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

Oral streptococci: modulators of health and disease

Streptococci are primary colonizers of the oral cavity where they are ubiquitously present and an integral part of the commensal oral biofilm microflora. The role oral streptococci play in the interaction with the host is ambivalent. On the one hand, they function as gatekeepers of homeostasis and are a prerequisite for the maintenance of oral health - they shape the oral microbiota, modulate the immune system to enable bacterial survival, and antagonize pathogenic species. On the other hand, also recognized pathogens, such as oral Streptococcus mutans and Streptococcus sobrinus, which trigger the onset of dental caries belong to the genus Streptococcus. In the context of periodontitis, oral streptococci as excellent initial biofilm formers have an accessory function, enabling late biofilm colonizers to inhabit gingival pockets and cause disease. The pathogenic potential of oral streptococci fully unfolds when their dissemination into the bloodstream occurs; streptococcal infection can cause extra-oral diseases, such as infective endocarditis and hemorrhagic stroke. In this review, the taxonomic diversity of oral streptococci, their role and prevalence in the oral cavity and their contribution to oral health and disease will be discussed, focusing on the virulence factors these species employ for interactions at the host interface.

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.

Effects of Rhein-8-O-β-D-glucopyranoside on the Biofilm Formation of Streptococcus mutans

Dental caries is the most frequent biofilm-related human infectious disease in the oral cavity. Streptococcus mutans is one of the primary etiological agents of dental caries. The aim of our study was to investigate the effects of rhein-8-O-β-D-glucopyranoside (Rg) on the development of S. mutans biofilms. Growth curves were generated, and biofilm oxygen sensitivity was detected after Rg treatment. The expression levels of luxS, brpA, ffh, recA, nth, and smx were analyzed by real-time PCR. The trypan blue exclusion assay was used to measure the effect of Rg on monocyte viability. The results showed that Rg could significantly inhibit the growth of S. mutans and suppress the biofilm formation of S. mutans in a concentration-dependent manner. In Rg-treated biofilms, the expression levels of luxS, brpA, ffh, recA, nth, and smx were all decreased. Our results further showed that Rg was nontoxic, as Rg did not affect monocyte viability or lactate dehydrogenase activity in the exposed cells. These results suggested that Rg inhibited the biofilm formation of S. mutans, and the decrease in luxS, brpA, ffh, recA, nth, and smx expression might contribute to the antibacterial effects of Rg.

MicroRNA-125a-3p participates in odontoblastic differentiation of dental pulp stem cells by targeting Fyn

Fyn is a member of the protein tyrosine kinase family and its overexpression is associated with various types of inflammation. MicroRNAs can regulate the expression of target genes and play an important role in varied physiological and pathological processes. Based on the important role of Fyn and microRNA-125a-3p (miR-125a-3p) in inflammation, and combined with the bioinformatics studies, we performed in this study and chose miR-125a-3p as the focus of our research. During the progression of inflammation, we found that the expression of miR-125a-3p was decreased while the expression of Fyn was up-regulated. Fyn formed a complex with Neuropilin-1, which inhibited odontoblastic differentiation and expanded inflammatory responses through nuclear factor-κB signal pathways in dental pulp stem cells (DPSCs). These findings suggested that miR-125a-3p plays an important role in odontoblastic differentiation of DPSCs by targeting Fyn, implying its therapeutic potential in dental caries.

Microbial functional amyloids serve diverse purposes for structure, adhesion and defence

The functional amyloid state of proteins has in recent years garnered much attention for its role in serving crucial and diverse biological roles. Amyloid is a protein fold characterised by fibrillar morphology, binding of the amyloid-specific dyes Thioflavin T and Congo Red, insolubility and underlying cross-β structure. Amyloids were initially characterised as an aberrant protein fold associated with mammalian disease. However, in the last two decades, functional amyloids have been described in almost all biological systems, from viruses, to bacteria and archaea, to humans. Understanding the structure and role of these amyloids elucidates novel and potentially ancient mechanisms of protein function throughout nature. Many of these microbial functional amyloids are utilised by pathogens for invasion and maintenance of infection. As such, they offer novel avenues for therapies. This review examines the structure and mechanism of known microbial functional amyloids, with a particular focus on the pathogenicity conferred by the production of these structures and the strategies utilised by microbes to interfere with host amyloid structures. The biological importance of microbial amyloid assemblies is highlighted by their ubiquity and diverse functionality.

Association of ENAM, TUFT1, MMP13, IL1B, IL10 and IL1RN gene polymorphism and dental caries susceptibility in Chinese children

OBJECTIVE

To investigate the association between single nucleotide polymorphisms (SNPs) in six candidate genes (enamelin [ ENAM]; tuftelin 1 [ TUFT1]; matrix metallopeptidase 13 [ MMP13]; interleukin 1 beta [ IL1B]; interleukin 10 [ IL10]; interleukin 1 receptor antagonist [ IL1RN]) and dental caries in children from northwest China.

METHODS

This case-control study enrolled children (12-15 years) who underwent routine dental examinations. The children were divided into two groups based on the presence of dental caries. A saliva sample was collected and seven SNPs (rs3806804A/G in ENAM, rs3811411T/G in TUFT1, rs2252070A/G and rs597315A/T in MMP13, rs1143627C/T in IL1B, rs1800872A/C in IL10 and rs956730G/A in IL1RN) were genotyped.

RESULTS

A total of 357 children were enrolled in the study: 161 with dental caries and 196 without dental caries. No significant difference was found in the alleles and genotypes of five genes ( ENAM, TUFT1, MMP13, IL10 and IL1RN) between those with and without dental caries. A significant relationship was found between the IL1B rs1143627C/T polymorphism and dental caries susceptibility with those carrying the rs1143627CT genotype having a lower risk of dental caries compared with those carrying the CC genotype (odds ratio 0.557; 95% confidence interval 0.326, 0.952).

CONCLUSION

The IL1B rs1143627C/T polymorphism may be associated with dental caries susceptibility in children from northwest China.

The Role of Neuropilin-1-FYN Interaction in Odontoblast Differentiation of Dental Pulp Stem Cells

Abnormal odontoblast differentiation of dental pulp stem cells (DPSCs) caused by inflammation is closely related to the development of dental caries. Neuropilin-1 (NRP1) is one of the members of neuropilin family. It can combine with disparate ligands involved in regulating cell differentiation. FYN belongs to the protein-tyrosine kinase family, which has been implicated in the control of cell growth, and the effect can be further strengthened by inflammatory factors. In our studies, we verified that NRP1 can form complexes with FYN and have the correlation changes in odontoblast differentiation of DPSCs. Therefore, we surmise that in the progress of dental caries, NRP1 interacts with FYN, by expanding inflammation and inhibition of odontoblast differentiation of DPSCs through nuclear factor kappa B (NF-κB) signaling pathway. In this subject, we first investigated the expression and interaction of NRP1 and FYN in DPSCs. And then, we researched the effect of this complex controlling downstream signal pathway in normal or inflammation stimulated DPSCs. Finally, we analyzed the relationship between this role and odontoblast differentiation of DPSCs. This research will provide the molecular mechanism of inflammation factors of dental caries through activating NF-κB signal regulating odontoblast differentiation in DPSCs for finding new potential drug targets for the clinical treatment of dental caries.

Sophoraflavanone G prevents Streptococcus mutans surface antigen I/II-induced production of NO and PGE2 by inhibiting MAPK-mediated pathways in RAW 264.7 macrophages

BACKGROUND

Sophora flavescens AITON (Leguminosae) is a typical traditional Korean medical herb considered to exhibit antibacterial, anti-inflammatory, and antipyretic effects, and is also used for the treatment of skin and mucosal ulcers, sores, diarrhea, gastrointestinal hemorrhage, arrhythmia, and eczema.

OBJECTIVE AND DESIGN

This study examined the inhibitory effects of sophoraflavanone G (SF) of S. flavescens on the bacterial fibrillar protein, Antigen I/II (AgI/II)-N recombinant protein isolated from Streptococcus mutans(rAg I/II)-induced production of nitric oxide (NO) and prostaglandin E2 (PGE2). The investigation was focused on whether SF could inhibit the production of proinflammatory mediators such as nitric oxide (NO) and prostaglandin (PG) E2 as well as the expression of inducible nitric oxide synthase (iNOS), cyclooxygenase (COX)-2, tumor necrosis factor (TNF)-a, interleukin (IL)-6, nuclear factor (NF)-κB and mitogen-activated protein kinases (MAPKs) in rAgI/II-stimulated RAW 264.7 cells using Griess reagent, Enzyme linked immunosorbent assay (ELISA), and Western blotting analysis.

RESULTS

SG significantly inhibited the production of NO and PGE2 and pro-inflammatory cytokines, such as interleukin (IL)-1β, IL-6, and tumor necrosis factor α in Ag I/II-N-stimulated RAW264.7 cells, which were mediated by the down-regulation of inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2) expression. The SF inhibited the phosphorylation of IκB-α, nuclear translocation of p65, and subsequent activation of NF- κB in the rAgI/II-stimulated cells. In addition, the SF suppressed the rAgI/II-stimulated activation of ERK MAPK as well as the MAPK inhibitor significantly reduced the rAgI/II-induced production of NO and PGE2.

CONCLUSION

Collectively, we suggest that the SF inhibits the expression and production of inflammatory mediators by blocking the ERK MAPK mediated pathway and inhibiting the activation of NF-κB.

Prophylactic effect of human lactoferrin against Streptococcus mutans bacteremia in lactoferrin knockout mice

Streptococcus mutans is the primary agent of dental caries, which is often detected in transient bacteremia. Lactoferrin is a multifunctional glycoprotein showing antibacterial activities against several Streptococcus species. We reported here the prophylactic effect of human lactoferrin (hLF) in a lactoferrin knockout mouse (LFKO-/-) bacteremic model. The hLF treatment significantly cleared S. mutans from the blood and organs of bacteremic mice when compared to the non-hLF treated mice. Further, analysis of serum cytokines, spleen and liver cytokine mRNA levels revealed that hLF prophylaxis modulates their release differently when compared to the non-hLF treated group. C-reactive protein level (P = 0.003) also decreased following hLF prophylaxis in S. mutans induced bacteremic mice. Additional quantitative RT-PCR analysis revealed that hLF prophylaxis significantly decreased the expression level of IFN-γ, TNF-α, IL-1β, IL-6, MPO and iNOS in spleen and liver. These results suggested that the hLF protects the host against S. mutans-induced experimental bacteremia.

Rapid detection of S. mutans surface antigen I/II using a sensitive monoclonal anti-Ag I/II antibody by ELISA

The cell-surface protein antigen I/II (Ag I/II) is expressed in oral streptococci, which are known as the causative agent of a number of diseases including dental caries, endocarditis, gingivitis, and periodontal disease. Consequently, monoclonal antibodies (MAb) capable of recognizing the streptococcal Ag I/II protein could be a useful tool for the diagnosis and cure of these diseases. In this study, a previously generated monoclonal anti-Ag I/II antibody, ckAg I/II, was used to detect a small amount of Streptococcus mutans (S. mutans) surface antigen Ag I/II. The ckAg I/II was proved to be very sensitive and able to detect as little as 1 ng of recombinant Ag I/II protein within 5 min and Ag I/II in saliva within 10 min, as well as native Ag I/II in 20 μL of culture supernatant by ELISA. These results suggest that ckAg I/II can be used as a fast and efficient diagnostic tool to detect Ag I/II.

Histone-like DNA binding protein of Streptococcus intermedius induces the expression of pro-inflammatory cytokines in human monocytes via activation of ERK1/2 and JNK pathways

Streptococcus intermedius is a commensal associated with serious, deep-seated purulent infections in major organs, such as the brain and liver. Histone-like DNA binding protein (HLP) is an accessory architectural protein in a variety of bacterial cellular processes. In this study, we investigated the mechanisms of pro-inflammatory cytokine inductions in THP-1 cells by stimulation with recombinant HLP of S. intermedius (rSi-HLP). rSi-HLP stimulation-induced production of pro-inflammatory cytokines (IL-8, IL-1 beta and TNF-alpha) occurred in a time- and dose-dependent manner. In contrast with the heat-stable activity of DNA binding, the induction activity of rSi-HLP was heat-unstable. In subsequent studies, rSi-HLP acted cooperatively with lipoteichoic acid, the synthetic Toll-like receptor 2 agonist, Pam3CSK4, and the cytosolic nucleotide binding oligomerization domain 2 receptor agonist, muramyldipeptide. Furthermore, Western blot and blocking assays with specific inhibitors showed that rSi-HLP stimulation induced the activation of cell signal transduction pathways, extracellular signal-regulated kinase 1/2 (ERK1/2) and c-Jun N-terminal kinase (JNK). In addition to its physiological role in bacterial growth through DNA binding, these results indicate that Si-HLP can trigger a cascade of events that induce pro-inflammatory responses via ERK1/2 and JNK signal pathways, and suggest that bacterial HLP may contribute to the activation of host innate immunity during bacterial infection.

Interaction forces between salivary proteins and Streptococcus mutans with and without antigen I/II

The antigen I/II family of surface proteins is expressed by oral streptococci, including Streptococcus mutans, and mediates specific binding to, among others, salivary films. The aim of this study was to investigate the interaction forces between salivary proteins and S. mutans with (LT11) and without (IB03987) antigen I/II through atomic force microscopy (AFM) and to relate these interaction forces with the adhesion of the strains to saliva-coated glass in a parallel plate flow chamber. Upon approach of the bacteria toward a saliva-coated AFM tip, both strains experienced a similar repulsive force that was significantly smaller at pH 6.8 (median 3.0 and 3.1 nN for LT11 and IB03987, respectively) than at pH 5.8 (median 4.6 and 4.7 nN). The decay length of these repulsive forces was between 19 and 37 nm. Upon retraction at pH 6.8, the combined specific and nonspecific adhesion forces were significantly stronger for the parent strain LT11 (median -0.4 nN) than for the mutant strain IB03987 (median 0.0 nN), whereas at pH 5.8 the median of the adhesion forces measured was 0.0 nN for both strains. Moreover, at pH 6.8, the parent strain LT11 adhered in significantly higher numbers (9.6 x 106 cm-2) to a salivary coating than the mutant strain IB03987 (2.5 x 106 cm-2). Similar to the difference in adhesion forces between both strains at pH 5.8, the difference in adhesion between both strains also disappeared at pH 5.8, which suggests the involvement of attractive electrostatic forces in the interaction between antigen I/II and salivary coatings. In summary, this study shows that antigen I/II at the surface of S. mutans LT11 is responsible for its increased adhesion to salivary coatings under flow through an additional attractive electrostatic force.

Calorimetric comparison of the interactions between salivary proteins and Streptococcus mutans with and without antigen I/II

Antigen I/II can be found on streptococcal cell surfaces and is involved in their interaction with salivary proteins. In this paper, we determine the adsorption enthalpies of salivary proteins to Streptococcus mutans LT11 and S. mutans IB03987 with and without antigen I/II, respectively, using isothermal titration calorimetry. In addition, protein adsorption to the cell surfaces was determined spectrophotometrically. S. mutans LT11 with antigen I/II, yielded a much higher, exothermic adsorption enthalpy at pH 6.8 (ranging from -2073 x 10(-9) to -31707 x 10(-9) microJ per bacterium) when mixed with saliva than did S. mutans IB03987 (-165 x 10(-9) to -1107 x 10(-9) microJ per bacterium) at all bacterial concentrations studied (5 x 10(9), 5 x 10(8), and 5 x 10(7) ml(-1)), largest effects per bacterium being observed for the lowest concentration. However, the enthalpy of salivary protein adsorption to S. mutans LT11 became smaller at pH 5.8. Adsorption isotherms for the S. mutans LT11 showed considerable protein adsorption at pH 6.8 (1.2 - 2.1 mg/m(2)), that decreased only slightly at pH 5.8 (1.1 - 1.6 mg/m(2)), with the largest amount adsorbed at the lowest bacterial concentration. This suggests that the protein(s) in the saliva with the strongest affinity for antigen I/II is (are) readily depleted from saliva. In conclusion, antigen I/II surface proteins on S. mutans play a determinant role in adsorption of salivary proteins through the creation of enthalpically favorable adsorption sites.

Contribution of cell surface protein antigen PAc of Streptococcus mutans to bacteremia

Streptococcus mutans, a major cariogenic bacterium, is occasionally isolated from the blood of patients with bacteremia and infective endocarditis. Mutant strains of S. mutans MT8148, defective in the major surface proteins glucosyltransferase (GTF) B-, C-, and D-, and protein antigen c (PAc), were constructed by insertional inactivation of each respective gene with an antibiotic resistant cassette. Susceptibility to phagocytosis was determined by analyses of interactions of the bacteria with human polymorphonuclear leukocytes, and the PAc-defective mutant strain (PD) showed the lowest rate of phagocytosis. Further, when PD and MT8148 were separately injected into the jugular veins of Sprague-Dawley rats, PD was recovered in significantly larger numbers and for a longer duration, and caused more severe systemic inflammation than MT8148, indicating that S. mutans PAc is associated with its systemic virulence in blood. Next, 100 S. mutans clinical isolates from 100 Japanese children and adolescents were analyzed by Western blotting using antisera raised against recombinant PAc, generated based on the pac sequence of MT8148. Four of the 100 strains showed no positive band and each exhibited a significantly lower phagocytosis rate than that of 25 randomly selected clinical strains (P < 0.01). In addition, three of the 100 strains possessed a lower molecular weight PAc and a significantly lower rate of phagocytosis than the 25 reference strains (P < 0.05). These results suggest that S. mutans PAc may be associated with phagocytosis susceptibility to human polymorphonuclear leukocytes, with approximately 7% of S. mutans clinical isolates possible high-risk strains for the development of bacteremia.

Streptococcus pyogenes collagen type I-binding Cpa surface protein. Expression profile, binding characteristics, biological functions, and potential clinical impact

The Streptococcus pyogenes collagen type I-binding protein Cpa (collagen-binding protein of group A streptococci) expressed by 28 serotypes of group A streptococci has been extensively characterized at the gene and protein levels. Evidence for three distinct families of cpa genes was found, all of which shared a common sequence encoding a 60-amino acid domain that accounted for selective binding to type I collagen. Surface plasmon resonance-based affinity measurements and functional studies indicated that the expression of Cpa was consistent with an attachment role for bacteria to tissue containing collagen type I. A cpa mutant displayed a significantly decreased internalization rate when incubated with HEp-2 cells but had no effect on the host cell viability. By utilizing serum from patients with a positive titer for streptolysin/DNase antibody, an increased anti-Cpa antibody titer was noted for patients with a clinical history of arthritis or osteomyelitis. Taken together, these results suggest Cpa may be a relevant matrix adhesin contributing to the pathogenesis of S. pyogenes infection of bones and joints.

Glucosyltransferases of viridans streptococci are modulins of interleukin-6 induction in infective endocarditis

The glucosyltransferases (GTFs) of viridans streptococci, common pathogens of infective endocarditis, are extracellular proteins that convert sucrose into exopolysaccharides and glucans. GTFs B, C, and D of Streptococcus mutans are modulins that induce, in vitro and in vivo, the production of cytokines, in particular interleukin-6 (IL-6), from monocytes. The roles of S. mutans GTFs in infectivity and inflammation in situ were tested in a rat experimental model of endocarditis. No significant differences in infectivity, in terms of 95% infective dose and densities of bacteria inside vegetations, were observed between laboratory strain GS-5 and two clinical isolates or isogenic mutant NHS1DD, defective in the expression of GTFs. In aortic valves and surrounding tissues, IL-6 was detected by Western blots and immunostaining 24 h after GS-5 infection, was maintained over 72 h, and was followed by production of tumor necrosis factor alpha but not IL-1beta. Animals infected with NHS1DD showed markedly lower levels of IL-6 (less than 5% of that of parental GS-5-infected rats), while tumor necrosis factor alpha was unaffected. In contrast, animals infected with NHR1DD, another isogenic mutant expressing only GtfB, showed a much smaller reduction (down to 56%). These results suggest that GTFs are specific modulins that act during acute inflammation, inducing IL-6 from endothelial cells surrounding the infected valves without affecting bacterial colonization in vegetations, and that IL-6 might persist in chronic inflammation in endocarditis.

Streptococcal antigen I/II binds to extracellular proteins through intermolecular beta-sheets

One of the functions associated with the oral streptococcal surface protein I/II is to bind to human extracellular matrix molecules or blood components, which could act as opportunistic ligands in pathological circumstances. In order to understand the relative specificity of the binding repertoire of this bacterial adhesin, we examined by infrared measurements the mode of binding of the protein I/II from Streptococcus mutans OMZ175 (I/IIf) to fibronectin and fibrinogen. This approach revealed the beta-structure forming capacity of I/IIf upon interaction with both proteins. The forming of intermolecular beta-structures may provide a non-selective way of interaction between I/IIf and its possible targets.

Insertional inactivation of pac and rmlB genes reduces the release of tumor necrosis factor alpha, interleukin-6, and interleukin-8 induced by Streptococcus mutans in monocytic, dental pulp, and periodontal ligament cells

Streptococcus mutans possesses different cell wall molecules, such as protein of the I/II family, the serotype f polysaccharide rhamnose glucose polymer (RGP), and lipoteichoic acid (LTA), which act as adhesins and modulins, allowing S. mutans to colonize teeth and cause dental caries and pulpitis. We tested several isogenic mutants of S. mutans defective in protein I/II and/or RGP, as well as purified modulins such as protein I/II, RGP, and LTA, for their binding and activation abilities on monocytic, dental pulp (DP), and periodontal ligament (PDL) cells. Our results demonstrate that both protein I/II and RGP play important roles in streptococcal adherence to human monocytic and fibroblastic cells, whereas LTA is only a minor adhesin. In the activation process, the cytokine response elicited is polarized toward a Th1 response which seems principally due to protein I/II and RGP. Even if protein I/II seems to be more efficient in its purified form in triggering cells to release interleukin-8 (IL-8), RGP is the most efficient cytokine-stimulating component in intact bacteria, while LTA plays only a minor role. In cell activation, we showed, by using either cytochalasin D or coated ligands, that internalization of either S. mutans, S. mutans isogenic mutants, or purified ligands is not necessary to trigger cells to release IL-8. We also showed that, besides the implication of monocytes in pulpal inflammation, fibroblast-like cells such as DP and PDL cells are also actively implicated in local inflammation and in the generation of a Th1 response after stimulation with S. mutans cells or antigens.

Induction of cytokines by glucosyltransferases of streptococcus mutans

Production of proinflammatory cytokines is implicated in the pathogenesis of viridans streptococcus-induced alpha-streptococcal shock syndrome and infective endocarditis. Streptococcus mutans, one of the opportunistic pathogens causing infective endocarditis, was reported previously to stimulate monocytes and epithelial and endothelial cells in vitro to produce various cytokines. We found that glucosyltransferases (GTFs) GtfC and GtfD of S. mutans stimulated predominantly the production of interleukin-6 (IL-6) from T cells cultured in vitro. The level of IL-6 but not of tumor necrosis factor alpha in blood was significantly elevated when rats were injected intravenously with S. mutans GS-5, whereas IL-6 was detected at a much lower level when rats were challenged with NHS1DD, an isogenic mutant defective in the expression of GTFs. The serum IL-6 level was elevated in patients with endocarditis caused by different species of viridans streptococci which express GTF homologues. Affinity column-purified GTFs reduced the levels of detectable IL-2 of T cells stimulated by another bacterial antigen, tetanus toxoid. These results suggested that GTFs might modulate the production of Th1-type cytokines and that GTFs of S. mutans play a significant role in stimulating the production of the proinflammatory cytokine IL-6 in vivo.

Crystal structure of the V-region of Streptococcus mutans antigen I/II at 2.4 A resolution suggests a sugar preformed binding site

Antigens I/II are large multifunctional adhesins from oral viridans streptococci that exert immunomodulatory effects on human cells and play important roles in inflammatory disorders. Among them, Streptococcus mutans plays a major role in the initiation of dental caries. The structure of the V-region (SrV+, residues 464-840) of the antigen I/II of S. mutans has been determined using the multiwavelength anomalous diffraction phasing technique with seleno-methionine-substituted recombinant protein and subsequently refined at 2.4 A resolution. The crystal structure of SrV+ revealed a lectin-like fold that displays a putative preformed carbohydrate-binding site stabilized by a metal ion. Inhibition of this binding site may confer to humans a protection against dental caries and dissemination of the bacteria to extra-oral sites involved in life-threatening inflammatory diseases. This crystal structure constitutes a first step in understanding the structure-function relationship of antigens I/II and may help in delineating new preventive or therapeutic strategies against colonization of the host by oral streptococci.

NF-kappaB and the MAP kinases/AP-1 pathways are both involved in interleukin-6 and interleukin-8 expression in fibroblast-like synoviocytes stimulated by protein I/II, a modulin from oral streptococci

As in rheumatoid arthritis (RA), it was demonstrated recently that bacterial fragments of DNA or rRNA are present in the joint and therefore could play a role in inducing or perpetuating the disease, this work was initiated to define mechanisms that account for the stimulatory activities of the oral streptococcal modulin, protein I/II, on fibroblast-like synoviocytes (FLSs) from RA patients. FLSs from RA patients were stimulated with protein I/II, and expression of interleukin (IL)-6 and IL-8 mRNA was evaluated by reverse transcription-polymerase chain reaction (RT-PCR). Immunoblotting by antibodies specific for activated forms of MAPKs and electrophoretic mobility shift assays (EMSAs) were performed to study downstream signalling, which allowed the synthesis of IL-6 and IL-8. We reported that protein I/II interactions with FLSs from RA patients trigger the synthesis and release of IL-6 and IL-8. We also demonstrated that protein I/II enhances the phosphorylation of ERK 1/2, p38 and JNKs and that ERK 1/2 and JNK MAPKs seem to play a more important role than p38 in protein I/II-mediated synthesis of IL-6 and IL-8. Our experiments also indicated that stimulation of FLSs with protein I/II induces nuclear translocation of NF-kappaB, AP-1-binding activity and that NF-kappaB plays a major role in IL-6 and IL-8 secretion from activated cells.

Expression and functional properties of the Streptococcus intermedius surface protein antigen I/II

Streptococcus intermedius is associated with deep-seated purulent infections. In this study, we investigated expression and functional activities of antigen I/II in S. intermedius. The S. intermedius antigen I/II appeared to be cell surface associated, with a molecular mass of approximately 160 kDa. Northern blotting indicated that the S. intermedius NCTC 11324 antigen I/II gene was transcribed as a monocistronic message. Maximum expression was seen during the early exponential phase. Insertional inactivation of the antigen I/II gene resulted in reduced hydrophobicity during early exponential phase, whereas no effect was detected during mid- and late exponential phases. Binding to human fibronectin and laminin was reduced in the isogenic mutant, whereas binding to human collagen types I and IV and to rat collagen type I was not significant for either the wild type or the mutant. Compared to the wild type, the capacity of the isogenic mutant to induce interleukin 8 (IL-8) release by THP-1 monocytic cells was significantly reduced. The results indicate that the S. intermedius antigen I/II is involved in adhesion to human receptors and in IL-8 induction.

Pro-inflammatory cytokine production by synoviocytes following exposure to protein I/II, a modulin from oral streptococci

We have tested the ability of protein I/II, an adhesin from oral streptococci, to stimulate the production of pro-inflammatory cytokines by synovial cells isolated from both rheumatoid arthritis and control patients. Protein I/II triggers synovial fluid cells to produce interleukin (IL)-6 and IL-8 while secretion of tumor necrosis factor-alpha (TNF-alpha) was less enhanced. Using fibroblast-like synoviocytes, we found that protein I/II also exerts an immunomodulatory effect (IL-6 and IL-8 release) on these cells. These findings indicate that, if it gains access to the joint cavity, protein I/II could participate in the initiation and/or perpetuation of rheumatic diseases, by stimulating pro-inflammatory cytokine release from various synovial cells.

Viridans-group streptococcal infections in immunocompromised hosts

Viridans streptococci, a diverse group of streptococcal species, are important causes of sepsis and pneumonia in the neutropenic host and sepsis and meningitis in the neonate. The oral mucosa is the most common portal of entry. Among the factors that predispose to development of viridans streptococcal sepsis are: profound neutropenia; mucositis, especially oral mucositis; cytarabine (Ara-C) therapy, which seems to have an effect beyond its association with mucositis; young age; and trimethoprim-sulphamethoxazole or quinolone administration. Fever is usually more than 39 degrees C and prolonged for several days even though blood cultures are typically negative after 24 h of therapy. The majority of patients recover uneventfully if appropriate therapy is initiated early. However, fulminant septic shock may occasional occur at onset. Delayed shock 2 or 3 days after presentation may also occur despite administration of microbiologically effective antibiotics. In severe cases, adult respiratory distress syndrome may be manifested two or three days after the initial bacteremia. There is considerable variability among institutions, but the median death rate associated with viridans streptococcal sepsis is about 10%. Local susceptibility patterns should be used to guide initial therapy for suspected viridans streptococcal infections. Some isolates of viridans streptococci are resistant to penicillins and cephalosporins, in which case vancomycin is preferred. Recurrence during subsequent neutropenic episodes is not unusual.

Production of cytokines by monocytes, epithelial and endothelial cells activated by Streptococcus bovis

There are numerous reports documenting the correlation between Streptococcus bovis bacteraemia and endocarditis in conjunction with colonic diseases. The adherence of S. bovis to either buccal or intestinal epithelial cells seems to be the initial process in colonization and subsequent infection of the host, allowing further adhesion of S. bovis to either endothelial cells or extracellular matrix components which leads to infective endocarditis. Bacterial entry at tumour sites is further assisted by the local action of cytokines that promotes vasodilatation and increased capillary permeability. Thus the ability of S. bovis to adhere to and to stimulate human cells may contribute to the pathogenicity of this bacteria. In the present study, we have shown the ability of S. bovis and wall-extracted antigens (WEA) to adhere to human buccal (KB) or intestinal (Caco-2) epithelial cell lines, to human saphenous vein endothelial cells, to human monocytic cell line (THP-1) and to extracellular matrix components (ECM) (fibronectin, collagen and laminin). The fixation of S. bovis on cells was followed by the synthesis of IL-8 from all the cells except Caco-2, whereas S. bovis WEA was able to induce cytokine synthesis from all of them, showing the immunomodulatory effect of S. bovis and S. bovis WEA on different cells.

Involvement of alpha5beta1 integrins in interleukin 8 production induced by oral viridans streptococcal protein I/IIf in cultured endothelial cells

Using human endothelial cells, we define a mechanism that accounts for the induction of interleukin 8 (IL-8) by protein I/IIf, an adhesin from Streptococcus mutans serotype f. We report that protein I/IIf interactions with endothelial cells increased the tyrosine phosphorylation of three cellular components with relative mass of 145,000, 125,000 and 70,000 in endothelial cells. These proteins were identified as phospholipase Cgamma (PLCy), focal adhesion kinase (FAK) and paxillin after immunoprecipitation with monoclonal antibodies (mAbs) and immunoblotting with antiphosphotyrosine mAbs. These results suggested that beta1 integrins could be one of the components implicated in the modulin activity of protein I/IIf. By incubating protein I/IIf with either purified alpha5beta1 integrins or with alpha5beta1 integrins overexpressing CHO cells, we demonstrated that alpha5beta1 integrins act as cell receptors for protein I/IIf. We also showed that protein I/IIf interactions with alpha5beta1 integrins lead to IL-8 secretion. Using specific inhibitors, we demonstrated that protein I/IIf-induced IL-8 release involves mitogen-activated protein kinases (MAPKs), and that PLCgamma and PKC also seem to contribute to protein I/IIf stimulation. However, PI-3K activation is not involved in IL-8 release. Altogether, these results indicate that, after binding to alpha5beta1 integrins, protein I/IIf induces IL-8 release by activating the MAPKs signalling pathways.

Design of highly immunogenic liposomal constructs combining structurally independent B cell and T helper cell peptide epitopes

We have designed liposomal diepitope constructs that allow the physical combination, within the same vesicle, of B and Th epitopes as structurally separate entities. The immune response against such constructs was explored using TPEDPTDPTDPQDPSS (TPE), a B cell epitope originating from a Streptococcus mutans surface adhesin and QYIKANSKFIGITEL (QYI), a "universal" Th epitope from tetanus toxin. The two peptides were linked to the outer surface of small (diameter approximately 100 nm) unilamellar liposomes by covalent conjugation to two different anchors. To that end we have developed a strategy that allows the controlled chemical coupling of TPE and QYI, functionalized at their N terminus with a thiol, to preformed liposomes containing thiol-reactive derivatives of phosphatidylethanolamine and the lipopeptide S-[2,3-bis (palmitoyloxy)-(2-RS)-propyl]-N-palmitoyl-(R)-cysteinyl-alanyl-gly cine (Pam3CAG), respectively. This synthetic construct (administered i.p. to BALB/c mice) induced highly intense (titers > 20,000), anamnestic and long-lasting (over 2 years) immune responses, indicating that this strategy is successful. Two parameters were of prime importance to elicit this response with our liposomal diepitope constructs: (1) the simultaneous expression of B and Th epitopes on the same vesicle, and (2) the lipopeptide Pam3CAG anchor of the Th epitope QYI could not be replaced by a phosphatidylethanolamine anchor (a lesser immune response was observed). Analysis of the antibody response revealed a complex pattern; thus, besides the humoral response (production of IgG1, IgG2a, IgG2b) a superposition of a T-independent (TI-2 type) response was also found (IgM and IgG3). These results indicate that liposomal diepitope constructs could be attractive in the development of synthetic peptide-based vaccines.

Protein I/II of oral viridans streptococci increases expression of adhesion molecules on endothelial cells and promotes transendothelial migration of neutrophils in vitro

As accumulation of leukocytes in perivascular tissues is a key step in inflammatory disorders, we have analyzed in the present work the up-regulation of expression of adhesion molecules, such as E-selectin, ICAM-1, and VCAM-1, on human endothelial cells, in response to protein I/II, a modulin from Streptococcus mutans OMZ 175. Using cultured human saphenous vein endothelial cells (HSVEC), we demonstrated that protein I/II directly and specifically up-regulated E-selectin, ICAM-1, and VCAM-1 expression. We confirmed also that the up-regulation of adhesion molecules in HSVEC is mediated by lectin activity for NANA- and fucose-containing receptors. The ability of protein I/II to promote the transendothelial migration of neutrophils was then examined. Using Transwell inserts, we found that protein I/II, in promoting the up-regulation of adhesion molecule expression, stimulates neutrophil migration through endothelial cells. These events may play a role in the etiology of inflammatory responses leading to the various pathologies associated with oral viridans streptococci.

The A and the extended V N-terminal regions of streptococcal protein I/IIf mediate the production of tumour necrosis factor alpha in the monocyte cell line THP-1

The induction of tumour necrosis factor (TNF)-alpha from the monocytic cell line THP-1 by the streptococcal antigen I/II from Streptococcus mutans serotype f (protein I/IIf) was studied by use of recombinant polypeptides containing the discrete domains of the protein. The derivatives carrying the N-terminal alanine-rich region (A region) and the adjacent variable region (extended V region) of the protein bound to THP-1 cell extracts in a saturable fashion, and one derivative lacking both the A and the extended V regions was not able to bind monocyte cell extracts, suggesting that the domains responsible for the binding of protein I/IIf to monocytes were the A and the extended V regions. Sodium metaperiodate pretreatment of THP-1 cell extracts, tunicamycin pretreatment of monocyte cells or competition with N-acetyl neuraminic acid (NANA) and fucose resulted in a 45-70% reduction in binding activity of the derivatives carrying the extended V region, demonstrating the lectin-like mode of recognition of the monocytic receptor by the extended V region and the role of NANA and fucose in this recognition process. Besides, the stimulation of monocytes to release TNF-alpha by the derivatives containing the A region and the extended V region was effective and was not affected by the addition of polymyxin B or vitamin D3, suggesting that CD14 does not play the role of receptor in stimulation of monocytes by protein I/IIf to release TNF-alpha.

Viridans streptococcal isolates from patients with septic shock induce tumor necrosis factor-alpha production by murine macrophages

Viridans streptococci are an important cause of bacteremia and septic shock in neutropenic patients, especially patients receiving chemotherapeutic agents that induce severe mucositis. The mechanisms by which viridans streptococci cause septic shock are unclear. We hypothesized that septic shock due to viridans streptococci is attributable to host cytokine production. Three clinical isolates of viridans streptococci were evaluated for their ability to induce production of tumor necrosis factor-alpha (TNF-alpha) by RAW 264.7 murine macrophages. These three strains of viridans streptococci induced TNF-alpha in a dose-dependent fashion, and the kinetics of TNF-alpha induction were similar to those observed with a clinical isolate of Escherichia coli.

The N-terminal half part of the oral streptococcal antigen I/IIf contains two distinct binding domains

In order to investigate the binding properties of the antigen I/IIf from Streptococcus mutans, we analyzed the binding activity of five I/IIf derivatives expressed by I/IIf gene derivatives obtained by insertion of a kanamycin resistance marker. ELISA-derived binding assays showed that the derivatives containing both the N-terminal alanine-rich domain (A-region) and an A-region distal domain extending to amino-acid 766 were the most effective in binding biotinylated (Biot-) human salivary components (SAC) and Biot-epithelial cell membrane components. Sodium metaperiodate treatment of SAC inhibited these interactions, suggesting a binding specificity of the A-region distal domain for carbohydrate residues. All the I/IIf derivatives were found to bind Biot-type I collagen, Biot-laminin, Biot-keratin, and Biot-fibronectin, the derivatives containing the A-region but lacking the A-region distal domain exhibiting the highest binding levels. Sodium metaperiodate treatment of laminin had no effect on its binding to the derivatives, suggesting that carbohydrate residues of the ligand were not involved.

Mucosal immunogenicity of a recombinant Salmonella typhimurium-cloned heterologous antigen in the absence or presence of coexpressed cholera toxin A2 and B subunits

An avirulent Salmonella typhimurium vaccine strain expressing a streptococcal protein adhesin and a similar clone which produces the same streptococcal antigen linked to the cholera toxin (CT) A2 and B subunits (CTA2/B) were compared for the ability to induce antibody responses to the expressed heterologous antigen after oral or intranasal immunization of mice. Expression of cloned immunogens in these systems is temperature regulated, being optimal at 37 degrees C, and the two clones under comparison were shown to produce similar levels of the streptococcal antigen. Both clones were found to stimulate high levels of serum immunoglobulin G (IgG) and mucosal IgA antibodies to the cloned immunogen. A consistent trend was observed toward higher mucosal IgA but lower serum IgG responses in the case of the S. typhimurium vector that coexpressed CTA2/B, a potential mucosal adjuvant, regardless of the route of administration. Also noteworthy was the capacity of these antigen delivery systems to induce anamnestic systemic and secretory responses to the cloned immunogen 15 weeks after the primary immunization, despite preexisting immunity to the Salmonella vectors. These antibody responses were sustained for at least 7 months following the booster immunization, at which time the secretory IgA antibody levels were significantly higher in mice given the Salmonella clone that coexpressed CTA2/B. Although the serum IgG response against the Salmonella vector was characterized by a high IgG2a/IgG1 ratio (indicative of the T helper type 1 [Th1]/Th2 profile), a mixed IgG1 and IgG2a pattern was observed for the carried heterologous antigen, which displayed a dominant IgG1 response when administered as a purified immunogen. Our findings indicate that the recombinant streptococcal antigen and CTA2/B are strong immunogens when expressed by the antigen delivery system used in this study and suggest that CTA2/B may have an additional immunoenhancing activity in the mucosal compartment besides its ability to target antigen uptake into the mucosal inductive sites. CTA2/B may thus be useful as an S. typhimurium-cloned adjuvant for coexpressed protein antigens.

Streptococcal adhesion and colonization

Streptococci express arrays of adhesins on their cell surfaces that facilitate adherence to substrates present in their natural environment within the mammalian host. A consequence of such promiscuous binding ability is that streptococcal cells may adhere simultaneously to a spectrum of substrates, including salivary glycoproteins, extracellular matrix and serum components, host cells, and other microbial cells. The multiplicity of streptococcal adherence interactions accounts, at least in part, for their success in colonizing the oral and epithelial surfaces of humans. Adhesion facilitates colonization and may be a precursor to tissue invasion and immune modulation, events that presage the development of disease. Many of the streptococcal adhesins and virulence-related factors are cell-wall-associated proteins containing repeated sequence blocks of amino acids. Linear sequences, both within the blocks and within non-repetitive regions of the proteins, have been implicated in substrate binding. Sequences and functions of these proteins among the streptococci have become assorted through gene duplication and horizontal transfer between bacterial populations. Several adhesins identified and characterized through in vitro binding assays have been analyzed for in vivo expression and function by means of animal models used for colonization and virulence. Information on the molecular structure of adhesins as related to their in vivo function will allow for the rational design of novel acellular vaccines, recombinant antibodies, and adhesion agonists for the future control or prevention of streptococcal colonization and streptococcal diseases.

Cytokine-inducing components of periodontopathogenic bacteria

Pro-inflammatory cytokines such as interleukin (IL)-1, IL-6, IL-8 and tumour necrosis factor (TNF) are believed to be the major pathological mediators of inflammatory diseases ranging from arthritis to the periodontal diseases. The stimuli inducing proinflammatory cytokine induction in the former disease is unclear but in the periodontal diseases it is obvious that the stimulus is the accumulation of bacteria in the subgingival region. As these bacteria do not invade the lesional tissues in large numbers, it is believed that their soluble components or products interact with host tissues to induce cytokine gene transcription. The paradigm is that lipopolysaccharide is the key bacterial component inducing pro-inflammatory cytokine gene expression. However, over the past decade a growing number of reports on non-oral bacteria have established that many other bacterial components, as well as secretory products, have the capacity to induce cytokine synthesis. Some of these, such as the protein pneumolysin from Streptococcus pneumoniae, are incredibly potent (in this case inducing cytokine synthesis at femtomolar concentrations). This review surveys the range of bacterial components and products which have been shown to stimulate cytokine synthesis with particular emphasis on the hypothesis that these components play a role in the pathology of the periodontal diseases.

Cytokine production by human epithelial and endothelial cells following exposure to oral viridans streptococci involves lectin interactions between bacteria and cell surface receptors

In order to examine the possible implication of human epithelial and endothelial cells in the pathogenesis of various diseases associated with oral viridans streptococci, we tested the immunomodulatory effects of 11 representative strains of oral viridans streptococci on human epithelial KB cells and endothelial cells. We then examined the possible role of two major adhesins from oral viridans streptococci, protein I/II and rhamnose-glucose polymers (RGPs), in this process. In this study we demonstrate that oral viridans streptococci are potent stimulators of interleukin-8 (IL-8) production from KB cells and of IL-6 and IL-8 production from endothelial cells. The ability of protein I/II and RGPs to contribute to these effects was then examined. Using biotinylated protein I/IIf and RGPs from Streptococcus mutans OMZ 175, we showed that these adhesins bind to KB and endothelial cells through specific interactions and that the binding of these molecules initiates the release of IL-8 from KB cells and of IL-6 and IL-8 from endothelial cells. These results suggest that protein I/IIf and RGPs play an important role in the interactions between bacteria and KB and endothelial cells in that similar cytokine profiles are obtained when cells are stimulated with bacteria or surface components. We also provide evidence that protein I/IIf binds to and stimulates KB and endothelial cells through lectin interactions and that N-acetyl neuraminic acid (NANA) and fucose present on cell surface glycoproteins may form the recognition site since binding and cytokine release can be inhibited by dispase and periodate treatment of cells and by NANA and fucose. These results demonstrate that oral viridans streptococci, probably by engaging two cell surface adhesins, exert immunomodulatory effects on human KB and endothelial cells.

Bacterial modulins: a novel class of virulence factors which cause host tissue pathology by inducing cytokine synthesis

Cytokines are a diverse group of proteins and glycoproteins which have potent and wide-ranging effects on eukaryotic cell function and are now recognized as important mediators of tissue pathology in infectious diseases. It is increasingly recognized that for many bacterial species, cytokine induction is a major virulence mechanism. Until recent years, the only bacterial component known to stimulate cytokine synthesis was lipopolysaccharide (LPS). It is only within the past decade that it has been clearly shown that many components associated with the bacterial cell wall, including proteins, glycoproteins, lipoproteins, carbohydrates, and lipids, have the capacity to stimulate mammalian cells to produce a diverse array of cytokines. It has been established that many of these cytokine-inducing molecules act by mechanisms distinct from that of LPS, and thus their activities are not due to LPS contamination. Bacteria produce a wide range of virulence factors which cause host tissue pathology, and these diverse factors have been grouped into four families: adhesins, aggressins, impedins, and invasins. We suggest that the array of bacterial cytokine-inducing molecules represents a new class of bacterial virulence factor, and, by analogy with the known virulence families, we suggest the term "modulin" to describe these molecules, because the action of cytokines is to modulate eukaryotic cell behavior. This review summarizes our current understanding of cytokine biology in relation to tissue homeostasis and disease and concisely reviews the current literature on the cytokine-inducing molecules produced by gram-negative and gram-positive bacteria, with an emphasis on the cellular mechanisms responsible for cytokine induction. We propose that modulins, by controlling the host immune and inflammatory responses, maintain the large commensal flora that all multicellular organisms support.