Secretory Immunity Following Mutans Streptococcal Infection or Immunization

PcsB Expression Diversity Influences on Streptococcus mitis Phenotypes Associated With Host Persistence and Virulence

S. mitis is an abundant member of the commensal microbiota of the oral cavity and pharynx, which has the potential to promote systemic infections. By analyzing a collection of S. mitis strains isolated from the oral cavity at commensal states or from systemic infections (blood strains), we established that S. mitis ubiquitously express the surface immunodominant protein, PcsB (also called GbpB), required for binding to sucrose-derived exopolysaccharides (EPS). Immuno dot blot assays with anti-PcsB antibodies and RT-qPCR transcription analyses revealed strain-specific profiles of PcsB production associated with diversity in pcsB transcriptional activities. Additionally, blood strains showed significantly higher levels of PcsB expression compared to commensal isolates. Because Streptococcus mutans co-colonizes S. mitis dental biofilms, and secretes glucosyltransferases (GtfB/C/D) for the synthesis of highly insoluble EPS from sucrose, profiles of S. mitis binding to EPS, biofilm formation and evasion of the complement system were assessed in sucrose-containing BHI medium supplemented or not with filter-sterilized S. mutans culture supernatants. These analyses showed significant S. mitis binding to EPS and biofilm formation in the presence of S. mutans supernatants supplemented with sucrose, compared to BHI or BHI-sucrose medium. In addition, these phenotypes were abolished if strains were grown in culture supernatants of a gtfBCD-defective S. mutans mutant. Importantly, GtfB/C/D-associated phenotypes were enhanced in high PcsB-expressing strains, compared to low PcsB producers. Increased PcsB expression was further correlated with increased resistance to deposition of C3b/iC3b of the complement system after exposure to human serum, when strains were previously grown in the presence of S. mutans supernatants. Finally, analyses of PcsB polymorphisms and bioinformatic prediction of epitopes with significant binding to MHC class II alleles revealed that blood isolates harbor PcsB polymorphisms in its functionally conserved CHAP-domain, suggesting antigenic variation. These findings reveal important roles of PcsB in S. mitis-host interactions under commensal and pathogenic states, highlighting the need for studies to elucidate mechanisms regulating PcsB expression in this species.

Salivary Protein Roles in Oral Health and as Predictors of Caries Risk

This work describes the current state of research on the potential relationship between protein content in human saliva and dental caries, which remains among the most common oral diseases and causes irreversible damage in the oral cavity. An understanding the whole saliva proteome in the oral cavity could serve as a prerequisite to obtaining insight into the etiology of tooth decay at early stages. To date, however, there is no comprehensive evidence showing that salivary proteins could serve as potential indicators for the early diagnosis of the risk factors causing dental caries. Therefore, proteomics indicates the promising direction of future investigations of such factors, including diagnosis and thus prevention in dental therapy.

Natural Immunoreactivity of Secretory IgA to Indigenous Strains of Streptococcus mutans From Chinese Spousal Pairs

Background

Dental caries is a well-known biofilm-mediated disease initiated by Streptococcus mutans, which should infect and colonize in a milieu perfused with components of the mucosal immune system. Little is known, however, regarding the relationship between the natural secretory IgA activity and S. mutans of a variety of diverse genotypes.

Objectives

The current study aimed to use spousal pairs to investigate the natural immunoreactivity of salivary secretory IgA to different genotype strains of S. mutans.

Patients and Methods

Indigenous strains were characterized from nine spousal pairs using polymerase reaction chain (PCR) and arbitrarily primed polymerase chain reaction (AP-PCR) by genotype monitoring. Unstimulated submandibular/sublingual secretions were collected and the concentrations of secretory IgA were determined by the enzyme-linked immunosorbent assay (ELISA). Each saliva sample was examined by Western blot to analyze the immunoreactivity of naturally occurring salivary secretory IgA antibodies for his/her own indigenous strain, spouse’s strain and reference strains including S. mutans GS-5 and Ingbritt (C).

Results

The results showed that naturally induced salivary IgA antibodies against S. mutans were present in all subjects. Almost all subjects had the similar individual immunoblotting profiles to different genotype strains.

Conclusions

The current study indicated that the immunoreactivity of secretory IgA might have no direct correlation with the colonization of indigenous flora and rejection of exogenous strains in adults. The relationship of microbes, host and dental caries should be in the light of coevolved microecosystem as a whole, but not caused by one factor alone.

The oral microbiome and the immunobiology of periodontal disease and caries

The composition of the oral microbiome differs from one intraoral site to another, reflecting in part the host response and immune capacity at each site. By focusing on two major oral infections, periodontal disease and caries, new principles of disease emerge. Periodontal disease affects the soft tissues and bone that support the teeth. Caries is a unique infection of the dental hard tissues. The initiation of both diseases is marked by an increase in the complexity of the microbiome. In periodontitis, pathobionts and keystone pathogens such as Porphyromonas gingivalis appear in greater proportion than in health. As a keystone pathogen, P. gingivalis impairs host immune responses and appears necessary but not sufficient to cause periodontitis. Historically, dental caries had been causally linked to Streptococcus mutans. Contemporary microbiome studies now indicate that singular pathogens are not obvious in either caries or periodontitis. Both diseases appear to result from a perturbation among relatively minor constituents in local microbial communities resulting in dysbiosis. Emergent consortia of the minor members of the respective microbiomes act synergistically to stress the ability of the host to respond and protect. In periodontal disease, host protection first occurs at the level of innate gingival epithelial immunity. Secretory IgA antibody and other salivary antimicrobial systems also act against periodontopathic and cariogenic consortia. When the gingival immune response is impaired, periodontal tissue pathology results when matrix metalloproteinases are released from neutrophils and T cells mediate alveolar bone loss. In caries, several species are acidogenic and aciduric and appear to work synergistically to promote demineralization of the enamel and dentin. Whereas technically possible, particularly for caries, vaccines are unlikely to be commercialized in the near future because of the low morbidity of caries and periodontitis.

Salivary IgA response to probiotic bacteria and mutans streptococci after the use of chewing gum containing Lactobacillus reuteri

We investigated whether ingestion of probiotic bacteria could influence salivary IgA levels, specific anti-mutans streptococci IgA levels and specific antibodies towards the ingested probiotic bacterium. The study was a randomised, double-blind, placebo-controlled trial, where the test group (n = 11) received twice daily chewing of gum containing Lactobacillus reuteri (2 × 10(8)  CFU per dose) and the control group (n = 12) received placebo. Resting saliva was collected before and after 12 weeks of treatment and 4 weeks after end of treatment. Total salivary IgA concentrations were measured by ELISA. Specific IgA reactivity was determined using a whole-cell ELISA. Results were expressed as % IgA per protein in saliva. The level of total IgA% per protein increased significantly between pretreatment levels (13.5%) and follow-up treatment levels (14.4%) within the test group only (P < 0.05). No changes were seen in the control group during the trial. The level of probiotic-reactive antibodies decreased significantly between pre- and post-treatment samples (from 12.2% to 9.0%, P < 0.05) in the test group. Similarly, the level of specific mutans streptococci antibodies decreased significantly between pre- and post-treatment samples (P < 0.05) in the test group only (for Streptococcus mutans from 20.1% to 15.0%; for Streptococcus sobrinus from 7.4% to 5.3%). Ingestion of probiotic bacteria might influence the adaptive immune response of the host.

Periodontal disease immunology: 'double indemnity' in protecting the host

During the last two to three decades our understanding of the immunobiology of periodontal disease has increased exponentially, both with respect to the microbial agents triggering the disease process and the molecular mechanisms of the host engagement maintaining homeostasis or leading to collateral tissue damage. These foundational scientific findings have laid the groundwork for translating cell phenotype, receptor engagement, intracellular signaling pathways and effector functions into a 'picture' of the periodontium as the host responds to the 'danger signals' of the microbial ecology to maintain homeostasis or succumb to a disease process. These findings implicate the chronicity of the local response in attempting to manage the microbial challenge, creating a 'Double Indemnity' in some patients that does not 'insure' health for the periodontium. As importantly, in reflecting the title of this volume of Periodontology 2000, this review attempts to inform the community of how the science of periodontal immunology gestated, how continual probing of the biology of the disease has led to an evolution in our knowledge base and how more recent studies in the postgenomic era are revolutionizing our understanding of disease initiation, progression and resolution. Thus, there has been substantial progress in our understanding of the molecular mechanisms of host-bacteria interactions that result in the clinical presentation and outcomes of destructive periodontitis. The science has embarked from observations of variations in responses related to disease expression with a focus for utilization of the responses in diagnosis and therapeutic outcomes, to current investigations using cutting-edge fundamental biological processes to attempt to model the initiation and progression of soft- and hard-tissue destruction of the periodontium. As importantly, the next era in the immunobiology of periodontal disease will need to engage more sophisticated experimental designs for clinical studies to enable robust translation of basic biologic processes that are in action early in the transition from health to disease, those which stimulate microenvironmental changes that select for a more pathogenic microbial ecology and those that represent a rebalancing of the complex host responses and a resolution of inflammatory tissue destruction.

Strategic protein target analysis for developing drugs to stop dental caries

Dental caries is the most common disease to cause irreversible damage in humans. Several therapeutic agents are available to treat or prevent dental caries, but none besides fluoride has significantly influenced the disease burden globally. Etiologic mechanisms of the mutans group streptococci and specific Lactobacillus species have been characterized to various degrees of detail, from identification of physiologic processes to specific proteins. Here, we analyze the entire Streptococcus mutans proteome for potential drug targets by investigating their uniqueness with respect to non-cariogenic dental plaque bacteria, quality of protein structure models, and the likelihood of finding a drug for the active site. Our results suggest specific targets for rational drug discovery, including 15 known virulence factors, 16 proteins for which crystallographic structures are available, and 84 previously uncharacterized proteins, with various levels of similarity to homologs in dental plaque bacteria. This analysis provides a map to streamline the process of clinical development of effective multispecies pharmacologic interventions for dental caries.

CovR and VicRK regulate cell surface biogenesis genes required for biofilm formation in Streptococcus mutans

The two-component system VicRK and the orphan regulator CovR of Streptococcus mutans co-regulate a group of virulence genes associated with the synthesis of and interaction with extracellular polysaccharides of the biofilm matrix. Knockout mutants of vicK and covR display abnormal cell division and morphology phenotypes, although the gene function defects involved are as yet unknown. Using transcriptomic comparisons between parent strain UA159 with vicK (UAvic) or covR (UAcov) deletion mutants together with electrophoretic motility shift assays (EMSA), we identified genes directly regulated by both VicR and CovR with putative functions in cell wall/surface biogenesis, including gbpB, wapE, smaA, SMU.2146c, and lysM. Deletion mutants of genes regulated by VicR and CovR (wapE, lysM, smaA), or regulated only by VicR (SMU.2146c) or CovR (epsC) promoted significant alterations in biofilm initiation, including increased fragility, defects in microcolony formation, and atypical cell morphology and/or chaining. Significant reductions in mureinolytic activity and/or increases in DNA release during growth were observed in knockout mutants of smaA, wapE, lysM, SMU.2146c and epsC, implying roles in cell wall biogenesis. WapE and lysM mutations also affected cell hydrophobicity and sensitivity to osmotic or oxidative stress. Finally, vicR, covR and VicRK/CovR-targets (gbpB, wapE, smaA, SMU.2146c, lysM, epsC) are up-regulated in UA159 during biofilm initiation, in a sucrose-dependent manner. These data support a model in which VicRK and CovR coordinate cell division and surface biogenesis with the extracellular synthesis of polysaccharides, a process apparently required for formation of structurally stable biofilms in the presence of sucrose.

Anti-caries DNA vaccine-induced secretory immunoglobulin A antibodies inhibit formation of Streptococcus mutans biofilms in vitro

AIM

To investigate the effects of anti-caries DNA vaccine-induced salivary secretory immunoglobulin A (S-IgA) antibodies on Streptococcus mutans (S. mutans) adherence and biofilms formation in vitro.

METHODS

Adult female Wistar rats were intranasally immunized with the anti-caries DNA vaccine pGJA-P/VAX. Their saliva samples were collected at different times after the immunization, and S-IgA antibody level in the saliva and its inhibition on S. mutans adherence were examined. The effects of S-IgA in the saliva with the strongest inhibitory effects were examined at 3 different stages, ie acquired pellicles, biofilm formation and production of mature biofilms. The number of viable bacteria and depth of the biofilm at 16 h in each stage were determined using counting colony forming units and using a confocal laser scanning microscopy (CLSM). The participation of S-IgA in acquired pellicles and its aggregation with S. mutans were also observed under CLSM.

RESULTS

The S-IgA titer in saliva reached its peak and exhibited the strongest inhibition on S. mutans adhesion at 10 weeks after the immunization. The colonies and depth of the biofilm in the saliva-pretreated group were 41.79% and 41.02%, respectively, less than the control group. The colonies and depth of the biofilm in the co-culture group were 27.4% and 22.81% less than the control group. The assembly of S. mutans and S-IgA was observed under CLSM after co-cultivation. In the mature-stage biofilm, no differences were observed between the different groups.

CONCLUSION

These results demonstrate that the anti-caries DNA vaccine induces the production of specific S-IgA antibodies that may prevent dental caries by inhibiting the initial adherence of S. mutans onto tooth surfaces, thereby reducing the accumulation of S. mutans on the acquired pellicles.

New aspects and new concepts of maintaining "microbiological" health

The human mouth is host to a diverse collection of microorganisms including bacteria, viruses, fungi and protozoa. Recent advances using molecular methods for the analysis of complex bacterial communities have demonstrated the richness of the oral bacterial biota and the presence of numerous previously undescribed lineages. Dental plaque forms in a structured way with pioneer species able to colonise pellicle-coated enamel followed by secondary plaque formers such as Fusobacterium nucleatum that have the capability of coaggregating with a range of other genera and species. The mature plaque biofilm has many features of multicellular organisms with the constituent organisms cooperating to make nutrients available and resist environmental stresses, and communicating to regulate their overall numbers. Control of the oral microbiota to prevent disease has conventionally been by mechanical means augmented with toothpastes and mouthrinses, but improved knowledge of oral microbial ecology is allowing the development of pre and pro-biotic approaches. Other possibilities include interference with the plaque formation process and the perturbation of bacterial communication networks.

Induction of neutralizing antibodies in mice immunized with an amino-terminal polypeptide of Streptococcus mutans P1 protein produced by a recombinant Bacillus subtilis strain

The oral pathogen Streptococcus mutans expresses a surface protein, P1, which interacts with the salivary pellicle on the tooth surface or with fluid-phase saliva, resulting in bacterial adhesion or aggregation, respectively. P1 is a target of protective immunity. Its N-terminal region has been associated with adhesion and aggregation functions and contains epitopes recognized by efficacious antibodies. In this study, we used Bacillus subtilis, a gram-positive expression host, to produce a recombinant N-terminal polypeptide of P1 (P1(39-512)) derived from the S. mutans strain UA159. Purified P1(39-512) reacted with an anti-full-length P1 antiserum as well as one raised against intact S. mutans cells, indicating preserved antigenicity. Immunization of mice with soluble and heat-denatured P1(39-512) induced antibodies that reacted specifically with native P1 on the surface of S. mutans cells. The anti-P1(39-512) antiserum was as effective at blocking saliva-mediated aggregation of S. mutans cells and better at blocking bacterial adhesion to saliva-coated plastic surfaces compared with the anti-full-length P1 antiserum. In addition, adsorption of the anti-P1 antiserum with P1(39-512) eliminated its ability to block the adhesion of S. mutans cells to abiotic surfaces. The present results indicate that P1(39-512), expressed and purified from a recombinant B. subtilis strain, maintains important immunological features of the native protein and represents an additional tool for the development of anticaries vaccines.

An examination of the advances in science and technology of prevention of tooth decay in young children since the Surgeon General's Report on Oral Health

This paper addresses a number of areas related to how effectively science and technology have met Healthy People 2010 goals for tooth decay prevention. In every area mentioned, it appears that science and technology are falling short of these goals. Earlier assessments identified water fluoridation as one of the greatest public health accomplishments of the last century. Yet, failure to complete needed clinical and translational research has shortchanged the caries prevention agenda at a critical juncture. Science has firmly established the transmissible nature of tooth decay. However, there is evidence that tooth decay in young children is increasing, although progress has been made in other age groups. Studies of risk assessment have not been translated into improved practice. Antiseptics, chlorhexidine varnish, and polyvinylpyrrolidone iodine (PVI-I) may have value, but definitive trials are needed. Fluorides remain the most effective agents, but are not widely disseminated to the most needy. Fluoride varnish provides a relatively effective topical preventive for very young children, yet definitive trials have not been conducted. Silver diamine fluoride also has potential but requires study in the United States. Data support effectiveness and safety of xylitol, but adoption is not widespread. Dental sealants remain a mainstay of public policy, yet after decades of research, widespread use has not occurred. We conclude that research has established the public health burden of tooth decay, but insufficient research addresses the problems identified in the report Oral Health in America: A Report of the Surgeon General. Transfer of technology from studies to implementation is needed to prevent tooth decay among children. This should involve translational research and implementation of scientific and technological advances into practice.

Beneficial immunomodulation by Streptococcus mutans anti-P1 monoclonal antibodies is Fc independent and correlates with increased exposure of a relevant target epitope

We showed previously that deliberate immunization of BALB/c mice with immune complexes (IC) of the cariogenic bacterium Streptococcus mutans and mAbs against its surface adhesin P1 results in changes in the specificity and isotype of elicited anti-P1 Abs. Depending on the mAb, changes were beneficial, neutral, or detrimental, as measured by the ability of the serum from immunized mice to inhibit bacterial adherence to human salivary agglutinin by a BIAcore surface plasmon resonance assay. The current study further defined changes in the host response that result from immunization with IC containing beneficial mAbs, and evaluated mechanisms by which beneficial immunomodulation could occur in this system. Immunomodulatory effects varied depending upon genetic background, with differing results in C57BL/6 and BALB/c mice. Desirable effects following IC immunization were observed in the absence of activating FcRs in BALB/c Fcer1g transgenic mice. mAb F(ab')(2) mediated desirable changes similar to those observed using intact IgG. Sera from IC-immunized BALB/c mice that were better able to inhibit bacterial adherence demonstrated an increase in Abs able to compete with an adherence-inhibiting anti-P1 mAb, and binding of a beneficial immumomodulatory mAb to S. mutans increased exposure of that epitope. Consistent with a mechanism involving a mAb-mediated structural alteration of P1 on the cell surface, immunization with truncated P1 derivatives lacking segments that contribute to recognition by beneficial immunomodulatory mAbs resulted in an improvement in the ability of elicited serum Abs to inhibit bacterial adherence compared with immunization with the full-length protein.

Construction of a New Fusion Anti-caries DNA Vaccine

Mutans streptococci (MS) are generally considered to be the principal etiological agent of dental caries. MS have two important virulence factors: cell- surface protein PAc and glucosyltransferases (GTFs). GTFs have two functional domains: an N-terminal catalytic sucrose-binding domain (CAT) and a C-terminal glucan-binding domain (GLU). A fusion anti-caries DNA vaccine, pGJA-P/VAX, encoding two important antigenic domains, PAc and GLU, of S. mutans, was successful in reducing the levels of dental caries caused by S. mutans in gnotobiotic animals. However, its protective effect against S. sobrinus infection proved to be weak. Does the DNA vaccine need an antigen of S. sobrinus to enhance its ability to inhibit infection? To answer this question, in this study, we cloned the catalytic ( cat) fragment of S. sobrinus gtf-I, which demonstrated its ability to inhibit water-insoluble glucan synthesis by S. sobrinus, into pGJA-P/VAX to produce a new anti-caries DNA vaccine.