Sequential development of helper and suppressor functions, antibody titers and functional avidities to a streptococcal antigen in rhesus monkeys

Cytokine induction by Streptococcus mutans and pulpal pathogenesis

Chronic pulpal inflammation under caries appears to be elicited by bacterial antigens that diffuse into the pulp through dentinal tubules. This prompted the hypothesis that cytokines elicited by antigens from Streptococcus mutans, which frequently dominates shallow lesions, could play a major role in eliciting the initial T-cell response in the pulp. To test this, we examined the ability of S. mutans to stimulate T cells and elicit cytokines and used Lactobacillus casei, which often predominates in deep carious lesions where B cells and plasma cells predominate, as a control. In addition, the presence of cytokines in the pulp was analyzed at the mRNA level. S. mutans elicited potent gamma interferon (IFN-gamma) responses in peripheral blood mononuclear cell cultures and reduced the CD4/CD8 ratio by promoting CD8(+) T cells. Multiple inflammatory cytokine mRNAs (IFN-gamma, interleukin 4 [IL-4], and IL-10) were detected in human dental pulp. A higher prevalence of IFN-gamma (67%) than IL-4 (19%) or IL-10 (29%) was obtained in shallow caries, suggesting a type 1 cytokine mechanism in early pulpitis where S. mutans predominates. In contrast, in deep caries no differences in cytokine frequency were observed. Furthermore, the presence of IFN-gamma in the pulp correlated with the presence of S. mutans. The extraordinary induction of type 1 cytokines and the preferential activation of CD8(+) T cells by S. mutans offers an explanation for the etiology of the CD8(+) T-cell-dominant lesion in early pulpitis and suggests that S. mutans may have a major impact on the initial lesion and pulpal pathology.

Inhibition of interleukin-2 by a Gram-positive bacterium, Streptococcus mutans

Generation of an effective cellular immune response is key to the successful development of both humoral and cellular immune defences against most pathogens. However, while the type of cellular immune response elicited by any given pathogen is dictated by the entire array of antigens and molecules which comprise that pathogen, most studies of human immune responses to bacterial pathogens tend to focus on selected antigens. This is a result, in part, of a desire to find those antigens that will generate a desired immune response, as well as limited technology for monitoring the complex array of responses generated by an intact organism. Utilizing Streptococcus mutans as a model Gram-positive organism, a novel flow cytometric assay that permits the identification of individual cells within a responding population, and highly sensitive cytokine assays, we show for the first time that CD8 T cells and natural killer (NK) cells comprise a significant component of the response to this organism in humans. This is despite the fact that CD8 T cells are traditionally thought to respond to endogenously derived antigens only. In addition, we provide the first evidence that a Gram-positive organism can actively inhibit interleukin-2 (IL-2), an important autocrine growth factor for T cells. The latter observation could represent an additional mechanism by which Gram-positive organisms evade host defences.

T-cell, adhesion, and B-cell epitopes of the cell surface Streptococcus mutans protein antigen I/II

The T-cell and antibody responses to a cell surface streptococcal antigen (SA I/II) were investigated in naturally sensitized humans. Serum antibody responses were directed predominantly to the N-terminal (residues 39 to 481) and central (residues 816 to 1213) regions of SA I/II which may be involved in bacterial adhesion to salivary receptors. T-cell responses were also directed predominantly towards the central region. The linear peptide relationship of the immunodominant and minor T- and B-cell as well as adhesion epitopes was mapped within residues 816 to 1213. Immunodominant T-cell and B-cell epitopes were identified within residues 803 to 853, which were separated in linear sequence from the adhesion epitopes (residues 1005 to 1044). Adhesion epitopes overlapped with minor B- and T-cell epitopes (residues 1005 to 1054 and 1085 to 1134). An immunodominant promiscuous T-cell epitope (residues 985 to 1004) was adjacent to an adhesion epitope (residues 1005 to 1024). The limited B-cell response to adhesion epitopes is consistent with the success of Streptococcus mutans in colonizing the oral cavity. The strategy of T-cell, adhesion, and B-cell epitope mapping has revealed a general approach for identifying components of subunit vaccines which may focus responses to critical functional determinants. Such epitopes of SA I/II may constitute the components of a subunit vaccine against dental caries.

Binding of Streptococcus mutans SR protein to human monocytes: production of tumor necrosis factor, interleukin 1, and interleukin 6

To examine the possible implication of protein SR, an I/II-related antigen from Streptococcus mutans OMZ 175 (serotype f), in inflammatory reactions, we tested the immunomodulatory effects of protein SR on human monocytes. Using biotinylated protein, we provide evidence that protein SR binds to human monocytes in dose-, time-, and calcium-dependent manners through specific interactions. These results were confirmed by competition experiments using either soluble human monocyte extract or anti-SR immunoglobulin G. Binding occurred through lectin-like interactions between SR and carbohydrate portions of monocyte membrane glycoproteins, since binding could be inhibited by several sugars, especially fucose and N-acetylneuraminic acid (NANA), which were confirmed by ligand blotting to be the primer ligands recognized by SR on human monocyte extracts. The ability of protein SR to stimulate the production of cytokines by human circulating monocytes was then examined. The release of tumor necrosis factor alpha (TNF-alpha), interleukin 1 beta, and interleukin 6 is time and dose dependent and not affected by the addition of polymyxin B. Activation of monocytes resulted from specific binding of SR to NANA and fucose present on cell surface glycoproteins since TNF-alpha release could be inhibited by sialidase and pronase treatment of monocytes and by NANA and fucose. These results confirm that sialic acid and fucose present on cell surface macromolecules and especially glycoproteins are needed for the binding of SR to monocytes and for the release of TNF-alpha.

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)

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.

An RSPCA/FRAME Survey of the Use of Non-human Primates as Laboratory Animals in Great Britain, 1984–1988

A literature-based survey of the use of non-human primates as laboratory animals in Great Britain in 1984–1988 was carried out as a background to extending debate about the ethical and practical issues involved. The 289 publications considered were grouped in 15 subject areas and reviewed in terms of scientific purpose, methods employed, numbers and species of animals used, and their source, care and ultimate fate. In addition, the Association of the British Pharmaceutical Industry provided a comment on the use of non-human primates by pharmaceutical companies. Specific causes for concern were identified, and future prospects considered.

Identification of T- and B-cell epitopes in synthetic peptides derived from a Streptococcus mutans protein and characterization of their antigenicity and immunogenicity

Natural immunity to synthetic peptides (SP) derived from the sequences of a 3800 Mr Streptococcus mutans antigen was found in human subjects. Significant serum IgG antibodies were detected both to the native streptococcal antigen and to the SP17, containing essentially residues 1-15. A series of short peptides with deletions at the amino- and carboxy-termini were then tested to identify the B-cell epitopes. Residues 8-13 and 1-6 bound significant serum IgG antibodies but only the former consistently inhibited human antibodies, suggesting that residues 8-13 constitute a major B-cell epitope. The human CD4 subset of T-cells was then examined and this showed a significant uptake of [3H]-thymidine when stimulated with both the native streptococcal antigen and the SP17. The series of short peptides was then used to stimulate CD4 cells, in order to determine the T-cell epitope. The synthetic peptide with residues 6-15 was the shortest peptide that stimulated significant [3H]-thymidine uptake and this peptide was designated as a T-cell epitope. The immunogenicity and antigenicity of SP17 was also investigated in macaques. Immunization of monkeys with the free SP17 failed to elicit serum antibodies or T-cell responses. However, immunization with SP17 linked to tetanus toxoid as a carrier elicited serum antibodies and proliferative responses of lymphocytes, not only to the synthetic peptide but also to the native streptococcal antigen. As in the human studies a B-cell epitope was found in residues 8-13, whereas an overlapping T-cell epitope was located in residues 7-15.(ABSTRACT TRUNCATED AT 250 WORDS)

Decreased immunologic responsiveness following intensified vaginal immunization against urinary tract infection

In an attempt to further increase the protective effect of vaginal immunization against urinary tract infections in Cynomolgus monkeys, the immunogen of killed E. coli was given more times, in larger amounts, and with the adjuvant MDP. Instead of increasing the protective effect, no protective effect on induced cystitis was observed. In addition, rises in urinary and serum immunoglobulins previously observed after vaginal immunization and induced cystitis were lessened. These observations appear to correspond with the classical concepts of immunologic unresponsiveness.

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.

The effect of immunization with a 14-kDa streptococcal antigen on primate T cell and B cell responses

A streptococcal antigen (SA) of 185 kDa was isolated from Streptococcus mutans and this antigen induced in vitro helper, suppressor and contrasuppressor activities with primate peripheral blood lymphocytes. The 185-kDa SA was then treated by sodium dodecyl sulfate and yielded a 4-kDa SA which was capable of eliciting only helper activity. We have now cleaved the 185-kDa SA with cyanogen bromide, in an attempt to identify suppressor and contrasuppressor determinants. A 14-kDa SA was separated from the cyanogen bromide digest and its ability to elicit T cell and B cell functional activities was tested in rhesus monkeys. Whereas the 185-kDa SA (and 4-kDa SA) elicited high serum anti-SA antibodies and the CD4 cells showed an increase in DNA synthesis, this was not demonstrable with the 14-kDa SA. However, the 14-kDa SA, unlike the 185-kDa SA, activated a significant proportion of CD4 and CD8 cells to bind the Vicia villosa lectin (VV) and this is a characteristic feature of contrasuppressor cells. We then studied the effect of sequential immunization of monkeys with the 14-kDa SA, followed by the 185-kDa SA. The results of this showed suppression of the CD4 proliferative response, in the presence of a normal antibody production. We suggest that the split tolerance between the T cell proliferative and B cell differentiating functions might be interpreted on the basis of suppressor CD8 cells inhibiting the CD4 proliferative phase and the VV-adherent CD8 cells contrasuppressing B cell antibody formation.

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.

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.

Immunization against dental caries

Prevention of dental caries has been investigated by immunization with Streptococcus mutans in rodents and subhuman primates. In addition to cells and cell walls of S. mutans, the enzyme glucosyl transferase and purified protein antigens prepared from S. mutans were successfully used in immunization against dental caries. Subcutaneous immunization of rhesus monkeys elicits significant levels of serum IgG, IgM and IgA antibodies, lymphorproliferative response and T cell helper activity to S. mutans cells and to streptococcal antigen (SA) I/II. These immune responses are associated with significant reduction of caries and colonization by S. mutans. However, oral immunization induced only a modest increase in salivary IgA antibodies to S. mutans and a small reduction in caries. Successful immunization in sub-human primates requires optimal T cell helper and minimal suppressor activities in order to elicit high titre and avidity of IgG antibodies. The SA dose required to elicit an optimal T cell helper function in man is HLA-DR dependent. Serum IgG antibodies pass through the gingival crevicular epithelium onto the tooth surface, where they may opsonize S. mutans for phagocytosis by the local neutrophils and prevent adherence of S. mutans, thereby preventing the development of caries.

Comparative immunogenicity and protective effect against dental caries of a low (3800) and a high (185,000) molecular weight protein in rhesus monkeys (Macaca mulatta)

The immunogenicity and protective effect of two peptides derived from the human oral bacterium Streptococcus mutans (serotype c) was examined. Furthermore, the effect of immunization was examined in monkeys previously given fluoride in their diet and which had developed a low incidence of dental caries when offered a human type of diet containing about 15 per cent sucrose. The 3800 peptide streptococcal antigen (SA) has two major antigenic determinants, similar to those in the 185,000 SA I/II. Immunization with 10 (or 1) micrograms of the 3800 SA, made up in an aluminium-hydroxide adjuvant, induced a consistent increase in serum IgG, IgM and IgA antibodies to SA I/II throughout the period of investigation. Salivary-IgA antibodies were only slightly raised. Sequential examination up to 76 weeks showed a significantly lower incidence of dental caries and a lower proportion of Strep. mutans in the immunized compared with sham-immunized, control monkeys. Thus immunization with the 185,000 or 3800 SA can almost completely prevent dental caries in rhesus monkeys which otherwise develop a low incidence of caries.