Blastogenic responsiveness of peripheral blood mononuclear cells from individuals with various forms of periodontitis and effects of treatment

Lymphocyte Numbers and Function in Relation to Periodontitis and Smoking

BACKGROUND

T and B lymphocytes play important roles in periodontitis. Smoking is considered a risk factor for periodontitis and may exert its negative effects through leukocytes. Taking smoking into consideration, the aim of this study was to analyze numbers of circulating T (CD3+) cells and their CD4+ and CD8+ subpopulations, B (CD19+) cells, and T-cell proliferative capacity in periodontitis.

METHODS

Lymphocyte immunophenotyping for T cells, their CD4+ and CD8+ subsets, and B cells was performed on peripheral blood from 76 periodontitis patients and 36 controls. Proliferative capacity of T cells was determined in whole-blood lymphocyte culture assays after mitogenic stimulation.

RESULTS

Total T cells, CD4+ and CD8+ subpopulations, and responsiveness to specific T-cell stimuli did not differ between patients and controls; in addition, B cells were not significantly elevated in periodontitis patients. However, more periodontal breakdown in smoking patients was associated with higher numbers of CD3+ T cells, as well as with CD4+ and CD8+ T-cell subsets, and increased T-cell proliferation. Numbers of B cells were not affected by smoking.

CONCLUSIONS

The increased numbers of T-cells and elevated T-cell responsiveness in patients who smoke may be one of several explanations why smoking is a risk factor for periodontitis. The mechanism of how T-cell function contributes to increase the severity of periodontal breakdown in smoking periodontitis patients needs to be investigated further.

A novel factor isolated from Actinobacillus actinomycetemcomitans stimulates mouse B cells and human peripheral blood mononuclear cells

A novel immunostimulating factor (ISTF) of Actinobacillus actinomycetemcomitans ATCC 29522 was isolated and characterized as inducing proliferation of mouse B cells and human peripheral blood mononuclear cells. This factor was isolated from the bacterial culture medium and purified by size exclusion chromatography, dye-ligand affinity chromatography, immunoaffinity chromatography using monoclonal antibodies, and preparative electrophoresis. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that the purified ISTF migrated as a single band corresponding to a molecular mass of 13 kDa. ISTF was a proteinaceous material distinct from lipopolysaccharide; it directly induced the proliferation of B lymphocytes but had no effect on the proliferation of T lymphocytes, even in the presence of antigen-presenting cells. A B-lymphocyte-mitogenic activity of ISTF was also shown by flow cytometric analysis of responding cell subpopulations. Immunoblot analysis revealed that ISTF was a component of the outer membranes of bacteria, could exist as a soluble form, and was released by growing and/or lysed bacteria. These results suggest that ISTF produced by A. actinomycetemcomitans may play an important role in immunopathologic changes associated with A. actinomycetemcomitans infections.

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.

Immunomodulatory and superantigen activities of bacteria associated with adult periodontitis

Immune dysfunctions are frequently associated with chronic inflammatory diseases. Several investigators have reported that patients with severe periodontitis show reduced or negligible levels of proliferative responses of peripheral blood and gingival lymphocytes to periodontopathic organisms. The purpose of this study was to evaluate the influences of products from Porphyromonas gingivalis (P. gingivalis) and Actinobacillus actinomycetemcomitans (A. actinomycetemcomitans) on lymphocytes obtained from periodontally diseased and non-diseased individuals in order to extend our understanding of the possible role of such bacterial components as immune modulators. Pooled cultures of either P. gingivalis or A. actinomycetemcomitans were disrupted using glass beads in a bead mill to prepare whole cell homogenates. These homogenates were then co-cultured with human peripheral blood mononuclear cells (PBMC) and known lymphocyte stimulators. Cultures were pulsed with tritiated thymidine, harvested, and radio label incorporation was determined. Responses to toxic shock syndrome toxin-1 (TSST-1) and pokeweed mitogen (PWM) were inhibited at high concentrations of bacterial homogenate. However, as the concentration was reduced, responses induced by PWM were restored while TSST-1 induced responses remained inhibited. Such results suggest that P. gingivalis and A. actinomycetemcomitans contain potent immunosuppressants with differential influences on lymphocyte population. These effects on B- and T-cells are independent of periodontal disease status and appear to exert their influence through non-toxic mechanisms. In addition, work currently underway presently indicates that obligate oral anaerobic bacteria such as P. gingivalis produce substances with some of the characteristics of superantigens.

Activated lymphocyte subsets in adult periodontitis*

The activation state of T and B lymphocytes in the peripheral blood of periodontitis patients may be a reflection of disease activity. We have utilized 2- and 3-color flow cytometric analyses using a new chromophore, peridinin chlorophyll A protein, and conventional dyes, fluorescein isothiocyanate and phycoerythrin, conjugated to monoclonal antibodies against activated lymphocyte surface markers to measure blood lymphocyte subsets from 18 periodontitis patients and 16 periodontally healthy control subjects. Two-color flow cytometric analysis demonstrated that the frequency of CD4+ and CD5+ T cells, CD20+ B cells, and CD16+ NK (natural killer) cells were increased in periodontitis patients. Of particular interest, CD4+ activated "memory" T cells, CD5+ B cells, and CD56+ NK effector cells were increased significantly in periodontitis patients (p less than 0.05). While the relationship of lymphocyte activation to periodontal disease activity remains unclear, there may be potential for using 2- and 3-color flow cytometry to subcategorize periodontitis patients into high- and moderate-risk groups.

Impaired autologous mixed-lymphocyte reaction of peripheral blood lymphocytes in adult periodontitis

The autologous mixed-lymphocyte reactions (AMLR) of peripheral blood lymphocytes from 80 patients with adult periodontitis were examined. Some but not all patients showed clearly low AMLR responses; 31 of 80 subjects (39%) showing consistently low responses in AMLR (less than the mean--2 standard deviations of the healthy control group values) were designated low-AMLR patients, whereas the 42 patients (53%) who showed normal AMLR responses were designated normal-AMLR patients. However, there were no significant differences in the clinical parameters between these two groups of patients. The phenotypic analysis of T-cell fractions revealed a lower percentage of CD45RA-positive cells in CD4-positive cells (CD4+ CD45RA+ T cells) in the low-AMLR patients than those in normal-AMLR patients and healthy control subjects. No significant differences were demonstrated between the two groups in terms of the proportion of CD4-positive and CD8-positive cells in the T-cell fractions or in the expression of human leukocyte antigen DR of the monocytes and B cells in the non-T-cell fractions. In the low-AMLR patients, the allogeneic MLR was found to be normal, but the interleukin 2 production in the AMLR was found to be significantly depressed. The depressed AMLR responses and the lower percentage of CD4+ CD45RA+ T cells in the low-AMLR patients were found to be normalized following the periodontal therapy. These results might reflect changes in regulatory T-cell function induced by development of periodontal diseases.

Effect of initial treatment of chronic inflammatory periodontal disease on the frequency of peripheral blood T-lymphocytes specific to periodontopathic bacteria

Limit dilution analysis (LDA) was used to determine the effect of initial treatment of chronic inflammatory periodontal disease on the frequency of periodontopathic bacteria-specific T-cells in peripheral blood. Eleven marginal gingivitis (MG) and 8 adult periodontitis (AP) subjects took part in the study. The proliferative T-lymphocyte precursor (PTL-P) frequencies to Porphyromonas gingivalis and Actinomyces viscosus were determined using LDA and Poisson statistics both before and after treatment. Tetanus toxoid was used as a control antigen. Treatment resulted in a significant reduction in clinical disease parameters in both groups. The median peak PTL-P frequency for P. gingivalis was significantly higher in the AP group compared with the MG group before treatment. This was not the case after treatment nor with A. viscosus. In the MG group the median peak PTL-P frequency with both P. gingivalis and A. viscosus declined as a result of treatment. Although this decline was not statistically significant it may indicate an antigen-specific response in this group. In the AP group the median peak PTL-P frequency with P. gingivalis before treatment was 83.76 x 10(-6) (approximately 1 in 12,000) and after treatment it was 36.17 x 10(-6) (approximately 1 in 28,000). Dose-response relationships showed at each concentration of organisms/well this trend for a decline in PTL-P frequency after treatment, suggesting that any increased responsiveness to this organism in this group may be largely antigen-specific. However, there was no difference in this group in the median peak PTL-P frequency with A. viscosus before and after treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Importance of the host response in the periodontium

Immunological mechanisms have been implicated in the pathogenesis of periodontal disease for over 25 years. Studies throughout the 1970s established that advanced forms of the disease were dominated by B-cells/plasma cells while early and putative stable forms of the disease were dominated by T-cells/lymphocytes. Based on these observations, a model of disease was put forward which highlighted a possible T-cell/macrophage immunoregulatory imbalance being involved in disease pathogenesis. Studies throughout the 1980s have supported such a concept although the precise nature of this imbalance remains elusive. At the same time, clinical studies have established that patient susceptibility may be of overriding importance in determining disease outcome. In this context therefore, factors which influence this susceptibility should be fundamental in determining periodontal disease activity. These factors may include genetic variation between individuals in the way in which they respond to periodontopathic bacteria upon which environmental factors would be superimposed. These environmental factors would include anything that altered the balance between the host and the parasite and may be as diverse as recent viral infections resulting in T-cell anergy or physical and mental stress. Recent studies have shown that in elite atheletes, physical stress during training and competition leads to a suppression of mucosal immunity as evidenced by a reduction in salivary IgA. The subsequent effect of these environmental factors at the level of the periodontium, however, remains to be determined.

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.

Serum antibodies and loss of periodontal bone in patients with rheumatoid arthritis

The number of teeth, % of alveolar bone loss, serum IgG, and serum antibodies to Bacteroides gingivalis, Capnocytophaga ochracea and Eubacterium saburreum were recorded in 37 patients diagnosed with rheumatoid arthritis (RA) and in an age- and sex-matched control group of 37 individuals free from RA. The RA group had a significantly increased loss of teeth and loss of alveolar bone compared to the control group. The RA patients also had a significantly increased level of serum IgG. In the total material, 26% of the variation in loss of alveolar bone was accounted for by age, diagnosis of rheumatoid arthritis, and levels of antibodies against B. gingivalis and E. saburreum. In the RA group, 48% of this variation was accounted for by age, total serum IgG and IgG antibodies to B. gingivalis and E. saburreum.

Spontaneous lymphocyte proliferation in severe periodontal disease: role of T and B cells

Spontaneous proliferation of T cells, B cells and unseparated lymphocytes was studied in patients with severe periodontal disease and control subjects. In the patient group only, spontaneous lymphocyte proliferation was reduced, whereas B cell proliferation was enhanced. The findings offer further support for the existence of a disturbance in immune regulation in patients with severe periodontal disease.

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.

Effect of initial treatment of chronic inflammatory periodontal disease in adults on spontaneous peripheral blood lymphocyte proliferation

The spontaneous proliferative response (SPR) of peripheral blood lymphocytes, as a measure of the autologous mixed lymphocyte reaction (AMLR), has been found to be depressed in adults with chronic inflammatory periodontal disease (CIPD). The aim of the present study was to test the hypothesis that initial treatment of CIPD in adults restores the SPR to normal levels. 10 periodontal disease subjects (mean probing attachment loss of 4.2 mm and a mean bleeding index of 0.65) and 10 age- and sex-matched healthy control subjects were studied. The SPR for each patient was evaluated on days 3, 5, 7, 9 and 11 in culture, before and after initial treatment for CIPD. The peak SPR, which occurred at day 5, was depressed in the untreated periodontal disease subjects compared to the healthy control subjects (p less than 0.01). In addition, the kinetics of the SPR were found to be significantly different in 4 of the 10 parameters compared with the untreated periodontal disease patients and the healthy control subjects. After treatment, there was a significant reduction in probing attachment loss and bleeding indexes (p less than 0.001). In addition, the magnitude of the peak SPR was not significantly different from that of the healthy control subjects. Nevertheless, a difference in 1 of the 10 kinetic parameters persisted, which suggested that complete restoration of the SPR to normal had not occurred so soon after treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of periodontal therapy on serum antibody (IgG) levels to plaque microorganisms

The influence of periodontal therapy on serum antibody titers to selected periodontal disease-associated microorganisms was assessed in 23 patients having chronic inflammatory periodontal disease (CIPD). The immunoglobulin G (IgG) titers were determined by the microELISA technique in serum samples obtained prior to treatment; following a hygienic phase which included scaling, root planing, and oral hygiene instruction; following surgical treatment; and one year and two years following hygienic phase (maintenance phase). Considerable individual variability existed in the magnitude of immune response to specific bacterial preparations. Significant reductions in the mean antibody titers were seen to A. viscosus, S. sanguis, F. nucleatum, S. sputigena, B. gingivalis, B. intermedius, B. melaninogenicus, T. vincentii, and T. denticola by the end of the second year of maintenance. There was no consistent response to Capnocytophaga. When individual patient responses were examined, 6 of the 23 were found to have elevated titers to at least one of the microorganisms in the interval between pretreatment and the end of the hygienic phase; however, in all but one case, the titers at the end of the second year of maintenance were below pretreatment levels. Antibody levels to bacteria such as S. sanguis were modified during therapy. This would indicate that immune responses to microbes not generally considered to be "periodontal pathogens" may be modified by adjuvant activity associated with subgingival plaque or changes in the environment of the sulcus and that subsequent changes in titer do not necessarily reflect a role of that microorganism in the disease process.

The effect of subgingival debridement with hand and ultrasonic instruments on the subgingival microflora

The effect of hand or ultrasonic instrumentation on the subgingival microflora of periodontal pockets was investigated. Pockets with probing depths of 6-9 mm were selected in 12 patients and were randomly assigned per patient to the experimental and control groups. After oral hygiene instruction, instrumentation of the experimental pockets was carried out either by ultrasonic or by hand instruments in a split-mouth design. The treatment effect on the subgingival microbiota was evaluated by microscopic and culture studies of subgingival plaque samples, while in addition, supragingival plaque, bleeding after probing and probing pocket depth were scored. Examinations were carried out before and 7, 21 and 49 days after treatment. The hand and ultrasonic treatments were equally effective in reducing probing pocket depths and bleeding scores. At the end of the experimental period, the probing depths of 54% of the hand-treated pockets and 43% of the ultrasonic-treated pockets were reduced to 4 mm or less while the bleeding scores were reduced to 29% and 22%, respectively. The analysis of microscopical and cultural data did not show any differences between hand and ultrasonic debridement. Both treatments reduced the microscopical counts of rods, spirochetes and motiles and reduced the total colony-forming units and number of black-pigmented Bacteroides and Capnocytophaga, resulting in a subgingival microbiota consistent with periodontal health.

Antibodies against lipopolysaccharide from Bacteroides gingivalis before and after periodontal treatment

Specific serum antibody activities of the IgG, IgA and IgM isotypes against lipopolysaccharide (LPS) prepared from Bacteroides gingivalis were measured by an enzyme-linked immunosorbent assay (ELISA) in a group of 12 periodontally healthy subjects and a group of 26 patients with periodontitis. The latter group received periodontal therapy, completed within about 1 yr. A serum sample was obtained from each participant at the first periodontal examination; a second sample was taken about 2 yr later. The mean antibody levels calculated for the healthy group did not change significantly between the first and second examination. The correlation coefficients computed between the two sets of measurements were 0.93, 0.90 and 0.96 for IgG, IgM and IgA respectively (P less than 0.05). Periodontal treatment significantly improved the clinical status of the patients and was followed by a statistically significant mean reduction in specific antibody levels to the LPS preparation (IgG: 15%, IgA: 30% and IgM: 15%).

Blastogenetic responsiveness of peripheral blood lymphocytes from patients with adult periodontitis, evaluated by a reverse hemolytic plaque assay

Peripheral blood lymphocytes were obtained from 10 patients with advanced periodontitis and from 5 normal control subjects. The lymphocytes were cultured with dental plaque, supernatant of homologous fibroblast cytoplasm and Pokeweed-mitogen (PWM). The number of immunoglobulin-secreting cells (ISC) was assessed after 7 days using a reverse hemolytic plaque assay (RHPA). The stimulation levels of lymphocytes from periodontitis patients and control subjects stimulated with dental plaque and PWM were not statistically different (p greater than 0.05). In contrast, the number of ISC produced after stimulation with fibroblast cytoplasm was increased significantly in the patients group (p less than 0.05). These data support the hypothesis that autologous substances play an important rôle in the cellular immune responses of patients with severe chronic inflammatory periodontal disease (CIPD).

Serum antibody levels to 4 periodontal pathogens remain unaltered after mechanical therapy of juvenile periodontitis

Serum antibody titers to Actinobacillus actinomycetemcomitans (A.a.) Y4, Bacteroides gingivalis, Capnocytophaga ochracea and Eubacterium saburreum were determined with an enzyme immunoassay in 12 patients with juvenile periodontitis (JP) at the beginning of treatment and 16 to 32 months later after clinically successful mechanical therapy without antibiotics. The values were compared to corresponding data obtained from 26 age- and sex-matched individuals with a healthy periodontium. 6 JP patients had significantly increased levels of IgG and IgA antibodies to A.a. and 2 patients had increased IgG and IgA antibodies to C.ochracea. About 75% of the JP patients had a level of IgG antibody to B.gingivalis and E.saburreum which was more than one SD lower than the mean of the healthy controls, and in the IgA class 80-100% had such decreased levels of antibodies to these bacteria. In the IgM class, the JP patients by and large had normal levels of antibodies to the 4 bacteria. After treatment, antibodies to A.a. had decreased in only 3 patients, but the levels were still significantly higher than in healthy controls. Minimal alterations were observed in the levels of antibodies to B.gingivalis, C.ochracea and E.saburreum after treatment.

Effect of subgingival scaling on systemic antibody responses to oral microorganisms

The effects of scaling and root planing treatment on systemic antibody responses were studied in patients with periodontal disease and in normal subjects. Immunoglobulin G antibody in serum to a battery of oral microorganisms was assessed in an enzyme-linked immunosorbent assay before and after treatment in 31 individuals. The majority (96%) of the diseased patients exhibited elevated antibody to one or more of the microorganisms before the scaling regime. Significant increases in antibody levels in serum were noted in 16 of 19 patients after scaling, whereas only 2 of 12 nonscaled subjects showed similar changes during monitoring intervals of up to 3 years. The bacterial specificities of the increases were found to differ among the patients; however, a significant correlation to preexisting elevated antibody levels was observed. Peak levels of responses were noted at approximately 2 to 4 months posttreatment; antibody returned to pretreatment levels by 8 to 12 months. The predominant organisms for which changes were noted included the black-pigmented Bacteroides spp., Eikenella corrodens, Campylobacter concisus, and Actinobacillus actinomycetemcomitans. In 18 of 19 instances, the homologous microorganism was detected in the subgingival plaque when elevated antibody was present after treatment. These findings indicated that specific changes in host systemic responses accompany scaling and root planing treatment of periodontal disease patients. These alterations in the host response may provide an additional means by which successful therapy can be accomplished.

Host responses to bacteria and bacterial products in periodontal disease: immunosuppressive effects of periodontitis-related microorganisms?

Several recent investigations indicate that some patients with adult periodontitis have lowered serum antibody levels or reduced lymphoproliferative responses to certain periodontitis-related microorganisms. Many such patients tend to show increased responses after therapy. Some suggested mechanisms of such responses are reviewed and the possible significance of immunosuppressive effects of periodontitis-related microorganisms are briefly discussed.

Effect of periodontal therapy on spontaneous lymphocyte response and neutrophil chemotaxis in localized and generalized juvenile periodontitis patients

The etiology and pathogenesis of juvenile periodontitis may involve dysfunctions of the host response. In particular, the neutrophil and the lymphocyte have been implicated in the disease. The purpose of the present study was to examine the in vitro spontaneous lymphocyte response and neutrophil chemotaxis in populations of localized juvenile periodontitis (LJP) and generalized juvenile periodontitis (GJP) patients and age- and sex-matched healthy subjects (HS). These laboratory values were also evaluated immediately following and 1 year after periodontal therapy. The results show that spontaneous lymphocyte responses reflecting the autologous mixed lymphocyte reaction (AMLR) are depressed for GJP patients. The decreased AMLR in the GJP group appears to represent an abnormal T-cell function which may reflect activity of the periodontal lesion. LJP patients have an increased AMLR response, although it was not statistically significant. 1 year following active periodontal therapy, spontaneous lymphocyte responsiveness returned to normal in most GJP patients. The increased spontaneous lymphocyte responsiveness of LJP patients was not changed either immediately following active periodontal therapy or 1 year later. LJP and GJP patients exhibited a neutrophil chemotaxis defect when compared to cells from HS. This neutrophil defect was still observed 1 year following active therapy.

An improved method for assessing the incorporation of labeled precursors into DNA by human mononuclear cells

The blastogenic responsiveness of activated lymphoid cells is usually assessed in vitro by measuring the incorporation of radioactive thymidine or iododeoxyuridine, a thymidine analog, into DNA. The accuracy of this method is compromised by the presence in activated and unactivated lymphocytes and in some of the substances used to activate them, of degradative enzymes which compete with DNA synthetase, the incorporation efficiency of exogenous precursor is inherently low. We have done studies aimed at improving both the efficiency and the accuracy of the assay system by selectively inhibiting the enzymes responsible for thymidylate synthesis de novo and DNA precursor degradation. Culture conditions were investigated and potential inhibitors were tested using human peripheral blood mononuclear cells activated with phytohemagglutinin. Nucleoside-degrading activity of mammalian and bacterial cells is due largely to nucleoside phosphorylases, enzymes that require orthophosphate for activity. We partly inhibited DNA precursor degradation by lowering the phosphate concentration in the culture medium and lowering the pH, thereby reducing the orthophosphate concentration. To reduce precursor degradation further, we tested several potential nucleoside phosphorylase and thymidylate synthetase inhibitors at various concentrations. Our data show that the addition of 1 mM fluorouracil and 1 mM deoxyuridine to the culture medium largely prevents degradation of radioactive thymidine and iododeoxyuridine without unduly compromising the DNA-labeling efficiency of cells activated with mitogens or bacterial homogenates. Under these conditions, label incorporation increases linearly as the number of blast cells or the labeling time increases.

Clinical and microbiological effects of subgingival restorations with overhanging or clinically perfect margins

The close association between restorations with overhanging margins and chronic destructive periodontitis has been known for many years. However, the mechanisms by which overhanging restorations will interact in the pathogenesis of periodontal disease are still unknown. Generally it is accepted that overhanging restorations contribute to the promotion of the disease process by virtue of their capacity to retain bacterial plaque. The purpose of the present study was to determine if the placement of subgingival restorations with overhanging margins results in changes in the subgingival microflora. 9 dental students with clean teeth and clinically healthy gingivae (GI less than 0.1) gave their consent to participate in the study. 5 MOD cast gold onlays with 1 mm proximal overhanging margins were placed in mandibular molars for 19-27 weeks. They were replaced in a cross-over design by 5 similar onlays with clinically perfect margins which served as controls. Another 5 onlays were placed in reverse order in the remaining patients. Prior to and every 2-3 weeks after insertion, subgingival microbiological samples were obtained by inserting a fine sterile paper point for 30 sec into the gingival sulcus subjacent to the restoration. The predominant cultivable flora was determined using continuous anaerobic culturing techniques. Following the placement of restorations with overhanging margins, a subgingival flora was detected which closely resembled that of chronic periodontitis. Increased proportions of Gram-negative anaerobic bacteria, black-pigmented Bacteroides and an increased anaerobe: facultative ratio were noted. Following the placement of the restorations with clinically perfect margins, a microflora characteristic for gingival health or initial gingivitis was observed. Black-pigmented Bacteroides were detected in very low proportions (1.6-3.8%). These changes in the subgingival microflora were obvious irrespective of whether the restorations with the overhanging margins were placed in the first period of the experiment or following the cross-over. Clinically, increasing gingival indices were detected at the sites where overhanging margins were placed. Bleeding on gentle probing always preceded the peak level of black-pigmented Bacteroides. Loss of attachment was not detected in any site. Changes in the subgingival microflora after the placement of restorations with overhanging margins document a potential mechanism for the initiation of periodontal disease associated with iatrogenic factors.

Effect of factors other than pathologic status on responsiveness of peripheral blood mononuclear cells from patients with chronic periodontitis

Studies were designed to assess factors other than pathologic status of the cell donor which affect the blastogenic responsiveness in vitro of peripheral blood mononuclear cells (PBMs) from normal donors and patients with periodontitis. Cultures were established and activated using phytohemagglutinin-P (PHA) or homogenates of Actinomyces viscosus (AVIS), a gram-positive plaque microorganism, and Fusobacterium nucleatum (FUSO), a gram-negative plaque microorganism. Activation was assessed by measuring the incorporation of labeled precursor into DNA. The effects of incubation time, vessel shape, cell concentration, prostaglandin E2 and indomethacin on blastogenic responsiveness were studied. Blastogenic responsiveness became maximal after 5 to 8 days' activation with the bacterial substances, and after 3 days' activation with PHA. Radioactivity incorporated by cultures in microtest wells with flat, round and conical bottoms was 5.9, 7.8 and 10.6 X 10(3) cpm, respectively. Cultures of cells from all of the patients and normal subjects were activated by PHA, AVIS and FUSO, and cell concentration was a major determinant of the magnitude of the blastogenic response. Responsiveness of cultures from all patients and control subjects activated with AVIS and FUSO was inhibited significantly by prostaglandin E-2 (PGE2) at a concentration of 10 microM. Inhibition was generally 50% or greater. Indomethacin, an inhibitor of prostaglandin production, at a concentration of 0.5 micrograms/ml significantly enhanced responsiveness of AVIS- and FUSO-activated cultures from control donors and patients, indicating that prostaglandins are produced endogenously, and that they affect cell responsiveness. The effect of PGE2 and indomethacin on PHA-activated cultures was more variable and, where present, of a lesser magnitude than that observed for cultures activated with bacterial homogenates. In most cultures the effects were not statistically significant. Our data show that in studies of lymphocyte activation, the incubation time, culture-vessel shape, cell concentration and presence of endogenous inhibitors need to be taken into account.