Leukotoxic effects of Actinobacillus actinomycetemcomitans. Modulation by serum components

Virulence and Pathogenicity Properties of Aggregatibacter actinomycetemcomitans

Aggregatibacter actinomycetemcomitans is a periodontal pathogen colonizing the oral cavity of a large proportion of the human population. It is equipped with several potent virulence factors that can cause cell death and induce or evade inflammation. Because of the large genetic diversity within the species, both harmless and highly virulent genotypes of the bacterium have emerged. The oral condition and age, as well as the geographic origin of the individual, influence the risk to be colonized by a virulent genotype of the bacterium. In the present review, the virulence and pathogenicity properties of A. actinomycetemcomitans will be addressed.

Antimicrobial capacity of Leucocyte-and Platelet Rich Fibrin against periodontal pathogens

Various studies have described the biological properties of the Leucocyte- and Platelet Rich Fibrin (L-PRF) such as the antimicrobial effect against wound bacteria, but less is known about the effect against periodontal pathogens. The aim of this study was to evaluate the antibacterial properties of the L-PRF membrane and L-PRF exudate against the main periopathogens cultured on agar plates and in planktonic solution. This study demonstrated the antibacterial effect of the L-PRF membrane against P. intermedia, F. nucleatum, and A. actinomycetemcomitans, but especially against P. gingivalis. The L-PRF exudate also showed a strong inhibition against P. gingivalis on agar plates. No inhibition could be observed for the other bacterial strains. Moreover, L-PRF exudate decreased the number of viable P.gingivalis in a planktonic solution in a dose-dependent way. However, A. actinomycetemcomitans showed an increased growth in planktonic solution when in contact with the L-PRF exudate.

Aggregatibacter (Actinobacillus) actimycetemcomitans leukotoxin and human periodontitis - A historic review with emphasis on JP2

Aggregatibacter (Actinobacillus) actimycetemcomitans (Aa) is a gram-negative bacterium that colonizes the human oral cavity and is causative agent for localized aggressive (juvenile) periodontitis (AgP). In the middle of 1990s, a specific JP2 clone of belonging to the cluster of serotype b strains of Aa with highly leukotoxicity (leukotoxin, LtxA) able to kill human immune cells was isolated. JP2 clone of Aa was strongly associated with in particularly in rapidly progressing forms of aggressive periodontitis. The JP2 clone of Aa is transmitted through close contacts. Therefore, AgP patients need intense monitoring of their periodontal status as the risk for developing severely progressing periodontitis lesions are relatively high. Furthermore, timely periodontal treatment, including periodontal surgery supplemented by the use of antibiotics, is warranted. More importantly, periodontal attachment loss should be prevented by early detection of the JP2 clone of Aa by microbial diagnosis testing and/or preventive means.

Aggregatibacter actinomycetemcomitans: virulence of its leukotoxin and association with aggressive periodontitis

Periodontitis is an infection-induced inflammatory disease that causes loss of the tooth supporting tissues. Much focus has been put on comparison of the microbial biofilm in the healthy periodontium with the diseased one. The information arising from such studies is limited due to difficulties to compare the microbial composition in these two completely different ecological niches. A few longitudinal studies have contributed with information that makes it possible to predict which individuals who might have an increased risk of developing aggressive forms of periodontitis, and the predictors are either microbial or/and host-derived factors. The most conspicuous condition that is associated with disease risk is the presence of Aggregatibacter actinomycetemcomitans at the individual level. This Gram-negative bacterium has a great genetic variation with a number of virulence factors. In this review we focus in particular on the leukotoxin that, based on resent knowledge, might be one of the most important virulence factors of A. actinomycetemcomitans.

Aggregatibacter actinomycetemcomitans leukotoxin: a powerful tool with capacity to cause imbalance in the host inflammatory response

Aggregatibacter actinomycetemcomitans has been described as a member of the indigenous oral microbiota of humans, and is involved in the pathology of periodontitis and various non-oral infections. This bacterium selectively kills human leukocytes through expression of leukotoxin, a large pore-forming protein that belongs to the Repeat in Toxin (RTX) family. The specificity of the toxin is related to its prerequisite for a specific target cell receptor, LFA-1, which is solely expressed on leukocytes. The leukotoxin causes death of different leukocyte populations in a variety of ways. It activates a rapid release of lysosomal enzymes and MMPs from neutrophils and causes apoptosis in lymphocytes. In the monocytes/macrophages, the toxin activates caspase-1, a cysteine proteinase, which causes a proinflammatory response by the activation and secretion of IL-1β and IL-18. A specific clone (JP2) of A. actinomycetemcomitans with enhanced leukotoxin expression significantly correlates to disease onset in infected individuals. Taken together, the mechanisms by which this toxin kills leukocytes are closely related to the pathogenic mechanisms of inflammatory disorders, such as periodontitis. Therapeutic strategies targeting the cellular and molecular inflammatory host response in periodontal diseases might be a future treatment alternative.

Caspase 1 involvement in human monocyte lysis induced by Actinobacillus actinomycetemcomitans leukotoxin

Actinobacillus actinomycetemcomitans, an oral bacterium implicated in the etiology of periodontal diseases, produces a leukotoxin that selectively lyses primate neutrophils and monocytes, the major populations of defense cells in the periodontium. Though lysis requires expression of the receptor lymphocyte function-associated molecule 1 (LFA-1) on the cell surface, not all LFA-1-expressing leukocyte populations are equally susceptible to the toxin. In this study, the susceptibility of human leukocytes to leukotoxin-induced lysis is compared to their expression of LFA-1 and the activity of caspase 1. Cytolysis was determined by the activity of lactate dehydrogenase released from peripheral human leukocytes after 1-h exposure to leukotoxin. Monocytes were lysed at leukotoxin concentrations of > or = 5 ng/ml, while the corresponding values for neutrophils and lymphocytes were approximately 10 times greater. Similar LFA-1 expression was found in all susceptible cell populations irrespective of their degree of sensitivity to the toxin. Exposure of monocytes to leukotoxin increased their caspase 1 activity about fivefold within 10 to 20 min. Presence of the caspase 1 inhibitor Ac-YVAD-CMK significantly blocked the leukotoxin-induced lysis of monocytes only. At sublytic concentrations, leukotoxin induced no apoptotic activity in monocytes, as revealed by the lack of caspase 3 activation and DNA fragmentation. Monocytes are the most lysis-sensitive leukocytes for A. actinomycetemcomitans leukotoxin. Their lysis by this toxin depends on caspase 1 activation and proceeds through a process that differs from classical apoptosis.

Serum-mediated release of leukotoxin from the cell surface of the periodontal pathogen Actinobacillus actinomycetemcomitans

The leukotoxin of the periodontopathogen Actinobacillus actinomycetemcomitans is an important virulence factor that lyses human neutrophils and monocytes and thus, it may enable the bacterium to evade the local host defense. The toxin also induces degranulation of neutrophils and cytokine release in monocytes. To trigger these biological activities, leukotoxin has to be released from the bacterium and diffuse into the periodontal tissues. To date, the conditions found to cause toxin release have been artificial and have included high ion concentration and alkaline conditions. To study the release of the toxin under conditions mimicking the natural environment of the periodontium the ability of human serum to enable leukotoxin release from the bacterial surface was examined. Suspensions of leukotoxic A. actinomycetemcomitans strains were incubated with various concentrations of human serum or serum albumin. The suspensions were centrifuged and the leukotoxin in the supernatants or the cell pellets was detected by gel electrophoresis and immunoblotting. Serum was found to cause the rapid release of leukotoxin from the bacteria in a concentration-dependent manner. Pure albumin exhibited a similar effect. The leukotoxin released was active against human neutrophils. Only a minor proportion of it was associated with membranous vesicles produced by the bacteria. The results indicate that serum, a fluid closely related to the exudate in inflamed periodontal pockets, releases leukotoxin from the cell surface of A. actinomycetemcomitans. The process may enable the diffusion of the toxin from the bacterial biofilm into the surrounding tissues, where it can exert its biological effect.

Lack of lipoprotein-dependent effects on the cytotoxic interactions of Actinobacillus actinomycetemcomitans leukotoxin with human neutrophils

A high odds ratio has been reported for hyperlipidemia and periodontal diseases in humans, and the severity of periodontitis seems to correlate with the hyperlipidemic status of the patients. Early studies indicated that the lipoprotein-containing fraction of the serum enhances the leukotoxic activity of the periodontopathogen Actinobacillus actinomycetemcomitans against human polymorphonuclear leukocytes (PMNL). The protease inhibitors of normal serum account for this enhancement, while delipidated serum has no effect on the leukotoxin-dependent PMNL cytolysis. No information exists for the effect of serum lipoproteins or hyperlipidemic serum. The aim of this study was to evaluate the role of serum lipoproteins in the interaction of the leukotoxin of A. actinomycetemcomitans with human PMNL. Purified leukotoxin was mixed with human PMNL prepared from venous blood of healthy subjects and various varying amounts of hyperlipidemic or delipidated serum, or purified serum lipoproteins. The cytolytic activity of leukotoxin was determined by activity of the cytosol enzyme lactate dehydrogenase released from injured PMNL. The degranulating activity of the toxin was measured through the release of the granule components elastase and lactoferrin. Normal human serum without leukotoxin-neutralizing antibodies caused a 4-fold enhancement of the leukotoxic activity when present at concentrations of 5-10% in the reaction mixture. Serum lipoproteins had no effect when added at concentrations that occur normally in serum. At high concentrations, purified low density and very low-density lipoproteins increased the leukotoxicity of the mixture. Nevertheless, hyperlipidemic serum prepared from a normal serum by the addition of autologous lipoproteins had no influence on the leukotoxin-caused cytolysis compared to the normal serum. Pre-incubation of PMNL for 1 h in hyperlipidemic or delipidated serum had no effect on the leukotoxin-induced degranulation of PMNL. The results indicate that the cytotoxic interactions of A. actinomycetemcomitans leukotoxin against human PMNL are not influenced by the presence of serum lipoproteins.

Inhibitory effect of synthetic histatin 5 on leukotoxin from Actinobacillus actinomycetemcomitans

Actinobacillus actinomycetemcomitans is a gram-negative bacterium strongly implicated in the pathogenesis of juvenile periodontitis. This periodontal pathogen synthesizes a leukotoxin that destroys human polymorphonuclear leukocytes (PMNs), and this toxin is thought to be responsible for the virulence of A. actinomycetemcomitans. It was therefore of interest to assess whether major virulence factors of periodontal pathogens were neutralized by salivary components. This study focuses on the effect of histatins, components of the nonimmune oral defense system, on leukotoxin activity. Leukotoxin was extracted with polymyxin B from freshly grown anaerobic cultures of A. actinomycetemcomitans strain Y4. PMNs isolated from blood of healthy human volunteers were incubated in a cytotoxicity assay containing PMNs (10(7) cells/ml) and leukotoxin preparation (0-500 microg/ml) in Hanks' balanced salt solution at 37 degrees C for 0-120 min with or without synthetic histatin 5 (0-500 microM). Cytotoxicity was measured by release of lactate dehydrogenase (LDH) at different time intervals. Histatin 5 neutralized the toxic effect of the leukotoxin preparation in a concentration-dependent manner, with an IC(50) value of 150 microM. When PMNs were preincubated with histatin 5 (300 microM), washed and subsequently exposed to leukotoxin, no protective effect was observed. This observation suggests a mechanism of inhibition whereby histatin 5 either directly neutralizes the leukotoxin or interferes with the leukotoxin-PMN interaction. The inhibitory effect of histatin 5 on leukotoxic activity may suggest a new biological function of histatins in the oral cavity as a naturally occurring secondary antibiotic.

Protease inhibitors, the responsible components for the serum-dependent enhancement of Actinobacillus actinomycetemcomitans leukotoxicity

Serum enhances the leukotoxic activity of Actinobacillus actinomycetemcomitans against human polymorphonuclear leukocytes (PMNL) by a mechanism that still is unknown. Early attempts to identify the serum components responsible for this enhancement gave no conclusive results, but indicated that the lipoprotein-containing fraction of the serum was involved in the interaction. This study aimed to clarify the role of serum lipoproteins in the leukotoxin interaction, and to identify other serum components involved. The main hypothesis examined was that the leukotoxicity enhancement might depend on serum protease inhibitors that block proteolytic cleavage of leukotoxin by enzymes released from the leukocytes. PMNL were isolated from human peripheral blood and incubated with purified leukotoxin in the presence of serum or purified serum components or lipoprotein-deficient serum. Leukotoxin was also incubated with purified elastase and cathepsin G or with enzyme mixtures from degranulated PMNL. The leukotoxic activity in these mixtures was determined as the extracellular release of lactate dehydrogenase from PMNL. Cleavage of the toxin was showed by gel electrophoresis and Western blot. Morphological changes in PMNL from the above mixtures were examined by electron microscopy. Enzymes from degranulated PMNL cleaved leukotoxin to non-cytotoxic fragments. Elastase and cathepsin G were mainly responsible for the cleavage. Inhibition of leukotoxin degradation was found in the presence of whole serum or of the serum protease inhibitors alpha2-macroglobulin and alpha1-proteinase inhibitor. Under these conditions enhanced PMNL lysis was also observed. A similar enhancement of PMNL lysis was found when PMNL degranulation was blocked by EDTA. On the other hand, lipoprotein-deficient serum had no influence on the leukotoxic activity. The results indicate that the increased leukotoxicity of A. actinomycetemcomitans observed in the presence of human serum is caused by the serum protease inhibitors that counteract proteolytic degradation of leukotoxin. The degradation is caused by enzymes from degranulated PMNL triggered by leukotoxin.

Immunodominant antigens in periodontal disease: a real or illusive concept?

The humoral arm of the immune system provides protection from many medically significant pathogens. The antigenic epitopes of the pathogens which induce these responses, and the subsequent characteristics of the host response, have been extensively documented in the medical literature, and in many cases have resulted in the development and implementation of effective vaccines or diagnostic tests. There is a substantial body of literature on the humoral immune response in periodontal disease, which is targeted at micro-organisms present within periodontal pockets. However, the significance and specificity of the immune response in periodontal disease have proved difficult to elucidate, due to the large number of potential pathogens in the plaque biofilm and the apparent commensal nature of many of these opportunistic pathogens. This review addresses our current knowledge of the approaches and strategies which have been used to elucidate and examine the concept of immunodominant antigens in medical infections and, more recently, periodontal disease. An identification/understanding of the immunodominant antigens would be informative with respect to: (i) the relative importance of the implicated pathogens, (ii) new approaches to immunological diagnosis, (iii) specific bacterial virulence determinants, (iv) natural protective responses, and (v) the selection of potential vaccine candidate antigens. We conclude that immunodominance of antigens in periodontal disease may be relevant to our understanding of periodontal disease pathogenesis, but due to the complexity and diversity of the 'pathogenic microbial ecology', it is currently an enigmatic topic requiring a multidisciplinary approach linking clinical, microbiological, and immunological investigations. We also conclude, after assessing the literature available on the topic of immunodominance, that it is a term that, if used, must be clearly defined and understood, since it is often used loosely, leading to a general misinterpretation by readers of oral and medical literature.

W, ITANO EN. Anticorpos antileucotoxina contra Actinobacillus actinomycetemcomitans em amostras de soro e saliva de pacientes com periodontite juvenil localizada

A leucotoxina de Actinobacillus actinomycetemcomitans é considerada seu principal fator de virulência com potencial de causar agressão às defesas do hospedeiro. No presente trabalho, foram analisados os níveis séricos e salivares de anticorpos antileucotoxina de A. actinomycetemcomitans em soros e salivas de pacientes com periodontite juvenil localizada (PJL) e controles saudáveis. Adicionalmente, foi realizada a análise de complexo imune (CI) nas amostras de saliva. Foram utilizados os métodos ELISA clássico com a leucotoxina obtida por gel filtração em Sephadex G-200 e ELISA de captura utilizando IgG de coelho anti-A. actinomycetemcomitans FDC Y4 leucotóxico adsorvido com uma cepa da mesma espécie, porém, não leucotóxica. Os resultados obtidos demonstraram níveis séricos de IgG significativamente mais elevados em pacientes com PJL em relação aos controles sadios, tanto por ELISA clássico como por ELISA de captura (p < 0,05). No entanto, não foram observadas diferenças entre os níveis de IgG, IgA-S e CI nas salivas dos indivíduos examinados. Estes resultados sugerem que, embora A. actinomycetemcomitans apresente vários fatores de virulência que afetam a resposta imune do hospedeiro, ocorre resposta imune à leucotoxina nos pacientes com PJL. Esse aumento de IgG na circulação sangüínea pode contribuir na defesa do hospedeiro, limitando a lesão nas regiões periodontais amplamente colonizadas por A. actinomycetemcomitans.

Inhibition of Actinobacillus actinomycetemcomitans leukotoxicity by bacteria from the subgingival flora

Actinobacillus actinomycetemcomitans produces a pore-forming leukotoxin that lyses human polymorphonuclear leukocytes and monocytes. Certain proteolytic bacteria may coexist with A. actinomycetemcomitans in periodontal pockets. We aimed therefore to examine whether oral bacteria can modify the leukotoxicity of A. actinomycetemcomitans. A total of 55 strains representing 45 bacterial species of the subgingival flora were tested. Each strain was incubated with the highly toxic strain of A. actinomycetemcomitans HK 1519 and the leukotoxic activity of the suspension against human polymorphonuclear leukocytes was determined from the activity of the lactate dehydrogenase released upon lysis of the leukocytes. Porphyromonas gingivalis, Prevotella intermedia, Prevotella nigrescens, Prevotella melaninogenica and Prevotella loeschii inhibited the leukotoxicity of A. actinomycetemcomitans cells as well as the activity of leukotoxin purified from the same strain. The bacterial strains without the ability to block leukotoxic activity also failed to destroy pure leukotoxin even after 5 h of incubation. The proteolytic degradation of leukotoxin by P. gingivalis was mainly dependent on the activity of the enzymes R- and K-gingipains. P. intermedia and P. nigrescens also degraded the leukotoxin by enzymes. The results imply a role of the periodontal microflora in modifying the virulence of A. actinomycetemcomitans by destroying its leukotoxin.

Actinobacillus actinomycetemcomitans leukotoxin induces apoptosis in HL-60 cells

Actinobacillus actinomycetemcomitans leukotoxin (Ltx) is a member of the repeats-in-toxin (RTX) family of pore-forming toxins and kills human immune cells. Currently, it remains unclear whether toxin-mediated killing of target cells involves the induction of necrosis or apoptosis. Therefore, the goal of this investigation was to determine whether Ltx is capable of causing apoptotic cell death in toxin-sensitive promyelocytic HL-60 cells. Multiparameter flow cytometric analysis of toxin-treated cells stained with Hoechst 33258 (or 33342) and 7-aminoactinomycin D allowed us to identify four populations: viable cells, early apoptotic cells, late apoptotic and/or secondarily necrotic cells, and a final population that was composed of cellular debris. Compared with control cells, HL-60 cells treated with Ltx exhibited a gradual decrease in forward light scatter with a coincident increase in side light scatter, indicative of a decrease in cell size and organelle condensation, respectively. Additional experiments demonstrated that Ltx-treated cells showed evidence of internucleosomal DNA fragmentation and phosphatidylserine translocation. The results of our studies clearly demonstrate that Ltx can kill HL-60 cells by inducing apoptosis. We hypothesize that elimination of acute inflammatory cells via this mechanism plays a critical role in the pathogenesis of diseases caused by A. actinomycetemeomitans.

Serum IgG2 level, Gm(23) allotype and FcgammaRIIa and FcgammaRIIIb receptors in refractory periodontal disease

The purpose of this investigation was to compare the levels of serum IgG2, the frequency of detection of Gm(23)-negative allotype and frequency of detection of FcgammaRIIa and FcgammaRIIIb receptor haplotypes in 32 refractory, 54 successfully treated and 27 periodontally healthy individuals. Refractory subjects showed mean full mouth attachment loss and/or >3 sites with attachment loss >2.5 mm within 1 year after both scaling and root planing, and surgery plus systemically administered tetracycline. Successfully treated subjects showed mean attachment level gain and no sites with attachment loss >2.5 mm 1 year post-therapy. Periodontally healthy subjects exhibited no pocket depth or attachment level >3 mm, and no evidence of progressing disease during 1 year of monitoring. Blood was obtained from each subject at baseline. Serum IgG2 and Gm(23) allotype were determined using radial immunodiffusion. DNA was extracted from whole blood and the FcgammaR genotypes determined using PCR and allele specific oligonucleotide probes. Significance of differences among clinical groups were sought using the Kruskal-Wallis or chi-square tests. Associations between 2 or more variables were tested using regression analysis. Refractory subjects exhibited higher mean attachment loss and pocket depth than successfully treated or periodontally healthy subjects. Smoking status did not differ significantly among groups. No significant differences in serum IgG2 levels and frequency of detection of Gm(23)-negative allotype were observed among the clinical groups. Serum IgG2 level was positively associated with the number of serum antibody responses to subgingival species (r=0.51, p<0.001). Subjects with the Gm(23)-negative allotype exhibited lower mean levels of serum IgG2 (3.06+/-0.3 versus 3.9+/-0.2, p<0.01) and mean number of serum antibodies to subgingival species (17.7+/-1.7 versus 23.3+/-1.4, p<0.05) than allotype positive individuals. No significant differences in FcgammaR haplotype distribution were observed among the 3 clinical groups. Associations of serum IgG2 level, Gm(23) allotype, FcgammaRIIa and FcgammaRIIIb receptor haplotypes and smoking status were weakly related or not related to clinical status. This lack of relationship may have been due to a reality of no relationship, or the inadvertent pooling of subjects where these factors were of primary importance with subjects in whom these factors played a less important role.

Strong cytotoxicity to human gingival fibroblasts by Porphyromonas gingivalis ATCC 33277

The aim of the present study was to analyze the cytotoxicity of some bacterial species associated with periodontal diseases. The specificity of cytotoxicity was estimated against cells of various origin and from different individuals. The reference bacteria were Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis and Fusobacterium nucleatum. These bacteria were cultured for 24 h in liquid media and the supernatants were used in cytotoxicity assays. The target cells used were human gingival fibroblasts (GF), dermal fibroblasts (K4), gingival epithelial cells (E) and HeLa-cells (HeLa). These cells were exposed at 4 h or 24 h, respectively, to various concentrations of culture supernatants from the selected bacteria. The influence on the viability and metabolism of the cells were estimated quantitatively as increase in neutral red uptake and lactic acid production. Growth medium supernatants of P. gingivalis 33277 were strongly cytotoxic to gingival fibroblasts after 24 h incubation, compared to supernatants of P. gingivalis 381 or W 50, A. actinomycetemcomitans or F. nucleatum cultures. The toxic effect of P. gingivalis 33277 decreased drastically after heat inactivation, which indicates effects of proteins. By adding anti-sera the cytotoxicity of P. gingivalis 33277 could be dose dependently neutralized, which was not the case when supernatants of A. actino-mycetemcomitans was tested. Target cells of epithelial origin did not show increased cytotoxicity to P. gingivalis 33277. The results of the present study strengthen the hypothesis that P. gingivalis remains as a suspect causative key component in periodontal diseases.

Gingival fibroblast cytokine profiles in Actinobacillus actinomycetemcomitans-associated periodontitis

Within the in vivo environment human gingival fibroblasts (HGF) may be challenged with bacteria or bacterial products. This interaction may result in the release of cytokines which are directly or indirectly involved in connective tissue and bone catabolism, such as interleukin (IL)-1 beta, IL-6, and IL-8. Our investigation has tested the hypothesis that HGF from Actinobacillus actinomycetemcomitans (Aa)-infected patients with rapidly destructive forms of periodontitis, such as localized juvenile periodontitis (LJP), respond to Aa challenge with an exaggerated secretion of IL-1 beta, IL-6, and IL-8. We have compared the in vitro profiles of these cytokines by Aa-challenged HGF obtained from 2 healthy subjects, 2 Aa-infected, slowly progressing adult periodontitis (AP) patients and 2 LJP patients. HGF were challenged throughout a 48-hour period with formalinized whole bacterial cells, and culture supernatants were analyzed for cytokine content using RIA. No differences were noted in the IL-1 beta secretion levels among the different HGF cultures. Although basal (unchallenged) IL-6 and IL-8 production was similar in all HGF cultures, HGF from the two LJP patients responded to Aa challenge with a more rapid IL-6 and a more pronounced IL-8 secretion than healthy or AP HGF. We also tested the ability of human serum antibodies against Aa to moderate the Aa-elicited HGF cytokine secretion by adding human serum, with normal or elevated antibody content. Both sera appeared to have an upregulating effect on IL-6 and IL-8 secretion. Depletion of 95% of the anti-Aa antibody from serum by absorption did not affect its activity. Based on the response of HGF from two LJP patients, we propose that Aa-induced pathology in LJP may be modulated by stimulation of rapid and/or exaggerated secretion of cytokines with potential catabolic effects, although studies with a larger group of LJP patients are needed to further test this hypothesis. Furthermore, serum antibodies against this microorganism do not appear to have a neutralizing effect in cytokine-eliciting HGF-Aa interactions.

Longitudinal dynamics of infection and serum antibody in A. actinomycetemcomitans periodontitis

OBJECTS

This report describes one of the first prospective studies delineating the relationship between infection, host antibody responses and disease exacerbations and remissions in a distinct subset of periodontitis patients infected with A. actinomycetemcomitans.

DESIGN

The design of this longitudinal study included visits for each patient approximately every 2 months for up to 3 years.

SUBJECTS AND METHODS

Subjects (n=51) included 16 adult periodontitis (AP) and 11 early-onset periodontitis (EOP) patients with elevated serum IgG antibody to A. actinomycetemcomitans and infection with this microorganism, 12 AP patients with normal levels of anti-Aa antibody, and 12 normal subjects. MEASUREMENT OUTCOMES: Clinical parameters included a gingival index, plaque index, bleeding on probing, pocket depth, and attachment level. Disease activity was defined as loss of attachment during the monitoring intervals. Serum IgG, IgM and IgA antibody to A. actinomycetemcomitans Y4 (serotype b) was quantitated using an ELISA. Subgingival plaque samples were examined for A. actinomycetemcomitans using colony immunoblotting. Human serum IgG antibody specificities to outer membrane antigens (OMA) of A. actinomycetemcomitans Y4 were determined using Western immunoblotting.

RESULTS

A. actinomycetemcomitans-infected AP patients had a higher frequency of teeth infected when compared to the EOP patients. However, the EOP patients exhibited a trend for higher levels of A. actinomycetemcomitans in those teeth that were infected. Active disease patients demonstrated a significantly greater frequency of infected sites, as well as significant elevations in the proportions of A. actinomycetemcomitans. Both EOP and AP groups showed significantly elevated IgG, IgM and IgA antibody to A. actinomycetemcomitans when compared to a periodontally normal group. The level of IgG antibody was significantly elevated in A. actinomycetemcomitans-positive patients with active disease, while IgA antibody was decreased in a number of the active group patients. Plaque samples derived from active sites showed a clear and significant increase in A. actinomycetemcomitans that occurred from 2-6 months prior to the identification of disease activity. Approximately 70% of the active disease patients showed an increase in IgG antibody level by 2-4 months prior to disease activity. Studies of the antigen reactivity patterns of serum IgG indicated that antibody to antigens of 65, 58, 48, 29 and 24 kDa were more frequent in patients who showed active disease, while those patients with the greatest frequency of active disease appeared to show a general decrease in the recognition of the A. actinomycetemcomitans OMA.

CONCLUSIONS

It appears that A. actinomycetemcomitans infection relates to a particular type of disease with accompanying antibody responses that reflect periods of active disease. The dynamics of A. actinomycetemcomitans infection and the level and specificity of systemic antibody responses to this pathogen support an important contribution of the immune response to managing this infection.

Physiopathology of primary periodontitis associated with plaque. Microbial and host factors. A review. Part 1

Microbial factors involved in the genesis of periodontitis include colonization, bacterial penetration of the epithelium, multiplication and invasive-destructive capacity. Colonization of the gingival sulcus is related, to a certain extent, to supragingival plaque. Bacterial multiplication is induced by nutrients in the gingival fluid, and nutrients produced by degradative and excretory microbial activity. Invasion and destruction are mediated by exotoxins, structural elements of the bacteria, enzymes, metabolites, polyclonal lymphocyte activity, fibroblastic cytotoxicity, and leukocyte chemotactic inhibition.

Subgingival distribution of A. actinomycetemcomitans in periodontitis

This investigation developed an experimental design that (1) detailed the distribution of A. actinomycetemcomitans in subgingival plaque related to the level of serum antibody to this pathogen; (2) used broad based subgingival plaque sampling to allow a definition of the distribution of A. actinomycetemcomitans infection in periodontitis patients; (3) described the distribution of A. actinomycetemcomitans serotypes in patients and within sites; and, (4) assessed how this infection impacted upon local clinical symptoms of disease. We noted a significant positive relationship between the level of IgG anti-A. actinomycetemcomitans antibody and the frequency of teeth infected until nearly 13 teeth demonstrated an infection. Furthermore, the results showed a generally negative relationship between the antibody level and the burden of A. actinomycetemcomitans in the infected sites. Interproximal sites associated with first molar teeth were the predominant sites for subgingival colonization; incisors were also frequently infected in this population. The first molar teeth also exhibited the greatest level of A. actinomycetemcomitans, while the incisors demonstrated a high level of A. actinomycetemcomitans in individual sites. The results clearly indicated the majority of the sites sampled were colonized by a single serotype of A. actinomycetemcomitans. We detected A. actinomycetemcomitans nearly 2 x times more frequently and a significant increase in the proportion of A. actinomycetemcomitans was found in samples obtained from teeth with bleeding on probing. The results also showed a significant trend for both pocket depth and attachment levels to be related to the presence and proportion of A. actinomycetemcomitans in the subgingival plaque. These findings detail the microbiological, immunological and clinical characteristics of a unique subset of periodontitis patients that appear to exhibit disease associated (caused?) with A. actinomycetemcomitans infection irrespective of clinical categorization. The results support a unique distribution of this microorganism in the subgingival ecology that is related to active host immune responses and clinical presentation of the tooth.

Specific antibodies and their potential role in periodontal diseases

Periodontal diseases are thought to result from inflammatory responses to bacterial challenges in the gingival crevicular area. Antibodies are a major host-protective mechanism in many bacterial infections. Consequently, the antibody responses to suspected periodontal pathogenic bacteria have been extensively measured as to their relationship to diseases and specificity for suspected pathogens associated with progressing disease sites. Recently, studies on the bacterial immunogen characterization, antibody-subclass identification, and antibody biological capabilities have been reported. Although increased antibody levels to certain suspected periodontal pathogens were associated with periodontal diseases in humans, little evidence exists as to the role of these antibodies in the infectious process. In vivo experiments in animals indicated that specific antibodies against certain suspected periodontal pathogens were associated with suppression of bacterial colonization, limiting the spread of infection, and a decrease in alveolar bone loss. However, in vitro as well as in vivo experiments suggested that phagocytic cells are required for efficient bactericidal activity of antibodies and that the presence of other sensitized immune cells may either have inhibited or enhanced the infectivity of certain periodontal pathogens. Possible explanations for the observed inconsistencies are presented and the potential for utilization of specific anti-periodontal pathogen responses in the understanding and prevention of diseases is discussed.

Role of suspected periodontopathogens in microbiological monitoring of periodontitis

Periodontal disease is the clinical result of a complex interaction between the host and plaque bacteria. Although a specificity to some degree is found for Actinobacillus actinomycetemcomitans in localized juvenile periodontitis (LJP), it has been difficult to obtain evidence for a specific etiological role of the bacteria associated with periodontal disease in adults. What we see is the net result of host-parasite interactions which in an unpredictable moment accumulate and exceed the threshold of tissue integrity. This hypothesis is concomitant with the view of periodontal disease as a polymicrobial infection, predominantly anaerobic, which occurs commonly in the oral cavity or elsewhere in the body. Some micro-organisms (risk markers) occur more frequently than others and may significantly determine the outcome of this host-parasite interaction. Microbiological sampling and analysis seem to be of limited value in risk assessment; however, they can be used as tools in diagnosis in LJP patients and acute infections, and in treatment decision and therapy control in "refractory" patients. Suspected pathogens (risk markers) are Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, and some species of spirochetes, while the roles of Prevotella intermedia, Bacteroidesforsythus, Fusobacterium nucleatum, Campylobacter rectus, and Peptostreptococcus micros are more uncertain. The presence of periodontopathogens as well as enterics, Staphylococcus aureus and Candida especially, should be considered in patients with systemic individual disorders--e.g., diabetes mellitus, neutropenia, agranulocytosis, and AIDS--or with implants.

Campylobacter rectus in human periodontitis

Campylobacter rectus (formerly Wolinella recta) in periodontitis lesions was studied relative to age and sex distribution, relationship to disease-active periodontitis, response to periodontal debridement and in vitro antimicrobial susceptibility. Subgingival C. rectus was collected with paper points, transported in VMGA III and plated onto nonselective enriched brucella blood agar and Hammond's selective medium for C. rectus, both incubated anaerobically. C. rectus was recovered from 80% of 1654 periodontitis patients. Although the organism showed similar age and sex occurrence, its proportional recovery in culture-positive adults was inversely related to increasing age (r = 0.999, P < 0.001). The organism was positively associated (summary odds ratio = 2.95) with disease activity in a 24-month longitudinal study of 93 adult periodontitis patients on maintenance therapy. C. rectus decreased from 8.2% to 0.7% following local periodontal debridement of 20 culture-positive adult periodontitis patients. The organism exhibited high in vitro susceptibility to therapeutic levels of tetracycline hydrochloride, metronidazole, penicillin G and ciprofloxacin. These findings further delineate the epidemiology and potential pathogenic role of C. rectus in human periodontitis.

Killing of Actinobacillus actinomycetemcomitans and Haemophilus aphrophilus by human polymorphonuclear leukocytes in serum and saliva

The ability of polymorphonuclear leukocytes from human peripheral blood to kill Actinobacillus actinomycetemcomitans and Haemophilus aphrophilus was examined with fresh isolates and laboratory strains from each species (5 strains within each group) under different conditions. Bacterial cells were mixed with a polymorphonuclear leukocyte suspension in the presence of either active serum or heat-inactivated serum or active serum together with sterile-filtered saliva. Surviving bacteria were determined by counting the number of bacterial colony-forming units in the mixtures after a 60-min incubation at 37 degrees C. Mixtures without polymorphonuclear leukocytes served as controls for the evaluation of the degree of killing of the bacteria. In general, A. actinomycetemcomitans resisted phagocytic killing to a greater extent than H. aphrophilus, and the killing of the former species mainly depended on the presence of heat-labile serum components, probably complement factors. Laboratory strains of A. actinomycetemcomitans were more easily killed than fresh isolates. The presence of saliva in the reaction mixtures decreased the degree of killing. However, strain-dependent variations in the killing were found under either condition. The leukotoxic activity of A. actinomycetemcomitans strains, determined by a [51Cr]-release assay, was not correlated with the resistance of these strains to the phagocytic killing. The results point out a strain-dependent difference in the ability of A. actinomycetemcomitans to evade the inflammatory response associated with polymorphonuclear leukocytes. This difference may constitute a potential virulence factor for this periodontopathogen. Furthermore, the leukotoxicity of the strains is not the main determinant that modifies the interaction of A. actinomycetemcomitans with human neutrophils.

Significance of serum antibody against surface antigens of Actinobacillus actinomycetemcomitans in patients with adult periodontitis

This study was undertaken to examine the prevalence of Actinobacillus actinomycetemcomitans, its serotype distribution and the serum immune responses against its surface antigens in 41 Japanese patients with adult periodontitis. The dominant A. actinomycetemcomitans serotype isolated was serotype c. Immunoblot analysis of 3 serotypes of A. actinomycetemcomitans-sonicated antigens and the patient sera revealed that the reactivities with serotype c were the most frequent and that heat-stable surface serotype-specific antigen appeared to be immunodominant. Elevated serum immunoglobulin G titers to extracted lipopolysaccharide and fimbriae antigen of A. actinomycetemcomitans were noted for the patient sera by enzyme-linked immunosorbent assay. High serum immunoglobulin G titers to the fimbriae antigen detected in patients without cultivable A. actinomycetemcomitans suggested the possibility that the elicited antibody to the antigen played a role in eliminating A. actinomycetemcomitans from the periodontal lesions.

Characteristics and utilization of antibody measurements in clinical studies of periodontal disease

The detection and quantitation of immune responses to infections have long been used as a diagnostic tool in medical infections. Recently, increasing evidence has supported that active, specific antibody responses to selected members of the subgingival microbiota are noted in periodontitis patients. This report describes the various specificities of this antibody as they relate to periodontitis classification and prognosis. The functional aspects of the serum antibody have come under increasing scrutiny to understand better the potential immunologic mechanisms acting in the periodontium. Data are available that describe opsonizing potential, complement fixing ability, blocking functions, and anti-toxic capacity for the antibody. Longitudinal alterations in specific antibody levels are shown to relate to infection and accompany changes in the burden of a specific microorganism in the subgingival plaque. Thus, these antibody changes could be useful indicators of altered host-parasite interactions that presage a disease-active episode. Finally, studies were designed to examine the ability of antibody to reflect the effects of treatment on the disease. The results indicated that specific antibody levels change with mechanical, antimicrobial, and anti-inflammatory treatments. The findings described in this report suggest that evaluation of the level and specificity of serum antibody can be a beneficial adjunct in designing and implementing clinical studies delineating the initiation, progression, and treatment of periodontitis.

The immunodominant outer membrane antigen of Actinobacillus actinomycetemcomitans is located in the serotype-specific high-molecular-mass carbohydrate moiety of lipopolysaccharide

Most patients with juvenile periodontitis manifest serum antibodies, sometimes at very high titers, to antigens of Actinobacillus actinomycetemcomitans, but the antigens inducing the immune response have been only partly characterized. We separated A. actinomycetemcomitans serotype b cells into protein, lipopolysaccharide (LPS), and soluble polysaccharide fractions and characterized them. Coomassie blue- and silver-stained sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels were used to detect protein and LPS components, and gas-liquid chromatography was used to determine their carbohydrate and fatty acid composition. Western blots, dot blots, and enzyme-linked immunosorbent assay inhibition with high-titer sera from juvenile periodontitis patients revealed which components were highest in antibody binding activity. These results showed that the major portion of the immunoglobulin G binding activity resides in the purified mannan-free LPS, with lesser amounts in the total protein fraction. Using Sephacryl S-300 chromatography, we separated LPS into high-molecular-mass components with high carbohydrate contents by gas-liquid chromatography and a low-molecular-mass component consisting mainly of lipid A and the inner core sugar heptulose. The results of quantitative dot blot assays and enzyme-linked immunosorbent assay inhibition show that the serotype-specific antibody binding activity is highly concentrated in the high-molecular-mass carbohydrate-rich LPS fraction and is almost completely absent in the low-molecular-weight lipid-rich fraction. Our observations contrast with previous reports that the predominant serotype antigen of A. actinomycetemcomitans resides in a mannan-rich polysaccharide isolated from spent culture medium. These observations support the conclusion that the immunodominant antigen of the outer membrane is the O antigen of the LPS.

New views on periodontal microbiota in special patient categories

The microorganisms in periodontitis of special patient categories have been only partially elucidated. The periodontitis microbiota of HIV-infected individuals, cancer patients on myelosuppressive therapy, and persons with other medical disorders includes common suspected periodontal pathogens as well as enteric rods, pseudomonads, staphylococci and yeasts. Failing implants also may be associated with classical periodontal pathogens as well as primarily nonoral potential pathogens. Refractory periodontitis in systemically healthy adults can show a great variety of oral and nonoral organisms. The frequent occurrence of unusual periodontal organisms in special patient categories may be due to a weakened host response and/or usage of various chemotherapeutic regimens. The unusual organisms may contribute to progressive periodontitis and in leukemia patients may even give rise to life-threatening systemic manifestations. The primary therapeutic goal in special periodontitis patients is control of pathogens and amid the wide range of pathogenic microfloras, an effective treatment strategy should include a comprehensive microbiological analysis, especially if systemic antimicrobial therapy is contemplated.

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 antibody in Actinobacillus actinomycetemcomitans-infected patients with periodontal disease

This study was designed to (i) delineate the characteristics of serum antibody responses to Actinobacillus actinomycetemcomitans in patients with periodontitis who are infected with A. actinomycetemcomitans; irrespective of disease classification; (ii) assess the relationship of the elevated antibody levels to colonization of the oral cavity by A. actinomycetemcomitans; and (iii) describe the serotype distribution of A. actinomycetemcomitans and antibodies to the microorganism in infected patients with various clinical classifications. To compare the levels of various isotype-specific antibodies to the different antigens, studies were performed that allowed quantitation of each isotype-specific antibody in a human reference standard. By using this reference standard, it was shown that the levels of immunoglobulin G (IgG), IgM, and IgA responses to A. actinomycetemcomitans were similar among the infected patients, irrespective of disease classification. Also, we demonstrated that the serum antibody response to serotype b was quantitatively greater in all isotypes. Our findings indicate that b was the most frequent A. actinomycetemcomitans serotype detected in the patients and appears to be capable of initiating a substantial serum IgG antibody response that may contain cross-reactive antibodies to other serotypes of A. actinomycetemcomitans. Generally, in cases in which the response to a single serotype was elevated, only that type of A. actinomycetemcomitans was detected in the plaque. Individuals exhibiting elevated antibodies to multiple serotypes were most consistently colonized by the serotype b microorganism. This study represents the first report detailing the distribution of IgG subclass antibodies to A. actinomycetemcomitans in periodontal disease. The results demonstrated that the primary responses of patients with periodontitis to A. actinomycetemcomitans were of the IgG1 and IgG3 subclasses, which is consistent with elicited responses to protein antigens. In contrast, the primary subclass response in normal subjects was limited to the IgG2 subclass and may represent broader cross-reactivity to polysaccharide antigens-lipopolysaccharide from the bacteria.

Antigens of Actinobacillus actinomycetemcomitans recognized by patients with juvenile periodontitis and periodontally normal subjects

Most juvenile periodontitis patients respond to infection by Actinobacillus actinomycetemcomitans by producing serum antibodies. Specific antigens inducing the humoral immune response have not been identified, nor has the role of the resulting antibodies in disease progression been determined. Adsorbed and unadsorbed sera from juvenile periodontitis patients and normal subjects were analyzed by enzyme-linked immunosorbent assay and Western blots (immunoblots), using digested and undigested bacterial sonicates and French pressure cell fractions to determine the biochemical class, cross-reactivity, and cellular location of the antigens in different A. actinomycetemcomitans serotypes. Antigens detected by using high-titer sera included the following: (i) serotype-specific nonprotein material located on the cell surface, (ii) soluble-fraction proteins showing highly variable antibody binding, (iii) cross-reactive proteins, and (iv) a protein present in soluble and cell wall fractions and immunopositive for all sera tested. In addition, one apparently nonprotein component that was enriched in the cell wall fraction was observed. Sera with high immunoglobulin G titers to one, two, three, or none of the three A. actinomycetemcomitans serotypes were observed. There was a high degree of variation from one patient to another in the humoral immune response to serotype-specific and cross-reactive antigens. As demonstrated by whole-cell adsorption experiments, the serotype-specific surface antigen accounted for approximately 72 to 90% of the total antibody-binding activity for sera with titers greater than 100-fold above background, while cross-reactive antigen accounted for less than 28%. Antibody binding the whole-cell sonicate for high-titer sera was inhibited 90% by lipopolysaccharide from the same serotype, strongly suggesting that lipopolysaccharide is the immunodominant antigen class.

Microbiological study of HIV-related periodontitis

The subgingival microbiota in 14 persons with HIV-periodontitis was examined. Subgingival plaque samples were collected with paper points, transported in VMGA III, and plated on anaerobic enriched brucella blood agar and various selective media. HIV-periodontitis sites revealed Actinobacillus actinomycetemcomitans, Wolinella recta, Peptostreptococcus micros, and Bacteroides intermedius, each averaging 7% to 16% of the cultivable subgingival flora in positive patients. High levels of spirochetes also were detected in diseased sites with phase-contrast microscopy. Low levels of Candida albicans or enteric Gram-negative rods were recovered in the subgingival flora in 7 HIV-periodontitis patients or Bacteroides fragilis, Fusobacterium necrophorum, Fusobacterium varium, and Eubacterium aerofaciens were recovered in 8 patients. These findings suggest that the major components of the subgingival microbial flora in HIV-periodontitis are similar to those associated with adult periodontitis in systemically healthy persons. However, HIV-periodontitis lesions also may contain organisms which are rarely found in common types of periodontitis. The etiological significance of specific periodontal organisms in HIV-periodontitis awaits further longitudinal study.

Repair potential in localized juvenile periodontitis. A case in point

An aggressive form of localized juvenile periodontitis (LJP) in a 12-year old West African female is reported. The case was treated with scaling, root planing, debridement, and tetracycline therapy, which resulted in complete resolution of the disease, including elimination of periodontal inflammation, regeneration of lost periodontal structures, and spontaneous repositioning of teeth that had pathologically migrated. A hopelessly involved mandibular right first molar was successfully replaced by an incompletely developed maxillary third molar tooth bud whose roots and pulp structure continued to develop after autotransplantation. It is suggested, that LJP can be successfully treated without periodontal surgery and that the potential for repair in LJP cases is apparently greater than what one can anticipate in adult forms of periodontitis.

Molecular approaches to leucotoxin as a virulence component in Actinobacillus actinomycetemcomitans

A strategy has been developed to examine the hypothesis that leucotoxin is a critical virulence factor of Actinobacillus actinomycetemcomitans in a non-human primate (Macaca fascicularis). Firstly the leucotoxin gene from A. actinomycetemcomitans was cloned and sequenced. This DNA contained a functional leucotoxin gene, as protein extracts of Escherichia coli with the cloned sequences lysed appropriate human cell lines. The protein encoded by lktA shared at least 42% identity with P. haemolytica leucotoxin and with the alpha-haemolysins from E. coli and A. pleuropneumoniae. The lktA gene of A. actinomycetemcomitans was linked to another gene, lktC, which is thought to be related to the LktC proteins from these other bacteria and with which it shared at least 49% amino acid identity. Despite the overall homology to the other leucotoxins/haemolysins, the LktA from A. actinomycetemcomitans has several unique properties including a very basic pI of 9.7, as compared to pIs approx. 6.2 for lktA proteins in other bacteria. Using the cloned genes as probes produced evidence that a TOX- strain contains the leucotoxin gene but fails to transcribe it at high levels. The second avenue of investigation was to develop methods for examining the humoral immune responses in the monkey to bacterial toxins such as lktA. A. actinomycetemcomitans was detected in subgingival plaque samples from approx. 40% of the animals. A. actinomycetemcomitans comprised less than 1% to 9% of the flora. Most A. actinomycetemcomitans isolates were serotype b and each of the monkeys had serum IgG antibody to A. actinomycetemcomitans serotype b (generally considered to be lktA-producing strains). An ELISA was developed to examine the isotype/subclass distribution, level and avidity of serum antibody in the monkey following parenteral immunization with a prototype bacterial exotoxin (tetanus toxoid). IgG1 and IgG3 antibody predominated over IgG2 and IgG4 after primary immunization. Secondary immunization elicited enriched IgG1 and IgG4 responses. Primary immunization increased avidity indices of IgG to tetanus toxoid from approx. 0.9 (baseline) to a mean of 1.72 and secondary immunization significantly increased the avidity index to 2.56.

Actinobacillus actinomycetemcomitans serotypes and leukotoxicity in Korean localized juvenile periodontitis

Actinobacillus actinomycetemcomitans is though to play an important role in the pathogenesis of localized juvenile periodontitis (LJP). Preliminary data suggested that the serotype distribution of A. actinomycetemcomitans in Korea and the United States differ. This study evaluated A. actinomycetemcomitans prevalence, serotype distribution, and leukotoxicity in Korean LJP patients by culture, enzyme-linked immunosorbent assay, indirect immunofluorescence, and lactate dehydrogenase release from polymorphonuclear leukocytes exposed to A. actinomycetemcomitans. A. actinomycetemcomitans occurred in 75% of LJP lesions and 6% of normal sites with approximately equal distribution of serotype a, b, and c. Single serotypes were isolated from nine patients while three patients harbored two serotypes either in the same or different disease sites. A. actinomycetemcomitans leukotoxicity occurred in 22% isolates with a 69% prevalence. Individual sites harbored both leukotoxic and non-leukotoxic strains with no serotype association. The distribution of serotypes and leukotoxic strains of A. actinomycetemcomitans in Korean LJP patients differed from those reported in the United States. This suggests that serotype b may not be more important in the pathogenesis of LJP.

Opsonic IgG antibody against Actinobacillus actinomycetemcomitans in localized juvenile periodontitis

Actinobacillus actinomycetemcomitans is a gram-negative bacterium frequently recovered from periodontal lesions of patients with localized juvenile periodontitis (LJP). Elevated levels of serum IgG and IgM antibodies to A. actinomycetemcomitans antigens are frequently observed in LJP patients, although the functional properties of such antibodies have not been characterized systematically. In this study, we analyzed serum from LJP subjects infected with A. actinomycetemcomitans with respect to the presence of IgG antibodies expressing opsonic, bactericidal and/or leukotoxin-neutralizing activity against this organism. The IgG fractions obtained from serum of 3 LJP patients with elevated antibody titers to A. actinomycetemcomitans contained opsonic activity against a non-leukotoxic Y4 strain, as well as for a highly leukotoxic JP2 strain. Opsonic activity required the presence of complement. The IgG fractions of pooled normal serum and serum from a fourth LJP subject with minimal ELISA-reactive IgG antibody against this organism lacked detectable opsonic activity. Leukotoxin-neutralizing IgG antibodies, although variably present, did not influence neutrophil killing of the leukotoxic JP2 strain. None of the sera tested contained bactericidal IgG antibodies capable of promoting direct complement-mediated killing of A. actinomycetemcomitans. These results indicate that LJP subjects infected with A. actinomycetemcomitans are capable of producing opsonic IgG antibodies which may facilitate neutrophil-mediated host defense against this periodontopathic organism.

The predominant cultivable microbiota of crevicular epithelial cells

The purpose of the present investigation was to compare the composition of the predominant cultivable microbiota associated with gingival crevicular epithelial cells with that of the unattached microbiota recovered from the same site. Samples were taken from 2 diseased sites from 8 periodontal patients, by scraping the epithelial lining of the pocket with a curette. The epithelial cells were separated from the unattached subgingival bacteria by centrifugation in a reduced 50% Percoll density gradient. Epithelial cells formed a band at the top of the gradient and were removed separately from the unattached bacteria located at the base. Each layer was dispersed, diluted and plated on Trypticase soy agar with 5% sheep blood and 50 isolates were characterized from each sample. The microorganisms associated with the epithelial layer harbored 5- to 20-fold higher mean percentages of Bacteroides gingivalis, Bacteroides intermedius and Peptostreptococcus micros. The layer of unattached organisms exhibited 4- to 10-fold higher mean percentages of Streptococcus uberis, Capnocytophaga ochracea, Eikenella corrodens and Veillonella parvula.

Intra-oral colonization of macaque monkeys by Actinobacillus actinomycetemcomitans

Actinobacillus actinomycetemcomitans was acquired by captive Macaca fascicularis 3 to 6 months after birth, and all monkeys aged over 6 months harbored detectable levels. This microorganism was most frequently isolated from the gingival plaque of the incisor (and other) teeth compared with other oral sites. Strains were leukotoxic by bioassay and Western blot analysis. Antibodies in macaque serum contained neutralized the leukotoxin of a human A. actinomycetemcomitans strain. High titres of maternal neutralizing anti-leukotoxin antibodies were detected in neonates; the titre then fell rapidly so that by 6 months the antibody titer was zero. Antileukotoxin antibody production was detected after 6 months of age, rapidly reaching a high level within 2 years after birth. The presence of leukotoxic strains of A. actinomycetemcomitans in the gingival region did not appear to be correlated with an increase in susceptibility to periodontal disease.

Outer membranous vesicles and leukotoxic activity of Actinobacillus actinomycetemcomitans from subjects with different periodontal status

Strains of A. actinomycetemcomitans (A.a) from juvenile periodontitis patients (JP), adult periodontitis patients (AP), and 14-yr-old healthy children were tested for the correlation between leukotoxin activity and the number of outer membranous vesicles measured in electron micrographs. To determine the potential for connective tissue destruction following the interaction of polymorphonuclear leukocytes (PMN) with the bacteria, the lysosomal release of neutrophil elastase was assessed. The highest potential to kill leukocytes and to release lysosomal elastase from them was observed in the strains isolated from JP patients. No correlation existed between leukotoxic activity and the number of outer membranous vesicles per bacterium when the data from A.a. strains from all sources were combined. Furthermore, no significant differences were found between the numbers of outer membranous vesicles in the three groups tested. The only significant correlation between the number of vesicles and leukotoxicity was found in the A.a. strains derived from the mouths of healthy children.