Immunoregulation in severe generalized periodontitis

Autoimmune responses in periodontal diseases

Periodontal diseases are characterized by localized infections and inflammatory conditions and 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. Lymphocytes, cytokines and complement system are reported to have an important role in the progression of periodontal disease. The present review describes the involvement of autoimmune responses in periodontal diseases. The mechanisms underlying these responses are also discussed.

Cell-mediated immune system regulation in periodontal diseases

The adaptive immune system consists of humoral and cell-mediated immunity. T-lymphocytes are the key components of cell-mediated immunity. CD4+ helper T-lymphocytes facilitate B-cells to differentiate and produce specific antibodies, whereas CD8+ cytotoxic T-lymphocytes kill virally infected cells. Periodontal diseases have been associated with a variety of imbalances in the regulation of immune responses. Changes in the ratios of peripheral blood CD4+ and CD8+ T-lymphocytes, depressed proliferative responses of peripheral blood lymphocytes, and increased frequency of CD45RO+ memory T-lymphocytes in diseased tissues have been reported in individuals with various forms of periodontal disease. While some studies have shown an increased frequency of gamma delta + T-cells in periodontal lesions, the role of gamma delta + T-cells in periodontal disease remains controversial. The ability of putative periodontopathic bacteria selectively to stimulate certain V beta-expressing T-cells is intriguing and could determine whether a CD4+ Th1 or a CD4+ Th2 cell response is elicited. The prominence of a particular subset of helper T-cells within the periodontal lesion could be a reflection of the stage and activity of the disease, or the types of bacteria present. Regardless, longitudinal studies of the involvement of T-cell subsets and cytokines in periodontal disease are clearly needed.

Host responses in periodontal diseases: current concepts

In periodontal diseases, bacteria trigger inflammatory host responses which, along with the direct destructive effects of the bacteria, cause most of the tissue destruction. Periodontal inflammatory responses are, by and large, immunologic, and our understanding of these reactions has been advanced by the explosion of knowledge in immunobiology, some of which is discussed in this review. Understanding the role of immune cells and their regulatory cell surface molecules such as the MHC, CD antigens, and receptors, as well as knowledge of effector systems set into motion such as phagocytes and cytotoxic T-cells, and the effector molecules such as antibodies, complement, and cytokines, have led to better understanding of the complex pathogenesis of periodontal disease. The role of mediators including the matrix metalloproteinases, proteoglycans, the kinins and anaphylatoxins, and low molecular weight mediators including products of arachidonic metabolism is beginning to be elucidated in periodontal disease. Important avenues of research for development of diagnostic tests based upon host response are apparent. For example, tissue products released during periodontal inflammation including the metalloproteinases, elastase, cytokines, prostaglandins, antibodies, and complement components may provide the basis for future diagnostic indicator tests. The recognition that the neutrophil/antibody/complement axis is critical for protection against periodontal bacteria and that abnormalities in this system often lead to increased periodontal susceptibility provide approaches for the development of diagnostic tests assessing risk. A group of factors which are negative regulators of inflammation including TGF-beta, gamma-interferon, and IL-1 receptor antagonist provide potential for assessment of periodontal disease in remission or in the healing phase. Finally, factors such as HLA associations and the molecular basis for neutrophil abnormalities may provide genetic markers for periodontal disease susceptibility. Diagnostic factors based upon host response measures offer great potential for predicting host susceptibility and will likely be used in combination with microbial diagnostics which identify specific infecting organisms.

Immunologic mechanisms of pathogenesis in periodontal diseases: an assessment

Principal lines of evidence that immune reactions are central to the pathogenesis of periodontitis are reviewed. Necessary components of immunologic reactions are present in gingiva in the periodontal diseases. Differences between healthy and periodontitis patients with respect to some measures of immune function further indicate that immune reactions do occur in the gingiva during periodontitis. They are probably responsible for at least some of the destruction of connective tissue and bone that occurs. Classical antibody-mediated hypersensitivity reactions probably do not provide the reasons. Mechanisms are more likely to be found in the pro-inflammatory and tissue-degrading effects of cytokines released in host-protective, antigen-specific and polyclonal responses to oral bacterial constituents or products. Some evidence suggests that limitation of clinical destruction in localized early onset periodontitis (JP) may in part be a function of a protective antibody response which develops after an initial rapidly progressive infection. A relatively deficient immune responsiveness may allow progression to more severe and generalized disease (RPP). Suggestions are made for studies needed to confirm suspected pathogenetic mechanisms, approach resultant targeted therapies, and test hypotheses for contrasting roles of immune reactions in different clinical expressions of periodontitis.

Cell-mediated and humoral immune response in diabetic patients with periodontitis

Cell-mediated and humoral immune responses were assessed in 50 patients with type II or non-insulin-dependent diabetes mellitus and 50 nondiabetic patients with periodontitis. The values were compared with those of 50 age and sex-matched control subjects. The cell-mediated immunity assessed by enumerating the total and high-affinity rosette-forming cells of the patient did not show any significant variation from that of the normal control subjects. The humoral immune response was assessed by estimating serum immunoglobulins G, A, M, D, and E by single radial immunodiffusion. Except IgD, all other immunoglobulins were found to be elevated significantly in both diabetic and nondiabetic subjects. The alteration in humoral immune response may be the cause or the effect of periodontitis. The defective host response reported in diabetic patients may be responsible for the increased incidence of periodontitis in diabetic patients as compared to nondiabetic patients.

Polyclonal B-cell activation in periodontitis

The evidence that periodontitis-associated bacteria contain potent PBA factors is very strong. Clearly, antibodies directed against non-oral antigens are produced in the inflamed periodontal lesion, and PBA appears to contribute to that production. It is also clear that B cells and plasma cells are the major cell types in the periodontal lesion. Furthermore, alterations in the regulation of B-cell responses to PBA factors are associated with severe periodontal disease. However, evidence demonstrating that activated B cells and plasma cells are directly involved in the pathogenic mechanisms leading to destruction of the periodontal support is still circumstantial. Polyclonal B-cell activation and potential pathways by which PBA-stimulated cells could be involved in periodontal destruction remain largely hypothetical. It appears that IL-1 is an important osteoclast-activating agent, and that LPS, which is a potent PBA factor in many systems, can elicit IL-1 production by B cells as well as by the monocyte/macrophage lineage. Recent data indicating that IL-1 is produced by numerous malignant B-cell lines lend support for the idea that B-cell IL-1 could be important in bone resorption. It is also likely that polyclonal activation may lead to production of autoantibody such as anti-type I and anti-type III collagens, and the destruction of self tissues through ADCC reactions, immune complex formation, and complement activation. Further research is needed to determine how the B cell/plasma cell may participate in tissue injury in periodontitis, and how the B-cell response to PBA factors is regulated.

Immunoregulatory aspects of periodontal disease

This manuscript reviews our studies of the composition and functional capabilities of gingival tissue lymphocytes from patients with periodontal disease. The emphasis has been on phenotyping the local lymphoid infiltration in gingival and periodontal disease. The preparation and phenotypic analyses of cells recovered from diseased and healthy human periodontal tissues indicated that T-cell subset ratios from diseased tissue were significantly decreased compared with peripheral blood or normal tissue ratios. These reductions were verified in a second study we performed using two-color immunofluorescence analyzed by flow cytofluorometry. Local variations in the CD4 + cell population were also found in diseased tissue cells when these were compared with normal tissue cells. The relative percentage of CD4+ cells labeled with anti-helper inducer (4B4) or anti-suppressor inducer (2H4) monoclonal antibodies was increased above that of normal tissue cells. Functional studies of immunoglobulin production by gingival cells from adult periodontitis tissues showed two discrete patterns of synthesis and also suppression of immunoglobulin synthesis after addition of mitogen to the cultures. Removal of macrophages also drastically reduced immunoglobulin synthesis by gingival cells. These results indicate that there is an abundance of suppressor T-cells in diseased tissue and that functional suppression is demonstrated by lymphocytes from periodontal disease tissue. The findings of these investigations have suggested potentially important roles for immune regulation in periodontal disease.

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.