TLR4, NOD1 and NOD2 mediate immune recognition of putative newly identified periodontal pathogens.

Periodontitis is a polymicrobial inflammatory disease that results from the interaction between the oral microbiota and the host immunity. Although the innate immune response is important for disease initiation and progression, the innate immune receptors that recognize both classical and putative periodontal pathogens that elicit an immune response have not been elucidated. By using the Human Oral Microbe Identification Microarray (HOMIM), we identified multiple predominant oral bacterial species in human plaque biofilm that strongly associate with severe periodontitis. Ten of the identified species were evaluated in greater depth, six being classical pathogens and four putative novel pathogens. Using human peripheral blood monocytes (HPBM) and murine bone-marrow-derived macrophages (BMDM) from wild-type (WT) and Toll-like receptor (TLR)-specific and MyD88 knockouts (KOs), we demonstrated that heat-killed Campylobacter concisus, Campylobacter rectus, Selenomonas infelix, Porphyromonas endodontalis, Porphyromonas gingivalis, and Tannerella forsythia mediate high immunostimulatory activity. Campylobacter concisus, C. rectus, and S. infelix exhibited robust TLR4 stimulatory activity. Studies using mesothelial cells from WT and NOD1-specific KOs and NOD2-expressing human embryonic kidney cells demonstrated that Eubacterium saphenum, Eubacterium nodatum and Filifactor alocis exhibit robust NOD1 stimulatory activity, and that Porphyromonas endodontalis and Parvimonas micra have the highest NOD2 stimulatory activity. These studies allowed us to provide important evidence on newly identified putative pathogens in periodontal disease pathogenesis showing that these bacteria exhibit different immunostimulatory activity via TLR4, NOD1, and NOD2 (Clinicaltrials.gov NCT01154855).

Serum antibody responses to periodontal microbiota in chronic and aggressive periodontitis: a postulate revisited.

BACKGROUND: The authors revisited the 1999 International Workshop postulate of robust serum antibody responses to infecting agents in localized aggressive periodontitis (LAgP) and weak responses in generalized aggressive periodontitis (GAgP). Antibody responses were further examined in localized and generalized chronic periodontitis (LCP and GCP). METHODS: The study includes 119 patients (60 males and 59 females, aged 11 to 76 years), 18 with LAgP, 37 with GAgP, 37 with LCP, and 27 with GCP. Multiple subgingival plaque samples/patient (1,057 in total) were analyzed with respect to 11 bacterial species using checkerboard DNA-DNA hybridizations, and serum immunoglobulin (Ig)G levels were measured against the same bacteria using checkerboard immunoblotting. Further, infection ratios (antibody level over the average bacterial colonization by the homologous species) were computed for each patient. Comparisons of bacterial colonization, serum IgG levels, and infection ratios were made across the diagnostic categories using multivariable linear regression models adjusting for age and race/ethnicity. RESULTS: There were no statistically significant differences in serum IgG levels to Aggregatibacter actinomycetemcomitans among the four diagnostic categories. IgG levels to several species, including Porphyromonas gingivalis, Treponema denticola, and Campylobacter rectus, were highest in patients with GAgP and significantly different from LCP and GCP, but not from LAgP. Comparisons based on infection ratios showed no statistically significant differences for any species between GAgP and LAgP. CONCLUSION: This study provides evidence against the 1999 Workshop's postulate of weak serum antibody responses in patients with GAgP and shows that serum IgG responses in GAgP are comparable to those in LAgP, but higher than in GCP or LCP for several species.

Epigenetic regulation of TNFA expression in periodontal disease.

BACKGROUND: Tumor necrosis factor-α (TNF-α) plays a central role in the molecular pathogenesis of periodontal disease. However, the epigenetic regulation attributable to microbial and inflammatory signals at the biofilm-gingival interface are poorly understood. In this study, the DNA methylation alteration within the TNFA promoter in human gingival biopsies from different stages of periodontal disease is investigated and the regulatory mechanism of TNFA transcription by DNA methylation is explored. METHODS: Gingival biopsies were obtained from 17 patients with chronic periodontitis (CP) and 18 periodontally healthy individuals. Another 11 individuals participated in an experimentally induced gingivitis study, and gingival biopsies were collected at the baseline, induction, and resolution phase. To confirm that TNFA promoter methylation modulated TNFA transcription, THP.1 cells were treated with a DNA methyltransferase inhibitor, 5-Aza-2-deoxycytidine (5-Aza-2dC), and an RAW294.7 cell line transfected with a TNFA promoter-specific luciferase reporter system with or without methylation was used. RESULTS: In gingival biopsies from individuals with severe CP, two individual cytosine-guanine dinucleotides (CpG sites) within the TNFA promoter (at -163 and -161 bp) displayed increased methylation in CP samples compared to those with gingival health (16.1% ± 5.1% versus 11.0% ± 4.6%, P = 0.02 and 19.8% ± 4.1% versus 15.4% ± 3.6%, P = 0.04, respectively). The methylation level at -163 bp was inversely associated with the transcription level of TNFA (P = 0.018). However, no significant difference in the TNFA promoter methylation pattern was observed in samples biopsied during the induction or resolution phase of experimentally induced gingivitis, which represented a reversible periodontal lesion. THP.1 cells treated with 5-Aza-2dC demonstrated a time-dependent increase in TNFA messenger level. It was also found that the luciferase activity decreased 2.6-fold in a construct containing an in vitro methylated TNFA promoter when compared to the unmethylated insert (P = 0.03). CONCLUSION: Although the biopsy samples represented a mixed cell population, the change in promoter methylation status in chronic periodontal disease suggested that DNA methylation may be an important regulatory mechanism in controlling TNFA transcriptional expression in periodontal disease.

Toll-like receptor 4 mediates intrauterine growth restriction after systemic Campylobacter rectus infection in mice.

Campylobacter rectus is associated with fetal exposure and low birthweight in humans. C. rectus also invades placental tissues and induces fetal intrauterine growth restriction (IUGR) in mice, along with overexpression of Toll-like receptors (TLR4), suggesting that TLR4 may mediate placental immunity and IUGR in mice. To test this hypothesis we examined the effect of in vitro TLR4 neutralization on trophoblastic proinflammatory activity and studied the IUGR phenotype in a congenic TLR4-mutant mouse strain after in vivo C. rectus infection. Human trophoblasts were pretreated with TLR4 neutralizing antibodies and infected with C. rectus; proinflammatory cytokine production was assessed by cytokine multiplex assays. Neutralizing TLR4 antibodies significantly impaired the production of proinflammatory cytokines in trophoblastic cells after infection in a dose-dependent manner. We used a subcutaneous chamber model to provide a C. rectus challenge in BALB/cAnPt (TLR4(Lps-d) ) and wild-type (WT) females. Females were mated with WT or TLR4(Lps-d) males once/week; pregnant mice were infected at (E)7.5 and sacrificed at (E)16.5 to establish IUGR phenotypes. Maternal C. rectus infection significantly decreased fetal weight/length in infected WT when compared with sham WT controls (P < 0.05, analysis of variance). However, infected TLR4(Lps-d -/-) mice did not show statistically significant differences in fetal weight and length when compared with WT controls (P > 0.05). Furthermore, heterozygous TLR4(Lps-d +/-) fetuses showed IUGR phenotype rescue. We conclude that TLR4 is an important mediator of trophoblastic proinflammatory responses and TLR4-deficient fetuses do not develop IUGR phenotypes after C. rectus infection, suggesting that placental cytokine activation is likely to be mediated by TLR4 during low birthweight/preterm birth pathogenesis.

Altered gene expression in murine placentas in an infection-induced intrauterine growth restriction model: a microarray analysis.

The biological mechanisms leading to incomplete intrauterine growth are not completely elucidated and few studies have investigated infection-mediated growth restriction. In this investigation we report the alterations induced by maternal infectious challenge in placental gene expression patterns using a murine model. Pregnant dams were challenged at day E7.5 with the oral human pathogen Campylobacter rectus to elicit fetal growth restriction. At embryonic day E16.5 placentas were collected to compare placental gene expression patterns from normal fetuses of unchallenged dams and growth restricted fetuses from infected dams. Differential gene expression patterns were determined using Agilent Oligo array (G4121A) with a false discovery rate of P<0.05 and pathway analyses were performed. Seventy-four genes were differentially expressed during infection-mediated growth restriction with 9 genes significantly up-regulated, indicating that the effects of maternal infection on gene expression were predominantly suppressive. Pathway analyses indicated that 46 of the 65 genes that were significantly down-regulated were associated with placental/fetal development, and 26 of those were imprinted genes. Among the 9 genes that were up-regulated, 4 are involved in oxygen supply to the fetus and the development of the vascular system. Microarray analysis demonstrated that in the pregnant mouse model, maternal infection that induced growth restriction was associated with down-regulated placental expression of critical growth and developmental related genes, including many imprinted genes. These findings may have significant implications for our understanding of the mechanisms underlying infection-associated human fetal growth restriction and the role of differential placental expression of imprinted genes in fetal growth.

Maternal periodontal disease and soluble fms-like tyrosine kinase-1 expression.

BACKGROUND: This study was conducted to examine the relationship between maternal periodontal disease and plasma angiogenic factor expression of soluble fms-like tyrosine kinase (sFlt)-1. METHODS: This was a nested case-control study of 220 women, including 45 healthy women with evidence of active periodontal disease, 98 women without evidence of active periodontal disease, 13 women with fetal exposure to oral pathogens, and 64 women without fetal exposure to oral pathogens. Active periodontal disease was defined as the presence of moderate/severe periodontal disease and evidence of periodontal disease progression. Fetal exposure to oral pathogens was determined by fetal immunoglobulin M (IgM) umbilical cord seropositivity. Maternal plasma was collected at <26 weeks of gestation; umbilical cord blood was collected at delivery. sFlt-1 was measured with an immunoradiometric assay. Demographic and medical data were chart abstracted. Maternal variables and sFlt-1 concentrations were compared between cases and controls using the Student t and chi(2) tests and analysis of variance. RESULTS: The median sFlt-1 concentration at the time of enrollment for all women was 2,374 pg/ml (interquartile range [IQR]: 1,504 to 3,194 pg/ml). Women with evidence of fetal exposure to oral pathogens had significantly higher sFlt-1 concentrations compared to IgM-negative fetuses (3,383 pg/ml [IQR: 2,610 to 4,244 pg/ml] versus 2,123 pg/ml [IQR: 1,456 to 3,011 pg/ml]; P = 0.03). CONCLUSION: Fetal exposure to oral pathogens was associated with increased plasma concentrations of sFlt-1 early in pregnancy.

Fetal exposure to oral pathogens and subsequent risk for neonatal intensive care admission.

BACKGROUND: Maternal periodontal infection has been associated with adverse maternal and neonatal outcomes. In utero fetal exposure to oral pathogens was also recognized as deleterious to the fetus. The objective of this study was to determine the relationship between fetal exposure to oral pathogens and neonatal intensive care unit (NICU) admission. METHODS: This was a secondary analysis of a prospective cohort study of maternal oral health and pregnancy outcome. Fetal immunoglobulin M against oral pathogens was detected in umbilical cord serum by immunoblot. The presence of at least one oral pathogen-specific antibody was considered seropositivity. The cord level of C-reactive protein was determined by enzyme-linked immunosorbent assay and categorized as detectable versus undetectable. Chi-square and logistic regression analyses were used to determine the association between cord serum seropositivity or detectable C-reactive protein and NICU admission and length of stay. RESULTS: Of 650 infants, 45 (6.9%) were admitted to the NICU. The admission rate was higher among seropositive infants compared to seronegative infants (11% versus 5%; P = 0.0019). Seropositive infants were also more likely than seronegative infants to stay >3 or >7 days (8% versus 3% and 6% versus 2%; P = 0.004 and 0.003, respectively). Adjusting for gestational age, the odds ratio (95% confidence interval) for NICU admission was 2.14 (1.01 to 4.54); for a length of stay >3 or >7 days, it was 2.38 (1.01 to 5.60) and 3.29 (1.13 to 9.58), respectively. The NICU admission rate was not significantly higher for those with detectable versus undetectable umbilical cord serum C-reactive protein (8% versus 6%; P = 0.3). CONCLUSIONS: In utero fetal exposure to oral pathogens increases the risk for NICU admission and the length of stay. Interventions that interrupt fetal exposure to oral pathogens may reduce these risks.

Systemic immune responses in pregnancy and periodontitis: relationship to pregnancy outcomes in the Obstetrics and Periodontal Therapy (OPT) study.

BACKGROUND: Our previous studies reported on the obstetric, periodontal, and microbiologic outcomes of women participating in the Obstetrics and Periodontal Therapy (OPT) Study. This article describes the systemic antibody responses to selected periodontal bacteria in the same patients. METHODS: Serum samples, obtained from pregnant women at baseline (13 to 16 weeks; 6 days of gestation) and 29 to 32 weeks, were analyzed by enzyme-linked immunosorbent assay for serum immunoglobulin G (IgG) antibody to Aggregatibacter actinomycetemcomitans (previously Actinobacillus actinomycetemcomitans), Campylobacter rectus, Fusobacterium nucleatum, Porphyromonas gingivalis, Prevotella intermedia, Tannerella forsythia (previously T. forsythensis), and Treponema denticola. RESULTS: At baseline, women who delivered live preterm infants had significantly lower total serum levels of IgG antibody to the panel of periodontal pathogens (P = 0.0018), to P. gingivalis (P = 0.0013), and to F. nucleatum (P = 0.0200) than women who delivered at term. These differences were not significant at 29 to 32 weeks. Changes in IgG levels between baseline and 29 to 32 weeks were not associated with preterm birth when adjusted for treatment group, clinical center, race, or age. In addition, delivery of low birth weight infants was not associated with levels of antibody at baseline or with antibody changes during pregnancy. CONCLUSIONS: Live preterm birth is associated with decreased levels of IgG antibody to periodontal pathogens in women with periodontitis when assessed during the second trimester. Changes in IgG antibody during pregnancy are not associated with birth outcomes.

Serum antibodies to periodontal bacteria as diagnostic markers of periodontitis.

BACKGROUND: Assessment of periodontal conditions in epidemiologic studies usually requires a clinical examination, which is resource-intensive. We investigated the ability of serum immunoglobulin G (IgG) antibodies to periodontal bacteria to reflect clinical periodontal status. METHODS: We used checkerboard immunoblotting to assess serum IgG levels to 19 species, including established/putative periodontal pathogens and non-pathogenic bacteria, in 5,747 dentate adults aged > or = 40 years who participated in the third National Health and Nutrition Examination Survey between 1988 and 1994. Three earlier described alternative definitions of periodontitis were used, based on specific combinations of probing depth and attachment level values. Optimized elevated titer thresholds and corresponding sensitivities and specificities were calculated for each definition. Titers significantly associated with periodontitis were identified in univariable and multivariable logistic regression models. Parsimonious models were subsequently developed using age, gender, race/ethnicity, education, smoking, and diagnosed diabetes. RESULTS: In unadjusted models, high titers to Porphyromonas gingivalis were most strongly associated with periodontitis across all definitions (odds ratio, 2.07 to 2.74; P <0.05). In parsimonious models including demographic data, smoking, and diagnosed diabetes, high P. gingivalis titers were consistently associated with periodontitis, whereas high Eubacterium nodatum titers were associated with periodontal health in two of three definitions. Receiver operating characteristic curves for the parsimonious multivariable models showed that the area under the curve ranged between 0.72 and 0.78. CONCLUSIONS: Serum IgG titers to selected periodontal species, combined with demographic and behavioral characteristics, resulted in a moderately accurate classification of periodontal status in epidemiologic studies. The external validity of these findings must be examined further.

Granulocyte chemotactic protein 2 (gcp-2/cxcl6) complements interleukin-8 in periodontal disease.

BACKGROUND AND OBJECTIVE: Mucosal inflammatory responses are orchestrated largely by pro-inflammatory chemokines. The chemokine granulocyte chemotactic protein 2 (CXCL6) is involved in neutrophil recruitment and migration. Previous studies have shown that granulocyte chemotactic protein 2 is up-regulated during mucosal inflammation (e.g. in inflammatory bowel disease), similarly to the functionally and structurally related chemokine interleukin-8. Nevertheless, unlike interleukin-8, a role of granulocyte chemotactic protein 2 in gingival inflammation has not been yet demonstrated. In this study we aimed to evaluate the expression of the chemokine granulocyte chemotactic protein 2 in clinically healthy vs. diseased gingival tissues and to explore possible correlations with clinical and microbiological markers of periodontitis. MATERIAL AND METHODS: Gene expression in 184 'diseased' and 63 'healthy' gingival tissue specimens from 90 patients with periodontitis was analyzed using Affymetrix U133Plus2.0 arrays. The expression of granulocyte chemotactic protein 2 was further confirmed by real-time reverse transcription-polymerase chain reaction, western blotting and enzyme-linked immunosorbent assay, while the localization of granulocyte chemotactic protein 2 in gingival tissues was analyzed by immunohistochemistry. Plaque samples from the adjacent periodontal pockets were collected and evaluated for 11 species of periodontal bacteria using checkerboard DNA-DNA hybridizations. RESULTS: Among all known chemokines, GCP-2 expression was the most up-regulated (3.8-fold, p < 1.1 x 10(-16)), in 'diseased' vs. 'healthy' tissue as compared to a 2.6-fold increased expression of interleukin-8 mRNA (p < 1.2 x 10(-15)). Increased expression of granulocyte chemotactic protein 2 correlated with higher levels of 'red' and 'orange' complex pathogens and with increased probing depth, but not with attachment loss. Immunohistochemistry showed that granulocyte chemotactic protein 2 was expressed in gingival vascular endothelium. CONCLUSION: The level of expression of granulocyte chemotactic protein 2 correlates with the severity of periodontitis and appears to act as a hitherto unrecognized functional adjunct to interleukin-8 in diseased gingival tissues.

Microbiologic and immunologic characteristics of periodontal disease in Hispanic americans with type 2 diabetes.

BACKGROUND: The microbiology of periodontitis in type 1 diabetes has been reported, but less is known about type 2 diabetes. Moreover, these data have not linked microbial colonization, host response, and clinical presentation in type 1 or type 2 diabetes. The objectives of this study were to relate periodontal status, periodontal microorganisms, and host-response characteristics in Hispanic Americans with type 2 diabetes. METHODS: Plaque and serum samples were obtained from 63 Hispanic American subjects with and without type 2 diabetes. The microbiology of subgingival plaque samples was evaluated using DNA checkerboard hybridization, and serum antibody to a battery of oral microorganisms was determined using an enzyme-linked immunosorbent assay. RESULTS: In general, similar pathogens were present in periodontitis sites from subjects with and without type 2 diabetes, although the periodontitis sites in diabetes showed a higher frequency of Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans (previously Actinobacillus actinomycetemcomitans), and Campylobacter spp. Serum antibody to Campylobacter rectus was elevated in type 2 diabetes, whereas antibody to P. gingivalis and C. rectus were elevated in subjects with periodontitis, irrespective of diabetes status. Stratification of the population based upon antibody to P. gingivalis or C. rectus suggested a linkage between elevated antibody to P. gingivalis, increased frequency of diabetes, and significantly worse periodontitis. CONCLUSION: The increased severity of periodontal disease with type 2 diabetes may reflect an alteration of the pathogenic potential of periodontal bacteria and/or a modification of the characteristics of the host's inflammatory response that may contribute to a breakdown in the homeostasis of the periodontium.

Porphyromonas gingivalis antagonises Campylobacter rectus induced cytokine production by human monocytes.

Porphyromonas gingivalis and Campylobacter rectus are two major bacterial species implicated in the pathogenesis of periodontitis. P. gingivalis can antagonise the inflammatory response to other periodontal pathogens, a property commonly attributed to its lipopolysaccharide (LPS). The aim of this study was to investigate the capacity of P. gingivalis to antagonise C. rectus induced cytokine stimulation from human monocytes, and to investigate the involvement of its LPS. Primary human monocytes and Monomac-6 cells were challenged with culture supernatants from P. gingivalis and C. rectus, and levels of IL-1beta, IL-6 and IL-8 produced were measured by ELISA after 6h incubation. Purified P. gingivalis LPS was also added alone or in combination with C. rectus culture supernatant. Both species significantly stimulated the production of all three cytokines from the two cell lines, but P. gingivalis was considerably weaker inducer. Co-stimulation of the cells with P. gingivalis and C. rectus suppressed the cytokine-stimulatory capacity of the latter. P. gingivalis LPS alone was sufficient to antagonise IL-6 and IL-8, but not IL-1beta stimulation by C. rectus. In conclusion, mixed infections may impair host immune responses by reducing pro-inflammatory cytokine levels, which may be of relevance to the pathogenesis of periodontitis.

Interleukin-1alpha stimulation in monocytes by periodontal bacteria: antagonistic effects of Porphyromonas gingivalis.

Periodontal pathogenic bacteria are associated with elevated levels of interleukin-1alpha (IL-1alpha) but it is unclear if all species can induce cytokine production equally. Porphyromonas gingivalis may be able antagonize IL-1alpha induced by other species through the activity of its proteases or lipopolysaccharide (LPS). Monomac-6 cells and primary human monocytes were treated with culture supernatants from Porphyromonas gingivalis, Fusobacterium nucleatum, Campylobacter rectus, Actinobacillus actinomycetemcomitans, Prevotella intermedius, Veillonella atypical and Prevotella nigrescens. IL-1alpha protein levels were measured after 6 h of incubation. In addition, monocytes were co-stimulated with supernatants from P. gingivalis and other bacteria. The role of P. gingivalis proteases was tested using Arg-X and Lys-X mutant strains. The role of LPS was investigated using purified P. gingivalis LPS and polymixin depletion. All species tested induced significant IL-1alpha production, but P. gingivalis was the weakest. Co-stimulation of monocytes with P. gingivalis antagonized the ability of other bacterial species to induce IL-1alpha production. This effect was at its greatest with C. rectus (resulting in a 70% reduction). Gingipain mutant strains and chemical inhibition of protease activity did not reduce antagonistic activity. However, 100 ng/ml of P. gingivalis LPS can reproduce the antagonistic activity of P. gingivalis culture supernatants. Periodontitis-associated bacterial species stimulate IL-1alpha production by monocytes. P. gingivalis can antagonize this effect, and its LPS appears to be the crucial component. This study highlights the importance of mixed infections in the pathogenesis of periodontal disease because reduction of pro-inflammatory cytokine levels may impair the ability of the host to tackle infection.

Salivary immunoglobulin A directed to oral microbial GroEL in patients with periodontitis and their potential protective role.

The aim of this study was to identify salivary immunoglobulin A (IgA) directed to oral microbial GroEL in patients with periodontitis and to demonstrate their potential protective role through a reduction of inflammatory cytokine production induced by microbial GroEL. Using five different proteins belonging to the heat-shock protein 60 family, Western immunoblot analysis of salivary IgA from 63 subjects revealed immunoreactivities with Campylobacter rectus GroEL and Porphyromonas gingivalis GroEL in subjects with periodontitis (P < 0.05) compared to control subjects. Using the BIACORE 1000 to measure the salivary IgA titers directed towards C. rectus GroEL, high resonance unit (RU) values were observed in the saliva samples from patients with periodontitis (P < 0.01). Furthermore, the number of teeth with deep pocket depth (>or=5 mm) showed a high correlation coefficient with the RU value (r = 0.50, P < 0.01). C. rectus GroEL possessed the ability to stimulate the production of interleukin-6 by gingival fibroblasts. Interestingly, salivary IgA antibody directed to C. rectus GroEL caused a partial inhibition of interleukin-6 production. This study showed a relationship between high levels of salivary IgA directed to GroEL and periodontal disease severity. Although additional investigations are required, salivary IgA to GroEL may have a protective role by reducing the inflammatory response induced by GroEL derived from periodontopathogenic bacteria.

Campylobacter surface-layers (S-layers) and immune evasion.

Many pathogenic bacteria have evolved mechanisms for evading host immune systems. One evasion mechanism is manifest by the surface layer (S-layer), a paracrystalline protein structure composed of S-layer proteins (SLPs). The S-layer, possessed by 2 Campylobacter species (C. fetus and C. rectus), is external to the bacterial outer membrane and can have multiple functions in immune avoidance. C. fetus is a pathogen of ungulates and immunocompromised humans, in whom it causes disseminated bloodstream disease. In C. fetus, the S-layer is required for dissemination and is involved in 2 mechanisms of evasion. First, the S-layer confers resistance to complement-mediated killing in non-immune serum by preventing the binding of complement factor C3b to the C. fetus cell surface. S-layer expressing C. fetus strains remain susceptible to complement-independent killing, utilizing opsonic antibodies directed against the S-layer. However, C. fetus has also evolved a mechanism for avoiding antibody-mediated killing by high-frequency antigenic variation of SLPs. Antigenic variation is accomplished by complex DNA inversion events involving a family of multiple SLP-encoding genes and a single SLP promoter. Inversion events result in the expression of antigenically variant S-layers, which require distinct antibody responses for killing. C. rectus is implicated in the pathogenesis of periodontal disease and also possesses an S-layer that appears to be involved in evading the human system. Although studied less extensively than its C. fetus counterpart, the C. rectus S-layer appears to confer resistance to complement-mediated killing and to cause the down-regulation of proinflammatory cytokines.