Differentiation and interaction of secretory immunoglobulin A and a calcium-dependent parotid agglutinin for several bacterial strains

Intestinal SALSA/dmbt1 levels are decreased in prematurely born infants

The first months of life represent a crucial time period for an infant. Alongside establishing the early microbiome, the mucosal immunological homeostasis is being developed. Both processes may be perturbed in prematurely born infants. The glycoprotein SALSA plays a role in mucosal inflammation and microbial clearance. It is one of the most abundant molecules on the intestinal mucosal surfaces in early life. SALSA binds to many types of microbes and host defence molecules like IgA, C1q and collectin molecules. We here describe the development in faecal SALSA levels during the first three months of life. During these 90 days, the median SALSA level in full-term babies decreased from 1100 μg/mL (range 49-17 000 μg/mL) to 450 μg/mL (range 33-1000 μg/mL). Lower levels of SALSA were observed in prematurely born infants in the same time period. Our novel observation thus indicates an impact of prematurity on an important component of the infant intestinal immune system. Changes in SALSA in early life may have an effect on the early establishment of the human microbiome.

Structures of SALSA/DMBT1 SRCR domains reveal the conserved ligand-binding mechanism of the ancient SRCR fold

The structures of SALSA SRCR domains 1 and 8 reveal a cation-dependent mechanism for ligand recognition, contributing to important roles in the immune system and cellular signalling. The cation-binding sites are conserved across all SRCR domains, suggesting conserved functional mechanisms.

The scavenger receptor cysteine-rich (SRCR) family of proteins comprises more than 20 membrane-associated and secreted molecules. Characterised by the presence of one or more copies of the ∼110 amino-acid SRCR domain, this class of proteins have widespread functions as antimicrobial molecules, scavenger receptors, and signalling receptors. Despite the high level of structural conservation of SRCR domains, no unifying mechanism for ligand interaction has been described. The SRCR protein SALSA, also known as DMBT1/gp340, is a key player in mucosal immunology. Based on detailed structural data of SALSA SRCR domains 1 and 8, we here reveal a novel universal ligand-binding mechanism for SALSA ligands. The binding interface incorporates a dual cation-binding site, which is highly conserved across the SRCR superfamily. Along with the well-described cation dependency on most SRCR domain–ligand interactions, our data suggest that the binding mechanism described for the SALSA SRCR domains is applicable to all SRCR domains. We thus propose to have identified in SALSA a conserved functional mechanism for the SRCR class of proteins.

DMBT1 expression in biliary carcinogenesis with correlation of clinicopathological data

AIMS

Deleted in malignant brain tumours 1 (DMBT1) exerts functions in the regulation of epithelial differentiation and inflammation and has been proposed as a tumour suppressor. Because chronic inflammation is a hallmark of cholangiocarcinogenesis, the aim of this study was to investigate the expression of DMBT1 in biliary tract cancer (BTC) and to correlate this expression with clinicopathological data.

METHODS AND RESULTS

The expression of DMBT1 protein was examined immunohistochemically in 157 BTC patients [41 intrahepatic (ICC), 60 extrahepatic cholangiocarcinomas (ECC) and 56 adenocarcinomas of the gallbladder (GBAC)]. Additionally, 56 samples of high-grade biliary intraepithelial neoplasia (BilIN 3) and 92 corresponding samples of histological non-neoplastic biliary tract tissues were included. DMBT1 expression was increased significantly in BilIN 3 compared to normal tissue (P < 0.0001) and BTC (P < 0.0001). BTC showed no significant difference in DMBT1 expression compared to non-neoplastic biliary tissue (P = 0.315). Absent DMBT1 expression in non-neoplastic biliary tissue of BTC patients was associated with poorer survival (P = 0.027). DMBT1 expression was correlated significantly with patients' age (P < 0.001).

CONCLUSION

DMBT1 is expressed differently in cholangiocarcinogenesis and poorer patients' survival rates are associated with absent DMBT1 expression in non-neoplastic biliary tissue, suggesting a tumour-suppressive role of DMBT1 in early cholangiocarcinogenesis.

Saliva: a Dynamic Proteome

The proteome of whole saliva, in contrast to that of serum, is highly susceptible to a variety of physiological and biochemical processes. First, salivary protein secretion is under neurologic control, with protein output being dependent on the stimulus. Second, extensive salivary protein modifications occur in the oral environment, where a plethora of host- and bacteria-derived enzymes act on proteins emanating from the glandular ducts. Salivary protein biosynthesis starts with the transcription and translation of salivary protein genes in the glands, followed by post-translational processing involving protein glycosylation, phosphorylation, and proteolysis. This gives rise to salivary proteins occurring in families, consisting of structurally closely related family members. Once glandular secretions enter the non-sterile oral environment, proteins are subjected to additional and continuous protein modifications, leading to extensive proteolytic cleavage, partial deglycosylation, and protein-protein complex formation. All these protein modifications occur in a dynamic environment dictated by the continuous supply of newly synthesized proteins and removal by swallowing. Understanding the proteome of whole saliva in an environment of continuous turnover will be a prerequisite to gain insight into the physiological and pathological processes relevant to oral health, and be crucial for the identification of meaningful biomarkers for oral disease.

Altered Exosomal RNA Profiles in Bronchoalveolar Lavage from Lung Transplants with Acute Rejection

RATIONALE

The mechanism by which acute allograft rejection leads to chronic rejection remains poorly understood despite its common occurrence. Exosomes, membrane vesicles released from cells within the lung allograft, contain a diverse array of biomolecules that closely reflect the biologic state of the cell and tissue from which they are released. Exosome transcriptomes may provide a better understanding of the rejection process. Furthermore, biomarkers originating from this transcriptome could provide timely and sensitive detection of acute cellular rejection (AR), reducing the incidence of severe AR and chronic lung allograft dysfunction and improving outcomes.

OBJECTIVES

To provide an in-depth analysis of the bronchoalveolar lavage fluid exosomal shuttle RNA population after lung transplantation and evaluate for differential expression between acute AR and quiescence.

METHODS

Serial bronchoalveolar lavage specimens were ultracentrifuged to obtain the exosomal pellet for RNA extraction, on which RNA-Seq was performed.

MEASUREMENTS AND MAIN RESULTS

AR demonstrates an intense inflammatory environment, skewed toward both innate and adaptive immune responses. Novel, potential upstream regulators identified offer potential therapeutic targets.

CONCLUSIONS

Our findings validate bronchoalveolar lavage fluid exosomal shuttle RNA as a source for understanding the pathophysiology of AR and for biomarker discovery in lung transplantation.

Altered Exosomal RNA Profiles in Bronchoalveolar Lavage from Lung Transplants with Acute Rejection

RATIONALE

The mechanism by which acute allograft rejection leads to chronic rejection remains poorly understood despite its common occurrence. Exosomes, membrane vesicles released from cells within the lung allograft, contain a diverse array of biomolecules that closely reflect the biologic state of the cell and tissue from which they are released. Exosome transcriptomes may provide a better understanding of the rejection process. Furthermore, biomarkers originating from this transcriptome could provide timely and sensitive detection of acute cellular rejection (AR), reducing the incidence of severe AR and chronic lung allograft dysfunction and improving outcomes.

OBJECTIVES

To provide an in-depth analysis of the bronchoalveolar lavage fluid exosomal shuttle RNA population after lung transplantation and evaluate for differential expression between acute AR and quiescence.

METHODS

Serial bronchoalveolar lavage specimens were ultracentrifuged to obtain the exosomal pellet for RNA extraction, on which RNA-Seq was performed.

MEASUREMENTS AND MAIN RESULTS

AR demonstrates an intense inflammatory environment, skewed toward both innate and adaptive immune responses. Novel, potential upstream regulators identified offer potential therapeutic targets.

CONCLUSIONS

Our findings validate bronchoalveolar lavage fluid exosomal shuttle RNA as a source for understanding the pathophysiology of AR and for biomarker discovery in lung transplantation.

SALSA: A Regulator of the Early Steps of Complement Activation on Mucosal Surfaces

Complement is present mainly in blood. However, following mechanical damage or inflammation, serous exudates enter the mucosal surfaces. Here, the complement proteins interact with other endogenous molecules to keep microbes from entering the parenteral tissues. One of the mucosal proteins known to interact with the early complement components of both the classical and the lectin pathway is the salivary scavenger and agglutinin (SALSA). SALSA is also known as deleted in malignant brain tumors 1 and gp340. It is found both attached to the epithelium and secreted into the surrounding fluids of most mucosal surfaces. SALSA has been shown to bind directly to C1q, mannose-binding lectin, and the ficolins. Through these interactions SALSA regulates activation of the complement system. In addition, SALSA interacts with surfactant proteins A and D, secretory IgA, and lactoferrin. Ulcerative colitis and Crohn's disease are examples of diseases, where complement activation in mucosal tissues may occur. This review describes the latest advances in our understanding of how the early complement components interact with the SALSA molecule. Furthermore, we discuss how these interactions may affect disease propagation on mucosal surfaces in immunological and inflammatory diseases.

Altered Exosomal RNA Profiles in Bronchoalveolar Lavage from Lung Transplants with Acute Rejection

RATIONALE

The mechanism by which acute allograft rejection leads to chronic rejection remains poorly understood despite its common occurrence. Exosomes, membrane vesicles released from cells within the lung allograft, contain a diverse array of biomolecules that closely reflect the biologic state of the cell and tissue from which they are released. Exosome transcriptomes may provide a better understanding of the rejection process. Furthermore, biomarkers originating from this transcriptome could provide timely and sensitive detection of acute cellular rejection (AR), reducing the incidence of severe AR and chronic lung allograft dysfunction and improving outcomes.

OBJECTIVES

To provide an in-depth analysis of the bronchoalveolar lavage fluid exosomal shuttle RNA population after lung transplantation and evaluate for differential expression between acute AR and quiescence.

METHODS

Serial bronchoalveolar lavage specimens were ultracentrifuged to obtain the exosomal pellet for RNA extraction, on which RNA-Seq was performed.

MEASUREMENTS AND MAIN RESULTS

AR demonstrates an intense inflammatory environment, skewed toward both innate and adaptive immune responses. Novel, potential upstream regulators identified offer potential therapeutic targets.

CONCLUSIONS

Our findings validate bronchoalveolar lavage fluid exosomal shuttle RNA as a source for understanding the pathophysiology of AR and for biomarker discovery in lung transplantation.

Excess Secretion of Gel-Forming Mucins and Associated Innate Defense Proteins with Defective Mucin Un-Packaging Underpin Gallbladder Mucocele Formation in Dogs

Mucosal protection of the gallbladder is vital yet we know very little about the mechanisms involved. In domestic dogs, an emergent syndrome referred to as gallbladder mucocele formation is characterized by excessive secretion of abnormal mucus that results in obstruction and rupture of the gallbladder. The cause of gallbladder mucocele formation is unknown. In these first mechanistic studies of this disease, we investigated normal and mucocele-forming dog gallbladders to determine the source, identity, biophysical properties, and protein associates of the culprit mucins with aim to identify causes for abnormal mucus behavior. We established that mucocele formation involves an adoptive excess secretion of gel forming mucins with abnormal properties by the gallbladder epithelium. The mucus is characterized by a disproportionally significant increase in Muc5ac relative to Muc5b, defective mucin un-packaging, and mucin-interacting innate defense proteins that are capable of dramatically altering the physical and functional properties of mucus. These findings provide an explanation for abnormal mucus behavior and based on similarity to mucus observed in the airways of people with cystic fibrosis, suggest that abnormal mechanisms for maintenance of gallbladder epithelial hydration may be an instigating factor for mucocele formation in dogs.

Alterations in immunodominance of Streptococcus mutans AgI/II: lessons learned from immunomodulatory antibodies

Streptococcus mutans antigen I/II (AgI/II) has been widely studied as a candidate vaccine antigen against human dental caries. In this report we follow up on prior studies that indicated that anti-AgI/II immunomodulatory monoclonal antibodies (MAbs) exerted their effects by destabilizing the native protein structure and exposing cryptic epitopes. We show here that similar results can be obtained by immunizing mice with truncated polypeptides out of the context of an intra-molecular interaction that occurs within the full-length molecule and that appears to dampen the functional response against at least two important target epitopes. Putative T cell epitopes that influenced antibody specificity were identified immediately upstream of the alanine-rich repeat domain. Adherence inhibiting antibodies could be induced against two discrete domains of the protein, one corresponding to the central portion of the molecule and the other corresponding to the C-terminus.

A variant form of the human deleted in malignant brain tumor 1 (DMBT1) gene shows increased expression in inflammatory bowel diseases and interacts with dimeric trefoil factor 3 (TFF3)

The protein deleted in malignant brain tumors (DMBT1) and the trefoil factor (TFF) proteins have all been proposed to have roles in epithelial cell growth and cell differentiation and shown to be up regulated in inflammatory bowel diseases. A panel of monoclonal antibodies was raised against human DMBT1^gp340. Analysis of lung washings and colon tissue extracts by Western blotting in the unreduced state, two antibodies (Hyb213-1 and Hyb213-6) reacted with a double band of 290 kDa in lung lavage. Hyb213-6, in addition, reacted against a double band of 270 kDa in colon extract while Hyb213-1 showed no reaction. Hyb213-6 showed strong cytoplasmic staining in epithelial cells of both the small and large intestine whereas no staining was seen with Hyb213-1. The number of DMBT1^gp340 positive epithelial cells, stained with Hyb213-6, was significantly up regulated in inflammatory colon tissue sections from patients with ulcerative colitis (p<0.0001) and Crohn’s disease (p = 0.006) compared to normal colon tissue. Immunohistochemical analysis of trefoil factor TFF1, 2 and 3 showed that TFF1 and 3 localized to goblet cells in both normal colon tissue and in tissue from patients with ulcerative colitis or Crohn’s disease. No staining for TFF2 was seen in goblet cells in normal colon tissue whereas the majority of tissue sections in ulcerative colitis and Crohn’s disease showed sparse and scattered TFF2 positive goblet cells. DMBT1 and TFF proteins did therefore not co-localize in the same cells but localized in adjacent cells in the colon. The interaction between DMBT1^gp340 and trefoil TFFs proteins was investigated using an ELISA assay. DMBT1^gp340 bound to solid-phase bound recombinant dimeric TFF3 in a calcium dependent manner (p<0.0001) but did not bind to recombinant forms of monomeric TFF3, TFF2 or glycosylated TFF2. This implies a role for DMBT1 and TFF3 together in inflammatory bowel disease.

The salivary scavenger and agglutinin binds MBL and regulates the lectin pathway of complement in solution and on surfaces

The salivary scavenger and agglutinin (SALSA), also known as gp340, salivary agglutinin and deleted in malignant brain tumor 1, is a 340-kDa glycoprotein expressed on mucosal surfaces and secreted into several body fluids. SALSA binds to a broad variety of microbes and endogenous ligands, such as complement factor C1q, surfactant proteins D and A, and IgA. Our search for novel ligands of SALSA by direct protein-interaction studies led to the identification of mannan-binding lectin (MBL) as a new binding partner. We observed that surface-associated SALSA activates complement via binding of MBL. On the other hand, soluble SALSA was found to inhibit Candida albicans-induced complement activation. Thus, SALSA has a dual complement activation modifying function. It activates the lectin pathway when bound to a surface and inhibits it when free in the fluid phase. These activities are mediated via a direct interaction with MBL. This suggests that SALSA could target the innate immune responses to certain microorganisms and simultaneously limit complement activation in the fluid phase.

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

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

Deleted in malignant brain tumors-1 protein (DMBT1): a pattern recognition receptor with multiple binding sites

Deleted in Malignant Brain Tumors-1 protein (DMBT1), salivary agglutinin (DMBT1(SAG)), and lung glycoprotein-340 (DMBT1(GP340)) are three names for glycoproteins encoded by the same DMBT1 gene. All these proteins belong to the scavenger receptor cysteine-rich (SRCR) superfamily of proteins: a superfamily of secreted or membrane-bound proteins with SRCR domains that are highly conserved down to sponges, the most ancient metazoa. In addition to SRCR domains, all DMBT1s contain two CUB domains and one zona pellucida domain. The SRCR domains play a role in the function of DMBT1s, which is the binding of a broad range of pathogens including cariogenic streptococci, Helicobacter pylori and HIV. Mucosal defense proteins like IgA, surfactant proteins and lactoferrin also bind to DMBT1s through their SRCR domains. The binding motif on the SRCR domains comprises an 11-mer peptide in which a few amino acids are essential for binding (GRVEVLYRGSW). Adjacent to each individual SRCR domain are glycosylation domains, where the attached carbohydrate chains play a role in the binding of influenza A virus and Helicobacter pylori. The composition of the carbohydrate chains is not only donor specific, but also varies between different organs. These data demonstrate a role for DMBT1s as pattern recognition molecules containing various peptide and carbohydrate binding motifs.

Review: Gp-340/DMBT1 in mucosal innate immunity

Deleted in Malignant Brain Tumour 1 (DMBT1) is a gene that encodes alternatively spliced proteins involved in mucosal innate immunity. It also encodes a glycoprotein with a molecular mass of 340 kDa, and is referred to as gp-340 (DMBT1(gp340)) and salivary agglutinin (DMBT1(SAG)). DMBT1(gp340) is secreted into broncho-alveolar surface lining fluid whereas DMBT(SAG) is present in the saliva. The two molecules were shown to be identical and both interact with and agglutinate several Gram-negative and Gram-positive bacteria including Streptococcus mutans, a bacterium responsible for caries in the oral cavity. DMBT1(gp340) interacts with surfactant proteins A and D (SP-D). DMBT1(gp340) and SP-D can individually and together interact and agglutinate influenza A virus. DMBT1(gp340) also binds to HIV-1 and facilitates transcytosis of the virus into epithelial cells. DMBT1 binds to a variety of other host proteins, including serum and secretory IgA, C1q, lactoferrin, MUC5B and trefoil factor 2 (TFF2), all molecules with involvement in innate immunity and/or wound-healing processes. Recent generation of Dmbt1-deficient mice has provided the research field of DMBT1 with a model that allows research to progress from in vitro studies to in vivo functional studies of the multifunctional proteins encoded by the DMBT1 gene.

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

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

Consequences of a sortase A mutation in Streptococcus gordonii

Sortase A (SrtA) is required for cell-wall anchoring of LPXTG-containing Gram-positive surface proteins. It was hypothesized, therefore, that disruption of the srtA gene would alter surface anchoring and functions of target LPXTG motif-bearing SspA and SspB proteins of Streptococcus gordonii. Mutant strains in srtA (V288srtA(-), DL1srtA(-)) were constructed in S. gordonii V288 (wtV288) and DL1 (wtDL1). When compared to wtV288, the V288srtA(-) mutant showed decreased biofilm formation on polystyrene, and reduced binding to immobilized purified salivary agglutinin (BIAcore analysis). The wtV288 and V288srtA(-) strains were similar in ultrastructure, but immunogold-labelled SspA/SspB surface expression was reduced on the V288srtA(-) mutant. DL1srtA(-) was also complemented to obtain DL1srtA(+). From the wild-type strains (wtV288, wtDL1), srtA(-) mutants (V288srtA(-), DL1srtA(-)), and the complemented mutant (DL1srtA(+)), cytoplasmic, cell-wall and released extracellular protein fractions were isolated. Each fraction was analysed by SDS-PAGE and immunoblotting with anti-P1. Spent medium from srtA(-) mutant cells contained over-represented proteins, including SspA/SspB (P1 antigen). Mutants showed less P1 on the cell surface than wild-types, as estimated using whole-cell ELISA, and no P1 appeared in the cytoplasmic fractions. Expression of several adhesin genes (sspA/B, cshA/B, fbpA) was generally upregulated in the mutants (V288srtA(-), DL1srtA(-)), but restored to wild-type levels in DL1srtA(+). These data therefore imply that in addition to its role in processing LPXTG-containing adhesins, sortase A has the novel function of contributing to transcriptional regulation of adhesin gene expression.

Salivary agglutinin/glycoprotein-340/DMBT1: a single molecule with variable composition and with different functions in infection, inflammation and cancer

Salivary agglutinin (SAG), lung glycoprotein-340 (gp-340) and Deleted in Malignant Brain Tumours 1 (DMBT1) are three names for identical proteins encoded by the dmbt1 gene. DMBT1/SAG/gp-340 belongs to the scavenger receptor cysteine-rich (SRCR) superfamily of proteins, a superfamily of secreted or membrane-bound proteins with SRCR domains that are highly conserved down to sponges, the most ancient metazoa. On the one hand, DMBT1 may represent an innate defence factor acting as a pattern recognition molecule. It interacts with a broad range of pathogens, including cariogenic streptococci and Helicobacter pylori, influenza viruses and HIV, but also with mucosal defence proteins, such as IgA, surfactant proteins and MUC5B. Stimulation of alveolar macrophage migration, suppression of neutrophil oxidative burst and activation of the complement cascade point further to an important role in the regulation of inflammatory responses. On the other hand, DMBT1 has been demonstrated to play a role in epithelial and stem cell differentiation. Inactivation of the gene coding for this protein may lead to disturbed differentiation, possibly resulting in tumour formation. These data strongly point to a role for DMBT1 as a molecule linking innate immune processes with regenerative processes.

Basis of beneficial immunomodulation by monoclonal antibodies against Streptococcus mutans adhesin P1

We previously identified five monoclonal antibodies (MAbs) against Streptococcus mutans adhesin P1 that modulate the humoral response when bound to whole bacteria and immune complexes (ICs) are administered to BALB/c mice. The two MAbs that redirected the response towards increased efficacy recognize discontinuous epitopes involving pre-alanine-rich domain sequence; therefore, to evaluate whether epitope specificity contributes to a desirable outcome a further MAb with this characteristic was tested. A beneficial immune response was promoted. None of the three MAbs that promoted a beneficial response was opsonic, suggesting that increased uptake of ICs by phagocytes does not mediate the improvement of the IC-elicited antibodies to inhibit bacterial adherence. Finally, two of the six anti-P1 MAbs activated complement but did not partition according to desirable vs. nondesirable effects.

Variant size- and glycoforms of the scavenger receptor cysteine-rich protein gp-340 with differential bacterial aggregation

Glycoprotein gp-340 aggregates bacteria in saliva as part of innate defence at mucosal surfaces. We have detected size- and glycoforms of gp-340 between human saliva samples (n = 7) and lung gp-340 from a proteinosis patient using antibodies and lectins in Western blots and ELISA measurements. Western blots of saliva samples, and of gp-340 purified, from the seven donors using a gp-340 specific antibody distinguished four gp-340 size variants, designated I to IV (n = 2,2,2 and 1). While saliva gp-340 variants I to III had single bands of increasing sizes, variant IV and lung gp-340 had double bands. Purified I to IV proteins all revealed a N-terminal sequence TGGWIP upon Edman degradation. Moreover, purified gp-340 from the seven donors and lung gp-340 shared N-glycans, sialylated Galbeta1-3GalNAc and (poly)lactosamine structures. However, the larger size gp-340 grouping II/III (n = 4) and smaller size grouping I/IV correlated with a secretor, Se(+), and a non secretor, Se(-), dependent glycoform of gp-340, respectively (p = 0.03). The Se(+) glycoforms contained ABH, Le(b), Le(y) and polylactosamine structures, while the Se(-) glycoforms lacked ABH antigens but expressed Le(a), Le(x) and lactosamine structures. By contrast, lung gp-340 completely lacked ABH, Le(a/b), Le(x/y) or sLe(x) structures. Gp-340 and secretor typing of saliva from additional donors (n = 29) showed gp-340 glycoforms I to IV for 6, 16, 4 and 0 donors, respectively, and 3 non-typeable donors, and verified that gp-340 glycoforms I and II/III correlate with Se(-) and Se(+) phenotypes, respectively (p < 0.0001). The glycoforms of saliva and lung gp-340 mediated differential aggregation of Le(b)- (Helicobacter pylori), sialylpolylactosamine- (Streptococcus suis) or sialic acid- (Streptococcus mutans) binding bacteria. In conclusion, variant size- and glycoforms of gp-340 are expressed by different individuals and may modulate the biological properties of gp-340 pertinent to health and disease.

A whole cell BIAcore assay to evaluate P1-mediated adherence of Streptococcus mutans to human salivary agglutinin and inhibition by specific antibodies

Researchers now recognize the utility of surface plasmon resonance technology to evaluate interactions of microbial pathogens with host components. The surface adhesin and candidate vaccine antigen P1 of Streptococcus mutans, the main causative agent of dental caries, interacts with a high molecular weight glycoprotein called salivary agglutinin, or gp340, in the salivary pellicle. We optimized a BIAcore assay to measure P1-mediated Ca(2+) dependent binding of S. mutans whole cells to this physiological ligand immobilized on a Pioneer F1 sensor chip. Regeneration conditions allowed cells to be eluted from the sensor chip permitting multiple reuse of the agglutinin-coated surface. An isogenic P1-deficient S. mutans mutant did not bind to immobilized agglutinin demonstrating specificity of the detected interaction. Glutaraldehyde-fixation of bacterial cells showed the assay measured a whole cell-ligand interaction and was not an artifact of solubilized or leached proteins. Adherence inhibition assays demonstrated varying degrees of disruption of the S. mutans-agglutinin interaction by anti-P1 monoclonal antibodies recognizing different epitopes, whereas a polyclonal reagent demonstrated more complete inhibition. This report describes an improved method to assess salivary agglutinin-mediated adherence of S. mutans in vitro under physiological-like conditions and to evaluate the effectiveness of antibodies of differing specificities to inhibit binding.

Binding of salivary agglutinin to IgA

SAG (salivary agglutinin), which is identical to gp-340 (glycoprotein-340) from the lung, is encoded by DMBT1 (deleted in malignant brain tumours 1). It is a member of the SRCR (scavenger receptor cysteine-rich) superfamily and contains 14 SRCR domains, 13 of which are highly similar. SAG in saliva is partially complexed with IgA, which may be necessary for bacterial binding. The goal of the present study was to characterize the binding of purified SAG to IgA. SAG binds to a variety of proteins, including serum and secretory IgA, alkaline phosphatase-conjugated IgGs originating from rabbit, goat, swine and mouse, and lactoferrin and albumin. Binding of IgA to SAG is calcium dependent and is inhibited by 0.5 M KCl, suggesting that electrostatic interactions are involved. Binding of IgA was destroyed after reduction of SAG, suggesting that the protein moiety is involved in binding. To pinpoint further the binding domain for IgA on SAG, a number of consensus-based peptides of the SRCR domains and SRCR interspersed domains were designed and synthesized. ELISA binding studies with IgA indicated that only one of the peptides tested, comprising amino acids 18-33 (QGRVEVLYRGSWGTVC) of the 109-amino-acid SRCR domain, exhibited binding to IgA. This domain is identical to the domain of SAG that is involved in binding to bacteria. Despite this similar binding site, IgA did not inhibit binding of Streptococcus mutans to SAG or peptide. These results show that the binding of IgA to SAG is specifically mediated by a peptide sequence on the SRCR domains.

Redirecting the humoral immune response against Streptococcus mutans antigen P1 with monoclonal antibodies

The adhesin P1 of Streptococcus mutans has been studied as an anticaries vaccine antigen. An anti-P1 monoclonal antibody (MAb) bound to S. mutans prior to mucosal immunization of mice was shown previously to alter the amount, specificity, isotype, and biological activity of anti-P1 antibodies. The present study was undertaken to screen this and four additional anti-P1 MAbs for immunomodulatory activity when complexed with S. mutans and administered by a systemic route and to evaluate sera from immunized mice for the ability to inhibit adherence of S. mutans to immobilized human salivary agglutinin. All five MAbs tested influenced murine anti-P1 serum antibody responses in terms of subclass distribution and/or specificity. The effects varied depending on which MAb was used and its coating concentration. Two MAbs promoted a more effective, and two others a less effective, adherence inhibition response. An inverse relationship was observed between the ability of the MAbs themselves to inhibit adherence and the ability of antibodies elicited following immunization with immune complexes to inhibit adherence. Statistically significant correlations were demonstrated between the levels of anti-P1 serum immunoglobulin G2a (IgG2a) and IgG2b, but not of IgG1 or IgG3, and the ability of sera from immunized animals to inhibit bacterial adherence. These results indicate that multiple anti-P1 MAbs can mediate changes in the immune response and that certain alterations are potentially more biologically relevant than others. Immunomodulation by anti-P1 MAbs represents a useful strategy to improve the beneficial immune response against S. mutans.

Salivary agglutinin/DMBT1SAG expression is up-regulated in the presence of salivary gland tumors

Salivary agglutinin (SAG) is encoded by the gene Deleted in Malignant Brain Tumors 1 (DMBT1) and represents the salivary variant of DMBT1 (DMBT1(SAG)). While SAG is a bona fide anti-caries factor, DMBT1 was proposed as a candidate tumor-suppressor for brain, digestive tract, and lung cancer. Though DMBT1(SAG) is expressed in the salivary glands, its expression in salivary gland tumors is unknown. Here we analyzed DMBT1(SAG) expression in 20 salivary gland tumors and 14 tumor-flanking tissues by immunohistochemistry. DMBT1(SAG) in salivary gland tumors resembles the changes of expression levels known from DMBT1 in tumors in other cancer types. Particularly, DMBT1(SAG) was up-regulated in 10/14 tumor-flanking tissues, and a strong staining of the luminal content in the tumor and/or the tumor-flanking tissue was observed in 14/20 cases. This suggests that, in addition to its role in caries defense, SAG may serve as a potential tumor indicator and/or tumor suppressor in salivary gland tissue.

Salivary micelles: identification of complexes containing MG2, sIgA, lactoferrin, amylase, glycosylated proline-rich protein and lysozyme

Micelles represent macromolecular structures in saliva and the aim of this study was to identify salivary proteins that occur in these globular particles. Micelles were isolated from whole saliva (WS) collected from three individuals and analysed in different experiments. Samples were subjected to polyacrylamide gel electrophoreses, hydrolysed to determine their amino acid composition and total protein concentration, examined by scanning electron microscopy and examined on Western blots probed with a panel of antibodies directed against salivary proteins. On Coomassie Brilliant Blue stained gels, the banding pattern of whole saliva and micelles was similar but the intensity of bands was quite different. Amino acid analysis confirmed that the amino acid composition of micelles was distinct from that of whole saliva. Scanning electron microscopy showed that micelles exhibit a complex pattern consisting of individual particles or clusters of particles with different sizes and shapes. Micelles contain proteins with high (MG2 and secretory IgA), intermediate (lactoferrin, amylase and glycosylated proline-rich protein (PRP)) and low (lysozyme) molecular weight that were immuno-detected on blots probed with specific antibodies. Micelles represent particulate multicomponent structures in whole saliva that contain a subset of salivary proteins known to be important components of the innate immune system and are likely to play an important role in the maintenance of homeostasis in the oral environment.

Adsorption of parotid saliva proteins and adhesion of Streptococcus mutans ATCC 21752 to dental fiber-reinforced composites

The use of fiber-reinforced composites (FRC) in dentistry has increased during recent years. In marginal areas of crowns and removable partial dentures the fibers may become exposed and come into contact with oral tissues, saliva, and microbes. To date, few articles have been published on oral microbial adhesion to FRCs. The aim of this study was to compare different FRCs, their components, and conventional restorative materials with respect to S. mutans ATCC 21752 adhesion and adsorption of specific S. mutans binding proteins. Surface roughness of the materials was also determined. Four different FRCs, a restorative composite, and a high-leucite ceramic material were studied. Polyethylene FRC was found to be significantly rougher than all other materials. Aramid FRC also showed higher surface roughness in comparison with all materials but polyethylene FRC. Without a saliva pellicle, adhesion of S. mutans coincided with surface roughness and polyethylene and aramid FRC promoted S. mutans adhesion better than the other smoother materials. In the presence of salivary pellicle, ceramic and polyethylene FRC bound more bacteria than the other materials studied. Higher quantities of S. mutans binding proteins in the pellicles may in part account for the higher S. mutans adhesion to saliva-coated ceramic and polyethylene FRC.

Towards saliva-based screening for sleeping sickness?

A pilot study was carried out on the detection of trypanosome-specific antibodies in saliva for diagnosis of sleeping sickness. All twenty-three saliva samples of parasitologically confirmed Trypanosoma brucei gambiense patients tested positive in an indirect enzyme-linked immunosorbent assay, whereas all 14 saliva samples of a negative control group remained negative. Trypanosome-specific antibody levels in patient saliva correlated with antibody levels in serum, but were about 250-fold lower. Eight of 23 undiluted saliva samples of sleeping sickness patients tested positive in CATT/T. b. gambiense and two of 23 in LATEX/T. b. gambiense. All fourteen saliva samples of the negative control group were also positive in CATT/T. b. gambiense, as were four of 14 in LATEX/T. b. gambiense. CATT and LATEX were thus inappropriate for antibody detection in saliva. These results indicate that trypanosome-specific antibody detection in saliva is possible. This could lead to the development of a simple, non-invasive, reliable saliva field test for diagnosis of sleeping sickness.

DMBT1, a regulator of mucosal homeostasis through the linking of mucosal defense and regeneration?

DMBT1 (deleted in malignant brain tumor 1), which encodes a large scavenger receptor cysteine rich (SRCR) B protein, has been proposed to be a tumor suppressor gene, due to the high frequency of its homozygous deletion and the lack of expression in a variety of cancers. However, studies on its physiological functions and its relationship with tumorigenesis are still at an initial stage. Two mucosal defense-related molecules, gp-340 and salivary agglutinin, have been identified to be alternatively spliced products of DMBT1, which suggests that DMBT1 is a pattern recognition receptor in innate immunity. Meanwhile, results from immunohistochemical staining and studies at the cellular level, began to associate DMBT1 with a proliferation to differentiation switching process in gastrointestinal epithelial cells. Together with its up-regulation in inflammation, these findings suggest that DMBT1 might be a local regulator of homeostasis, possibly through linking mucosal inflammation to the modulation of epithelial regeneration, and whose abnormality is a frequent cause of malignancy.

Roles of sortase in surface expression of the major protein adhesin P1, saliva-induced aggregation and adherence, and cariogenicity of Streptococcus mutans

Sortase is a newly discovered transpeptidase that covalently links LPXTGX-containing surface proteins to the gram-positive bacterial cell wall. In this study, the sortase gene (srtA) was isolated from Streptococcus mutans NG8 by PCR. The gene encoded a 246-amino-acid protein, including a 40-amino-acid signal peptide. The srtA gene was insertionally inactivated by a tetracycline resistance cassette. P1, a major surface protein adhesin previously shown to anchor to the peptidoglycan by the LPXTGX motif, was secreted into the culture medium by the srtA mutant. In contrast, the wild-type P1 remained cell wall associated. Complementation of the mutant with srtA restored the P1 surface expression phenotype. P1 produced by the mutant, but not that produced by the wild type and the srtA-complemented mutant, was recognized by an antibody raised against the hydrophobic domain and charged tail C terminal to the LPXTGX motif. These results suggest that the failure to anchor P1 to the cell wall is due to the lack of cleavage of P1 at the LPXTGX motif. The srtA mutant was markedly less hydrophobic than the wild type and the complemented mutant. The srtA mutant failed to aggregate in the presence of saliva or salivary agglutinin and adhered poorly to saliva- or salivary agglutinin-coated hydroxylapatite. In rats, the srtA mutant colonized the teeth poorly when sucrose was absent. When sucrose was present, the srtA mutant colonized the teeth but less effectively and induced significantly less caries (P < 0.05) than the wild-type strain. In conclusion, the sortase enzyme in S. mutans is responsible for anchoring P1 to the cell surface and plays a role in modulating the surface properties and cariogenicity of S. mutans.

Human salivary agglutinin binds to lung surfactant protein-D and is identical with scavenger receptor protein gp-340

Salivary agglutinin is a 300-400 kDa salivary glycoprotein that binds to antigen B polypeptides of oral streptococci, thereby playing a role in their colonization and the development of caries. A mass spectrum was recorded of a trypsin digest of agglutinin. A dominant peak of 1460 Da was sequenced by quadrupole time-of-flight (Q-TOF) tandem MS. The sequence showed 100% identity with part of the scavenger receptor cysteine-rich ('SRCR') domain found in gp-340/DMBT1 (deleted in malignant brain tumours-1). The mass spectrum revealed 11 peaks with an identical mass as a computer-simulated trypsin digest of gp-340. gp-340 is a 340 kDa glycoprotein isolated from bronchoalveolar lavage fluid that binds specifically to lung surfactant protein-D. DMBT1 is a candidate tumour suppressor gene. A search in the human genome revealed only one copy of this gene. The molecular mass, as judged from SDS/PAGE and the amino acid composition of agglutinin, was found to be nearly identical with that of gp-340. It was shown by Western blotting that monoclonal antibodies against gp-340 reacted with salivary agglutinin, and monoclonals against agglutinin reacted with gp-340. It was demonstrated that gp-340 and agglutinin bound in a similar way to Streptococcus mutans and surfactant protein-D. Histochemically, the distribution of gp-340 in the submandibular salivary glands was identical with the agglutinin distribution, as shown in a previous paper [Takano, Bogert, Malamud, Lally and Hand (1991) Anat. Rec. 230, 307-318]. We conclude that agglutinin is identical with gp-340, and that this molecule interacts with S. mutans and surfactant protein-D.

Salivary non-immunoglobulin agglutinin inhibits human leukocyte elastase digestion of acidic proline-rich salivary proteins

Saliva contains acidic proline-rich salivary proteins that are involved in the formation of the salivary pellicle coating supragingival tooth surfaces. However, human leukocyte elastase, arriving in gingival exudates from inflamed periodontal tissues, degrades the acidic proline-rich salivary proteins, preventing binding to hydroxylapatite surfaces. Here it is reported that high-molecular-weight non-immunoglobulin salivary agglutinin inhibited the proteolytic action of human leukocyte elastase on purified acidic proline-rich salivary proteins. Inhibition was eliminated with monoclonal antibody to a protein determinant on the salivary agglutinin. The addition of antibody against salivary agglutinin blocked the inhibitory effect of parotid saliva on exogenously applied human leukocyte elastase, allowing for the elastase-mediated digestion of the salivary acidic proline-rich salivary proteins. Salivary agglutinin, therefore, is a physiologically important inhibitor of human leukocyte elastase and is able to inhibit elastase-mediated digestion of salivary acidic proline-rich proteins.

Active detachment of Streptococcus mutans cells adhered to epon-hydroxylapatite surfaces coated with salivary proteins in vitro

Although the formation of biofilms has been much studied, detachment of adherent cells from biofilms has been relatively neglected. Recent results have shown that adherent Streptococcus mutans cells can actively detach from epon-hydroxylapatite (EHA) rods conditioned with hog gastric mucin. The mechanisms for adherence and detachment of Strep. mutans cells in this system was uncertain. In the present study, resting Strep. mutans cells were used to form a simple monolayer on EHA rods coated with saliva and salivary agglutinin (SAG). Preliminary experiments defined the variables for conditioning EHA with saliva and SAG and establishing the adherence of Strep. mutans to the conditioned surfaces. The results showed that salivary proteins including SAG adsorbed rapidly to EHA and that a relatively stable Strep. mutans NG8 monolayer was formed within 60 min of incubation. The monolayers were subsequently used for detachment studies. The results showed that adherent Strep. mutans cells detached in a temperature-dependent manner and responded to the addition of a preparation of surface protein-releasing enzyme (SPRE) obtained from Strep. mutans in a dose-dependent fashion. The effect of the exogenous SPRE on detachment could be abrogated by pronase treatment. Two putative SPRE-defective mutants (A and E) were generated by Tn917 mutagenesis. Both mutants possessed a single transposon insertion as demonstrated by Southern hybridization and appeared to be different from one another based on the hybridization patterns. Mutant A displayed an increased quantity of cell-surface antigen P1, an adhesin that interacts with SAG. At the same time mutant A was unable to release P1 and other high molecular-weight proteins from the cell surface. Mutant A detached at a significantly lower rate (21%) than the parent strain (37%) (p=0.05). SPRE prepared from mutant A was unable to release Strep. mutans NG8 adherent cells as compared to SPRE obtained from the wild-type cells. Collectively, these results suggest that the detachment of Strep. mutans adherent cells formed on salivary protein-coated EHA was an active process mediated by the action of SPRE.

Current status of a mucosal vaccine against dental caries

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

Binding of salivary glycoprotein-secretory immunoglobulin A complex to the surface protein antigen of Streptococcus mutans

The interaction between a surface protein antigen (PAc) of Streptococcus mutans and human salivary agglutinin was analyzed with a surface plasmon resonance biosensor. The major component sugars of the salivary agglutinin were galactose, fucose, mannose, N-acetylglucosamine, N-acetylgalactosamine, and N-acetylneuraminic acid. Binding of salivary agglutinin to PAc was calcium dependent and heat labile and required a pH greater than 5. Binding was significantly inhibited by N-acetylneuraminic acid and alpha2,6-linked sialic acid-specific lectin derived from Sambucus sieboldiana in a dose-dependent manner. Pretreatment of the salivary agglutinin with sialidase reduced the binding activity of the agglutinin to the PAc molecule. The agglutinin was dissociated into high-molecular-mass glycoprotein and secretory immunoglobulin A (sIgA) components by electrophoretic fractionation in the presence of 1% sodium dodecyl sulfate and 1% 2-mercaptoethanol. Neither of the components separated by electrophoretic fractionation, high-molecular-mass glycoprotein or sIgA, bound to the PAc molecule. Furthermore, the high-molecular-mass glycoprotein strongly inhibited the binding of the native salivary complex to PAc. These results suggest that the complex formed by the high-molecular-mass salivary glycoprotein and sIgA is essential for the binding reaction and that the sialic acid residues of the complex play an important role in the interaction between the agglutinin and PAc of S. mutans.

On the rôle of human salivary micelle-like globules in bacterial agglutination

The hypothesis to be tested in this in vitro study was that the salivary micelle-like globules (SMGs) have a rôle in the agglutination of some oral bacteria. An attempt to determine the mechanisms for the interactions involved was also carried out. 4 laboratory and 4 native streptococci strains were tested. Human whole (HWS) and parotid (HPS) saliva was collected from 4 subjects, and SMGs were isolated from both salivas, and agglutination was recorded in the various bacterial suspensions over time. HPS, HWS and SMGs isolated from HPS and HWS caused typical agglutination patterns for the mutans strains. Salivary supernatants (without SMGs) caused a much delayed or no agglutination. Electron microscopy showed SMG-like structures on the surface of the agglutinated bacteria. Addition of pyrophosphate to HPS prevented agglutination, whereas guanidine HCl prevented normal agglutination of a sanguis strain, and urea had no obvious effect. Together, these results indicate that the SMGs are important in the agglutination of streptococci, and that both calcium-dependent, electrostatic and hydrophobic interactions may be involved.

Saliva mediated adherence, aggregation and prevalence in dental plaque of Streptococcus mutans, Streptococcus sanguis and Actinomyces spp, in young and elderly humans

Salivary components in the pellicle mediate bacterial adherence to the tooth. Such components may also aggregate bacteria in saliva and prevent them becoming established in dental plaque. In the present study, the adherence and aggregation of Streptococcus mutans strain Ingbritt, S. sanguis strain 10556 and Actinomyces viscosus-strain 19246 mediated by parotid and whole saliva from groups of young and elderly people were examined. Significant differences were found between test strains, salivary secretions and age groups. S. sanguis 10556 and A. viscosus 19246 generally adhered more strongly than S. mutans Ingbritt, which adhered better to pellicles from parotid saliva than from whole saliva Strain 19246 bound in higher numbers to parotid saliva pellicles from elderly compared to young individuals. Strain 10556 adhered better to whole saliva than parotid saliva pellicles, and the difference was significant among the young individuals, indicating reduced adherence ability in elderly whole saliva. The streptococci were aggregated by parotid and whole saliva, and S. sanguis aggregation was less with whole saliva from the elderly than from the young participants. Besides a correlation between whole saliva aggregation of S. mutans and proportions of bacteria in plaque, no correlations were found for the individual binding properties of saliva and prevalence of bacteria in vivo. However, the level of saliva-mediated adherence in vitro was in the following order: S. mutans. Actinomyces S sanguis, which corresponded to their isolation frequency in plaque. These findings emphasize the importance of initial adherence to salivary receptors in bacterial colonization on teeth. Further studies are needed to reveal if individual patterns in the in vitro binding characteristics of saliva lead to variation of colonization in vivo.

Characterization of a P1-deficient strain of Streptococcus mutans that expresses the SpaA protein of Streptococcus sobrinus

The Streptococcus sobrinus SpaA protein and the Streptococcus mutans P1 protein share 66% sequence homology at the amino acid level. To determine if the SpaA protein can be expressed in S. mutans and functionally replace the P1 protein, the spaA gene of S. sobrinus 6715 was isolated from plasmid pX1303 and inserted into the Escherichia coli-Streptococcus shuttle vector pVA838. The resulting plasmid pX1600 was transformed into the P1-deficient strain S. mutans 834 that has defects in saliva-mediated aggregation and in the ability to adhere to saliva-coated hydroxyapatite surfaces. Western blot (immunoblot) analysis of cellular protein fractions of S. mutans 834 (pX1600) detected in mutanolysin-solubilized cell walls a major protein of 210 kDa with an electrophoretic mobility similar to that of S. sobrinus SpaA protein and a minor 210-kDa protein and a major 64-kDa protein in the extracellular protein fraction. Analysis of virulence traits showed that expression of SpaA protein by S. mutans 834(pX1600) cells had restored the ability of the S. mutans 834 cells to aggregate in the presence of saliva or salivary agglutinin but not to adhere to saliva-coated hydroxyapatite. This cell aggregation was inhibited specifically by antisera to S. sobrinus SpaA protein. These results indicate that SpaA plays a role in the virulence of S. sobrinus by specifically interacting with fluid-phase salivary agglutinin to mediate cell aggregation.

Human oral microbial ecology and dental caries and periodontal diseases

In the human oral cavity, which is an open growth system, bacteria must first adhere to a surface in order to be able to colonize. Ability to colonize a non-shedding tooth surface is necessary prior to any odontopathic or periodontopathic process. Complex microbe-host relationships occur and must be studied before the commensal-to-pathogenic nature of the human indigenous oral flora can be understood. Medical pathogens, if present in the appropriate host, always produce specific disease. Caries and periodontal diseases are conditional diseases, requiring numbers of certain indigenous species at various sites, particularly the tooth surface. In the case of caries, the condition is related to sugar consumption. Periodontal disease/s may require certain host and environmental conditions, such as local environment or nutritional factors in gingival crevicular fluids. Nonetheless, critical numbers of certain indigenous species must be present in order for these diseases to occur. The aim of this review is to understand the acquisition of the indigenous oral flora and the development of human dental plaque. The role of the salivary pellicle and adherence of indigenous bacteria to it are critical first steps in plaque development. Bacterial interactions with saliva, nutritional factors, growth factors, and microbial physiologic processes are all involved in the overall process of microbial colonization.

Saliva-mediated binding in vitro and prevalence in vivo of Streptococcus mutans

The contention that the colonization of oral tissues requires the adhesion of bacteria is undisputed, but adherence can only be studied quantitatively in vitro. It has never been seriously challenged whether the adherence phenomena measured in vitro reflect differences in levels of in vivo colonization. The objective of this study was to investigate the adherence-promoting ability of saliva from persons harbouring Strep. mutans in the range from non-detectable levels to more than 106 colony-forming units/ml. Saliva-mediated adherence of Strep. mutans is promoted by high molecular-weight glycoproteins, agglutinins, which also causes aggregation of the bacteria. Adherence and aggregation of Strep. mutans was investigated individually using parotid saliva from 41 persons. Heavily colonized individuals did not promote adherence better than those with relatively few indigenous bacteria. Aggregation was found to be less rapid with parotid saliva from the heavily colonized individuals (p < 0.05). The results indicate that parotid saliva primarily affects the in vivo prevalence of Strep. mutans by clearing the bacteria from the mouth rather than promoting adherence.

Monoclonal antibodies against a high-molecular-weight agglutinin block adherence to experimental pellicles on hydroxyapatite and aggregation of Streptococcus mutans

High-molecular-weight (HMW) glycoproteins, agglutinins, in parotid saliva induce the aggregation of S. mutans and mediate binding of the bacteria to saliva-coated hydroxyapatite (SHA). Two types of monoclonal antibodies (mAb) directed against, respectively, protein and carbohydrate epitopes on the agglutinin have been reported to inhibit the aggregation of S. mutans. In this study, the mAbs were tested for their ability to block aggregation and adherence to SHA of S. mutans serotype c mediated by parotid, submaxillary, and whole saliva from three subjects. Both types of antibody inhibited the adherence and aggregation in a dose-dependent manner. However, individual variations were noted for the effects of the antibodies. Sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) and subsequent immunoblotting with the antibodies revealed a > 300 kDa agglutinin component in all types of saliva and in the proteins desorbed from SHA. The degree of staining of this component in immunoblots of the salivas and the desorbates seemed to be paralleled by the rates of aggregation and adherence, respectively. Thus, our results indicate that the adherence to SHA as well as the aggregation of S. mutans serotype c is primarily mediated by structurally related, HMW glycoproteins in parotid, submaxillary, and whole saliva.

Allosteric regulation by calcium of rabbit polyclonal anti-cyclic GMP antibody

Calcium increased the binding of rabbit polyclonal antibodies and cGMP by increasing antibody affinity without altering the number of binding sites (Bmax). Competitive binding studies revealed that calcium increased the affinity of antibody for cGMP derivatives similarly, suggesting that the effects of this cation were antigen-independent. Kinetic binding studies demonstrated that calcium increased affinity by decreasing the dissociation rate without altering the association rate of antigen and antibody. Studies of the dissociation of antigen-antibody complexes preformed in the absence of calcium suggested that this cation regulated antibody function allosterically. These data contrast with those obtained previously suggesting that calcium regulated the interaction of cAMP and antibodies by increasing Bmax without altering affinity by reaction coupling. Re-analysis of those data demonstrated that calcium increased the affinity without altering the number of binding sites of antibodies to cAMP, in close agreement with the present results. These data suggest that allosteric modulation of antibody function by calcium may be a general mechanism regulating the interaction of polyclonal antibodies with cyclic nucleotides.

Saliva-bacterium interactions in oral microbial ecology

Saliva is thought to have a significant impact on the colonization of microorganisms in the oral cavity. Salivary components may participate in this process by one of four general mechanisms: binding to microorganisms to facilitate their clearance from the oral cavity, serving as receptors in oral pellicles for microbial adhesion to host surfaces, inhibiting microbial growth or mediating microbial killing, and serving as microbial nutritional substrates. This article reviews information pertinent to the molecular interaction of salivary components with bacteria (primarily the oral streptococci and Actinomyces) and explores the implications of these interactions for oral bacterial colonization and dental plaque formation. Knowledge of the molecular mechanisms controlling bacterial colonization of the oral cavity may suggest methods to prevent not only dental plaque formation but also serious medical infections that may follow microbial colonization of the oral cavity.

Affinity and specificity of the interactions between Streptococcus mutans antigen I/II and salivary components

Adherence to salivary pellicle-coated tooth surfaces and aggregation by salivary components of Streptococcus mutans involves a major cell surface protein termed antigen (Ag) I/II. The objectives of this study were to evaluate the affinity and specificity of the interactions between AgI/II and human saliva in assays of 125I-AgI/II binding to saliva-coated hydroxyapatite (SHA) and of S. mutans aggregation by salivary agglutinin (SAG), monitored turbidimetrically. 125I-AgI/II binding to SHA followed saturation kinetics, and Scatchard plot analysis indicated two binding sites with dissociation constants of the order of 10(-10) mol/L and 10(-9) mol/L. The binding to SHA of the C-terminal one-third of AgI/II which corresponds to AgII was less than one-fifth that of the whole molecule and did not show evidence of saturation. The binding of 125I-AgI/II was inhibited by native or recombinant fragments that mapped in the N-terminal part of the molecule and that contained the alanine-rich repeat region, whereas fragments mapping at the central or C-terminal one-third had no effect. As with binding to SHA, the regions of AgI/II which inhibited aggregation mapped at the N-terminal part of the molecule, but, in addition, a recombinant segment mapping at the central part and containing the proline-rich repeat region was also inhibitory. The S. mutans-aggregating activity of SAG or whole saliva was inhibited by amino compounds, and most strongly by L-lysine and analogues possessing omega-primary amine groups. These data support the role of AgI/II as an adhesin with high-affinity binding for SHA receptors, mediated by the N-terminal part of the molecule. This region is also involved in SAG-induced S. mutans aggregation, which is sensitive to amino compounds.

Saliva-binding region of Streptococcus mutans surface protein antigen

A 190-kDa surface protein antigen (PAc) of Streptococcus mutans binds to human salivary components. For detection of specific binding of the PAc protein to human salivary components, a simple sandwich assay was used. Microtiter plates precoated with recombinant PAc (rPAc), PAc fragments, or S. mutans whole cells were allowed to react with human whole saliva and then were incubated with biotinylated rPAc. The biotinylated rPAc bound to salivary components was detected by use of alkaline phosphatase-conjugated streptavidin and p-nitrophenylphosphate. In this assay, the binding of whole cells of S. mutans and purified rPAc to salivary components was confirmed. For determination of a saliva-binding region of the PAc molecule, 14 truncated PAc fragments were constructed by use of the polymerase chain reaction and an expression vector, pAX4a+. The binding of these truncated PAc fragments to human salivary components was determined by the sandwich assay. Among the truncated PAc fragments, fragments corresponding to residues 39 to 864 and residues 39 to 1000 of PAc showed a high ability to bind to salivary components. Shorter recombinant fragments corresponding to residues 39 to 217, residues 200 to 481, residues 470 to 749, and residues 688 to 864 did not exhibit any binding ability. The fragment that corresponds to a proline-rich repeating region (residues 828 to 1000) bound directly to the PAc protein. These results suggest that residues 39 864 of the PAc molecule are important in the binding of the surface protein to human salivary components, and the proline-rich repeating region of the PAc protein may contribute to spontaneous self-aggregation of the PAc protein.

Role of cations and IgA in saliva-mediated aggregation of Pseudomonas aeruginosa in cystic fibrosis patients

Oral colonization by Pseudomonas aeruginosa possibly precedes the pulmonary infection process in cystic fibrosis (CF) patients. As bacterial aggregates may play a role in establishment of pulmonary infections, involvement of IgA and cations in CF patient saliva-mediated aggregation of P. aeruginosa was investigated. For colonized patients, P. aeruginosa aggregation correlated with bacterial-specific and total salivary IgA. Cation or IgA depletion reduced P. aeruginosa aggregation by saliva from all patients. However, if cations were removed before IgA, and saliva was then reconstituted with calcium, only colonized patient saliva showed reduced aggregation. Aggregation by IgA-depleted saliva was augmented by reconstituting with original IgA. CF patient saliva-mediated aggregation of P. aeruginosa thus is cation-dependent and enhanced by bacterial-specific IgA. Characterizing the interactions among bacterial aggregating factor(s), cations, and antibodies in CF saliva will help clarify the link between P. aeruginosa oral colonization and pulmonary infections in CF patients.

Agglutination of Streptococcus mutans serotype C cells but inhibition of Porphyromonas gingivalis autoaggregation by human lactoferrin

The ability of various forms of human lactoferrin (LF) to agglutinate oral Streptococcus mutans, Strep. sobrinus, Strep. rattus, Strep. sanguis, Porphyromonas gingivalis and Actinobacillus actinomycetemcomitans cells was studied spectrophotometrically. Fe3+ saturated LF was unable to agglutinate these bacteria, whereas iron-free LF (apo LF) effectively agglutinated Strep. mutans cells but not the other bacteria. The efficiency and rate of agglutination of Strep. mutans were somewhat lower with apo LF than with human whole saliva. However, secretory IgA, phosphate and whole saliva almost totally abolished the apo LF-mediated agglutination of Strep. mutans, suggesting binding to the same target sites on bacterial cell surfaces, or to each other. The presence of exogenous iron (Fe2+, Fe3+), lactoperoxidase or serum albumin did not affect the agglutination by apo LF. Low Ca2+ (50-100 microns) slightly enhanced the agglutination by apo LF but higher concentrations (0.5-1.0 mM) totally blocked the apo LF-mediated agglutination of Strep. mutans. Both saliva and apo LF significantly delayed the rapid autoaggregation of P. gingivalis cells. Aggregation of P. gingivalis is considered a potential virulence factor and a protective mechanism against the host's cellular defences in the gingival crevice. These findings show a novel, strain-specific antibacterial mechanism for LF against Strep. mutans and P. gingivalis and adds a new compound to the group of agglutinating proteins in human saliva.