Detection of, and anti-collagen antibody produced by, CD5-positive B cells in inflamed gingival tissues

The role of acquired host immunity in periodontal diseases

The aim of this narrative review is to relate the contribution of European researchers to the complex topic of the host immune system in periodontal disease, focusing on acquired immunity. Other chapters in this volume will address the genetics and autoantibody responses and other forms of immunity to periodontal disease. While the contribution of European authors is the focus, global literature is included in this descriptive narrative for contextual clarity, albeit many with European co-authors. The topic is relatively intense and is thus broken down into sections outlined below, tackled as descriptive narratives to enhance understanding. Any attempt at a systematic or scoping review was quickly abandoned given the descriptive nature and marked variation of approach in almost all publications. Even the most uniform area of this acquired periodontal immunology literature, antibody responses to putative pathogens in periodontal diseases, falls short of common structures and common primary outcome variables one would need and expect in clinical studies, where randomized controlled clinical trials (RCTs) abound. Addressing 'the host's role' in immunity immediately requires a discussion of host susceptibility, which necessitates consideration of genetic studies (covered elsewhere in the volume and superficially covered here).

Immunomodulation—What to Modulate and Why? Potential Immune Targets

Despite over 50 years of research into the immunology of periodontal disease, the precise mechanisms and the role of many cell types remains an enigma. Progress has been limited by the inability to determine disease activity clinically. Understanding the immunopathogenesis of periodontal disease however is fundamental if immunomodulation is to be used as a therapeutic strategy. It is important for the clinician to understand what could be modulated and why. In this context, potential targets include different immune cell populations and their subsets, as well as various cytokines. The aim of this review is to examine the role of the principal immune cell populations and their cytokines in the pathogenesis of periodontal disease and their potential as possible therapeutic targets.

Circulating inflammatory cell profiling and periodontitis: A systematic review and meta-analysis

Inflammation is a key driver of common noncommunicable diseases. Among common triggers of inflammation, chronic gingival inflammation (periodontitis) triggers a consistent humoral host inflammatory response, but little is known on its impact on circulating inflammatory cell profiles. We aimed to systematically appraise all the evidence linking periodontitis and its treatment to circulating inflammatory cell profiles. From 6 databases, 157 studies were eligible for qualitative synthesis and 29 studies for meta-analysis. Our meta-analysis showed that participants with periodontitis exhibited a significant mean increase in circulating CD4⁺ , CD4⁺ CD45RO⁺ , IFNγ-expressing CD4⁺ and CD8⁺ T cells, CD19⁺ CD27⁺ and CD5⁺ B cells, CD14⁺ CD16⁺ monocytes, and CD16⁺ neutrophils but decrease in CD8⁺ T and CD14⁺⁺ CD16^- monocytes. Our qualitative synthesis revealed that peripheral blood neutrophils of patients with periodontitis consistently showed elevated production of reactive oxygen species (ROS) when compared with those of healthy controls. Some evidence suggested that the treatment of periodontitis reversed the exaggerated ROS production, but limited and inconclusive data were found on several circulating inflammatory cell profiling. We conclude that periodontitis and its treatment are associated with minor but consistent alterations in circulating inflammatory cell profiles. These changes could represent key mechanisms explaining the association of periodontitis with other comorbidities such as cardiovascular disease, diabetes, and rheumatoid arthritis.

Phenotypes, roles, and modulation of regulatory lymphocytes in periodontitis and its associated systemic diseases

Periodontitis is a common chronic inflammatory disease that can result in tooth loss and poses a risk to systemic health. Lymphocytes play important roles in periodontitis through multiple mechanisms. Regulatory lymphocytes including regulatory B cells (Bregs) and T cells (Tregs) are the main immunosuppressive cells that maintain immune homeostasis, and are critical to our understanding of the pathogenesis of periodontitis and the development of effective treatments. In this review, we discuss the phenotypes, roles, and modulating strategies of regulatory lymphocytes including Bregs and Tregs in periodontitis and frequently cooccurring inflammatory diseases such as rheumatoid arthritis, Alzheimer disease, diabetes mellitus, and stroke. The current evidence suggests that restoring immune balance through therapeutic targeting of regulatory lymphocytes is a promising strategy for the treatment of periodontitis and other systemic inflammatory diseases.

Application of specialized pro-resolving mediators in periodontitis and peri-implantitis: a review

Scaling and root planning is a key element in the mechanical therapy used for the eradication of biofilm, which is the major etiological factor for periodontitis and peri‐implantitis. However, periodontitis is also a host mediated disease, therefore, removal of the biofilm without adjunctive therapy may not achieve the desired clinical outcome due to persistent activation of the innate and adaptive immune cells. Most recently, even the resident cells of the periodontium, including periodontal ligament fibroblasts, have been shown to produce several inflammatory factors in response to bacterial challenge. With increased understanding of the pathophysiology of periodontitis, more research is focusing on opposing excessive inflammation with specialized pro‐resolving mediators (SPMs). This review article covers the major limitations of current standards of care for periodontitis and peri‐implantitis, and it highlights recent advances and prospects of SPMs in the context of tissue reconstruction and regeneration. Here, we focus primarily on the role of SPMs in restoring tissue homeostasis after periodontal infection.

Oral Dysbiosis and Autoimmunity: From Local Periodontal Responses to an Imbalanced Systemic Immunity. A Review

The current paradigm of onset and progression of periodontitis includes oral dysbiosis directed by inflammophilic bacteria, leading to altered resolution of inflammation and lack of regulation of the inflammatory responses. In the construction of explanatory models of the etiopathogenesis of periodontal disease, autoimmune mechanisms were among the first to be explored and historically, for more than five decades, they have been described in an isolated manner as part of the tissue damage process observed in periodontitis, however direct participation of these mechanisms in the tissue damage is still controversial. Autoimmunity is affected by genetic and environmental factors, leading to an imbalance between the effector and regulatory responses, mostly associated with failed resolution mechanisms. However, dysbiosis/infection and chronic inflammation could trigger autoimmunity by several mechanisms including bystander activation, dysregulation of toll-like receptors, amplification of autoimmunity by cytokines, epitope spreading, autoantigens complementarity, autoantigens overproduction, microbial translocation, molecular mimicry, superantigens, and activation or inhibition of receptors related to autoimmunity by microorganisms. Even though autoreactivity in periodontitis is biologically plausible, the associated mechanisms could be related to non-pathologic responses which could even explain non-recognized physiological functions. In this review we shall discuss from a descriptive point of view, the autoimmune mechanisms related to periodontitis physio-pathogenesis and the participation of oral dysbiosis on local periodontal autoimmune responses as well as on different systemic inflammatory diseases.

[Differences of B cells, plasma cells, and related cytokines expression in gingival tissues between periodontitis and periodontal healthy subjects]

OBJECTIVE

This study aimed to compare the differences of B cells, plasma cells, and related cytokines expression in gingival tissues between periodontitis and periodontal healthy subjects.

METHODS

Gingival tissues were collected from periodontal healthy subjects (periodontal healthy group, n=12) and periodontitis patients (periodontitis group, n=15). Hematoxylin-eosin (HE) staining was used for histopathological examination. Immunohistochemical staining (CD19, CD38, and CD138) was applied to detect the expression of B cells and plasma cells. B cell-activating factor (BAFF) and soluble receptor activator of nuclear factor-κB ligand (sRANKL) were detected by enzyme-linked immunosorbent assay.

RESULTS

Extensive inflam-matory cell infiltration was found in the gingival tissues of the periodontitis group. The number of CD19(+), CD38(+), and CD138(+) cells of the periodontitis group was significantly higher than that of the periodontal healthy group (P<0.000 1). BAFF and sRANKL levels of the periodontitis group were higher than those of the periodontal healthy group (P<0.01, P<
0.001, respectively).

CONCLUSIONS

The expression of B cells, plasma cells, and their related BAFF and sRANKL cytokines were significantly higher in periodon-titis patients than those in the periodontal healthy subjects, sug-gesting that B cells and plasma cells may be involved in the development of periodontitis.

Porphyromonas gingivalis, a Long-Range Pathogen: Systemic Impact and Therapeutic Implications

Periodontitis is an inflammatory disease associated with a dysbiosis of the oral flora characterized by a chronic sustained inflammation leading to destruction of tooth-supporting tissues. Over the last decade, an association between periodontitis and systemic disorders such as cardiovascular diseases, rheumatoid arthritis and obesity has been demonstrated. The role of periodontal pathogens, notably Porphyromonas gingivalis (P. gingivalis), in the onset or exacerbation of systemic diseases has been proposed. P. gingivalis expresses several virulence factors that promote its survival, spreading, and sustaining systemic inflammation. Recently, the impact of periodontitis on gut dysbiosis has also been suggested as a potential mechanism underlying the systemic influence of periodontitis. New therapeutic strategies for periodontitis and other dysbiotic conditions, including the use of beneficial microbes to restore healthy microbial flora, may pave the way to improved therapeutic outcomes and more thorough patient management.

Rheumatoid Arthritis-Associated Mechanisms of Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans

Rheumatoid arthritis (RA) is an autoimmune disease of unknown etiology characterized by immune-mediated damage of synovial joints and antibodies to citrullinated antigens. Periodontal disease, a bacterial-induced inflammatory disease of the periodontium, is commonly observed in RA and has implicated periodontal pathogens as potential triggers of the disease. In particular, Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans have gained interest as microbial candidates involved in RA pathogenesis by inducing the production of citrullinated antigens. Here, we will discuss the clinical and mechanistic evidence surrounding the role of these periodontal bacteria in RA pathogenesis, which highlights a key area for the treatment and preventive interventions in RA.

B cell subset distribution is altered in patients with severe periodontitis

Several studies have recently highlighted the implication of B cells in physiopathogenesis of periodontal disease by showing that a B cell deficiency leads to improved periodontal parameters. However, the detailed profiles of circulating B cell subsets have not yet been investigated in patients with severe periodontitis (SP). We hypothesised that an abnormal distribution of B cell subsets could be detected in the blood of patients with severe periodontal lesions, as already reported for patients with chronic inflammatory diseases as systemic autoimmune diseases. Fifteen subjects with SP and 13 subjects without periodontitis, according to the definition proposed by the CDC periodontal disease surveillance work group, were enrolled in this pilot observational study. Two flow cytometry panels were designed to analyse the circulating B and B1 cell subset distribution in association with the RANKL expression. A significantly higher percentage of CD27⁺ memory B cells was observed in patients with SP. Among these CD27⁺ B cells, the proportion of the switched memory subset was significantly higher. At the same time, human B1 cells, which were previously associated with a regulatory function (CD20⁺CD69^-CD43⁺CD27⁺CD11b⁺), decreased in SP patients. The RANKL expression increased in every B cell subset from the SP patients and was significantly greater in activated B cells than in the subjects without periodontitis. These preliminary results demonstrate the altered distribution of B cells in the context of severe periodontitis. Further investigations with a larger cohort of patients can elucidate if the analysis of the B cell compartment distribution can reflect the periodontal disease activity and be a reliable marker for its prognosis (clinical trial registration number: NCT02833285, B cell functions in periodontitis).

The emerging roles of B cells as partners and targets in periodontitis

Initial studies of periodontal disease suggested that T cell-mediated immunity against oral Gram-negative microorganisms is a key player in the pathogenesis of this inflammatory disease. Recent investigations, however, revealed that B cells are also engaged. Given their chief role in innate-like and adaptive immune responses, B cells could exert protective functions in periodontitis. However, the periodontal bacteria-specific antibody response is generally unable to halt disease progression in affected subjects, suggesting that the antibodies produced could exhibit low anti-bacterial blocking functions or opsonophagocytic potential, and/or unfavorable effects. Moreover, although microbial antigens are involved in the induction of the inflammatory responses in human adult periodontitis, endogenous antigens also may contribute to the chronicity of this common disease. Not only antibodies to self-antigens, such as collagen, are locally produced, but the autoreactivities observed in aggressive periodontitis are more severe and diverse than those observed in chronic periodontitis, suggesting that autoimmune reactivity could play a role in the tissue destruction of periodontal disease. Further support for a pathological role of B cells in periodontitis comes from the finding that B cell-deficient mice are protected from bacterial infection-induced alveolar bone loss. Studies in patients indicate that B cells and plasma cells, together with osteoclastogenic factors (RANKL and osteoprotegerin) and specific cytokines involved in their growth and differentiation (BAFF and APRIL) participate in the induction of the pathological bone loss in periodontitis. This novel insight suggests that selective targeting of B cells could represent a future therapeutic avenue for severe periodontal disease.

Regulatory T-cells Infiltrate Periodontal Disease Tissues

CD4+CD25+ regulatory T (Tr) cells are critical in regulating the immune response and thereby play an important role in the defense against infection and control of autoimmune diseases. Our previous studies demonstrated the involvement of autoimmune responses in periodontitis. The aim of this study was to identify CD4+CD25+ Tr cells in periodontitis tissues and compare them with those in gingivitis tissues. Immunohistological analysis of CD4, CD25, and CTLA-4 and the gene expression analysis of FOXP3, TGF-β1, and IL-10 on gingival biopsies revealed the presence of CD4+CD25+ Tr cells in all tissues. In periodontitis, the percentage of CD4+CD25+ Tr cells increased with increasing proportions of B-cells relative to T-cells. FOXP3, a characteristic marker for CD4+CD25+ Tr cells, TGF-β1 and IL-10 were expressed more highly in periodontitis compared with gingivitis. These findings suggest that CD4+CD25+ Tr cells and possibly other regulatory T-cell populations do exist and may play regulatory roles in periodontal diseases.

Autoimmunity-Basics and link with periodontal disease

Autoimmune reactions reflect an imbalance between effector and regulatory immune responses, typically develop through stages of initiation and propagation, and often show phases of resolution (indicated by clinical remissions) and exacerbations (indicated by symptomatic flares). The fundamental underlying mechanism of autoimmunity is defective elimination and/or control of self-reactive lymphocytes. Periodontal diseases are characterized by inflammatory conditions that directly affect teeth-supporting structures, which are the major cause of tooth loss. Several studies have demonstrated the involvement of autoimmune responses in periodontal disease. Evidence of involvement of immunopathology has been reported in periodontal disease. Bacteria in the dental plaque induce antibody formation. Autoreactive T-cells, natural killer cells, ANCA, heat shock proteins, autoantibodies, and genetic factors are reported to have an important role in the autoimmune component of periodontal disease. The present review describes the involvement of autoimmune responses in periodontal diseases and also the mechanisms underlying these responses.

Cellular composition of long-standing gingivitis and periodontitis lesions

BACKGROUND AND OBJECTIVE

Insufficient information on the cellular composition of long-standing gingivitis lesions without signs of attachment loss makes an understanding of differences in cellular composition between "destructive" and "nondestructive" periodontal lesions difficult. The aim of the current study was to analyze differences in cell characteristics between lesions representing long-standing gingivitis and severe periodontitis.

MATERIAL AND METHODS

Two groups of patients were recruited. One group consisted of 36 patients, 33-67 years of age, with severe generalized periodontitis (periodontitis group). The second group consisted of 28 patients, 41-70 years of age, with overt signs of gingival inflammation but no attachment loss (gingivitis group). From each patient a gingival biopsy was obtained from one selected diseased site and prepared for immunohistochemical analysis.

RESULTS

Periodontitis lesions were twice as large and contained significantly larger proportions, numbers and densities of cells positive for CD138 (plasma cells) and CD68 (macrophages) than did gingivitis lesions. The proportion of B cells that expressed the additional CD5 marker (B-1a cells) was significantly larger in periodontitis lesions than in gingivitis lesions. The densities of T cells and B cells did not differ between periodontitis lesions and gingivitis lesions. T cells were not the dominating cell type in gingivitis lesions, as B cells together with their subset plasma cells comprised a larger number and proportion than T cells.

CONCLUSION

Periodontitis lesions at teeth with advanced attachment and bone loss exhibit quantitative and qualitative differences in relation to gingivitis lesions at teeth with no attachment and bone loss. It is suggested that the large number and high density of plasma cells are the hallmarks of advanced periodontitis lesions and the most conspicuous difference in relation to long-standing gingivitis lesions.

Levels of HIV-1 in subgingival biofilm of HIV-infected patients

AIM

The aims of the current study were to compare the levels of HIV-1 in the subgingival biofilm (SHVL) between detectable and undetectable plasmatic HIV-1 viral load (PHVL) in HIV-infected patients as well as to determine the association of SHVL with PHVL and clinical periodontal parameters.

MATERIAL AND METHODS

Forty-one HIV-infected individuals were divided into two groups: detectable (21) and undetectable (20) PHVL. Subgingival biofilm samples were obtained for detection and quantification of HIV-1 by real-time RT-PCR. To estimate the effect of co-variables on the outcome undetectable SHVL, the Generalized Estimation Equation (GEE) was employed.

RESULTS

Detectable SHVL was observed only in the detectable PHVL group and the detection of the HIV-1 was observed in 40% of these individuals. In the bivariate analysis between co-variables from the individual level and the outcome SHVL, significant difference was observed only for the CD4+ T lymphocytes levels (p = 0.017). The multiple logistic model demonstrated that only CD4+ T lymphocytes levels had a significant effect on the outcome undetectable SHVL [OR 8.85 (CI 3.6-9.2), p = 0.002].

CONCLUSION

HIV-1 can be detected and quantified in the subgingival biofilm of HIV-infected individuals, but these findings are not associated with PHVL and periodontal clinical parameters.

Role of autoimmune responses in periodontal disease

Periodontal diseases are characterized by localized infections and inflammatory conditions that directly affect teeth supporting structures which are the major cause of tooth loss. Several studies have demonstrated the involvement of autoimmune responses in periodontal disease. Evidences of involvement of immunopathology have been reported in periodontal disease. Bacteria in the dental plaque induce antibody formation. Autoreactive T cells, natural killer cells, ANCA, heat shock proteins, autoantibodies, and genetic factors are reported to have an important role in the autoimmune component of periodontal disease. The present review describes the involvement of autoimmune responses in periodontal diseases and also the mechanisms underlying these responses. This review is an attempt to throw light on the etiopathogenesis of periodontal disease highlighting the autoimmunity aspect of the etiopathogenesis involved in the initiation and progression of the disease. However, further clinical trials are required to strengthen the role of autoimmunity as a cause of periodontal disease.

The role of osteoimmunology in periodontal disease

Periodontal disease is a pathological condition that involves inflammation of the tooth supporting structures. It occurs in response to the presence of bacterial plaque on the tooth structure. The host defense system, including innate and adaptive immunity, is responsible for combating the pathologic bacteria invading the periodontal tissue. Failure to eradicate the invading pathogens will result in a continuous state of inflammation where inflammatory cells such as lymphocytes, PMNs, and macrophages will continue to produce inflammatory mediators in an effort to destroy the invaders. Unfortunately, these inflammatory mediators have a deleterious effect on the host tissue as well as foreign microbes. One of the effects of these mediators on the host is the induction of matrix degradation and bone resorption through activation of proteases and other inflammatory mediators that activate osteoclasts.

Involvement of autoimmunity in the pathogenesis of aggressive periodontitis

The aim of this study was to investigate the involvement of autoimmune reactions to native and post-translationally modified extracellular matrix components in the pathogenesis of periodontitis. Sera from individuals with aggressive periodontitis (AgP, n = 25), chronic periodontitis (CP, n = 14), and gingivitis (G, n = 18) were tested for the presence of autoantibodies against: (a) native collagen type I (CI) and collagen type III (CIII); (b) CI and CIII post-translationally modified by reactive oxygen species (ROS) of the type present during inflammation; and (c) citrullinated filaggrin-derived peptides (CCP). Autoantibodies to native and ROS-modified CI and CIII as well as autoantibodies to CCP were observed exclusively in patients with AgP and not in those with CP or G. In conclusion, autoimmune reactions to native and post-translationally modified self-antigens may play a role specifically in the pathogenesis of AgP.

Autoreactivity of serum immunoglobulin to periodontal tissue components: a pilot study

BACKGROUND

Periodontal diseases are inflammatory diseases resulting in the destruction of tissues of the periodontium. Although bacteria must be present for periodontal disease to occur, a susceptible host is also required, which is determined by genetic, environmental, and acquired factors. One such factor, autoimmunity, may play a role in the tissue destruction. Data indicate that some antibodies that occur in the gingival lesion are directed to host tissue components, such as type I collagen, although investigations of other periodontal autoimmune targets are limited.

METHODS

Histologic sections and extracts from periodontally healthy teeth and the associated soft tissues were probed with serum from localized aggressive periodontitis (LAgP), chronic periodontitis (CP), and periodontally healthy subjects to determine autoreactivity to components of the periodontium. Any autoreactivity observed was characterized further by mass spectrometry and enzyme-linked immunosorbent assay.

RESULTS

Autoreactivity to components of the periodontium was observed in CP and LAgP. Known autoimmune targets, such as collagen and heat shock protein, were identified along with multiple potential autoimmune targets, including members of the extracellular matrix, such as vimentin, spectrin, filamin, actin, lamin, keratin, and tubulin. Finally, it was determined that the autoreactivity observed in LAgP was more severe and diverse than that observed in CP.

CONCLUSION

These data demonstrated that autoimmune reactivity can play a role in the tissue destruction of periodontal disease but that the nature of the autoreactivity may differ based on the type and/or stage of periodontal disease.

Destructive periodontitis lesions are determined by the nature of the lymphocytic response

It is now 35 years since Brandtzaeg and Kraus (1965) published their seminal work entitled "Autoimmunity and periodontal disease". Initially, this work led to the concept that destructive periodontitis was a localized hypersensitivity reaction involving immune complex formation within the tissues. In 1970, Ivanyi and Lehner highlighted a possible role for cell-mediated immunity, which stimulated a flurry of activity centered on the role of lymphokines such as osteoclast-activating factor (OAF), macrophage-activating factor (MAF), macrophage migration inhibition factor (MIF), and myriad others. In the late 1970s and early 1980s, attention focused on the role of polymorphonuclear neutrophils, and it was thought that periodontal destruction occurred as a series of acute exacerbations. As well, at this stage doubt was being cast on the concept that there was a neutrophil chemotactic defect in periodontitis patients. Once it was realized that neutrophils were primarily protective and that severe periodontal destruction occurred in the absence of these cells, attention swung back to the role of lymphocytes and in particular the regulatory role of T-cells. By this time in the early 1990s, while the roles of interleukin (IL)-1, prostaglandin (PG) E(2), and metalloproteinases as the destructive mediators in periodontal disease were largely understood, the control and regulation of these cytokines remained controversial. With the widespread acceptance of the Th1/Th2 paradigm, the regulatory role of T-cells became the main focus of attention. Two apparently conflicting theories have emerged. One is based on direct observations of human lesions, while the other is based on animal model experiments and the inability to demonstrate IL-4 mRNA in gingival extracts. As part of the "Controversy" series, this review is intended to stimulate debate and hence may appear in some places provocative. In this context, this review will present the case that destructive periodontitis is due to the nature of the lymphocytic infiltrate and is not due to periodic acute exacerbations, nor is it due to the so-called virulence factors of putative periodontal pathogens.

Autoantibodies directed to extracellular matrix components in patients with different clinical forms of periodontitis

BACKGROUND

Periodontal disease occurs in different clinical forms, from mild and easily controllable to more aggressive inflammatory manifestations, with difficult clinical or surgical control. There is evidence that a local autoimmune reaction may participate in the onset and persistence of the aggressive forms of periodontal disease. As the underlying mechanism in this process is not fully understood, we decided to investigate whether patients bearing this form of disease presented higher levels of antibodies directed to extracellular matrix (ECM) components such as type I collagen, fibronectin, and laminin.

METHODS

Three groups of patients were selected by clinical criteria: 22 subjects with aggressive periodontitis (AgP) = group A; 18 subjects with chronic periodontitis (CP) = group B; and 10 healthy (H) volunteers without periodontal disease = group C. Autoantibody levels were evaluated in the sera of these patients using the enzyme-linked immunosorbent assay (ELISA) method.

RESULTS

The levels of autoantibodies directed to ECM components (type I collagen, fibronectin and laminin) in the sera of patients with AgP and CP were shown to be statistically different (P <0.05).

CONCLUSIONS

Although the present findings suggest an involvement of autoantibodies directed to ECM components per se in the pathogeny of certain types of periodontal disease, the available data do not support the classification of the lesions as autoimmune. Nevertheless, the findings open a possibility for the development of an additional method for a differential diagnosis of the aggressive forms of periodontal disease.

Hypothesis: the humoral immune response to oral bacteria provides a stimulus for the development of rheumatoid arthritis

Rheumatoid arthritis (RA) and adult periodontitis share common pathogenetic mechanisms and immunologic and pathological findings. One oral pathogen strongly implicated in the pathogenesis of periodontal disease, Porphyromonas gingivalis, possesses a unique microbial enzyme, peptidylarginine deiminase (PAD), the human equivalent of which has been identified as a susceptibility factor for RA. We suggest that individuals predisposed to periodontal infection are exposed to antigens generated by PAD, with de-iminated fibrin as a likely candidate, which become systemic immunogens and lead to intraarticular inflammation. PAD engendered antigens lead to production of rheumatoid factor-containing immune complexes and provoke local inflammation, both in gingiva and synovium via Fc and C5a receptors.

Aspects of adaptive host response in periodontitis

OBJECTIVE

To review host response in periodontitis with respect to cellular composition of lesions, T cell receptor (TCR) gene expression, cytokine profiles of T-helper (Th) cells and autoimmune components.

MATERIAL AND METHODS

The studies included were confined to human material (biopsies, gingival crevicular fluid, blood from subjects with periodontitis).

RESULTS AND CONCLUSIONS

In periodontitis lesions, plasma cells are the most common cell type and represent about 50% of all cells, while B cells comprise about 18%. The proportion of B cells is larger than that of T cells and Th cells occur in larger numbers than T cytotoxic cells. Polymorphonuclear cells and macrophages are found in fractions of less than 5% of all cells. Lesions in aggressive and chronic forms of periodontitis exhibit similar cellular composition. Differences in disease severity, however, may reflect increases in plasma cell and B cell densities. B cells serve as important antigen-presenting cells in periodontitis. The periodontitis lesion expresses a unique TCR gene repertoire that is different from that in blood. The role of superantigens in periodontitis is unclear. There are few studies using comparative designs and unbiased quantitative methods regarding Th-1 and Th-2 cells in periodontitis. The relative dominance of B cells and plasma cells in periodontitis lesions cannot entirely be explained by enhanced Th-2 functions but maybe because of an imbalance between Th-1 and Th-2. Autoimmune reactions are evident in periodontitis lesions. The role of auto-antibodies in the regulation of host response in periodontitis, however, needs to be clarified. Auto-reactive B cells occur in larger proportions in subjects with periodontitis than in healthy controls.

Immune processes in periodontal disease: a review

The inflammatory and immune processes in periodontitis are complex and, although a great deal of information is available, many questions remain. Variation in human susceptibility to periodontitis has long been accepted, but the pathological basis of this is poorly understood. Similarly, we know little of the differences, if any, between the pathology of chronic and aggressive periodontitis. Genetics and environmental influences play a role in the susceptibility process, but if and how that translates through the immune and inflammatory processes to produce the plasma cell-dominated lesions seen in periodontitis remain to be elucidated. This review will focus on immunological aspects of the inflammatory changes seen in gingivitis and periodontitis, addressing both humoral and cellular responses to the microbial insult from dental plaque. A tendency for an individual or site to form an extensive plasma cell infiltrate may indicate an inability to defend against periodontopathogens and thus a predisposition to periodontitis. The issues to be considered include: 1) homing of immune and inflammatory cells to target tissues; 2) their local proliferation and synthetic activity; 3) the cytokine profile of the leukocytes; 4) the immunoglobulin subclasses of locally produced antibodies; 5) mucosal and systemic immune characteristics of the response; 6) the humoral immune response in periodontal health and disease states; and 7) the antigenic target of the immune response in periodontal lesions.

The presence of local and circulating autoreactive B cells in patients with advanced periodontitis

AIM

The aim of the present investigation was to study the local (gingival) and systemic occurrence of autoreactive B cells (CD5+CD19 positive) in subjects with a high or low susceptibility to periodontitis.

MATERIAL AND METHODS

2 groups of subjects (Group A and B) susceptible to periodontitis were included. Group A consisted of 22 adult patients (7 females and 15 males, aged 24-66 years) with advanced and generalized chronic periodontitis and group B comprised 7 children (4 girls and 3 boys aged 9-13 years) with localized aggressive periodontitis. 26 periodontally healthy subjects, Group C (aged 23-80 years, mean 49.6+/-16.3), were also recruited. Assessment of clinical and radiographical characteristics of periodontal disease was performed. Gingival biopsies and peripheral blood samples were obtained and prepared for immunohistochemical analysis. Blood samples only were obtained from the periodontally healthy subjects (group C).

RESULTS

The proportion of autoreactive B cells (CD5+CD19 positive) of peripheral blood lymphocytes was about 6 times higher in group A and 4 times higher in group B than in the samples from the control subjects (group C). About 40-50% of the B cells in the peripheral blood of the periodontitis susceptible individuals expressed markers for autoreactive features while less than 15% of the circulating B cells in the subjects of group C exhibited such markers. The periodontitis lesion in the adult periodontitis patients contained a substantial number of B cells out of which about 30% demonstrated autoreactive features.

CONCLUSION

It is suggested that both circulating and local B cells in periodontitis susceptible individuals have a higher propensity to autoreactive properties than B cells of patients with a low susceptibility to periodontitis.

Is collagen breakdown during periodontitis linked to inflammatory cells and expression of matrix metalloproteinases and tissue inhibitors of metalloproteinases in human gingival tissue?

BACKGROUND

Evidence of the role of matrix metalloproteinases (MMPs) produced by resident and inflammatory cells in periodontal destruction is now well established. The purpose of this study was to quantify, in healthy and diseased upper gingival connective tissue, the area fraction (AA%) occupied by collagen fibers, the cell number belonging to inflammatory cell subsets, and the amounts of MMPs and TIMPs (tissue inhibitors of MMPs) in order to investigate the possible correlations, if any, between such molecules, collagen loss, and inflammatory cell subsets.

METHODS

Gingival tissue specimens from 6 healthy controls (C) and 6 patients with severe periodontitis (P) were divided into 2 groups. The first group of specimens was frozen and used for the staining of collagen fibers by sirius red F3Ba and for immunohistochemistry with antibodies against CD8, CD4, CD22, CD68, and TIA-1 molecules. The second group was used for organ culture, zymography, Western blotting, and dot blotting. Morphometric and automated image analysis was performed for the evaluation of the area fraction occupied by collagen fibers, the number of inflammatory cell subsets and for enzymatic activities developed by MMPs, and the amounts of TIMPs expressed during periodontal disease.

RESULTS

In group P, the area fraction of collagen fibers (33 +/- 10%) was significantly decreased (P < 0.0002) when compared to group C (60 +/- 7%), and was correlated with the number of all inflammatory cells and amounts of MMPs and TIMPs. In group P, there were significant increases of CD8+, CD22+, CD68+, and TIA-1+ cells, as well as increases in the amounts of MMP-1, MMP-2, MMP-3, MMP-9, and the active form of MMP-9. The active form of MMP-9 and the amount of TIMP-1 were positively correlated with the number of CD22+, CD68+, and TIA-1+ cells.

CONCLUSIONS

The present study showed an imbalance between MMPs and TIMPs associated with the pathologic breakdown of the extracellular matrix during periodontitis. The active form of MMP-9 could be a marker for the clinical severity of periodontal disease.

Clinical, pathological and immunological aspects of periodontal disease

The inflammatory and immune responses during the development and progression of periodontitis are reviewed. Susceptibility to periodontitis may be related to whether plasma cells predominate in the tissues of an individual, or a site, in response to the microbial insult from dental plaque. The tendency for an individual or site to form an extensive plasma cell infiltrate may indicate an inability to defend against periodontopathogenic bacteria and thus a predisposition to periodontitis. Selected pertinent areas of current interest in cellular and humoral immunology are considered within the periodontal context. These topical issues include (a) homing of immune and inflammatory cells to target tissues; (b) the local proliferation and synthetic activity of immune and inflammatory cells; (c) the cytokine profile of the inflammatory and immune cells; and (d) the immunoglobulin subclasses of locally produced antibodies.

Induction of anti-thymocyte/T lymphocyte antibodies in mice injected with lipopolysaccharides from periodontopathic bacteria

We examined the levels of anti-thymocyte/T lymphocyte autoantibody (ATA) in the serum of mice injected intraperitoneally with lipopolysaccharides (LPS) from periodontopathic bacteria; Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans, Fusobacterium nucleatum, Capnocytophaga ochracea, and non-oral Escherichia coli. All of the LPS induced IgM-ATA. Among these, LPS from C. ochracea induced the highest level of IgM-ATA, whereas that of P. gingivalis induced the lowest. The peritoneal T lymphocytes of mice injected with LPS were bound by IgM-ATA. Peritoneal B-1 (CD5+B) cells stimulated by each LPS produced much more IgM-ATA than splenic B-2 (CD5-B) cells, suggesting that B-1 cells might be responsible for the production of these antibodies. Serum of mice injected with C. ochracea and F. nucleatum LPS showed cytotoxicity against thymocytes in the presence of rabbit complements. Binding and cytotoxicity were confirmed by IgM purified from serum of the mice injected with C. ochracea LPS. Furthermore, serum of mice treated with C. ochracea, F. nucleatum or A. actinomycetemcomitans LPS inhibited the proliferation of thymocytes. However, purified IgM from the serum of mice treated with C. ochracea LPS failed to produce the same inhibition. Our results suggest that LPS from certain species of periodontopathic bacteria can induce IgM-ATA in the serum and these antibodies may modulate the local immune network in periodontal tissues.

Presence of activated B-1 cells in chronic inflamed gingival tissue

B-1 cells are physically and functionally unique B cells that produce polyreactive natural antibody. This study examined the activation of B-1 cells in inflamed gingival tissue. Serum IgG antibodies to phosphorylcholine, E. coli LPS, DNA, and some commensal bacteria were examined in adult periodontitis patients and healthy subjects. In addition, the proportion of B-1a (CD20+CD5+) cells and the amount of IL-6 and IL-10 in the inflamed gingival tissues were examined. The serum levels of IgG antibodies to phosphorylcholine, E. coli LPS, and commensal bacteria were significantly higher in the adult periodontitis patients than the healthy subjects. The proportion of B-1a cells and the amount of IL-6 and IL-10 were significantly higher in the inflamed gingival tissues than in peripheral blood from the healthy subjects. These results suggest the activation of B-1 cells in the inflamed gingival tissue of adult periodontitis patients, and that B-1 cells may serve as the first line of defense by producing polyreactive antibodies to phosphorylcholine, LPS, and commensal bacteria.

Characterization of the mitogenic response of murine CD5+ and conventional B lymphocytes to lipopolysaccharide

The nature of the response of conventional and CD5+ B cells to stimulation in vitro with optimal mitogenic concentrations of LPS was examined to elucidate the contributions of these B cell subsets in polyclonal B lymphocyte responses. Stimulation of murine splenic lymphocytes with LPS resulted in an increase in total biomass, peaking at 72 h of culture. The viability of the cultures remained high (> 90%) until 48 h of culture. A combination of trypan blue and 7-aminoactinomycin D (7AAD) exclusion in conjunction with PE-anti-CD5 and FITC-anti-B220 enabled more detailed analysis of the cultures. The total number of conventional B cells, viable and non-viable, increased until 48 h of culture and then decreased when stimulated with LPS, while CD5+ B cells increased over the culture period. The numbers of conventional B cells in the control cultures decreased, but the CD5+ B cell numbers remained stable. An examination of the modes of death of the B cell subsets using 7AAD showed that unstimulated conventional B cells were apoptotic rather than degenerate but, following stimulation with LPS, apoptotic and degenerate cells were found. Apoptotic and degenerate CD5+ B cells were found in both stimulated and unstimulated cultures, but the percentage of these apoptotic and degenerate cells was increased significantly only at 72 h and 96 h of culture in stimulated cultures compared with 24 h onwards in the control cultures. Morphological analysis and gel electrophoretic studies of extracted DNA reflected these findings. It was also found that the increase in the number and percentage of non-viable cells in the cultures was not equal to the decrease in the number and percentage of viable cells. Activation of B cells was examined using expression of B7-1 (CD80) as a marker. When stimulated with LPS a greater proportion of conventional B cells expressed B7-1 after 24 h of culture than in the control cultures; however, only at 72 h and 96 h of culture was the proportion of CD5+ B cells expressing B7-1 significantly higher than in the control cultures. These results show that conventional B cells are stimulated to proliferate and to become activated by LPS and that death is apoptotic rather than degenerate or necrotic. CD5+ B cells were also shown to be stimulated by LPS; they became activated and death was delayed. The data suggest that in addition to the proliferative role, LPS acts to delay death and to activate conventional and CD5+ B cells.

Interleukin-10 promotes anti-collagen antibody production in type I diabetic peripheral B lymphocytes

Previous studies have shown that type I diabetes (IDDM) increases the risk of developing periodontitis by 2-3-fold. IDDM patients exhibit destruction of the pancreatic beta cells, most probably caused by an autoimmune reaction. Evidence is accumulating to support the role of the autoimmune response in periodontal pathogenesis. A cytokine, interleukin (IL)-10, has been reported to selectively promote the expansion of a B lymphocyte lineage (CD5/LY1/B1) which has the propensity for secreting high levels of autoantibody. Therefore, the purpose of this project was to evaluate IL-10 production, percentage of CD5 B cells and the frequency of anti-collagen secreting cells in peripheral blood mononuclear cells of age, gender and race matched IDDM patients and controls. IL-10 production was evaluated by an ELISA using the supernatant of adherent peripheral blood cells cultured for 24 h in the presence of Porphyromonas gingivalis lipopolysaccharide (LPS). In 8 of 31 patients, IL-10 levels were significantly increased in IDDM compared to controls and a higher percentage of CD5 B cells was also observed by flow cytometry. In addition, these patients exhibited a higher frequency of anti-collagen secreting cells as elucidated by an ELISPOT. Moreover, treatment with a neutralizing anti-IL-10 antibody diminished the anti-collagen antibody response by 70%. These findings support the concept that a subset of IDDM patients possess an extremely robust IL-10 response following exposure to Gram-negative LPS, which could predispose them to the development of periodontitis through a heightened autoimmune mechanism.

Serum rheumatoid factor induced by intraperitoneal administration of periodontopathic bacterial lipopolysaccharide in mice

Serum rheumatoid factor (RF) level and peritoneal and splenic CD5+B (B-1) cells in mice were examined after intraperitoneal administration of purified lipopoly-saccharides (LPS) from oral periodontopathic bacteria; Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans, Fusobacterium nucleatum and Capnocytophaga ochracea. F. nucleatum and C. ochracea LPS induced higher levels of serum IgM- and IgG-RF, while P. gingivalis LPS showed the least induction. In addition, wet weights of spleen and serum IgM and IgG concentration were markedly increased in F. nucleatum LPS injected group. On the other hand, the proportion of CD5+ B cells to lymphocytes in the peritoneal cavity and spleen did not increase. The reason for this was not clear but conventional B cells (CD5- B cells) might increase more rapidly with splenic enlargement than CD5+ B cells. These results suggested that RF induced by bacterial LPS may modulate immune responses against bacteria and plays an important role for defence and destruction of periodontal tissue.

In situ localization of cell synthesis and proliferation in periodontitis gingiva and tonsillar tissue

OBJECTIVE

Previous work indicates that large numbers of B and T cells accumulate in the periodontal soft tissues although we know little about cellular synthetic activity and proliferation in this site. The aim of this study was to examine lymphocytic cell synthetic activity and proliferation in periodontitis gingiva and compare this to a known site of leucocyte proliferation, namely the oropharyngeal tonsils.

MATERIALS AND METHODS

Messenger RNA (mRNA) and 28S ribosomal (28S rRNA) expressing cells in formalin-fixed/paraffin-embedded gingival and tonsillar tissue sections were detected by in situ hybridisation (ISH) using poly-deoxyribothymidine and 28S probes respectively. In addition S-phase proliferating and cycling cells were also detected by ISH with histone probes and by Ki-67 immunohistochemistry. Ten gingival biopsy samples were obtained from adult periodontitis patients and five tonsillar biopsies from tonsillectomy patients.

RESULTS

Both mRNA and 28S rRNA-expressing cells were detected in all the samples tested. Plasma cells showed the strongest signal for the two probes and slight to moderate staining could be seen in epithelium, fibroblasts and endothelial cells. In contrast, gingival lymphocytes were either weakly stained or were unstained for these probes of synthetic activity. In tonsils, most lymphocytes in germinal centres showed moderate staining and mantol zone cells were much more weakly stained. In gingival samples, histone mRNA-expressing and cycling (Ki-67) cells were detected in 4/10, 10/10 cases respectively. These positive cells were mainly basal and suprabasal epithelial cells and a few mononuclear cells, whereas most germinal centre lymphocytes (B cells) were positive for this probe. The number of Ki67 positive cells was greater than histone mRNA bearing cells both in gingiva and tonsillar tissue. In contrast, mantol zone cells (mainly T cells) were sparsely stained by probes of cell proliferation.

CONCLUSION

These results indicate that local proliferation of B cells does not occur in periodontitis gingiva in contrast with tonsillar tissue, although plasma cells showed strong synthetic activity in both tissues. T cells did not appear to proliferate greatly nor undergo active synthesis in either of these tissues. These findings substantiate previous hypotheses that specific leucocytes predominate in the gingival tissue through selective homing rather than by local proliferation.

Immunohistochemical study of gamma delta T cells in human gingival tissues

The distribution and the density of gamma delta T cells in human gingival tissues were examined immunohistochemically in biopsy samples obtained from 20 subjects. Few gamma delta T cells were observed in gingival tissue free from inflammatory cell infiltration, but were found, albeit in low numbers, in association with inflammatory cell infiltration, especially T cells. This relationship with T cells was confirmed statistically. The ratios of gamma delta T cells to T cells in the epithelia and in the connective tissue were calculated in the sections in which more than 500 CD3-positive cells were identified. Seven of eight such epithelial specimens showed a ratio of less than 1% and one less than 2% (mean +/- SD; 0.8% +/- 0.4). In the connective tissue, 8 of 13 such specimens showed less than 1%, three less than 2%, one 3%, and one 7% (1.4% +/- 1.9). These results suggest that basically gamma delta T cells are not resident cells in the gingival epithelium such as comprise the first defense line against exogenous irritation. They may play some role in the pathogenesis of periodontal disease collaborating with alpha beta T cells in the inflammatory response.

Cloning, characterization, and antigen specificity of T-lymphocyte subsets extracted from gingival tissue of chronic adult periodontitis patients

Chronic periodontitis is characterized by dense infiltrations of B and T lymphocytes within the gingival connective tissue. Distinct anaerobic gram-negative bacteria as well as autoimmunity to collagen have been reported to play a role in the etiology and the pathogenesis of this disease. Here we describe the cloning and characterization of CD4+ and CD8+ T lymphocytes isolated from inflamed gingival tissue obtained from four patients with chronic periodontitis. Clones were raised with phytohemagglutinin and interleukin-2 and tested for proliferation in response to whole-cell antigens of Porphyromonas gingivalis, Prevotella intermedia, Actinobacillus actinomycetemcomitans, human collagen type I, and two bacterial heat shock proteins. CD4+ T-cell clones reactive with collagen type I were obtained from all four patients. Eighty percent of these clones had phenotypes resembling the mouse type 2 T helper (Th) phenotype, i.e., they produced high levels of interleukin-4 and low levels of gamma interferon. No collagen-type-I-reactive CD8+ clones were obtained. Bacterial-antigen-reactive CD4+ and/or CD8+ T-cell clones were also obtained from each patient, and the majority of the clones showed a Th0-like cytokine pattern and produced equal amounts of interleukin-4 and gamma interferon. Although most clones were reactive with P. intermedia, it seems that the immune response is not strictly directed against this particular microorganism, as clones reactive with one of the other bacteria were also obtained from two patients. We propose that collagen-specific CD4+ Th2-like T cells contribute to the chronicity of periodontitis but that their modes of activation might be controlled by Th0-like T cells specific for periodontitis-associated bacteria.

The immunopathology of chronic inflammatory periodontal disease

Chronic inflammatory periodontal disease is known to be under the control of the immune response. However, the precise mechanism of the immunopathogenesis of this lesion has not yet been fully elucidated. In this review, the regulatory role of both lymphoid and non-lymphoid cells as well as cytokines and accessory molecules in the course of chronic inflammatory periodontal disease is discussed. Finally, based upon previous evidences, an attempt to establish a model of chronic inflammatory periodontal disease is made herein.