Characterization of monoclonal antibodies to Streptococcus mutans antigenic determinants I/II, I, II, and III and their serotype specificities

Development and characterization of p1025-loaded bioadhesive liquid-crystalline system for the prevention of Streptococcus mutans biofilms

Formation of a dental biofilm by Streptococcus mutans can cause dental caries, and remains a costly health problem worldwide. Recently, there has been a growing interest in the use of peptidic drugs, such as peptide p1025, analogous to the fragments 1025-1044 of S. mutans cellular adhesin, responsible for the adhesion and formation of dental biofilm. However, peptides have physicochemical characteristics that may affect their biological action, limiting their clinical performance. Therefore, drug-delivery systems, such as a bioadhesive liquid-crystalline system (LCS), may be attractive strategies for peptide delivery. Potentiation of the action of LCS can be achieved with the use of bioadhesive polymers to prolong their residence on the teeth. In line with this, three formulations - polyoxypropylene-(5)-polyoxyethylene-(20)-cetyl alcohol, oleic acid, and Carbopol C974P in different combinations (F1C, F2C, and F3C) were developed to observe the influence of water in the LCS, with the aim of achieving in situ gelling in the oral environment. These formulations were assessed by polarized light microscopy, small-angle X-ray scattering, rheological analysis, and in vitro bioadhesion analysis. Then, p1025 and a control (chlorhexidine) were incorporated into the aqueous phase of the formulation (F + p1025 and F + chlorhexidine), to determine their antibiofilm effect and toxicity on epithelial cells. Polarized light microscopy and small-angle X-ray scattering showed that F1C and F2C were LCS, whereas F3C was a microemulsion. F1C and F2C showed pseudoplastic behavior and F3C Newtonian behavior. F1C showed the highest elastic and bioadhesive characteristics compared to other formulations. Antibiofilm effects were observed for F + p1025 when applied in the surface-bound salivary phase. The p1025-loaded nanostructured LCS presented limited cytotoxicity and effectively reduced S. mutans biofilm formation, and could be a promising p1025-delivery strategy to prevent the formation of S. mutans dental biofilm.

Optimisation of contained Nicotiana tabacum cultivation for the production of recombinant protein pharmaceuticals

Nicotiana tabacum is emerging as a crop of choice for production of recombinant protein pharmaceuticals. Although there is significant commercial expertise in tobacco farming, different cultivation practices are likely to be needed when the objective is to optimise protein expression, yield and extraction, rather than the traditional focus on biomass and alkaloid production. Moreover, pharmaceutical transgenic tobacco plants are likely to be grown initially within a controlled environment, the parameters for which have yet to be established. Here, the growth characteristics and functional recombinant protein yields for two separate transgenic tobacco plant lines were investigated. The impacts of temperature, day-length, compost nitrogen content, radiation and plant density were examined. Temperature was the only environmental variable to affect IgG concentration in the plants, with higher yields observed in plants grown at lower temperature. In contrast, temperature, supplementary radiation and plant density all affected the total soluble protein yield in the same plants. Transgenic plants expressing a second recombinant protein (cyanovirin-N) responded differently to IgG transgenic plants to elevated temperature, with an increase in cyanovirin-N concentration, although the effect of the environmental variables on total soluble protein yields was the same as the IgG plants. Planting density and radiation levels were important factors affecting variability of the two recombinant protein yields in transgenic plants. Phenotypic differences were observed between the two transgenic plant lines and non-transformed N. tabacum, but the effect of different growing conditions was consistent between the three lines. Temperature, day length, radiation intensity and planting density all had a significant impact on biomass production. Taken together, the data suggest that recombinant protein yield is not affected substantially by environmental factors other than growth temperature. Overall productivity is therefore correlated to biomass production, although other factors such as purification burden, extractability protein stability and quality also need to be considered in the optimal design of cultivation conditions.

Differential activation of human neutrophils by Streptococcus mutans isolates from root surface lesions and caries-free and caries-active subjects

Phagocytosis of bacterial pathogens is an important defense mechanism and may contribute to regulating Streptococcus mutans-induced dental caries, particularly at root surfaces. This study was undertaken to examine and compare differences in polymorphonuclear leukocyte or neutrophil activation by clinical isolates of S. mutans collected from the saliva of caries-free or caries-active individuals with S. mutans isolates from root surface lesions. S. mutans clinical isolates (5 caries-free, 5 caries-active, 5 root caries isolates and a laboratory strain) were incubated with neutrophils in the presence of normal human serum and the luminol dependent chemiluminescence was measured for 1 h at 37 degrees C. Results indicated that the caries active and laboratory strains activated neutrophils equally. The mean integration stimulated by caries-free strains, however, displayed a 25-30% enhanced neutrophil activation over the caries-active and laboratory strains. In contrast, neutrophil activation by root caries strains of S. mutans was 45-50% lower than all other S. mutans strains, possibly suggesting a natural selection for S. mutans strains that can evade neutrophil recognition and subsequent phagocytosis. Stimulation of neutrophils with the cell wall and membrane surface component preparations indicated that extracts from all four groups activated neutrophils significantly. Again, caries-free preparations activated neutrophils significantly more than caries active, laboratory strain and root caries isolates. This selection may become more important on root surfaces due to increased exposure to crevicular fluid and neutrophils. The data provide evidence for the presence or onset of mechanisms or biological alterations in S. mutans developed to circumvent neutrophil recognition and/or phagocytosis, thus increasing S. mutans survival and colonization on tooth surfaces, resulting in an enhanced risk of dental caries, particularly at root surfaces.

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.

Antigenic characterization of fimbria preparations from Streptococcus mutans isolates from caries-free and caries-susceptible subjects

The adhesion of pathogenic bacteria to the host surface is an essential step in the development of numerous infections, including dental caries. Attachment of Streptococcus mutans, the main etiological agent of human dental caries, to the tooth surface may be mediated by glucan synthesized by glucosyltransferase (GTF) and by cell surface proteins, such as P1, which bind to salivary receptors. Fimbriae on the surfaces of many microorganisms are known to function in bacterial adhesion. Previous studies in this laboratory have initially characterized the fibrillar surface of S. mutans. The purpose of this investigation was the comparison of the antigenic properties of fimbria preparations of S. mutans isolates from five caries-resistant (CR) and six caries-susceptible (CS) subjects. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of S. mutans fimbrial preparations revealed five major protein bands at 200, 175, 157, 86, and 66 kDa in preparations from CR and CS subjects. Immunoblot analysis indicated the presence of the same major bands recognized by anti-S. mutans fimbria antisera. Furthermore, the 175- and 157-kDa bands were recognized by antibodies to P1 and GTF, respectively. Immunoblot analysis with antisera to the fimbria preparation, to P1, or to GTF indicated that the levels of fimbria-reactive components and P1 and GTF antigens were higher in S. mutans fimbria preparations from CS subjects than in those from CR individuals. For example, four of six fimbria preparations from CS patients had demonstrable P1, and all had GTF. In contrast, only two of five CR fimbrial preparations exhibited P1 and GTF. Enzyme-linked immunosorbent assay demonstrated similar results for levels of GTF antigen in the fimbrial preparations from CR and CS subjects. The results suggest that differences between the compositions of S. mutans fimbriae in CR and CS individuals may play an important role in the virulence of this microorganism in dental caries.

Assembly of monoclonal antibodies with IgG1 and IgA heavy chain domains in transgenic tobacco plants

The genes encoding the heavy and light chains of a murine monoclonal antibody (mAb Guy's 13) have been cloned and expressed in Nicotiana tabacum. Transgenic plants have been regenerated that secrete full-length Guy's 13 antibody. By manipulation of the heavy chain gene sequence, constant region domains from an immunoglobulin alpha heavy chain have been introduced, and plants secreting Guy's 13 mAb with chimeric gamma/alpha heavy chains have also been produced. For each plant antibody, light and heavy chains have been detected by Western blot analysis and the fidelity of assembly confirmed by demonstrating that the antibody is fully functional, by antigen binding studies. Furthermore, the plant antibodies retained the ability to aggregate streptococci, which confirms that the bivalent antigen-binding capacity of the full length antibodies is intact. The results demonstrate that IgA as well as IgG class antibodies can be assembled correctly in tobacco plants and suggest that transgenic plants may be suitable for high-level expression of more complex genetically engineered immunoglobulin molecules. Since mAb Guy's 13 prevents streptococcal colonization in humans, transgenic plant technology may have therapeutic applications.

A protein fragment of streptococcal cell surface antigen I/II which prevents adhesion of Streptococcus mutans

Attachment of Streptococcus mutans to the tooth surface involves a cell surface protein with an M(r) of 185,000, termed streptococcal antigen (SA) I/II. Four overlapping fragments of the gene encoding SA I/II were amplified by polymerase chain reaction, cloned, and expressed in Escherichia coli. The recombinant polypeptides were assayed for adhesion-binding activity to salivary receptors and for recognition by a panel of monoclonal antibodies (MAbs) raised against SA I/II. Two of the MAbs which are known to prevent colonization of S. mutans in vivo bound the recombinant polypeptide comprising residues 816 to 1161. In vitro adhesion of S. mutans to saliva-coated hydroxyapatite beads was also inhibited specifically by a polypeptide (residues 816 to 1213) encompassing the same region. The evidence from the MAbs preventing colonization of S. mutans and the adherence inhibition assay suggests that an adhesion-binding activity resides within the portion of SA I/II comprising residues 816 to 1213, which is highly conserved among oral streptococcal species.

First characterization in Italy of clinical isolates of mutans streptococci by using specific monoclonal antibodies

The aim of this investigation was to gain further insight into the prevalence of different serotypes of mutans streptococci in the Italian population by using specific monoclonal antibodies in an enzyme immunoassay. Isolates from dental plaque samples, collected from an adult population living in Pisa (Italy), were identified as mutans streptococci on the basis of their morphological and biochemical properties, and were then serotyped. The results show that 77.5% of the strains isolated belonged to serotype c or f (i.e., S. mutans), 15.9% were serotype e (i.e., S. mutans) and only two strains (1.4%) belonged to serotype g (i.e., S. sobrinus). These data are partially in agreement with other studies in Europe and in the U.S.A. The distribution pattern of the various serotypes turned out to be substantially similar among the different groups of patients, subdivided on the basis of their caries status, indicating that none of the serotypes was particularly associated with dental caries.

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.

Sequence and structural analysis of surface protein antigen I/II (SpaA) of Streptococcus sobrinus

Streptococcal antigen I/II or the surface protein antigen A (SpaA) of Streptococcus sobrinus is an adhesin which mediates binding of the organism to tooth surfaces. The complete sequence of the gene which encodes SpaA has been determined. The gene consists of 4,584 bp and encodes a protein of 1,528 amino acid residues. The deduced amino acid sequence shows extensive homology with those of the cell surface adhesins from Streptococcus mutans serotypes c and f and from Streptococcus sanguis. Structural analysis of the N-terminal region (residues 50 to 550), which is rich in alanine and includes four tandem repeats of an 82-residue sequence, suggests that it adopts an alpha-helical coiled-coil conformation. Cell surface hydrophobicity may be associated with this region. The C-terminal region is more conserved and includes two tandem repeats of a 39-residue proline-rich sequence. A further proline-rich sequence in this region is predicted to span the cell wall. Although a hydrophobic sequence is present in the C-terminal region, it appears to be too short to span the cell membrane. Anchoring of SpaA in the cell membrane may therefore require some form of posttranslational modification or association with another membrane protein.

Conservation of the gene encoding streptococcal antigen I/II in oral streptococci

The spaP gene of Streptococcus mutans serotype c encodes a major cell surface protein, streptococcal antigen (SA) I/II, with an Mr of 185,000, that is thought to be involved in bacterial adhesion to teeth. Proteins with significant amino acid sequence homology to SA I/II have also been found in S. sobrinus and S. sanguis. The objectives of this study were to investigate the conservation of the spaP gene in the mutans groups of streptococci and to determine whether homologous genes were present in other species of alpha-hemolytic streptococci. DNA extracted from representative strains of 19 streptococcal species was examined by Southern hybridization and partial DNA sequence analysis. A series of five overlapping DNA probes from the spaP gene were amplified by the polymerase chain reaction and used in the Southern hybridizations. The entire gene was found to be well conserved in all strains of S. mutans serotypes c, e, and f investigated. A probe from the 3' region of the gene, which encodes residues 857 to 1207 of the SA I/II protein, hybridized with DNA from a number of mutans streptococci, as well as with DNA from nonmutans alpha-hemolytic streptococci. Conservation within this region was further demonstrated by sequencing gene fragments of two strains of S. intermedius and S. oralis. The results show that some regions of the spaP gene are highly conserved not only in the mutans group of streptococci but also in other nonmutans alpha-hemolytic streptococci. This suggests that a family of cell surface proteins which, by analogy with the 185,000-Mr SA I/II of S. mutans, could be involved in bacterial adhesion might exist.

Identification of mutans streptococci with monoclonal antibodies

Mutans streptococci have been correlated with dental caries. The identification of the species within this group is still a problem. The characterization of a monoclonal antibody (Mab) OMVU10 against S. sobrinus as well as the isolation and characterization of Mabs against S. mutans (OMVU30 and OMVU31), S. cricetus (OMVU40) and mutans streptococci (OMVU2) is described. The epitope specificity for OMVU10 and OMVU31 was cell-wall antigen B in both cases although both Mabs recognized different species-specific epitopes. OMVU40 was cross reactive with Streptococcus sanguis taxon 3. All other Mabs were specific for one species. Using these Mabs, a key to the identification of mutans streptococci is developed. This key was tested for 85 wild type isolates of mutans streptococci and proved to be highly reliable and easy to perform.

Immunological cross-reactivity between Streptococcus mutans and human heart tissue examined by cross-immunization experiments

Hyperimmunization of rabbits with Streptococcus mutans or other related cariogenic streptococci sometimes induces serum antibodies that react with human heart muscle. To determine whether antigen I/II (AgI/II), a major surface protein antigen present in most human isolates of these organisms, was responsible for inducing cross-reactive antibodies, we tested it for antigenic similarity to heart components, exploiting the ability of immune systems to mount anamnestic responses to antigens previously encountered. Mice immunized with a strain of Streptococcus pyogenes type M6, known to be heart cross-reactive, or with intact S. mutans cells developed antibodies that could be detected on a human heart sarcolemmal preparation. However, mice immunized with AgI/II and boosted with sarcolemma were unable to develop significant antisarcolemmal antibodies attributable to prior sensitization by AgI/II. Similarly, AgI/II was unable to recall antisarcolemmal responses in mice previously immunized with sarcolemma. Nevertheless, strong immunoglobulin G antibody responses to AgI/II were detected at the single-cell level in spleens and as circulating antibodies in all mice immunized with AgI/II or AgI/II-bearing S. mutans. We conclude that the ability of S. mutans to induce heart-reactive antibodies is not due to antigenic similarity between AgI/II and components of human heart but may be caused by other cross-reactive antigens in the bacterial cells or by nonspecific stimulation of the immune system.

Cross-reactivity between the immunodominant determinant of the antigen I component of Streptococcus sobrinus SpaA protein and surface antigens from other members of the Streptococcus mutans group

Most members of the Streptococcus mutans group of microorganisms specify a major cell surface-associated protein, SpaA, that is defined by its antigenic properties. The region of the spaA gene from Streptococcus sobrinus 6715 encoding the immunodominant determinant of the major antigenic component (antigen I) of the SpaA protein has recently been characterized. This study examined whether recognition of the immunodominant determinant is independent of the immunized animal host and whether antibodies elicited by the immunodominant determinant cross-react with cell surface proteins from S. mutans of various serotypes. Mouse and rabbit antisera to the undenatured SpaA protein reacted similarly both with the immunodominant determinant and with other antigenic structures of the protein in Western immunoblots with SpaA polypeptides that were specified by spaA gene fragments expressed in recombinant Escherichia coli. This suggests that the antibody responses of inbred and outbred animals were similar. Furthermore, antibodies raised against both the S. sobrinus SpaA immunodominant determinant expressed by recombinant E. coli and the purified protein from S. sobrinus displayed similar strain specificities and protein band profiles towards cells surface proteins from S. mutans of various serotypes in immunodot and Western blot analyses, respectively. This suggests that for S. sobrinus serotype g, the immune response against the SpaA protein is governed by the immunodominant determinant of antigen I. In addition, it indicates that the SpaA protein domain containing the immunodominant determinant overlaps the domain conferring cross-reactivity to cell surface proteins of S. mutans of various serotypes.

Streptococcus mutans and the problem of heart cross-reactivity

Investigations of immune responses to Streptococcus mutans have fostered consideration of vaccination as a possible preventive measure against dental caries. However, the finding that hyperimmune rabbit antisera to S. mutans sometimes give immunofluorescent reactions on human heart raised concerns over safety, especially as most individuals display circulating antibodies to this common oral organism. Recent progress in elucidating the molecular mechanisms of the well-established immunological cross-reactivity between group A streptococci and human heart tissue and the structure of S. mutans antigens permits a re-evaluation of this problem. This review examines the evidence for heart cross-reactivity induced by S. mutans in relation to studies on group A streptococci and current understanding of autoimmunity. Although the mechanisms involved in this phenomenon need further clarification, it now appears that it cannot be ascribed to antigenic similarity between heart tissue and a high-molecular-weight surface protein antigen of S. mutans.

Cloning of the amino terminal nucleotides of the antigen I/II of Streptococcus sobrinus and the immune responses to the corresponding synthetic peptides

A portion of the antigen I/II (spaA, B, P1) gene of Streptococcus sobrinus 6715, containing the coding sequence for the amino terminal 684 amino acids of the protein, was cloned in bacteriophage lambda GT10. Selection was by immunological detection using a polyclonal antiserum to the antigen I/II from Strep. mutans. From the amino acid sequence, peptides were synthesized, 15 amino acids in length, that covered the entire sequence. In total, 260 synthetic peptides were synthesized and evaluated for their immunogenicity in Balb/C mice. Thirty-nine peptides were immunogenic, without carrier, and the antisera generated were tested for their ability to bind cells of Strep. mutans and Strep. sobrinus in a solid-phase assay. Antisera corresponding to peptides from five regions on the I/II molecule bound cells of both bacterial species. These peptides were then evaluated for their ability to stimulate in vitro murine lymphocyte proliferation, after in vivo immunization with Strep. sobrinus cells. Two of the peptides were capable of stimulating proliferation, as determined by incorporation of [3H]-thymidine into murine lymph node cells. The sequences of these 5 peptides were then compared to sequences found in the antigen I/II from Strep. mutans (Kelly et al., 1989). As expected, there was considerable homology between the cross-reactive peptides synthesized and the analogous region from Strep. mutans. This homology was not usually contiguous and suggests that the antibodies bind a face of antigen I/II that is in an alpha-helical conformation.(ABSTRACT TRUNCATED AT 250 WORDS)

Cloning and inactivation of the gene responsible for a major surface antigen on Streptococcus mutans

To understand more fully the biological function(s) and investigate the reported cross-reactivity with heart tissue of antigen P1 (I/II) of Streptococcus mutans (serotype c), this molecular biological study of the responsible gene, spaP, was undertaken. A 5.2 kb Hin dIII fragment of strain NG5 was cloned into Escherichia coli JM109 by a shotgun procedure with pUC18 as the vector. Recombinant SM2949 expressed a P1 fusion protein under the control of the streptococcal promoter. Southern analysis revealed hybridization of pSM2949 with DNA from Strep. mutans (serotypes c, e, f), Strep. cricetus (a) and Strep. sobrinus (d), but not Strep. sobrinus (g), Strep. rattus (b) or Strep. downei (h). Recombinant (r) antigen was detected in E. coli periplasm, indicating the presence of a signal sequence. This product (of Mr 155K) showed partial identity to the native streptococcal P1 antigen by Ouchterlony double-diffusion analysis. The N-terminal 28 amino acid residues of rP1 were determined by Edman degradation analysis and an end-labelled oligonucleotide probe corresponding to residues 8-13 was used to determine the 5'-3' orientation of spaP by Southern hybridization with restriction enzyme digests of pSM2949. Rabbit antisera made against native and rP1 did not cross-react with human heart tissue. Isogenic mutants of strain NG8 were isolated after transformation with insertionally inactivated spaP. Each mutant was non-reactive with anti-P1 antisera. Selected mutants were shown to have a defective spaP gene incorporated into their chromosomal DNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Sequencing and characterization of the 185 kDa cell surface antigen of Streptococcus mutans

The gene spa P (formerly designated as spa P1) encoding the Mr 185,000 surface antigen I/II of Streptococcus mutans, serotype c (strain NG5) has been sequenced. The deduced amino acid sequence of antigen I/II (1561 residues) includes a putative signal peptide (residues 1-38), as well as a transmembrane region (residues 1537-1556). The N-terminal part of the protein (residues 39-550) is particularly rich in alanine and includes three tandem repeats of a sequence of 82 residues. This region is predicted to be alpha-helical, adopting a coiled-coil formation, and may account for the cell surface hydrophobicity associated with expression of antigen I/II. In contrast the C-terminal region (residues 800-1549) is proline-rich, favouring an extended conformation. Comparison with the sequence determined from Strep. mutans strain MT8148 showed that antigen I/II is highly conserved with the exception of a short central region (residues 750-805). N-terminal sequencing of purified antigens I and II components indicated that antigen I extends from the amino-terminus of the intact Mr 185,000 surface antigen while antigen II extends from residue 996.

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

Topical application of Streptococcus mutans-specific MAbs was examined as a means of preventing colonization in the mouth. The MAbs recognize the cell surface antigen (SA I/II) of Strep. mutans and also bind to the intact bacterial cell. In experiments with implantation of an exogenous Strep. mutans strain, specific MAb significantly reduced the levels of implantation when compared with that in controls given a non-specific MAb. In a second investigation, the effect of MAb on recolonization by indigenous Strep. mutans was studied in subjects after treatment with a topical antibacterial mouthwash (chlorhexidine), which had decreased Strep. mutans to undetectable levels. In control subjects, the indigenous Strep. mutans started to recolonize within days, but those receiving MAb remained free of Strep. mutans for up to 2 yr. By using different Strep. mutans-specific MAbs, it was found that the serotype and epitope specificities of the IgG MAb were essential, but that the IgG sub-class may not be important. No clinical side-effects were detected in any of the subjects receiving MAb and there was no evidence of serum, salivary or gingival fluid antibody responses against the antibody. Local passive immunization with MAbs is a safe method for preventing colonization of Strep. mutans in the mouth.

Monoclonal antibodies for enumeration and identification of mutans streptococci in epidemiological studies

Two members of the mutans streptococci, Streptococcus mutans and Strep. sobrinus, are often found in human dental plaque. Different cariogenic characteristics between these species have been reported and therefore these species should be detected and identified separately. Identification of mutans streptococci based on sugar fermentation is troublesome and easily leads to erroneous conclusions. Furthermore, the recovery for the two species differs on selective media. This causes incorrect enumeration of Strep. mutans and Strep. sobrinus in clinical samples. The aim of this study was to develop an improved method for simultaneous identification and enumeration of Strep. mutans and Strep. sobrinus in dental plaque and saliva samples. The immunoblot technique described is based on growth of the microorganisms on non-selective media, followed by immunological detection with specific monoclonal antibodies. With the immunoblot significantly more plaque samples containing Strep. sobrinus were detected than on the selective medium TYCSB (p less than 0.01). The number of plaque samples harbouring Strep. mutans was equal on TYCSB and immunoblot. However, the numbers of c.f.u. of Strep. mutans and Strep. sobrinus detected with the blot were significantly higher than those obtained on TYCSB (p less than 0.01). The recovery of Strep. sobrinus on primary isolations on TYCSB appeared to be inhibited in 29 out of the 45 Strep. sobrinus-containing plaque samples. False-positive and false-negative reactions with the immunoblot were not found. The results indicate that the presence and numbers of Strep. sobrinus and Strep. mutans can be studied reliably using the immunoblot technique.

Sequence analysis of the cloned streptococcal cell surface antigen I/II

The gene spa P (formerly designated as spa P1) encoding the Mr 185,000 surface antigen (I/II) of Streptococcus mutans, serotype c (NG5), has been sequenced. The gene (4683 bp) encodes a protein of 1561 amino acid residues including putative signal peptide (residues 1-38) and transmembrane (residues 1537-1556) sequences. The N-terminal region (60-550) has alanine-rich repeats and is predicted to be alpha-helical. However, the C-terminal region (800-1540) is proline-rich and favours an extended structure. Except for a short central variable region the sequences appear to be highly conserved for S. mutans serotype c. N-Terminal sequencing of separated antigen I and antigen II polypeptides suggests that the former represents the N-terminal and the latter the C-terminal portions of the intact antigen.

Specificity of monoclonal antibodies in local passive immunization against Streptococcus mutans

Local oral passive immunization in human subjects with a monoclonal antibody (MoAb) raised against the 185-kD antigen I/II from S. mutans significantly reduced or prevented oral colonization of an exogenous strain of the organism. In subjects sham-immunized with either saline or an unrelated MoAb, however, significantly greater proportions of S. mutans persisted for a longer duration than in those immunized with the specific anti-streptococcal MoAb. Recolonization of indigenous S. mutans after this organism was reduced to undetectable levels by an antimicrobial agent has also been completely prevented with specific MoAb. Indeed, S. mutans was not detected for a period of over 1 year, as compared with recolonization within 10-82 days in the control subjects. The specificity of MoAb in preventing colonization of the streptococci was studied with four MoAb. This revealed that: (1) the sub-class of antibody is not an essential factor, as both MoAb Guy's 1 and 13 prevented colonization, although Guy's 1 is an IgG2a and Guy's 13 is an IgG1 class of antibody; (2) serotype specificity is important, as MoAb Guy's 9, which only recognizes S. sobrinus (serotypes d and g), does not prevent colonisation by S. mutans (serotype c); (3) neither protein nor carbohydrate nature of the putative adhesin was a determining factor, because MoAb Guy's 1 recognizes a carbohydrate and Guy's 13 a protein determinant and both MoAb prevented adherence of S. mutans; and (4) epitope specificity appears to be the most important factor in preventing adherence of S. mutans, as MoAb Guy's 11 and 13 share the same serotype specificity and both recognize a protein determinant, yet only Guy's 13 prevents colonisation. The long duration of protection from re-colonization by indigenous S. mutans, lasting about 1 year after application of the specific MoAb was stopped, cannot be accounted for by functional MoAb remaining on the teeth. We suggest that initially the MoAb prevents colonization by S. mutans and that the ecological niche vacated by this streptococcus is filled by other organisms from the oral flora, thereby discouraging re-colonization by S. mutans.

Characterisation of monoclonal antibodies to common protein epitopes on the cell surface of Streptococcus mutans and Streptococcus sobrinus

Three monoclonal antibodies (MAb) were prepared against a cell surface antigen which cross-react between Streptococcus mutans (serotypes c, e and f) and Streptococcus sobrinus (serotypes d and g). Two of the MAb also recognise a determinant on the surface of Streptococcus cricetus (serotype a). The common antigen shared between S. mutans and S. sobrinus was demonstrated by Western blotting to be about 200 kD in size. This antigen is shared not only by the cell surfaces of serotypes a, c, d, e, f and g, but also by the major cell surface antigen of S. mutans of 185 kD and another of 150 kD. These MAb identify all but one mutans type of streptococci and can be utilised as analytical reagents.

Proteolysis of the 185,000 MW streptococcal cell wall antigen generating 4000 and 6000 MW peptides with distinct antigenic determinants

A 185,000 MW glycoprotein antigen derived from Streptococcus mutans was digested with subtilisin. Purification by reversed phase high-powered liquid chromatography (HPLC) resulted in a homogeneous 20,000 MW protein which possesses the streptococcal antigen (SA) I and II determinants. This protein was immunogenic in mice both for the 20,000 MW and the native 185,000 MW SA. Further proteolysis with subtilisin generated four peptides of 18,000, 10,000, 6000 and 4000 MW. Whereas the 20,000, 18,000 and 10,000 MW peptides contained both SAI and SAII determinants, the 4000 MW peptide possessed only the SAI and the 6000 MW peptide the SAII determinant. The 4000-SAI peptide is of special significance, as the smallest SAI material separated in the past was 150,000 MW. This was difficult to purify and proved to be protective against dental caries on immunization of rhesus monkeys.

Separation and characterization of a 14,000-dalton cyanogen bromide-generated peptide from a 185,000-dalton streptococcal antigen

The cell surface streptococcal antigen (SA) (185,000 molecular weight [185K SA]) was isolated from Streptococcus mutans and digested with cyanogen bromide. Three major products with molecular weights of 100,000, 50,000, and 14,000 appeared within 1 h of digestion. Time course studies of digestion by polyacrylamide gel electrophoresis showed maximal intensity of the 14K band after 8 h. However, other bands appeared as well, notably 70K and 20K bands. Several bands were eluted from the gels, and their antigenicity was studied. They reacted with antisera to the native 185K SA I/II, as well as with those to the SA I and SA II antigens, though antibody binding by radioimmunoassay was significantly lower than that with the native SA. The 14K SA was identified on Western blots (immunoblots) with anti-SA I/II, I, and II antisera. The digested SAs were then tested for their immunogenicity by injecting CBA mice with the separated SA mixed in complete Freund adjuvant. Whereas the unseparated cyanogen bromide-treated SA and separated 70K and 20K SAs were immunogenic, the 14K SA failed to elicit serum antibodies. Further investigation of the 14K SA revealed that although it is apparently not immunogenic, it can induce a primary antibody response in mice when followed by the native 185K SA and a secondary response when mice are immunized first with the 185K SA.

Molecular cloning and expression of a Streptococcus mutans major surface protein antigen, P1 (I/II), in Escherichia coli

Antigen P1, also called I/II, is one of the most abundant cell wall proteins of the mutans streptococci. It has been suggested that P1 may be involved in cell adherence to tooth surfaces and in sucrose-induced cell aggregation. As a first step toward fully understanding its biological functions, the P1 gene, which has been designated spaP1, from Streptococcus mutans NG5 (serotype c) has been cloned into Escherichia coli JM109 by a shotgun procedure with pUC18 as the vector. The recombinant strain expressing P1 carries a 5.2-kilobase DNA insert whose restriction map has been determined. This map is completely different from that of spaA of Streptococcus sobrinus (serotype g), even though P1 and SpaA are antigenically related. Southern hybridization revealed that DNA sequences closely homologous to spaP1 were present in serotypes c, e, and f, and similar sequences also existed in strains of serotypes a and d. The expression of the cloned spaP1 was found to be independent of the lac inducer and the orientation of the DNA insert, suggesting that it carries its own promoter. Western blotting (immunoblotting) revealed at least 20 bands reacting with a mixture of three anti-P1 monoclonal antibodies. The highest-molecular-weight reactive band was comparable in size to the parent P1 (185 kilodaltons [kDa]); however, the major reactive bands were smaller (approximately 160 kDa). Expression of cloned P1 in E. coli LC137 (htpR lonR9) resulted in the increased prominence of the 185-kDa protein reactive band. Ouchterlony immunodiffusion showed partial identity between the parent and cloned P1. In E. coli, P1 was detected primarily in the periplasm and extracellular fluid.

Isolation and characterization of monoclonal antibodies specific for antigen P1, a major surface protein of mutans streptococci

A panel of 15 murine monoclonal antibodies (MAbs; 14 immunoglobulin G1, 1 immunoglobulin G2a) directed against antigen P1, a major surface protein of mutans streptococci, was prepared. All of these MAbs reacted by the enzyme-linked immunosorbent assay with solubilized wall material from Streptococcus mutans Ingbritt 175 (a serotype c strain which retains significant amounts of P1 in its cell wall), culture supernatant fluid from Ingbritt 162 (a strain which excretes large amounts of P1 into the culture medium), and purified P1. By Western immunoblotting, these MAbs were observed to react with a high-molecular-weight polypeptide which comigrated with antigen P1. None of these MAbs cross-reacted with human heart tissue or with various eucaryotic proteins. When whole cells of various strains of mutans streptococci were screened against the panel of MAbs, the strongest reactivities were noted with strains of serotype c and e S. mutans, while a serotype f strain of S. mutans, along with S. sobrinus and S. cricetus strains, reacted somewhat more weakly. S. rattus strains were completely negative. Results obtained with bacterial culture supernatants were qualitatively similar. The surface localization of antigen P1 was confirmed by electron microscopy with an indirect immunogold technique. In sectioned S. mutans cells, labeling appeared to be associated with a fibrillar "fuzzy coat" layer, which was far more prominent on cells of Ingbritt 175 than on those of Ingbritt 162.

Use of monoclonal antibodies in local passive immunization to prevent colonization of human teeth by Streptococcus mutans

Local passive immunization with monoclonal antibodies (MAbs) raised against streptococcal antigen (SA) I/II protects monkeys against colonization of teeth by Streptococcus mutans and the subsequent development of dental caries. In this study we extended the preclinical experiments to human subjects. In the first study of eight healthy subjects, four had anti-SA I/II MAb (immunoglobulin G2a [IgG2a]) and four had saline applied to their teeth on three occasions. A streptomycin-resistant S. mutans strain (Guy K2 strain, serotype c) was then implanted onto the teeth, and the organism was cultured sequentially from dental plaque and saliva up to 100 days after the first treatment with MAb. Decreased colonization by S. mutans was found in the dental plaque collected from smooth surfaces and fissures and in saliva of subjects whose teeth were treated with the MAb, as compared with the saline-treated control subjects. The experiment was then repeated on seven new subjects, and the effect of anti-SA I/II MAb was compared with that of an unrelated MAb to Campylobacter jejuni. The results again showed a consistently lower level of colonization of teeth in the anti-SA I/II MAb-treated subjects as compared with those sham immunized with the unrelated MAb. There was little difference in serum IgG, IgM, or IgA, gingival fluid IgG, or salivary IgA anti-SA I/II antibodies between the immunized and sham-immunized subjects, before and after the investigation. No side effects were observed, and the gingival and plaque indices remained unchanged. A sensitive radioimmunoassay failed to detect changes in anti-MAb (IgG2a) antibodies in any of the three fluids examined. We suggest that local passive immunization by means of MAb might be an alternative approach in the prevention of colonization of teeth by S. mutans and the development of dental caries.

Recognition of carbohydrate and protein epitopes by monoclonal antibodies to a cell wall antigen from Streptococcus mutans

The nature of the determinants recognized by a panel of monoclonal antibodies (MAbs) raised against a cell wall antigen of Streptococcus mutans (SA I/II) was investigated. Mild periodate oxidation of SA I/II showed that MAbs Guy 1, 2, 3, and 5 recognized carbohydrate epitopes on the antigen. Glycosidases were used to identify the nature of the sugars involved in their binding. Treatment with beta-glucosidase inhibited the binding of Guy 1, 2, 3, and 5 by 90%. No competition was found for any of the MAbs between SA I/II and a series of carbohydrates, including the serotype c polysaccharide from S. mutans. The results show that MAbs Guy 1, 2, 3, and 5 recognize carbohydrate epitopes on SA I/II which are distinct from the serotype polysaccharide. The other MAbs recognized protein epitopes on SA I/II.

Local active gingival immunization by a 3,800-molecular-weight streptococcal antigen in protection against dental caries

Local gingival immunization was attempted in an effort to confine the immune response to the oral cavity and bypass the systemic immune response. A low-molecular-weight (3.8K) streptococcal antigen (SA) I/II was applied 10 times over a period of 1 year to the gingival crevices of rhesus monkeys. The antigen was maintained in situ by means of silicone rubber appliances. Serial examinations over a period of 1 year showed that topical gingival immunization with the 3.8K SA results in a significantly lower incidence of dental caries and colonization of Streptococcus mutans compared with that of the sham-immunized controls. This was associated with an increase in gingival crevicular immunoglobulin G and salivary immunoglobulin A anti-SA I/II antibodies, whereas no change occurred in serum antibodies to SA I/II. The immune mechanism which prevents the colonization of S. mutans and the development of caries may involve antibodies that prevent the adherence of S. mutans to the teeth and facilitate phagocytosis and killing by the local neutrophils. This novel route of local immunization is noninvasive, does not cause side effects, and bypasses systemic immunization.

Local passive immunization by monoclonal antibodies against streptococcal antigen I/II in the prevention of dental caries

Local passive immunization with monoclonal antibodies (Mc Ab) to Streptococcus mutans was attempted as an alternative approach to active systemic immunization. We prepared an immunoglobulin G class Mc Ab to the cell surface protein determinant of streptococcal antigen I/II and applied it repeatedly to the teeth of rhesus monkeys. This resulted in decreased colonization by S. mutans in fissures and smooth surfaces of teeth and no dental caries, unlike the results in control animals, which developed caries and showed a high proportion of S. mutans on their teeth. There was no significant difference in serum, salivary, or gingival fluid antibodies to S. mutans between the two groups of animals. Any objections raised over systemic immunization inducing cross-reactive antibodies are therefore overcome by local passive immunization. The mechanism of prevention of colonization has not been established, but we postulate that the Mc Ab which is directed against an important cell surface antigenic determinant of S. mutans (streptococcal antigen I/II) prevents adherence of S. mutans to the acquired pellicle on the tooth surface. S. mutans reacts with the Mc Ab and becomes opsonized, phagocytosed, and killed by the local gingival traffic of neutrophils.

Helper and suppressor functions of human mononuclear cells depleted of antigen-binding T8+ cells

We have utilized the antigen-binding function of a subset of T8+ cells to remove these cells in vitro from human peripheral blood mononuclear cells. This was carried out by treating the cells with streptococcal antigen (SA), monoclonal anti-SA antibody and complement. The concentration of SA binding to T8+ cells differs with the HLA-DR type of the cells: 1 ng SA binds to DRw6+ cells and elicits T helper activity, whereas 1000 ng SA elicits T suppressor activity, in an assay for antibody-forming cells. After depletion of the antigen-binding cells by the SA-specific complement-dependent killing technique, the helper function of the DRw6+ cells was lost but suppression was elicited not only by 1000 ng but also by 1 ng SA. Similarly, DRw6- cells which bind 1000 ng SA to elicit helper activity and 1 ng to elicit suppression, when depleted of the SA-binding cells, resulted in loss of helper activity but again, suppression could be elicited by both 1000 and 1 ng SA. We suggest that treatment of mononuclear cells with antigen, the specific antibody and complement removes the T8+ antigen-binding cells which present antigen to T helper cells and results in the loss of helper function. Suppressor function is however, not only retained with the original concentration of SA but also expressed with that required to elicit helper function in the untreated cells. These findings are consistent with our hypothesis that the antigen-binding and presenting T8+ cells also function as contrasuppressor cells. Thus, the T8+ subset of cells have a dual function, to present antigen and to activate T helper cell function, and to prevent suppressor cells from inhibiting the helper cells.