G. J. Seymour

The pathogenesis of oral lichen planus

Both antigen-specific and non-specific mechanisms may be involved in the pathogenesis of oral lichen planus (OLP). Antigen-specific mechanisms in OLP include antigen presentation by basal keratinocytes and antigen-specific keratinocyte killing by CD8(+) cytotoxic T-cells. Non-specific mechanisms include mast cell degranulation and matrix metalloproteinase (MMP) activation in OLP lesions. These mechanisms may combine to cause T-cell accumulation in the superficial lamina propria, basement membrane disruption, intra-epithelial T-cell migration, and keratinocyte apoptosis in OLP. OLP chronicity may be due, in part, to deficient antigen-specific TGF-beta1-mediated immunosuppression. The normal oral mucosa may be an immune privileged site (similar to the eye, testis, and placenta), and breakdown of immune privilege could result in OLP and possibly other autoimmune oral mucosal diseases. Recent findings in mucocutaneous graft-versus-host disease, a clinical and histological correlate of lichen planus, suggest the involvement of TNF-alpha, CD40, Fas, MMPs, and mast cell degranulation in disease pathogenesis. Potential roles for oral Langerhans cells and the regional lymphatics in OLP lesion formation and chronicity are discussed. Carcinogenesis in OLP may be regulated by the integrated signal from various tumor inhibitors (TGF-beta 1, TNF-alpha, IFN-gamma, IL-12) and promoters (MIF, MMP-9). We present our recent data implicating antigen-specific and non-specific mechanisms in the pathogenesis of OLP and propose a unifying hypothesis suggesting that both may be involved in lesion development. The initial event in OLP lesion formation and the factors that determine OLP susceptibility are unknown.

Cytokines in periodontal disease: where to from here?

Numerous studies have attempted to elucidate the cytokine networks involved in chronic periodontitis, often with conflicting results. A variety of techniques were used to study cells in situ, cells extracted from gingival tissues, peripheral blood mononuclear cells, purified cell populations, and T cell lines and clones. Bacterial components, including sonicates, killed cells, outer membrane components, and purified antigens, have all been used to stimulate cells in vitro, making comparisons of cytokine profiles difficult. As it is likely that different cells are present at different disease stages, the inability to determine disease activity clinically is a major limitation of all these studies. In the context of tissue destruction, cytokines such as IL-1, IL-6 and IL-18 are likely to be important, as are their regulating cytokines IL-10 and IL-11. In terms of the nature of the inflammatory infiltrate, two apparently conflicting hypotheses have emerged: one based on direct observations of human lesions, the other based on animal experimentation and the inability to demonstrate IL-4 mRNA in gingival extracts. In the first of these, Th1 responses are responsible for the stable lesion, while in the second Th2 responses are considered protective. Using Porphyromonas gingivalis-specific T cell lines we have shown a tendency for IFN-γ production rather than IL-4 or IL-10 when antigen is presented with peripheral blood mononuclear cells which may contain dendritic cells. It is likely that the nature of the antigen-presenting cell is fundamental in determining the nature of the cytokine profile, which may in turn open up possibilities for new therapeutic modalities.

Invited Review: Possible Mechanisms Involved in the Immunoregulation of Chronic Inflammatory Periodontal Disease

It is generally agreed that immunological mechanisms are involved in the pathogenesis of periodontal disease; however, regulation of these mechanisms has hitherto received scant attention. Regulatory networks exist at both a cellular and a molecular level. At the cellular level, the existence of helper (T4-positive) and suppressor (T8-positive) T lymphocytes, the expression of Class II major histocompatibility complex antigens, and the heterogeneity of macrophage subpopulations are central to an understanding of the regulatory mechanisms involved. It is only recently that studies of these separate components, in both humans and experimental animals, have begun to provide a basis for understanding the complex interactions occurring in periodontal disease. Studies using the human experimental gingivitis model have shown an immunoregulatory picture consistent with a controlled immunological reaction with an essentially normal T4:T8 ratio of 2.0. In contrast, studies utilizing cells extracted from adult periodontitis lesions have shown a reduced T4:T8 ratio (approximately 1.0) and an inability to respond in, or to stimulate, an autologous mixed lymphocyte reaction. Animal studies using athymic nude rats have supported the concept of a central role for T-cell control in periodontal disease and the possibility of an imbalance in this control with disease progression. These results are reviewed and areas of future research explored.

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.

Decreased salivary immunoglobulin A secretion rate after intense interval exercise in elite kayakers

SummaryEndurance athletes have been shown to suffer a high incidence of upper respiratory tract infection (URTI; e.g. colds, sore throat) during intense training and after competition. Previous studies have shown that concentrations of secretory immunoglobulin A (IgA), the major effector of host defense against micro-organisms causing URTI, decrease after intense endurance exercise. Many athletes perform intense interval exercise as part of their normal training. The purpose of this study was to determine whether salivary IgA concentrations also decrease after intense interval exercise during the normal training regime in elite athletes. Timed saliva samples were obtained from eight elite male kayakers immediately before and after three on-water training sessions during a 3-week period. The concentrations of IgA, IgG and IgM were determined separately by enzyme-linked immunosorbent assay, and secretion rates calculated for each Ig. The IgA secretion rate (μg·min−1) decreased 27%–38% after all three training sessions (P=0.007); the largest decrease (38%) was noted after the most intense session at the end of an especially intense week of training. The IgA concentration relative to total protein (μg·mg protein−1) was significantly lower (P<0.05) on this training day compared with the other 2 days. Concentrations and secretion rates of IgG and IgM did not change after exercise, indicating a specific effect on IgA. These data would suggest that, in elite athletes, IgA concentration and secretion rate are reduced by intense interval exercise, and that exercise-induced changes in IgA output may be be one mechanism contributing to URTI in elite athletes.

Cytokine Profiles of Cells Extracted from Humans with Periodontal Diseases

FACS analysis was used to determine the percent interferon (IFN)-gamma-, interleukin (IL)-4-, IL-10-, and CD30-positive T-cells extracted from adult periodontitis (AP) and healthy/gingivitis (H/G) subjects. Additionally, the percentages of IL-1β-, IL-10- and IL-12-producing B-cells and macrophages were ascertained. The percent IL-10+ CD8 cells extracted from AP lesions was decreased compared with H/G tissues (p = 0.033), and the percent CD30+ CD4 (p = 0.001) and CD30+ CD8 (p = 0.028) cells was higher in AP than in H/G tissues. The percentages of IL-1β+ macrophages (p = 0.003) and IL-12+ B-cells (p = 0.034) were both higher in AP lesions than in H/G tissues. The specific effect of Porphyromonas gingivalis on the cytokine profiles of peripheral blood mononuclear cells isolated from P. gingival is-infected AP and H/G patients was also determined. While there were no significant differences in the percent cytokine-positive T-cells after stimulation with P. gingival is outer membrane antigens (OM) for 6 days compared with cells incubated in medium only, the percent CD30+ CD4 cells increased significantly (p = 0.047 and p = 0.063 for AP and H/G groups, respectively). There was also an increase in the percent IL-1β+ B-cells from AP patients (p = 0.029), and the percent IL-12+ monocytes from AP and H/G subjects was higher than the percent IL-12+ B-cells, both after stimulation with P. gingivalis OM (p = 0.005 for the AP group and p = 0.058 and therefore not quite significant for the H/G group) and when incubated in medium alone (p = 0.016 and p = 0.015 for AP and H/G groups, respectively). This study has shown that IL-10+ CD8 cells may be significant in gingival lesions, and that CD30+ T-cells indicative of Th2 or Th0 cells may play a role in progressive periodontal disease. This study has also shown that B-cells produce IL-1 in the gingival lesion and that P. gingivalis may be significant in the induction of B-cell-induced IL-1.

Distribution of interleukin-2, -4, -10, tumour necrosis factor-α and transforming growth factor-β mRNAs in oral lichen planus

In the present study. MRNA for the cytokines interleukin-2 (IL-2), IL-4, IL-10 tumour necrosis factor-α (TNF-α) and transforming growth factor β-1 (TGF-β-1) were investigated in oral lichen planus (OLP) lesions using in situ hybridization with 35S-labelled oligonucleotide probes on frozen tissue sections. In addition, the expression of interferon-γ (IFN-γ), IL-10 and IL-4 mRNAs was analysed in cultured lesional T lymphocytes from oral lichen planus by polymerase chain reaction. Cells expressing mRNA for IL-2, IL-4, IL-10, TNF-α and TGF-β1 were found in all the biopsies studied. Approximately 1–2% of the total number of infiltrating cells in the lesions were positive for each of the different cytokine mRNAs. Most biopsies contained basement membrane-oriented, mRNA-positive cells. In the cultured T-cell lines, message for IFN-γ was detected in all the patients, IL-10 in all but one, and IL-4 in just one of the seven patients investigated. The results suggest that mRNA for both pro- and anti-inflammatory cytokines, i.e., mixed T-helper 1 (TH1) and TH2 cytokine profiles, are generated simultaneously by a limited number of cells in chronic lesions of OLP.

The immunopathogenesis of periodontal disease

Treatment planning in periodontics, as with any disease, must be based on an understanding of the aetiology and pathogenesis of the disease. In this context, it has slowly become recognized over the past three decades that while plaque is the cause of the disease, it is the innate susceptibility of the host that determines the ultimate outcome of the disease process. Innate susceptibility, in turn, is determined by the nature of the immune response to the specific periodontopathic complexes comprising the plaque biofilm. The aim of this review was to examine current understanding of the immunopathogenesis of chronic periodontitis with respect to its possible clinical implications in terms of treatment planning and risk assessment. Numerous studies have demonstrated that the periodontitis lesion itself involves predominantly B cells and plasma cells, while the gingivitis lesion is primarily a T cell mediated response. This led to the concept over 30 years ago that the development of periodontitis involves a switch from a T cell lesion to one involving large numbers of B cells and plasma cells. It is also well recognized that control of this shift is mediated by a balance between the so-called Th1 and Th2 subsets of T cells, with chronic periodontitis being mediated by Th2 cells. More recently, T regulatory (Treg) and Th17 cells have been demonstrated in periodontal tissues, raising the possibility that these cells are also important in the immunoregulation of periodontal disease. The clinical implications of these observations can be seen in the fact that identification of Th1/Th2 and Treg/Th17 cytokine gene expression in the peripheral blood and salivary transcriptomes is now being trialled as a possible marker of disease susceptibility. If this proves to be the case, a chairside salivary diagnostic could be developed within the next five to 10 years.

Periodontal disease and systemic illness: will the evidence ever be enough?

The concept of focal infection or systemic disease arising from infection of the teeth was generally accepted until the mid-20th century when it was dismissed because of lack of evidence. Subsequently, a largely silo approach was taken by the dental and medical professions. Over the past 20 years, however, a plethora of epidemiological, mechanistic and treatment studies have highlighted that this silo approach to oral and systemic diseases can no longer be sustained. While a number of systemic diseases have been linked to oral diseases, the weight of evidence from numerous studies conducted over this period, together with several systematic reviews and meta-analyses, supports an association between periodontitis and cardiovascular disease, and between periodontitis and diabetes. The association has also been supported by a number of biologically plausible mechanisms, including direct infection, systemic inflammation and molecular mimicry. Treatment studies have shown that periodontal treatment may have a small, but significant, systemic effect both on endothelial function and on glycemic control. Despite this, however, there is no direct evidence that periodontal treatment affects either cardiovascular or diabetic events. Nevertheless, over the past 20 years we have learnt that the mouth is an integral part of the body and that the medical and dental professions need to work more closely together in the provision of overall health care for all patients.

Accumulation of Human Heat Shock Protein 60-Reactive T Cells in the Gingival Tissues of Periodontitis Patients

ABSTRACT Heat shock protein 60s (hsp60) are remarkably immunogenic, and both T-cell and antibody responses to hsp60 have been reported in various inflammatory conditions. To clarify the role of hsp60 in T-cell responses in periodontitis, we examined the proliferative response of peripheral blood mononuclear cells (PBMC), as well as the cytokine profile and T-cell clonality, for periodontitis patients and controls following stimulation with recombinant human hsp60 and Porphyromonas gingivalis GroEL. To confirm the infiltration of hsp60-reactive T-cell clones into periodontitis lesions, nucleotide sequences within complementarity-determining region 3 of the T-cell receptor (TCR) β-chain were compared between hsp60-reactive peripheral blood T cells and periodontitis lesion-infiltrating T cells. Periodontitis patients demonstrated significantly higher proliferative responses of PBMC to human hsp60, but not to P. gingivalis GroEL, than control subjects. The response was inhibited by anti-major histocompatibility complex class II antibodies. Analysis of the nucleotide sequences of the TCR demonstrated that human hsp60-reactive T-cell clones and periodontitis lesion-infiltrating T cells have the same receptors, suggesting that hsp60-reactive T cells accumulate in periodontitis lesions. Analysis of the cytokine profile demonstrated that hsp60-reactive PBMC produced significant levels of gamma interferon (IFN-γ) in periodontitis patients, whereas P. gingivalis GroEL did not induce any skewing toward a type1 or type2 cytokine profile. In control subjects no significant expression of IFN-γ or interleukin 4 was induced. These results suggest that periodontitis patients have human hsp60-reactive T cells with a type 1 cytokine profile in their peripheral blood T-cell pools.