were gram-positive or gram-negative, not whether they were commensal or pathogenic. In general, gram-negative oral bacteria, except for periodontopathic Porphyromonas gingivalis, stimulated DC maturation and cytokine production at lower concentrations than gram-positive oral bacteria. The threshold of bacteria needed to stimulate chemokine production was 100-fold to 1000-fold lower than that needed to induce cytokines. In addition, very low doses of oral commensal bacteria triggered monocytes to migrate toward DC-derived MCP-1.

CONCLUSION

Oral commensal and pathogenic bacteria do not differ qualitatively in how they program DCs. DC-derived MCP-1 induced in response to oral commensal bacteria may play a role, at least in part, in the maintenance of oral tissue integrity by attracting monocytes.

Increase of gingival matured dendritic cells number in elderly patients with chronic periodontitis

OBJECTIVE

The purpose of this study was to evaluate the inflammatory cell subset proportions in the upper gingival connective tissue, including mature dendritic cells (DC) in elderly and younger patients with generalized chronic periodontitis in order to further understand the effect of aging on gingival inflammatory phenomenon.

METHODS

Gingival tissue specimens presenting chronic periodontitis from 8 elderly patients aged >75 (test group, group T) and from 8 younger patients aged 50-60 (considered as controls, group C) were analysed by immunohistochemistry using monoclonal antibodies against CD45RB, CD4, CD8, CD19, CD68, DC-SIGN, DC-LAMP molecules. The number of each immunolabelled cells subset was counted using image analysis.

RESULTS

The difference in the number of CD45RB+leucocytes in the upper gingival connective tissue between groups was not significant permitting to use it as reference. As compared to group C, the lymphocyte subsets/CD45RB+leucocytes ratios tended to decrease in group T but the decrease was significant only for CD4+T lymphocytes/CD45RB+cells ratio (p<0.03). On the opposite, the ratios of antigen-presenting cells DC-SIGN+cells/CD45RB+cells and DC-LAMP+cells/CD45RB+cells were significantly increased (p<0.03 and <0.0001, respectively) in group T. Moreover, in group T the DC-LAMP+cells/DC-SIGN+cells ratio was significantly increased (p<0.05) showing an increased number of matured dendritic cells.

CONCLUSION

During chronic periodontitis in elderly patients, our results show a decrease in the ratio of gingival CD4+lymphocyte subset associated with an increase in the ratios of antigen-presenting cells subsets and more particularly maturated DC-LAMP+dendritic cells.

Dendritic cells at the osteo-immune interface: implications for inflammation-induced bone loss

Within the past decade, the critical roles of T cells and T cell-mediated immunity in inflammation-induced osteoclastogenesis and subsequent bone loss have been extensively studied, thereby establishing the new paradigm of osteoimmunology. Therefore, dendritic cells (DCs), the most potent antigen-presenting cells, responsible for activation of naïve T cells and orchestration of the immune response, became critically situated at the osteo-immune interface. Today, emerging new evidence suggests that DC may be directly involved in inflammation-induced osteoclastogenesis and bone loss, by acting as osteoclast (OC) precursors that can further develop into DC-derived OCs (DDOC) under inflammatory conditions. These findings have tremendous implications, because in addition to DC's important roles in regulating innate and adaptive immunity, a direct contribution by these cells to inflammation-induced bone loss may provide a promising therapeutic target not only for controlling inflammation but also for modulating bone destruction.

Inflammatory events in a vascular remodeling model induced by surgical injury to the rat carotid artery

1.--The aim of our study was to gain insight into the molecular and cellular mechanisms of the inflammatory response to arterial injury in a rat experimental model. 2.--Rats (five for each experimental time) were subjected to brief clamping and longitudinal incision of a carotid artery and monitored for 30 days. Subsequently, Nuclear Factor-kappaB (NF-kappaB) expression was measured by electrophoretic mobility shift assay. Heat shock protein (HSP) 27, HSP47 and HSP70 were evaluated by Western blot. Morphological changes of the vessel wall were investigated by light and electron microscopy. 3.--In injured rat carotid artery NF-kappaB activity started immediately upon injury, and peaked between 2 and 3 weeks later. Western blot showed a significant increase of HSP47 and HSP70 7 days after injury. At 2 weeks postinjury, HSP27 expression peaked. Light microscopy showed a neointima formation, discontinuity of the media layer and a rich infiltrate. Among infiltrating cells electron microscopy identified dendritic-like cells in contact with lymphocytes. 4.--Our model of surgical injury induces a significant inflammatory process characterized by enhanced NF-kappaB activity and HSPs hyperexpression. Dendritic-like cells were for the first time identified as a novel component of tissue repair consequent to acute arterial injury.

Do Langerhans cells behave similarly in elderly and younger patients with chronic periodontitis?

OBJECTIVE

The purpose of this study was to compare the number, the distribution and the expression of markers of maturation of Langerhans cells (LC) in elderly and younger patients with chronic periodontitis in order to evidence the effect of aging on LC in inflammatory gingival tissue.

METHODS

Gingival tissue specimens presenting chronic periodontitis from 8 elderly patients aged >75 (group E) and from 8 younger patients aged 50-60 (considered as controls, group C) were used for immunohistochemistry with monoclonal antibodies against CD45RB (leucocytes), CD1a (LC), markers of LC maturation (DC-LAMP, CD83) and number of immunolabelled cell subsets was evaluated using image analysis.

RESULTS

The difference in the number of CD45RB+ leucocytes in the upper connective tissue between groups was not significant. In group E, the number of CD1a+ LC was significantly decreased (P<0.002) in the epithelium and significantly increased (P<0.0004) in the upper connective tissue. Furthermore, in group E, intraepithelial CD1a+ LC are more often observed in the upper epithelium and their dendritic processes were shorter and less numerous. Concerning the expression of markers of maturation, the numbers of intraepithelial DC-LAMP+ cells and CD83+ cells were significantly increased (P<0.0007 and P<0.02, respectively) in group E.

CONCLUSION

During chronic periodontitis in elderly patients, the decrease in the number of intraepithelial LC and the alteration of dendritic processes could be balanced by a cellular distribution often observed in the upper epithelium associated with changes in cell maturation in response to bacterial elements.

Immune interactions with CD4+ T cells promote the development of functional osteoclasts from murine CD11c+ dendritic cells

Dendritic cells (DC) are innate immune effectors and are critically involved in regulating T cell immunity. Osteoclasts (OC) are bone-resorbing cells derived from the monocyte/macrophage lineage in response to receptor activator of NF-kappaB ligand (RANKL). DC and T cells form aggregates in the inflammatory infiltrates at active disease sites in human and in experimental rheumatoid arthritis and periodontitis. We investigated whether DC interactions with T cells in the bone environment can support the development of functional OC. In the present study, we demonstrate that upon proper activation by microbial or protein Ags (namely Actinobacillus actinomycetemcomitans, bovine insulin, and outer membrane protein-1) and during immune interactions with CD4+ T cells in vitro, murine BM-derived and splenic CD11c+ DC (CD11b- F4/80- Ly-6C- CD31-) develop into TRAP+ CT-R+ cathepsin-k+ functional OC in a RANKL/RANK-dependent manner. Rescue and blocking experiments using CD11c+ DC derived from Csf-1(-/-) op/op mice show that M-CSF is required "before" developing such osteoclastogenic potential upstream of RANKL/RANK signaling, suggesting that immature CD11c+ DC can indeed act like OC precursors. In addition, these CD11c+ DC-derived OC are capable of inducing bone loss after adoptive transfer in vivo. These data suggest a direct contribution of DC during immune interactions with CD4+ T cells to inflammation-induced osteoclastogenesis. Therefore, our findings not only provide further evidence for DC plasticity, but also extend the current paradigm of osteoimmunology.

Dendritic cells at the oral mucosal interface

The mucosal lining of the respiratory and digestive systems contains the largest and most complex immune system in the body, but surprisingly little is known of the immune system that serves the oral mucosa. This review focuses on dendritic cells, particularly powerful arbiters of immunity, in response to antigens of microbial or tumor origin, but also of tolerance to self-antigens and commensal microbes. Although first discovered in 1868, the epidermal dendritic Langerhans cells remained enigmatic for over a century, until they were identified as the most peripheral outpost of the immune system. Investigators' ability to isolate, enrich, and culture dendritic cells has led to an explosion in the field. Presented herein is a review of dendritic cell history, ontogeny, function, and phenotype, and the role of different dendritic cell subsets in the oral mucosa and its diseases. Particular emphasis is placed on the mechanisms of recognition and capture of microbes by dendritic cells. Also emphasized is how dendritic cells may regulate immunity/tolerance in response to oral microbes.

Dendritic-NK cell interactions in P. gingivalis-specific responses

Patients with localized aggressive periodontitis have type-1 cytokines in gingival crevicular fluid and high titers of IFN-gamma-dependent IgG2 reactive with P. gingivalis in gingival crevicular fluid and serum. Localized aggressive periodontitis monocytes spontaneously differentiate into dendritic cells that can stimulate IFN-gamma production by NK cells. These relationships prompted the hypothesis that P. gingivalis-dendritic cell-NK cell interactions might promote type-1 cytokine responses. Although P. gingivalis is not a potent inducer of Th1 responses, it stimulated strong IL-12 responses by monocyte-derived dendritic cells in the presence of IFN-gamma, and IFN-gamma was produced by NK cells within 24 hrs in the presence of dendritic cells. Anti-P. gingivalis IgG2 responses were enhanced by dendritic cells, and removal of NK cells reduced IFN-gamma- and P. gingivalis-specific IgG2. Thus, P. gingivalis-dendritic cell-NK cell interactions apparently resulted in reciprocal stimulation and increased type-1 cytokine production by both dendritic cells and NK cells, and increased P. gingivalis-specific IgG2.

Expression of major histocompatibility complex class II and CD80 by gingival epithelial cells induces activation of CD4+ T cells in response to bacterial challenge

HLA-DR (major histocompatibility complex [MHC] class II) is often expressed by epithelial cells in gingival tissues with periodontal disease but not by cells in healthy gingival tissues. Confocal microscopic analyses revealed that gingival epithelial cells (GEC) from tissue with periodontal disease express both HLA-DR and B7-1 (CD80) costimulatory molecules. Rat GEC lines were established to elucidate the possible role of MHC class II and B7-1 expression by GEC. Stimulation of a rat GEC line with gamma interferon (IFN-gamma) induced the expression of MHC class II, whereas the cell line constitutively expressed B7-1 costimulatory molecules as determined by reverse transcription-PCR and flow cytometry. Actinobacillus actinomycetemcomitans Omp29-specific CD4(+) Th1 clone cells proliferated in response to pretreatment of GEC with fixed A. actinomycetemcomitans and IFN-gamma. However, the Th1 cells did not respond to pretreatment of GEC with the bacteria alone or IFN-gamma alone. The activation of Th1 clone cells induced by the GEC was inhibited by antibody to MHC class II or by CTLA4 immunoglobulin (CTLA4-Ig). Lymph node T cells did not demonstrate superantigen activity to A. actinomycetemcomitans, although both lymph node T cells and Th1 clone cells were sensitive to superantigen activity of staphylococcal enterotoxin A as cultured in the presence of IFN-gamma-treated GEC. These results suggested that GEC can take up bacterial antigen and consequently process and present the bacterial antigen to CD4(+) T cells by MHC class II in conjunction with B7 costimulation. GEC appeared to play a role in the adaptive immune response by stimulating antigen-specific CD4(+) T cells.

Dendritic cells stimulated with Actinobacillus actinomycetemcomitans elicit rapid gamma interferon responses by natural killer cells

Human immunoglobulin G2 (IgG2) responses are gamma interferon (IFN-gamma) dependent, and monocyte-derived dendritic cells (mDCs) promote IgG2 production. DCs spontaneously emerge from monocytes in cultures prepared from localized aggressive periodontitis (LagP) patients, and these patients have high levels of IgG2 that is reactive with Actinobacillus actinomycetemcomitans. These results prompted the hypothesis that an interaction between mDCs and A. actinomycetemcomitans promotes IFN-gamma production, and IFN-gamma is known to promote both immunopathology and protective IgG2. A. actinomycetemcomitans induced mDCs to produce interleukin-12 (IL-12), and the addition of A. actinomycetemcomitans and DCs to cultured peripheral blood lymphocytes elicited high levels of IFN-gamma within just 24 h. In contrast, IL-4 was not detectable although DC-derived IL-10 production was apparent. A. actinomycetemcomitans-stimulated macrophages prepared from the same monocytes lacked the ability to induce IL-12 or IFN-gamma responses. NK cells of the innate immune system were the primary source of this early IFN-gamma, although CD8 T cells also contributed some. The NK cell-derived IFN-gamma was IL-12 dependent, and A. actinomycetemcomitans-DC interactions were Toll-like receptor 4 dependent. A. actinomycetemcomitans and A. actinomycetemcomitans lipopolysaccharide (LPS) were more potent than Escherichia coli and E. coli LPS in the ability to induce DC IL-12 and IFN-gamma. The ability of A. actinomycetemcomitans-stimulated DCs to induce NK cells to rapidly produce IFN-gamma in the absence of detectable IL-4 suggests their potential for skewing responses toward Th1. This may help explain the presence of Th1-associated cytokines in gingival crevicular fluid (GCF) from LagP patients and the high levels of IgG2 in their serum and GCF that is reactive with A. actinomycetemcomitans.

Fimbriated Porphyromonas gingivalis is more efficient than fimbria-deficient P. gingivalis in entering human dendritic cells in vitro and induces an inflammatory Th1 effector response

Porphyromonas gingivalis is a fimbriated mucosal pathogen implicated in chronic periodontitis (CP). The fimbriae are required for invasion of the gingival mucosa and for induction of CP in animal models of periodontitis. CP is associated with infection of immature dendritic cells (DCs) by P. gingivalis in situ and with increased numbers of dermal DCs (DDCs) and mature DCs in the lamina propria. The role of fimbriae in gaining entry into human DCs and how this modulates the inflammatory and effector immune responses, however, have not been explored. To address this, we generated monocyte-derived DCs (MDDCs) in vitro which phenotypically and functionally resemble DDCs. We show here that virulent fimbriated P. gingivalis 381, in contrast to its fimbria-deficient mutant, P. gingivalis DPG3, efficiently gains entry to MDDCs in a manner dependent on active cell metabolism and cytoskeletal rearrangement. In addition, uptake of 381, unlike DPG3, induces DCs to undergo maturation, upregulate costimulatory molecules, and secrete inflammation cytokines interleukin-1beta (IL-1beta), IL-6, tumor necrosis factor alpha, IL-10, and IL-12. Moreover, MDDCs pulsed with 381 also stimulated a higher autologous mixed lymphocyte reaction and induced a Th1-type response, with gamma interferon (IFN-gamma) being the main cytokine. Monocytes used as controls demonstrated fimbria-dependent uptake of 381 as well but produced low levels of inflammatory cytokines compared to MDDCs. When MDDCs were pulsed with recombinant fimbrillin of P. gingivalis (10 micro g/ml), maturation of MDDCs was also induced; moreover, matured MDDCs induced proliferation of autologous CD4(+) T cells and release of IFN-gamma. Thus, these results establish the significance of P. gingivalis fimbriae in the uptake of P. gingivalis by MDDCs and in induction of immunostimulatory Th1 responses.

Expression of cys–cys chemokine ligand 21 on human gingival lymphatic vessels

The cys-cys (C-C) chemokine ligand 21 is a member of the C-C chemokines that constitute a group of heparin-binding cytokines with a pattern of four or six conserved cysteines. The CCL21 is known to be expressed in secondary lymphoid tissues, however it has rarely been reported for the expression on peripheral lymphatic vessels in somatic tissue. Here we investigated the expression of CCL21 on lymphatic vessels identified by anti-desmoplakin in uninflamed and inflamed human gingiva. In uninflamed tissue the expression of CCL21 was detected on lymphatic vessels in gingiva. In uninflamed gingiva the expression of CCL21 was detected on all lymphatic capillaries of the mucosal connective tissue papillae. There were two types of collecting lymphatic vessels in the lamina propria mucosae expressing CCL21 strongly or very weakly. In inflamed gingiva no expression of CCL21 was detected on lymphatic vessels. In all tissue sections no blood vessels expressing CCL21 were observed. These results may suggest that the expression of CCL21 is predominantly induced in the peripheral lymphatic endothelium of the uninflamed mucosal microcirculation, and that under inflamed conditions a reduction of CCL21 occurs in lymphatic endothelium.

Expression of MHC Class II, CD70, CD80, CD86 and pro-inflammatory cytokines is differentially regulated in oral epithelial cells following bacterial challenge

Oral epithelium may play a regulatory role in local immune responses when interacting with bacteria. The present study was undertaken to investigate the effects of selected bacterial pathogens found in periodontal and endodontic infections on oral epithelial cells. Expression of cell surface molecules (major histocompatibility complex (MHC) Class II, CD54, CD70, CD80 and CD86) and secretion of inflammatory cytokines (interleukin (IL)-1beta, IL-6, and tumor necrosis factor (TNF)-alpha) in response to selected bacterial challenge were examined on an immortalized oral epithelial cell line, HOK-18A and a skin epithelial cell line, HaCaT. Actinomyces viscosus, Actinomyces israelii, Fusobacterium nucleatum lipopolysaccharide (LPS) or primary human periradicular exudate from a granuloma were co-cultured with epithelial cells for 4 or 24 h. Subsequently, cell surface expression of MHC Class II, CD54, CD70, CD80 and CD86, along with pro-inflammatory cytokine levels were determined using flow cytometry, ELISA and RT-PCR. Results indicated that the selected oral bacteria have greater effects on oral versus skin epithelial cells. F. nucleatum increased MHC Class II and CD54 (ICAM-1) cell surface expression on HOK-18A and HaCaT cells. A. israelii also had enhancing effects on the expression of CD54 and MHC Class II. A. israelii and LPS induced a 2.8-fold (P < 0.001) and 4.4-fold (P < 0.005) TNF-alpha secretion, respectively, while F. nucleatum and LPS induced a 10-fold (P < 0.0004) and 6-fold (P < 0.01) IL-1beta secretion, respectively by HOK-18A. Interestingly, CD70, CD80, and CD86 were generally decreased upon bacteria and LPS challenge on HOK-18A. The effects of increased MHC Class II and decreased CD70 were also evident with challenge of human periradicular exudate on HOK-18A. The implications of the study are unique in that oral epithelial cells may play both activating and inhibitory roles in the host immune response towards infection by oral bacteria. We introduce a concept of 'dormancy' where the differential expression of key cell surface antigens on oral epithelial cells may keep the recruited immune effector cells in a state of unresponsiveness, thus contributing to the long term quiescent period observed in many periodontal and endodontic lesions.

Multiple dendritic cell (DC) subpopulations in human gingiva and association of mature DCs with CD4+ T-cells in situ

Gingival epithelium is a site of active trafficking of Langerhans cells (LCs), while the lamina propria in chronic periodontitis (CP) contains CD83+ mature dendritic cells (mDCs) and CD4+ T-cells. The immune cells that contribute to the mDCs, and whether mDCs engage with T-cells in situ, are unclear. Using several immunohistochemical approaches, combined with fluorescence-, light-, and scanning laser confocal-microscopy, we show that, in addition to LCs, the gingiva contains dermal DCs (DDCs) in the lamina propria; moreover, DDCs increase in number during CP. Furthermore, DDCs, LCs, and B-cells co-express CD83 in CP and contribute to the mDC pool. Double-staining for CD83 and CD4 revealed that mDCs associate with clusters of CD4+ T-cells in the lamina propria. Analysis of these data suggests that multiple DC subsets mature in the gingiva and that mature DCs engage in antigen presentation with T-cells in chronic periodontitis.

The role of acquired immunity and periodontal disease progression

Our understanding of the pathogenesis in human periodontal diseases is limited by the lack of specific and sensitive tools or models to study the complex microbial challenges and their interactions with the host's immune system. Recent advances in cellular and molecular biology research have demonstrated the importance of the acquired immune system not only in fighting the virulent periodontal pathogens but also in protecting the host from developing further devastating conditions in periodontal infections. The use of genetic knockout and immunodeficient mouse strains has shown that the acquired immune response-in particular, CD4+ T-cells-plays a pivotal role in controlling the ongoing infection, the immune/inflammatory responses, and the subsequent host's tissue destruction. In particular, studies of the pathogen-specific CD4+ T-cell-mediated immunity have clarified the roles of: (i) the relative diverse immune repertoire involved in periodontal pathogenesis, (ii) the contribution of pathogen-associated Th1-Th2 cytokine expressions in periodontal disease progression, and (iii) micro-organism-triggered periodontal CD4+ T-cell-mediated osteoclastogenic factor, 'RANK-L', which is linked to the induction of alveolar bone destruction in situ. The present review will focus on some recent advances in the acquired immune responses involving B-cells, CD8+ T-cells, and CD4+ T-cells in the context of periodontal disease progression. New approaches will further facilitate our understanding of their underlying molecular mechanisms that may lead to the development of new treatment modalities for periodontal diseases and their associated complications.

Langerin+ versus CD1a+ Langerhans cells in human gingival tissue: a comparative and quantitative immunohistochemical study

Langerhans cells (LC) are dendritic cells of the immune system able to capture intraepithelial pathogens and migrate to regional lymph nodes to present them to naive T cells. Up to now immunohistological studies on human gingival LC have been carried out using antibodies against HLA-DR or CD1a molecules. A new marker of LC called Langerin (CD207) and described, among other subcellular localisations, in the Birbeck granules is now available in immunohistochemistry. The purpose of this in situ study was to quantify and to compare Langerin+ versus CD1a+ LC number in order to show differences in the expression of these molecules, if any, and to determine which marker is the most specific. The present study was conducted using nine frozen healthy gingival samples. Double immunofluorescence procedures were performed with an anti-Langerin antibody revealed by FITC and with an anti-CD1a-PE antibody. Mounted slides were analysed by fluorescence microscopy and quantifications were performed on projected slides associated with a grid of 0.015 mm(2). Our results have shown that 1/ the number of CD1a+ LC was significantly increased (P=0.01) when compared with Langerin+ LC 2/ 92% of Langerin+ LC co-expressed CD1a 3/ only 82% of CD1a+ cells co-expressed Langerin 4/ a positive correlation was noted between CD1a+ and Langerin+ LC numbers. The present study has revealed the heterogeneity in the phenotype of gingival LC population and shown that Langerin seems the most specific marker for the study of LC.