Evidence of a substantial genetic basis for IgG2 levels in families with aggressive periodontitis.

IgG2 is elevated in localized but not in generalized aggressive periodontitis (AgP). Exposure to pathogenic bacteria is essential for disease. Immune responses are dominated by IgG2 reactive with bacterial surface carbohydrates. We used variance component analyses to assess IgG2 heritability and determine whether genes that influence IgG2 are the same genes that influence disease susceptibility. We studied 17 Caucasian and 43 African American families with two or more localized or generalized AgP-affected members (274 subjects with IgG2 measurements). Only 16% of the variance in IgG2 was attributable to age, race, and smoking. Even with the addition of localized AgP, the model still explained only 19% of IgG2 variance. By contrast, heritability of IgG2 levels was estimated to be 38% and highly significant (P = 0.0006), demonstrating a substantial genetic basis. Bi-trait variance component analyses of IgG2 and quantitative measures of AgP indicate that different genes appear to control IgG2 levels and disease susceptibility.

The genetic relatedness of Porphyromonas gingivalis clinical and laboratory strains assessed by analysis of insertion sequence (IS) element distribution.

OBJECTIVES: Porphyromonas gingivalis is frequently found in periodontitis lesions. This organism contains a large number of insertion sequence (IS) elements. We sought to determine the distribution of seven IS elements from strain W83 among nine P. gingivalis laboratory strains and nine clinical isolates and to use these findings to determine strain relationships. METHODS: Southern blots of BamHI digested genomic DNA digests were probed with insertion sequence elements ISPg1-7. RESULTS: The restriction fragment length polymorphism (RFLP) patterns revealed that five of the nine laboratory strains, including strain W83, were nearly identical for all seven IS elements. Two of nine clinical isolates were similar to the five laboratory strains. Two of the four remaining laboratory strains had similar or identical RFLP patterns. The remaining two laboratory strains had limited similarity to clinical strains. Four of the clinical isolates had identical RFLP patterns for all seven IS elements. The three remaining clinical isolates were unique in their RFLP patterns. Several strains lacked from one to four of the IS elements. Similar strain relationships were suggested regardless of the IS element examined. CONCLUSIONS: Transposition and recombination between IS elements are not sufficiently pervasive to obscure strain relationships, though this does not preclude the possibility that such events play an important role in allowing P. gingivalis to adapt to new environments. Given the level of genetic diversity observed, it may be especially important to examine genetically diverse strains when drawing conclusions based on the W83 P. gingivalis genomic database.

Evidence of a substantial genetic basis for risk of adult periodontitis.

BACKGROUND: A few previous studies have suggested that risk for adult periodontitis (AP) has a genetic (heritable) component. We estimated genetic and environmental variances and heritability for gingivitis and adult periodontitis using data from twins reared together. METHODS: One hundred seventeen (117) pairs of adult twins (64 monozygotic [MZ] and 53 dizygotic [DZ] pairs) were recruited. Probing depth (PD), attachment loss (AL), plaque, and gingivitis (GI) were assessed on all teeth by two examiners. Measurements were averaged over all sites, teeth, and examiners. Extent of disease in subjects was defined at four thresholds: the percentage of teeth with AL > or = 2, AL > or = 3, PD > or = 4, or PD > or = 5 mm. Genetic and environmental variances and heritability were estimated using path models with maximum likelihood estimation techniques. RESULTS: MZ twins were more similar than DZ twins for all clinical measures. Statistically significant genetic variance was found for both the severity and extent of disease. AP was estimated to have approximately 50% heritability, which was unaltered following adjustments for behavioral variables including smoking. In contrast, while MZ twins were also more similar than DZ twins for gingivitis scores, there was no evidence of heritability for gingivitis after behavioral covariates such as utilization of dental care and smoking were incorporated into the analyses. CONCLUSIONS: These results confirm previous studies and indicate that approximately half of the variance in disease in the population is attributed to genetic variance. The basis for the heritability of periodontitis appears to be biological and not behavioral in nature.

Characterization of Porphyromonas gingivalis insertion sequence-like element ISPg5.

Porphyromonas gingivalis, a black-pigmented, gram-negative anaerobe, is found in periodontitis lesions, and its presence in subgingival plaque significantly increases the risk for periodontitis. In contrast to many bacterial pathogens, P. gingivalis strains display considerable variability, which is likely due to genetic exchange and intragenomic changes. To explore the latter possibility, we have studied the occurrence of insertion sequence (IS)-like elements in P. gingivalis W83 by utilizing a convenient and rapid method of capturing IS-like sequences and through analysis of the genome sequence of P. gingivalis strain W83. We adapted the method of Matsutani et al. (S. Matsutani, H. Ohtsubo, Y. Maeda, and E. Ohtsubo, J. Mol. Biol. 196:445-455, 1987) to isolate and clone rapidly annealing DNA sequences characteristic of repetitive regions within a genome. We show that in P. gingivalis strain W83, such sequences include (i) nucleotide sequence with homology to tRNA genes, (ii) a previously described IS element, and (iii) a novel IS-like element. Analysis of the P. gingivalis genome sequence for the distribution of the least used tetranucleotide, CTAG, identified regions in many of the initial 218 contigs which contained CTAG clusters. Examination of these CTAG clusters led to the discovery of 11 copies of the same novel IS-like element identified by the repeated sequence capture method of Matsutani et al. This new 1,512-bp IS-like element, designated ISPg5, has features of the IS3 family of IS elements. When a recombinant plasmid containing much of ISPg5 was used in Southern analysis of several P. gingivalis strains, including clinical isolates, diversity among strains was apparent. This suggests that ISPg5 and other IS elements may contribute to strain diversity and can be used for strain fingerprinting.

Antibody reactive with Porphyromonas gingivalis serotypes K1-6 in adult and generalized early-onset periodontitis.

BACKGROUND: Six serotypes of Porphyromonas gingivalis have recently been described. We sought to test the hypothesis that serotype specific carbohydrates from these strains are important antigens that elicit potent immune responses. METHODS: Serum concentrations of IgG reactive with P. gingivalis serotypes K1-K6 were determined for 28 adult (AP) and 28 generalized early-onset (G-EOP) periodontitis patients previously determined to be seropositive for a broken cell preparation of P. gingivalis. To confirm relationships suggested for K1, K2, and K6 in the analysis of initial data, the study population was increased to 133. RESULTS: Frequency of seropositivity for the 6 serotypes ranged from 26 to 54% of subjects. IgG concentrations ranged from 0 to 453 microg/ml with many subjects seropositive to more than one serotype. Concentrations for the subset of patients who was seropositive were high (mean responses ranged from 20 to 105 microg/ml for the 6 serotypes). Significant correlations between seropositivity to serotypes K1 and K5 as well as between K5 and K6 were found. CONCLUSIONS: We examined the relationship of diagnosis, race, gender, smoking, probing depth, attachment loss, and antibody reaction with the P. gingivalis serotypes by analysis of variance. Initial findings suggested potential relationships between diagnosis, smoking, race, gender, and antibody reactive with serotypes K1, K2, and K6. A significant relationship did exist between smoking and decreased antibody reactive with P. gingivalis serotype K2. No other relationships were substantiated. We also examined the IgG subclass distribution and found that responses were almost exclusively IgG2. These data support the concept that antibody responses to all 6 serotypes are common in both AP and G-EOP and that these K serotype carbohydrates elicit potent IgG2 responses.

Linkage disequilibrium of interleukin-1 genetic polymorphisms with early-onset periodontitis.

BACKGROUND: Genetic polymorphisms at interleukin (IL)-1alpha and IL-1beta were recently suggested to be associated with severity of adult periodontitis. We evaluated whether these polymorphisms might also be associated with early-onset periodontitis (EOP) in 28 African American families and 7 Caucasian American families with 2 or more affected members. METHODS: Genomic DNA from peripheral blood was amplified, followed by restriction endonuclease digestion and acrylamide gel electrophoresis to distinguish alleles of different fragment sizes. Genetic epidemiological methods suitable for family data were used that are robust to false-positive findings due to mismatching of cases and controls or mixed subpopulations of different ethnic or geographic origin. The 2 major EOP subtypes, localized juvenile periodontitis (LJP), and generalized early-onset periodontitis (G-EOP, encompassing rapidly progressive periodontitis and generalized juvenile periodontitis), were analyzed both separately and together. RESULTS: We obtained highly significant evidence of linkage disequilibrium for both African American and Caucasian G-EOP subjects. A similar trend was noted for LJP. The IL- alleles associated with high risk of EOP had been suggested previously to be correlated with low risk for severe adult periodontitis. Disequilibrium with G-EOP was equally strong for smoking and non-smoking subjects. IL-1alpha and IL-1beta polymorphisms were in strong disequilibrium with each other in Caucasians, but not in African Americans. Haplotype analyses evaluating both polymorphisms simultaneously indicated that the IL-1beta variant is likely to be most important for EOP risk. Sibpair linkage analyses, by contrast, provided only marginal support for a gene of very major effect on EOP risk attributable to these IL-1 polymorphisms. CONCLUSIONS: Recent theoretical analyses indicate that our findings are most consistent with an interpretation of EOP as a complex, oligogenic disorder, with IL-1 genetic variation contributing an important but not exclusive influence on disease risk.

The effect of smoking on serum IgG2 reactive with Actinobacillus actinomycetemcomitans in early-onset periodontitis patients.

High titers of serum IgG2 reactive with Actinobacillus actinomycetemcomitans are present in early-onset periodontitis (EOP) patients and it appears that anti-A. actinomycetemcomitans may be protective. Smoking is associated with increased periodontal disease severity in generalized early-onset periodontitis (G-EOP) patients, but is not associated with periodontal disease severity in patients with localized juvenile periodontitis (LJP). Furthermore, smoking is associated with reduced serum IgG2 levels in black patients with G-EOP but not in those with LJP. Based on this selective effect of smoking, we hypothesized that smoking would be associated with a reduction of specific IgG2 reactive with A. actinomycetemcomitans in black G-EOP patients but not black LJP patients. In addition, we examined IgG2 responses to carbohydrate antigens from non-periodontal pathogens including Haemophilus influenzae b oligosaccharide antigen (Hib) and the Streptococcus pneumoniae antigen phosphocholine (PC). Smoking status was assessed from serum cotinine levels, and IgG2 specific for A. actinomycetemcomitans, Hib, and PC was assessed by ELISA. Our study revealed that smoking was correlated with a dramatic reduction in serum IgG2 anti-A. actinomycetemcomitans in G-EOP smokers but not in LJP smokers. In contrast, anti-Hib IgG2 and anti-PC IgG2 were not affected in either G-EOP or LJP patients. In short, these results indicate that smoking is associated with a reduction in serum IgG2 anti-A. actinomycetemcomitans in black G-EOP subjects, but IgG2 reactive with other antigens may not be reduced in G-EOP smokers.

Heterogeneity of antibodies reactive with the dominant antigen of Actinobacillus actinomycetemcomitans.

The serotype b-specific carbohydrate antigen (SbAg) of Actinobacillus actinomycetemcomitans Y4 is reported to be the O antigen of lipopolysaccharide, and the highest titers of serum antibody reactive with A. actinomycetemcomitans in early-onset periodontitis (EOP) patients bind SbAg. These high titers of serum antibody reactive with SbAg are associated with a lesser extent and severity of periodontal disease. The aim of this study was to determine if a limited number of genes code for anti-SbAg antibodies as has been shown for immunoglobulin G (IgG) reactive with the type b polysaccharide from Haemophilus influenzae. Serum IgG reactive with the SbAg was prepared from 20 high-titer EOP patients by affinity chromatography. The IgG subclass concentrations were determined, and heterogeneity was analyzed by isoelectric focusing (IEF). IgG2 was the dominant subclass (83% of total IgG) in the anti-SbAg IgG fraction and represented an average of 1.33% of total serum IgG2. The IgG2 reactive with SbAg was isolated from the affinity-purified IgG fraction by affinity chromatography with protein A and subclass-specific monoclonal antibodies. On IEF gels, only 4 to 20 bands were observed in the anti-SbAg IgG fractions, indicating limited heterogeneity. N-terminal amino acid sequence analysis of eight representative anti-SbAg IgG2 preparations indicated that variable heavy and light chains consisted largely of V(H)III and V(kappa)II, respectively. However, a significant fraction of anti-SbAg may use V(H) and V(lambda) genes with blocked N termini. In short, these findings indicate that IgG reactive with SbAg is very much like the antibody reactive with H. influenzae type b polysaccharide. Similarities include IgG2 dominance, limited bands on IEF gels, supporting an oligoclonal response, and use of genes from V(H)III and V(kappa)II regions.

A comparison of IgG antibody reactive with Bacteroides forsythus and Porphyromonas gingivalis in adult and early-onset periodontitis.

Recent work has indicated that Bacteroides forsythus and Porphyromonas gingivalis are significant local risk factors for periodontitis. Several reports find that both organisms are frequently associated with periodontitis lesions and often are present together. We have previously shown that early-onset periodontitis patients seropositive for P. gingivalis have less attachment loss than seronegative patients. In this study, we determined serum IgG antibody concentrations reactive with B. forsythus in adult and early-onset periodontitis patients using an ELISA and used P. gingivalis in the same populations as a positive control. The results for P. gingivalis were consistent with previous work and indicated that 47%, 36%, and 33% of adult, generalized early-onset, and localized juvenile patients were seropositive, respectively. Mean serum IgG concentrations for the three groups were 5.36 microg/ml, 5.65 microg/ml, and 5.44 microg/ml for adult, generalized early-onset, and localized juvenile patients, respectively. In contrast, for B. forsythus only 11%, 14%, and 10% of adult, generalized early-onset, and localized juvenile patients were seropositive, with mean serum IgG concentrations of 0.46 microg/ml, 0.46 microg/ml, and 0.47 microg/ml, respectively. This suggests that B. forsythus is either poorly immunogenic or less invasive than P. gingivalis. If most patients fail to mount an immune response to B. forsythus and it is invasive, it may explain why this organism is a risk factor for disease.

Antibody reactive with Actinobacillus actinomycetemcomitans leukotoxin in early-onset periodontitis patients.

The objective of this study was to determine whether a relationship exists between antibody reactive with the Actinobacillus actinomycetemcomitans leukotoxin and the severity of periodontal disease. Serum concentrations of antibody reactive with the leukotoxin were determined for 119 early-onset periodontitis patients and 59 non-periodontitis subjects using limiting dilution analysis on Western blots. Immunoglobulin G (IgG) antibody reactive with the A. actinomycetemcomitans leukotoxin ranged from undetectable to 29 micrograms/ml (mean = 3.13 +/- 0.97 micrograms/ml for the generalized early-onset periodontitis and 2.17 +/- 0.86 micrograms/ml for the localized juvenile periodontitis patients vs 0.32 +/- 0.24 ng/ml for 59 non-periodontitis controls), and the dominant subclass was IgG1. Analysis of the relationship between antibody reactive with A. actinomycetemcomitans sonicate, A. actinomycetemcomitans leukotoxin and attachment loss patterns indicates that seropositive generalized early-onset periodontitis patients had decreased attachment loss compared with patients lacking this antibody. The statistical relationship appeared to be stronger for the sonicate than the purified leukotoxin. These data suggest that antibody reactive with A. actinomycetemcomitans leukotoxin may be protective in early-onset periodontitis, but given that the sonicate appeared better than the leukotoxin alone, it is not likely that leukotoxin is the only antigen of importance to host defense.

Influence of anti-Actinobacillus actinomycetemcomitans Y4 (serotype b) lipopolysaccharide on severity of generalized early-onset periodontitis.

The objective of this study was to determine if a relationship exists between antibody reactive with the Actinobacillus actinomycetemcomitans serotype b lipopolysaccharide (LPS) and severity of periodontal disease in generalized early-onset periodontitis (G-EOP). The concentration of antibody reactive with A. actinomycetemcomitans serotype b LPS was determined for 102 G-EOP subjects. Analysis of the relationship between antibody reactive with A. actinomycetemcomitans serotype b LPS and measures of periodontal attachment loss indicated that the patients with the highest concentrations of antibody reactive with A. actinomycetemcomitans serotype b LPS had significantly less attachment loss. These high-responder subjects also had anti-A. actinomycetemcomitans serotype b LPS with significantly higher relative avidity. The results suggest that antibody reactive with A. actinomycetemcomitans serotype b LPS is protective in G-EOP patients.

Genetic segregation analyses of serum IgG2 levels.

Summary : The aim of this study was to determine whether there was evidence for a genetic component in the immune response as measured by IgG2 levels. The study was motivated by our studies of early-onset periodontitis (EOP), a group of disorders characterized by rapid destruction of the supporting tissues of the teeth in otherwise healthy individuals. EOP has two subforms, localized juvenile periodontitis (LJP) and a generalized form (G-EOP). IgG2 levels are elevated in LJP but not G-EOP individuals; and African-American IgG2 levels are higher than Caucasian levels regardless of EOP status. IgG2 levels were determined in 123 EOP families and in 508 unrelated non-EOP control individuals. Segregation analysis under the regressive model approach of Bonney was used to analyze IgG2 levels for evidence of major locus segregation. After adjusting for LJP status, race, sex, and age, the best fitting model was an autosomal codominant major locus model (accounting for approximately 62% of the variance in IgG2), plus residual parent/offspring and spousal correlations. Smoking and GM23 are also known to affect IgG2 levels. If additional adjustments are made for smoking and GM23, the best-fitting model is still a codominant major locus but with no significant residual correlations.

Longitudinal assessment of early onset periodontitis.

The purpose of this study was to determine the clinical course of early onset periodontitis and to investigate factors which may influence its clinical course. For the past 15 years we have been conducting a study of families with early onset periodontitis, and have examined 142 localized juvenile periodontitis and 185 severe generalized early onset periodontitis patients. In order to study the clinical course of early onset periodontitis we recalled our subject population to determine their periodontal status. Forty (40) patients with localized early onset periodontitis (LJP) and 48 with generalized early onset periodontitis (SP) were re-examined. The time since the most recent visit for LJP patients was approximately 3 years and for SP patients almost 4 years. LJP patients who received periodontal therapy on the average gained periodontal attachment. In contrast, LJP patients who did not receive therapy lost periodontal attachment. SP patients lost periodontal attachment regardless of whether or not they had periodontal therapy. SP patients also lost an average of one tooth during the approximately 4 years of observation. LJP patients lost very few teeth with only 4 teeth being lost in 40 patients. The results of this study suggest that localized juvenile periodontitis is a stable disease in most individuals. In contrast, patients with severe generalized early onset periodontitis continued to lose both periodontal attachment and teeth.

Immunoglobulin class and subclass distribution of antibodies reactive with the immunodominant antigen of Actinobacillus actinomycetemcomitans serotype b.

The aims of this study were to determine the immunodominant antigens of Actinobacillus actinomycetemcomitans serotype b (Aab) for the different immunoglobulin (Ig) classes and subclasses and to determine the relative levels of these different Igs in serum. Seropositive early-onset periodontitis patients were sampled, and the Ig classes IgG, IgA, and IgM and subclasses IgG1, IgG2, IgG3, IgG4, IgA1, and IgA2 were studied. Reactivity with Aab antigens was assessed by using the Western blot (immunoblot) in limiting dilution analysis and radioimmunoassay with sera from 13 early-onset periodontitis subjects. A smeared antigen in the upper portion of the immunoblots, typical of high-molecular-weight LPS, was immunodominant for IgG, IgA, IgM, IgG1, IgG2, IgG3, IgA1, and IgA2. This smeared antigen was present in every patient for all of these Igs at the endpoint. A few additional antigens were also present at the endpoint in some patients, but none were present in more than half of the subjects. The distribution of antibody titers by Ig classes reactive with the Aab immunodominant antigen was IgG > IgA > IgM. The distribution of antibody titers by IgG subclass was IgG2 > IgG1 approximately IgG3. Further quantitation by radioimmunoassay revealed that the mean concentration of IgG2 (65.7 micrograms/ml) was significantly greater than that of IgG1 (8.8 micrograms/ml). The IgA subclass distribution was IgA1 >> IgA2, with IgA1 apparently being second only to IgG2. Therefore, the Aab antigen eliciting the highest antibody level in virtually all Ig classes and subclasses appeared to be lipopolysaccharide, and IgG2 was markedly elevated over all other serum Ig classes or subclasses reactive with Aab.

Immunodominant antigens of Actinobacillus actinomycetemcomitans serotype b in early-onset periodontitis patients.

Previous work with Actinobacillus actinomycetemcomitans strain Y4 (serotype b) indicates that the immunodominant antigen in high-responding patients (top 10%, 80% of which were black) is the serotype-specific antigen. In this study we examined the immunodominant antigens of A. actinomycetemcomitans strain Y4 in both black and white patients having a range of antibody titers. We sought to test the hypothesis that the immunodominant antigen in these subjects was the same antigen found in high responders. Seropositive white early-onset periodontitis (EOP) patients were selected from 99 EOP patients. Black subjects were then selected with comparable antibody titers. Double immunodiffusion and competition assays were used to determine whether reactive antibodies were A. actinomycetemcomitans serotype b-specific or whether the response was to serotype a or c. The immunodominant antigens were then determined for the patients reacting specifically to A. actinomycetemcomitans Y4 using limiting dilution analysis on Western blots. The immunodominant antigen for the A. actinomycetemcomitans Y4-specific patients appeared to be the serotype-specific carbohydrate for most subjects (19/20 or 95%, including: 13/14 black and 6/6 white patients). In conclusion, the immunodominant antigen for A. actinomycetemcomitans Y4 was the serotype-specific carbohydrate regardless of antibody titer for both black and white specifically reactive patients.

Immunodominant antigens of Actinobacillus actinomycetemcomitans serotypes a and c in high-responder patients.

This study was undertaken to examine the characteristics of the immunodominant antigens of Actinobacillus actinomycetemcomitans serotypes a and c. The top responders for A. actinomycetemcomitans serotypes a and c were selected (19 for serotype a and 21 for serotype c) from 150 clinically characterized patients. Competition assays revealed that 9 of 19 of these patients were reacting specifically to serotype a and 12 of 21 for serotype c. Limiting dilution analysis on Western blots revealed that most antigen bands apparent at low dilution disappeared as the patient's serum was diluted. The antigen band(s) remaining at the endpoint or the dilution corresponding to the antibody titer were defined as immunodominant. For serotype a there were several different immunodominant antigens but none was present in more than half of the subjects. For serotype c the immunodominant antigens included a number of discrete bands and a diffuse smeared polysaccharide band. Only 2 of these antigens were present in the majority of the high-responders: 92% had the smeared antigen and 67% had a 15 kDa antigen. The 15 kDa band was a protein common to all A. actinomycetemcomitans serotypes. The smeared antigen was unaffected by protease K treatment and gave a reaction of identity with the serotype c specific rabbit antiserum. This rabbit antiserum is specific for a mannan carbohydrate and does not react with LPS (23). Therefore, the smeared immunodominant antigen appears to be a polysaccharide containing mannan.

Immunodominant antigen of Actinobacillus actinomycetemcomitans Y4 in high-responder patients.

This study was undertaken to look for characteristics of the immunodominant antigen(s) of Actinobacillus actinomycetemcomitans Y4 that might help explain the high antibody titers in periodontitis patients. Radioimmunoassays (RIA) were performed on sera from 481 patients; sera from the 32 patients with the highest anti-Y4 titers (above 128,000 RIA U/ml) were further analyzed. Y4 antigen was boiled for 45 min or treated with papain, and antibody responses were analyzed by RIA and Western blotting (immunoblotting). In addition, carbohydrate was purified from Y4 and examined by Western blotting. The results indicated that the immunodominant antigen of Y4 in high responders was stable after papain treatment or boiling for 45 min. Papain or boiling eliminated protein bands but a large diffuse band persisted on Western blots. With increasing dilutions of sera, bands on Western blots corresponding to protein antigens disappeared, while the large diffuse band resembling that of carbohydrate persisted. Partially purified Y4 carbohydrate contained the large diffuse band. Double-immunodiffusion analysis indicated that rabbit serotype b-specific antiserum and patient sera recognized the same antigen. When the carbohydrate extract was passed over a lipid A-binding column to remove lipopolysaccharide, the smear corresponding to the immunodominant antigen was still present on Western blots. The immunodominant antigen of Y4 in high-responder individuals appears to be a carbohydrate and is possibly the capsular polysaccharide.