Prevention of colonization of Streptococcus mutans by topical application of monoclonal antibodies in human subjects

Mouthwashes: Alternatives and Future Directions

This narrative review summarises "alternative" or "natural" over-the-counter (OTC) mouthwashes not covered elsewhere in this supplement and newly emerging products, as potential mouthwashes of the future. The "natural" mouthwashes reviewed include saltwater, baking soda, coconut oil, charcoal, propolis, seaweeds, and probiotics. Other than essential oils, it is apparent that their clinical effectiveness is still under debate, but there is some evidence to suggest that propolis reduces plaque and gingivitis. This review also covers the host immune response, via novel anti-inmmunomodulant mouthwashes, such as erythropoietin to reduce inflammation with oral mucositis (OM) after radiotherapy. The emerging concept of nanoparticle-containing mouthwashes, such as iron oxide, is further discussed for OM, this agent having the potential for more targeted delivery of chemical antimicrobials. Unfortunately, there are impacts on the environment of widening mouthwash use with more new products, including increased use of packaging, antimicrobial resistance, and possible detrimental effects on marine life. Further, there are roadblocks, relating to regularly approvals and side effects, that still need to be overcome for any OTC deivered immunomodulant or nanoformulation mouthwashes. Despite these caveats, there are many new mouthwashes under development, which could help manage major oral diseases such as caries, gingivitis, and periodontal disease.

The Multifaceted Nature of Streptococcal Antigen I/II Proteins in Colonization and Disease Pathogenesis

Streptococci are Gram-positive bacteria that belong to the natural microbiota of humans and animals. Certain streptococcal species are known as opportunistic pathogens with the potential to cause severe invasive disease. Antigen I/II (AgI/II) family proteins are sortase anchored cell surface adhesins that are nearly ubiquitous across streptococci and contribute to many streptococcal diseases, including dental caries, respiratory tract infections, and meningitis. They appear to be multifunctional adhesins with affinities to various host substrata, acting to mediate attachment to host surfaces and stimulate immune responses from the colonized host. Here we will review the literature including recent work that has demonstrated the multifaceted nature of AgI/II family proteins, focusing on their overlapping and distinct functions and their important contribution to streptococcal colonization and disease.

Simple and rapid analysis of tocilizumab using HPLC-fluorescence detection method

We developed a novel assay using high-performance liquid chromatography (HPLC) with fluorescence detection for the determination of tocilizumab (TCZ), after it has undergone a facile and rapid pretreatment. TCZ belongs to the same subclass as IgG1 (Immunoglobulin G subclass 1), and we could separate TCZ from IgG1 without antigen-antibody reactions, with the novel detection method. The separation of these antibodies was achieved by pretreatment with an organic solvent containing a base, such as trimethylamine and triethylamine. The effect of these bases on the separation of TCZ is related to the hydrophobicity of the base rather than the electrostatic charge. The results indicated that the surface charge of antibodies changed because of the structural change, even though the difference in the amino acid sequences of the antibodies was very low. Our method is available for the separation of the antibody subclasses, and it would be useful to assay TCZ in blood.

Plant-Derived Monoclonal Antibodies for Prevention and Treatment of Infectious Disease

Numerous monoclonal antibodies (MAbs) that recognize and neutralize infectious pathogens have been isolated and developed over the years. The fact that infectious diseases can involve large populations of infected individuals is an important factor that has motivated the search for both cost-effective and scalable methods of antibody production. The current technologies for production of antibodies in plants allow for very rapid expression and evaluation that can also be readily scaled for multikilogram production runs. In addition, recent progress in manipulating glycosylation in plant production systems has allowed for the evaluation of antibodies containing glycans that are nearly homogeneous, are mammalian in structure, and have enhanced neutralizing capabilities. Among the anti-infectious disease antibodies that have been produced in plants are included those intended for prevention or treatment of anthrax, Clostridium perfringens, Ebola virus, human immunodeficiency virus, herpes simplex virus, rabies, respiratory syncytial virus, staphylococcal enterotoxin, West Nile virus, and tooth decay. Animal and human efficacy data for these MAbs are discussed.

Reduction of enterotoxin induced fluid accumulation in ileal loops of neonatal calves with anti-F5 fimbriae recombinant antibody

Neonatal calf colibacillosis caused by enterotoxigenic Escherichia coli (ETEC) is an economically significant problem in most parts of the world. The most common ETEC found in calves express the F5 (K99) fimbriae, which are necessary for the attachment of the bacteria to the ganglioside receptors on enterocytes. It is known that prevention of ETEC F5(+) adhesion to its ganglioside receptors with specific antibodies protects calves from colibacillosis. Previously we have described the development and characterization of a mouse recombinant antibody fragment (moRAb) that prevents F5 fimbrial protein induced agglutination of horse red blood cells (HRBC), which exhibit the same gangloside receptor for F5 fimbriae. Here we demonstrate that this recombinant antibody fragment inhibits in vitro the attachment of ETEC F5(+) bacteria to HRBC as well as isolated calf enterocytes, and in vivo it decreases fluid accumulation in intestinal loops of calves. Thus, correct oral administration of this anti-F5 moRAb may serve as an immunoprophylactic for cost effective control of colibacillosis in calves.

Immunogenicity and in vitro and in vivo protective effects of antibodies targeting a recombinant form of the Streptococcus mutans P1 surface protein

Streptococcus mutans is a major etiologic agent of dental caries, a prevalent worldwide infectious disease and a serious public health concern. The surface-localized S. mutans P1 adhesin contributes to tooth colonization and caries formation. P1 is a large (185-kDa) and complex multidomain protein considered a promising target antigen for anticaries vaccines. Previous observations showed that a recombinant P1 fragment (P1(39-512)), produced in Bacillus subtilis and encompassing a functional domain, induces antibodies that recognize the native protein and interfere with S. mutans adhesion in vitro. In the present study, we further investigated the immunological features of P1(39-512) in combination with the following different adjuvants after parenteral administration to mice: alum, a derivative of the heat-labile toxin (LT), and the phase 1 flagellin of S. Typhimurium LT2 (FliCi). Our results demonstrated that recombinant P1(39-512) preserves relevant conformational epitopes as well as salivary agglutinin (SAG)-binding activity. Coadministration of adjuvants enhanced anti-P1 serum antibody responses and affected both epitope specificity and immunoglobulin subclass switching. Importantly, P1(39-512)-specific antibodies raised in mice immunized with adjuvants showed significantly increased inhibition of S. mutans adhesion to SAG, with less of an effect on SAG-mediated bacterial aggregation, an innate defense mechanism. Oral colonization of mice by S. mutans was impaired in the presence of anti-P1(39-512) antibodies, particularly those raised in combination with adjuvants. In conclusion, our results confirm the utility of P1(39-512) as a potential candidate for the development of anticaries vaccines and as a tool for functional studies of S. mutans P1.

Lab-Test(®) 4: Dental caries and bacteriological analysis

Dental caries is one of the most common infectious ultifactorial diseases worldwide, characterized by the progressive demineralization of the tooth, following the action of bacterial acid metabolism. The main factors predisposing the onset of the carious process are: 1) the presence of bacterial species able to lower the pH until critical values of 5.5, 2) the absence of adequate oral hygiene, 3) an inefficient immune response anti-caries, 4) the type of alimentary diet and 5) the structure of the teeth. Among the 200 bacterial species isolated from dental plaque the most pathogenic for dental caries are: Streptococcus mutans, Streptococcus sobrinus, Lactobacillus acidophilus, Actinomices viscusus and Bifidobacterium dentium. Our laboratory (LAB^® s.r.l., Codigoro, Ferrara, Italy) has developed a test for absolute and relative quantification of the most common oral cariogenic bacteria. The test uses specific primers and probes for the amplification of bacteria genome sequences in Polymerase Chain Reaction Real Time. The results provide a profile of patient infection, helpful for improving the diagnosis and planning of preventive treatment to reduce the bacterial load.

A therapeutic anti-Streptococcus mutans monoclonal antibody used in human passive protection trials influences the adaptive immune response

The adhesin known as Antigen I/II, P1 or PAc of the cariogenic dental pathogen Streptococcus mutans is a target of protective immunity and candidate vaccine antigen. Previously we demonstrated that immunization of mice with S. mutans complexed with anti-AgI/II monoclonal antibodies (MAbs) resulted in changes in the specificity, isotype and functionality of elicited anti-AgI/II antibodies in the serum of immunized mice compared to administration of bacteria alone. In the current study, an anti-AgI/II MAb reported in the literature to confer unexplained long term protection against S. mutans re-colonization following passive immunization in human clinical trials (MAb Guy's 13), and expressed in tobacco plants (MAb Guy's 13 plantibody), was evaluated for its potential immunomodulatory properties. Immunization of BALB/c mice with immune complexes of Guy's 13 plantibody bound to S. mutans whole cells resulted in a similar change in specificity, isotype, and functionality of elicited anti-AgI/II antibodies as had been observed for other immunomodulatory MAbs. This new information, coupled with the recently solved crystal structure of the adhesin, now provides a rational explanation and plausible mechanism of action of passively administered Guy's 13/Guy's 13 plantibody in human clinical trials, and how long-term prevention of S. mutans carriage well past the application period of the therapeutic antibody could have been achieved.

Evolution of plant-made pharmaceuticals

The science and policy of pharmaceuticals produced and/or delivered by plants has evolved over the past twenty-one years from a backyard remedy to regulated, purified products. After seemingly frozen at Phase I human clinical trials with six orally delivered plant-made vaccines not progressing past this stage over seven years, plant-made pharmaceuticals have made a breakthrough with several purified plant-based products advancing to Phase II trials and beyond. Though fraught with the usual difficulties of pharmaceutical development, pharmaceuticals made by plants have achieved pertinent milestones albeit slowly compared to other pharmaceutical production systems and are now at the cusp of reaching the consumer. Though the current economic climate begs for cautious investment as opposed to trail blazing, it is perhaps a good time to look to the future of plant-made pharmaceutical technology to assist in planning for future developments in order not to slow this technology's momentum. To encourage continued progress, we highlight the advances made so far by this technology, particularly the change in paradigms, comparing developmental timelines, and summarizing the current status and future possibilities of plant-made pharmaceuticals.

Clinical trial of a plant-derived antibody on recolonization of mutans streptococci

OBJECTIVE

This double-blinded, placebo-controlled clinical trial tested the safety and efficacy of a topical secretory IgA antibody manufactured in tobacco plants (plantibody) in preventing recolonization of mutans streptococci (MS) in human plaque as measured by whole stimulated saliva samples.

METHODS

Following a 9-day antimicrobial treatment with chlorhexidine (CHX), 56 eligible adults (enrollment salivary MS > or = 10(4) CFU/ml; no current caries) were randomized equally to a group receiving 0, 2, 4, or 6 topical applications of plantibody followed by 6, 4, 2, or 0 applications of placebo, respectively, over a 3-week period.

RESULTS

Among the 54 subjects who completed the trial, the CHX regimen eliminated salivary MS in 69%. After 6 months, there were no significant differences in MS levels by number of applications, relative to placebo (p > 0.43). No adverse effects were observed.

CONCLUSION

Plantibody is safe but not effective at the frequency, concentration, and number of applications used in this study.

Characterization of the Streptococcus mutans P1 epitope recognized by immunomodulatory monoclonal antibody 6-11A

Monoclonal antibody (MAb) 6-11A directed against Streptococcus mutans surface adhesin P1 was shown previously to influence the mucosal immunogenicity of this organism in BALB/c mice. The specificity of anti-P1 serum immunoglobulin G (IgG) and secretory IgA antibodies and the subclass distribution of anti-P1 serum IgG antibodies were altered, and the ability of elicited serum antibodies to inhibit S. mutans adherence in vitro was in certain cases increased. MAb 6-11A is known to recognize an epitope dependent on the presence of the proline-rich region of the protein, although it does not bind directly to the isolated P-region domain. In this report, we show that MAb 6-11A recognizes a complex discontinuous epitope that requires the simultaneous presence of the alanine-rich repeat domain (A-region) and the P-region. Formation of the core epitope requires the interaction of these segments of P1. Residues amino terminal to the A-region also contributed to recognition by MAb 6-11A but were not essential for binding. Characterization of the MAb 6-11A epitope will enable insight into potential mechanisms of immunomodulation and broaden our understanding of the tertiary structure of P1.

Passive immunization with milk produced from an immunized cow prevents oral recolonization by Streptococcus mutans

Cell surface protein antigen (PAc) and water-insoluble glucan-synthesizing enzyme (GTF-I) produced by cariogenic Streptococcus mutans are two major factors implicated in the colonization of the human oral cavity by this bacterium. We examined the effect of bovine milk, produced after immunization with a fusion protein of functional domains of these proteins, on the recolonization of S. mutans. To prepare immune milk, a pregnant Holstein cow was immunized with the fusion protein PAcA-GB, a fusion of the saliva-binding alanine-rich region (PAcA) of PAc and the glucan-binding (GB) domain of GTF-I. After eight adult subjects received cetylpyridinium chloride (CPC) treatment, one subgroup (n = 4) rinsed their mouths with immune milk and a control group (n = 4) rinsed with nonimmune milk. S. mutans levels in saliva and dental plaque decreased after CPC treatment in both groups. Mouth rinsing with immune milk significantly inhibited recolonization of S. mutans in saliva and plaque. On the other hand, the numbers of S. mutans cells in saliva and plaque in the control group increased immediately after the CPC treatment and surpassed the baseline level 42 and 28 days, respectively, after the CPC treatment. The ratios of S. mutans to total streptococci in saliva and plaque in the group that received immune milk were lower than those in the control group. These results suggest that milk produced from immunized cow may be useful for controlling S. mutans in the human oral cavity.

Production of secretory IgA antibodies in plants

Functional antibodies produced in tobacco plants were first reported over a decade ago (1989). The basic protocol used to generate these 'plantibodies' involved the independent cloning of H and L chain antibody genes in Agrobacterium tumefaciens vectors, the transformation of plant tissue in vitro with the recombinant bacterium, the reconstitution of whole plants expressing individual chains, and their sexual cross. In a 'Mendelian' fashion, a fully assembled and functional antibody was recovered from plant tissue in some double-transgenic plants. In mammalian cells, the antibody H and L chains are produced as precursor proteins that are translocated into the endoplasmic reticulum (ER), under the guidance of signal sequences. Within the ER, the signal peptides are proteolytically cleaved, and several stress proteins act as chaperonins to bind the unassembled antibody chains, and direct subsequent folding and tetramer formation. A similar process occurs in plant cells, and expression can be directed via signal sequences (even of foreign origin) into the aqueous environment of the apoplasm, or to be accumulated in other specific plant tissues, including tubers, fruit, or seed. Plants can facilely assemble secretory IgA, which is comprised of four chains, H and L chains, J chain and secretory component. Plant 'bioreactors' are expected to yield over 10 kg of therapeutic antibody/acre in tobacco, maize, soybean, and alfalfa [(Ann. NY Acad. Sci.)721(1994)235; (Biotechnol. Bioeng.)20(1999)135]. Compared with conventional steel tank bioreactors using mammalian cells, or microorganisms, the costs of GMP plantibodies are expected to perhaps one tenth. The differences in glycosylation patterns of plant and mammalian cell produced antibodies apparently have no effect on antigen-binding or specificity, but there is some concern about potential immunogenicity in humans. N-linked glycans of plants differ from human by having fucose-linked alpha 1,3 and the sugar xylose. No adverse effects or human anti-mouse antibodies (HAMA) have been observed in >40 patients receiving topical oral application of a plant produced secretory IgA specific to Streptococcus mutans, for the control of caries [(Nat. Med.)4(1998)601]. The progressive improvement of expression vectors for plantibodies, and purification strategies, as well as the increase in transformable crop species, is expected to lead to almost limitless availability of inexpensive (even edible forms of) recombinant immunoglobulins free of human pathogens for human and animal therapy, and for novel industrial applications (e.g. catalytic antibodies).

Passive transfer of immunoglobulin Y antibody to Streptococcus mutans glucan binding protein B can confer protection against experimental dental caries

Active immunization with Streptococcus mutans glucan binding protein B (GBP-B) has been shown to induce protection against experimental dental caries. This protection presumably results from continuous secretion of salivary antibody to GBP-B, which inhibits accumulation of S. mutans within the oral biofilm. The purpose of this study was to explore the influence of short-term (9- or 24-day) passive oral administration of antibody to S. mutans GBP-B on the longer-term accumulation and cariogenicity of S. mutans in a rat model of dental caries. Preimmune chicken egg yolk immunoglobulin Y (IgY) or IgY antibody to S. mutans GBP-B was supplied in lower (experiment 1) and higher (experiment 2) concentrations in the diet and drinking water of rats for 9 (experiment 1) or 24 (experiment 2) days. During the first 3 days of IgY feeding, all animals were challenged with 5 x 10(6) streptomycin-resistant S. mutans strain SJ-r organisms. Rats remained infected with S. mutans for 78 days, during which rat molars were sampled for the accumulation of S. mutans SJ-r bacteria and total streptococci. Geometric mean levels of S. mutans SJ-r accumulation on molar surfaces were significantly lower in antibody-treated rats on days 16 and 78 of experiment 2 and were lower on all but the initial (day 5) swabbing occasions in both experiments. Relative to controls, the extent of molar dental caries measured on day 78 was also significantly decreased. The decrease in molar caries correlated with the amount and duration of antibody administration. This is the first demonstration that passive antibody to S. mutans GBP-B can have a protective effect against cariogenic S. mutans infection and disease. Furthermore, this decrease in infection and disease did not require continuous antibody administration for the duration of the infection period. This study also indicates that antibody to components putatively involved only in cellular aggregation can have a significant effect on the incorporation of mutans streptococci in dental biofilm.

Maintaining mutans streptococci suppression with xylitol chewing gum

BACKGROUND

One strategy for treating dental caries is to suppress oral mutans streptococci, or MS, with chlorhexidine, or CHX, mouthrinse. Oral MS levels, however, tend to quickly return to baseline values without further intervention. In this clinical study, the authors evaluated the effect of xylitol chewing gum on MS regrowth.

METHODS

The authors selected 151 subjects with elevated oral MS levels (> or = 105 colony-forming units per milliliter, or CFU/mL, of paraffin-stimulated saliva). Subjects rinsed with 0.12 percent CHX gluconate mouthrinse twice daily for 14 days. The authors then randomly assigned the subjects to one of three groups. Those in the test group (n = 51) chewed a commercial xylitol gum three times daily for a minimum of five minutes each time for three months. The placebo group subjects (n = 50) used a commercial sorbitol gum, and the control group subjects (n = 50) did not chew gum. The authors estimated MS load on the dentition using paraffin-stimulated saliva samples. The authors serially diluted the samples, plated them on selective media and incubated them anaerobically; they then enumerated the colonies under a stereomicroscope.

RESULTS

MS levels were not significantly different between the three groups at baseline (mean log CFU/mL +/- standard deviation: 5.4 +/- 0.7, 5.4 +/- 0.8, 5.2 +/- 0.7, respectively) nor after CHX therapy (2.7 +/- 0.8, 3.1 +/- 1.1, 3.0 +/- 1.1, respectively). After three months of gum chewing, the test group subjects had significantly lower salivary MS levels (3.6 +/- 1.2) than did the placebo (4.7 +/- 1.2) or control (4.4 +/- 1.3) group subjects.

CONCLUSIONS

Xylitol chewing gum appears to have the ability to prolong the effect of CHX therapy on oral MS.

CLINICAL IMPLICATIONS

Maintaining long-term caries-pathogen suppression is feasible with currently available commercial products and can be expected to result in significant caries inhibition.

Preventing infectious disease with passive immunization

Antibodies can prevent infectious diseases by providing passive immune protection. Here we review successful clinical trials of passive immunization and consider some of the unique qualities monoclonal antibodies are now beginning to offer for developing methods for passive immunization against a wide range of infectious diseases.

Current status of a mucosal vaccine against dental caries

The evidence of a specific bacterial cause of dental caries and of the function of the salivary glands as an effector site of the mucosal immune system has provided a scientific basis for the development of a vaccine against this highly prevalent and costly oral disease. Research efforts towards developing an effective and safe caries vaccine have been facilitated by progress in molecular biology, with the cloning and functional characterization of virulence factors from mutans streptococci, the principal causative agent of dental caries, and advancements in mucosal immunology, including the development of sophisticated antigen delivery systems and adjuvants that stimulate the induction of salivary immunoglobulin A antibody responses. Cell-surface fibrillar proteins, which mediate adherence to the salivary pellicle, and glucosyltransferase enzymes, which synthesize adhesive glucans and allow microbial accumulation, are virulence components of mutans streptococci, and primary candidates for a human caries vaccine. Infants, representing the primary target population for a caries vaccine, become mucosally immunocompetent and secrete salivary immunoglobulin A antibodies during the first weeks after birth, whereas mutans streptococci colonize the tooth surfaces at a discrete time period that extends around 26 months of life. Therefore, immunization when infants are about one year old may establish effective immunity against an ensuing colonization attempts by mutans streptococci. The present review critically evaluates recent progress in this field of dental research and attempts to stress the protective potential as well as limitations of caries immunization.

Comparison of an anti-HSV-2 monoclonal IgG and its IgA switch variant for topical immunoprotection of the mouse vagina

An IgG2a monoclonal antibody (Mab) directed against glycoprotein D of herpes simplex virus 2 (HSV-2) was compared with an IgA heavy chain Mab switch variant to investigate the effect of isotype for topical immunoprotection of the murine vagina. The IgA Mab, a mixture of monomeric and polymeric IgA, was indistinguishable from its IgG parent in an in vitro HSV-2 neutralization assay. When these class switched Mabs were delivered to the mouse vagina, we also found no significant difference between the IgG and IgA for preventing vaginal transmission of HSV-2 infection. The implications of these results for active and passive immunization strategies against vaginal transmission of genital herpes infections are discussed.

Prevention of early childhood caries: a public health perspective

This paper proposes strategies for preventing early childhood caries (ECC), preferably for the greatest number of children at the lowest cost. Population-based, public health approaches are more likely to reach the target population groups at risk of developing ECC than individual, private practice-based approaches. Different prevention and early intervention strategies are discussed and the following recommendations are made: 1) Continue to promote community water fluoridation. 2) Evaluate the effectiveness of other public health oriented measures to prevent ECC. 3) Develop a national ECC and rampant caries registry. 4) Link oral health screening and easily implemented, low-cost interventions with immunization schedules and public health nursing activities. 5) Increase opportunities for community-based interventions conducted by dental hygienists. 6) Change insurance reimbursement schedules to provide incentives for dentists to prevent disease. 7) Include dentistry in new child health insurance legislation for children as well as parents of infants and preschool children.

Production of antibodies in transgenic plants

Plants offer a cost-effective bioreactor to produce antibodies of diverse types. Recent studies demonstrate that secretory IgA, the predominant antibody isotype of the mucosal immune system, can be made in large quantities in plants. CaroRx, the lead SIgA antibody being developed by Planet Biotechnology Inc., has demonstrated activity in pilot phase II trials versus S. mutans, the major pathogen contributing to development of dental caries. Numerous other SIgA plantibodies are in preclinical development.

Influence of heat inactivation of human serum on the opsonization of Streptococcus mutans

Phagocytosis of bacteria, such as Streptococcus mutans, is important to host defense. One mechanism by which phagocytosis can be enhanced is by antibody or complement-mediated opsonization of bacteria. Many studies utilize opsonization of bacteria to enhance a cellular response, but little information has been found examining methodology or validity of the opsonization process following the denaturization of the serum. Human serum was inactivated by heat in order to disrupt the classical and alternative pathways of the complement cascade. S. mutans isolated from human subjects were opsonized with heat-inactivated human serum before exposing them to viable neutrophils in vitro. Luminol-dependent chemiluminescence (CL) was used to measure neutrophil activation. Human serum used to opsonize the bacteria was denatured by incubation at 57 degrees C for intervals of 30 and 60 min to inactivate complement. The results from the opsonization data indicated that there was significantly increased CL with 60-min inactivation of the serum (34% increase in mean integration mV.min; p < or = 0.05) over the nonopsonized control. This indicated a successful opsonization of the bacteria. In addition, the data demonstrate that the inactivation of serum requires a minimum of 60 min at 57 degrees C to disrupt the complement cascade, while 30- and 15-min inactivations produced no significant increase in CL activity over the control. Standard sandwich ELISA assays, detecting complement binding to S. mutans, confirmed successful heat inactivation of serum showing a significant decrease (p < or = 0.001) in complement binding to S. mutans after 30 min, but could not explain the increased CL response after 60-min heat deactivation of the serum.

Streptococcus mutans major adhesion surface protein, P1 (I/II), does not contribute to attachment to valvular vegetations or to the development of endocarditis in a rat model

Streptococcus mutans P1 antigen functions as an adhesion factor for binding to salivary pellicle on tooth surfaces. It induces increased antibody titres in patients with Strep. mutans endocarditis. A mutant of Strep. mutans deficient in the function of the gene (spa P) encoding the surface antigen P1, and its isogenic parental strain, were used in a rat endocarditis experiment. Absence of P1 did not decrease adhesion to vegetations determined l h after intravenous infection. The number of bacteria recovered from valvular vegetations after 48 h from animals with manifest endocarditis did not differ between the strains. Consequently, the Pl antigen appears to be unimportant both for adhesion and virulence in endocarditis caused by Strep. mutans.

Caries prevention: current strategies, new directions

Despite major advances in caries prevention, a large subset of the U.S. population still needs additional control measures. In numerous other countries, needs are escalating as caries rates continue to rise. Building on current strategies and new insights into the specific mechanisms of caries initiation, researchers are creatively using a variety of new technologies, especially in molecular biology, to fashion a new generation of preventive measures.

A mechanism of passive immunization with monoclonal antibodies to a 185,000 M(r) streptococcal antigen

The cell surface streptococcal antigen (SA) I/II of 185,000 M(r) is an immunodominant molecule that expresses one or more adhesion determinants. A series of 14 monoclonal antibodies (MAb) to defined parts of SA I/II were generated and some of these were used in passive immunization of macaques. Topical administration of selected MAb to the teeth of macaques prevented colonization of endogenous or implanted exogenous Streptococcus mutans for a period of 1 year. Significant reduction of both smooth surface and fissure caries was found in macaques who had MAb (Guy's 1) applied to their teeth, as compared with saline-treated animals. A series of in vivo passive immunization experiments was then carried out in 57 human subjects. Topical application of MAb to SA I/II prevented colonization of both artificially implanted exogenous strains of S. mutans, as well as natural recolonization by indigenous S. mutans. The properties of the protective MAb were then investigated and the epitope specificity within the SA I/II molecule was found to be essential but not the isotype specificity of the immunoglobulin (Ig). The requirement for complement activating and the phagocyte binding sites of the Fc fragment of MAb was not essential, as the F(ab')2 fragment of the MAb was as protective as the intact IgG, but the Fab fragment failed to prevent recolonization of S. mutans. Prevention of recolonization was specifically restricted to S. mutans, as the proportion of other organisms, such as S. sanguis, failed to show a significant change. The surprising feature of these experiments was that protection of re-colonization of S. mutans lasted up to 2 years, although MAb was applied for only 3 weeks and functional MAb was detected on the teeth only 3 days following application of the MAb. The long-term protection could therefore not be accounted for by a persistence of MAb on the teeth, but may be due to a shift in the microbial balance in which other bacteria occupy the ecological niche vacated by S. mutans, resulting in colonization resistance to S. mutans. Gene cloning and sequencing the SA from S. mutans, S. sobrinus and S. sanguis identified a conserved region (residues 955-1213) which on Southern hybridization and partial DNA sequence analysis was also found in 19 alpha-haemolytic oral streptococci. The results suggest that the SA molecule may constitute a family of adhesins in oral alpha haemolytic streptococci.(ABSTRACT TRUNCATED AT 400 WORDS)

Molecular, immunological and functional characterization of the major surface adhesin of Streptococcus mutans

In the 15 years since the last major NIH conference that dealt with anti-caries vaccines, we have learned much. Certainly, whole bacteria or bacterial fractions may not be proper immunogens due to the possibility of inducing tissue cross-reactivity. Our own experience (van de Rijn et al., 1976) illustrates that pitfall. But even in the era of genetically engineered vaccines, we first must understand the biological functions of our chosen immunogen before employing that pure protein in a vaccine. Our recent work (Brady et al., 1991c) indicates that antigen P1, a ubiquitous protein found on several oral streptococci, may possess different, but possibly overlapping, functional domains influencing reactions with fluid-phase salivary agglutinin (aggregation) versus fixed agglutinin (adherence). A proper vaccine would induce antibodies against the latter domain(s) thereby retarding colonization. An improper vaccine that induces antibodies against aggregation-related domains on P1 would lessen the host's ability to clear those bacteria from the oral cavity. After carefully identifying appropriate functional domains and obtaining sub-clones of the larger gene that yield truncated polypeptides typical of adherence-specific regions that are also immunogenic, we may be in a position to create the most effective vaccine. In studies employing the polymerase chain reaction (PCR) and standard cloning procedures, we have already begun to produce such polypeptides. Once a library of polypeptides is assembled, they may be tested for functional activity and for lack of induction of cross-reactivity with nonpathogenic streptococci (i.e., S. gordonii). Certain of these recombinant-specified polypeptides could serve as the basis for an anti-caries vaccine. Alternatively, peptides may be synthesized that resemble these sub-molecular regions for use in a vaccine or as competitive inhibitors of adherence but not aggregation. Clearly, a vaccine against dental caries remains a real possibility for the future.