Interaction of a salivary mucin-secretory immunoglobulin A complex with mucosal pathogens

Role of secretory immunoglobulin A and secretory component in the protection of mucosal surfaces

The contribution of secretory immunoglobulin A (SIgA) antibodies in the defense of mucosal epithelia plays an important role in preventing pathogen adhesion to host cells, therefore blocking dissemination and further infection. This mechanism, referred to as immune exclusion, represents the dominant mode of action of the antibody. However, SIgA antibodies combine multiple facets, which together confer properties extending from intracellular and serosal neutralization of antigens, activation of non-inflammatory pathways and homeostatic control of the endogenous microbiota. The sum of these features suggests that future opportunities for translational application from research-based knowledge to clinics include the mucosal delivery of bioactive antibodies capable of preserving immunoreactivity in the lung, gastrointestinal tract, the genito-urinary tract for the treatment of infections. This article covers topics dealing with the structure of SIgA, the dissection of its mode of action in epithelia lining different mucosal surfaces and its potential in immunotherapy against infectious pathogens.

Electron microscopic immunogold localization of statherin in human minor salivary glands

In this study, which supplements a recent article on the localization of statherin in human major salivary glands, we investigated the intracellular distribution of this peptide in minor salivary glands by immunogold cytochemistry at the electron microscopy level. In the lingual serous glands of von Ebner, gold particles were found in serous granules of all secreting cells, indicating that statherin is released through granule exocytosis. In buccal and labial glands, mostly composed of mucous tubuli, statherin reactivity was detected in the serous element, which represents only a small population of the glandular parenchyma. In these serous cells, however, statherin labeling was absent in secretory granules and restricted to small cytoplasmic vesicles near or partially fused with granules. Vesicle labeling could be related to the occurrence of an alternative secretory pathway for statherin in buccal and labial glands.

Mucin-bacterial interactions in the human oral cavity and digestive tract

Mucins are a family of heavily glycosylated proteins that are the major organic components of the mucus layer, the protective layer covering the epithelial cells in many human and animal organs, including the entire gastro-intestinal tract. Microbes that can associate with mucins benefit from this interaction since they can get available nutrients, experience physico-chemical protection and adhere, resulting in increased residence time. Mucin-degrading microorganisms, which often are found in consortia, have not been extensively characterized as mucins are high molecular weight glycoproteins that are hard to study because of their size, complexity and heterogeneity. The purpose of this review is to discuss how advances in mucus and mucin research, and insight in the microbial ecology promoted our understanding of mucin degradation. Recent insight is presented in mucin structure and organization, the microorganisms known to use mucin as growth substrate, with a specific attention on Akkermansia muciniphila, and the molecular basis of microbial mucin degradation owing to availability of genome sequences.

Identification of salivary mucin MUC7 binding proteins from Streptococcus gordonii

BACKGROUND

The salivary mucin MUC7 (previously known as MG2) can adhere to various strains of streptococci that are primary colonizers and predominant microorganisms of the oral cavity. Although there is a growing interest in interaction between oral pathogens and salivary mucins, studies reporting the specific binding sites on the bacteria are rather limited. Identification and characterization of the specific interacting proteins on the bacterial cell surface, termed adhesins, are crucial to further understand host-pathogen interactions.

RESULTS

We demonstrate here, using purified MUC7 to overlay blots of SDS-extracts of Streptococcus gordonii cell surface proteins, 4 MUC7-binding bands, with apparent molecular masses of 62, 78, 84 and 133 kDa from the Streptococcus gordonii strain, PK488. Putative adhesins were identified by in-gel digestion and subsequent nanoLC-tandem mass spectrometry analysis of resultant peptides. The 62 kDa and 84 kDa bands were identified as elongation factor (EF) Tu and EF-G respectively. The 78 kDa band was a hppA gene product; the 74 kDa oligopeptide-binding lipoprotein. The 133 kDa band contained two proteins; alpha enolase and DNA-directed RNA polymerase, beta' subunit. Some of these proteins, for example alpha enolase are expected to be intracellular, however, flow cytometric analysis confirmed its location on the bacterial surface.

CONCLUSION

Our data demonstrated that S. gordonii expressed a number of putative MUC7 recognizing proteins and these contribute to MUC7 mucin binding of this streptococcal strain.

Host polymorphisms in interleukin 4, complement factor H, and C-reactive protein associated with nasal carriage of Staphylococcus aureus and occurrence of boils

BACKGROUND

Staphylococcus aureus is capable of persistently colonizing the vestibulum nasi. We hypothesized that polymorphisms in host inflammatory response genes and genetic variation in S. aureus contribute to susceptibility to S. aureus carriage and infection.

METHODS

The prevalence of persistent nasal carriage of S. aureus in 3851 participants aged 61-101 years was 18% (678 of 3851 participants), whereas 73% of volunteers (2804 of 3851) were not colonized. A total of 1270 individuals had boils. Polymorphisms in TNFA (C -863T), IL4 (C -542T), CFH (Tyr402His), and CRP (C1184T, C2042T, and C2911G) were determined. Genetic similarity among 428 S. aureus isolates was determined by use of amplified fragment length polymorphism analysis (AFLP)-mediated genotyping.

RESULTS

The IL4 -524 C/C host genotype was associated with an increased risk of persistent S. aureus carriage, irrespective of S. aureus AFLP genotype. The CRP haplotype 1184C; 2042C; 2911C was overrepresented in individuals who were not colonized . In individuals with boils, carriers of the CFH Tyr402 variant, and the CRP 2911 C/C genotype were overrepresented.

CONCLUSION

Persistent carriage of S. aureus is influenced by genetic variation in host inflammatory response genes. As would be expected in multifactorial host-microbe interactions, these effects are limited. Interestingly, host genotype was associated with the carriage of certain S. aureus genotypes. Apparently, a close interaction between host and bacterial determinants are prerequisites for long-term colonization.

Comparison of the composition of oral mucosal residual saliva with whole saliva

OBJECTIVE

Compared with whole saliva, residual saliva comprising the oral mucosal film shows a high protein concentration. The purpose of this study was to compare the composition of residual saliva with unstimulated and stimulated whole saliva in normosalivators.

MATERIALS AND METHODS

The composition of oral mucosal residual saliva in 30 healthy individuals was investigated and compared with that of whole saliva. The concentrations of total protein, secretory immunoglobin A (sIgA), lactoferrin, total carbohydrate, and sialic acid were examined. The activities of peroxidase, lysozyme and alpha-amylase were determined.

RESULTS

Residual saliva had higher levels of total protein and carbohydrate than whole saliva, with a higher carbohydrate to protein ratio in the residual saliva suggesting that salivary glycoproteins are concentrated on the oral mucosal surface. sIgA, lactoferrin and sialic acid were present as highly concentrated forms in residual saliva. The enzymatic activity of peroxidase in residual saliva was higher than that of whole saliva.

CONCLUSIONS

These concentrated carbohydrate and antimicrobials on the oral mucosal surface work for mucosal defence and could be used for targeting sites for the delivery of therapeutic agents.

The immune geography of IgA induction and function

The production of immunoglobulin A (IgA) in mammals exceeds all other isotypes, and it is mostly exported across mucous membranes. The discovery of IgA and the realization that it dominates humoral mucosal immunity, in contrast to the IgG dominance of the systemic immune system, was early evidence for the distinct nature of mucosal immunology. It is now clear that IgA can function in high-affinity modes for neutralization of toxins and pathogenic microbes, and as a low-affinity system to contain the dense commensal microbiota within the intestinal lumen. The basic map of induction of IgA B cells in the Peyer's patches, which then circulate through the lymph and bloodstream to seed the mucosa with precursors of plasma cells that produce dimeric IgA for export through the intestinal epithelium, has been known for more than 30 years. In this review, we discuss the mechanisms underlying selective IgA induction of mucosal B cells for IgA production and the immune geography of their homing characteristics. We also review the functionality of secretory IgA directed against both commensal organisms and pathogens.

Saliva as research material: Biochemical, physicochemical and practical aspects

Whole saliva is a complex mixture of proteins and other molecules which originate from several sources. The biochemical and physicochemical properties of saliva contribute to the numerous functions of saliva in, e.g., speech, maintaining oral and general health, and food processing. Interest in saliva has increased in the last few years for its potential to diagnose viral, bacterial and systemic diseases. The use of saliva as research material may pose particular problems due to its inherent variability and instability. This review describes practical aspects of salivary as research material with emphasis on protein biochemistry and physical chemistry.

The functional interactions of commensal bacteria with intestinal secretory IgA

PURPOSE OF REVIEW

The aim of this article is to describe the immune geography of IgA induction by commensal intestinal bacteria and the underlying mechanisms of cytokine and costimulatory signalling between dendritic cells, B cells and T cells.

RECENT FINDINGS

Intestinal dendritic cells sample commensal intestinal bacteria that penetrate the epithelial layer and induce IgA+ B cells to seed the mucosa with IgA plasma cells. Constitutive secretion of retinoic acid by intestinal dendritic cells directs the specificity of the IgA class switch and homing receptor expression in Peyer's patch B cells. In-vivo experiments have shown that TGF-beta is a vital cytokine for IgA induction in vivo, and the tumour necrosis factor family members BAFF and APRIL provide key costimulatory signals. After transport through the epithelial layer secretory IgA limits penetration of commensal bacteria back through the epithelium and shapes the density of different bacterial species in the intestinal lumen.

SUMMARY

Production of IgA is an important adaptation to the presence of commensal intestinal bacteria and induction of the response is compartmentalized within the intestinal mucosal immune system. This compartmentalization allows a vigorous mucosal immune response to commensals without needing the systemic immune system to be tolerant of these organisms.

Do salivary antibodies reliably reflect both mucosal and systemic immunity?

Two major antibody classes operate in saliva: secretory IgA (SIgA) and IgG. The former is synthesized as dimeric IgA by plasma cells (PCs) in salivary glands and is exported by the polymeric Ig receptor (pIgR). Most IgG in saliva is derived from serum (mainly via gingival crevices), although some is locally produced. Gut-associated lymphoid tissue (GALT) and nasopharynx-associated lymphoid tissue (NALT) do not contribute equally to mucosal PCs throughout the body. Thus, enteric immunostimulation is an inadequate mode of stimulating salivary IgA antibodies, which are poorly associated with the intestinal SIgA response, for instance after enteric cholera vaccination. Nevertheless, the IgA response in submandibular/sublingual glands is better related to B cell induction in GALT than the parotid response. Such disparity is suggested by the elevated levels of IgA in submandibular secretions of AIDS patients, paralleling their highly upregulated intestinal IgA system. Moreover, in patients with active celiac disease, IgA antibodies to disease-precipitating gliadin are reliably represented in whole saliva but not in parotid secretion. Parotid SIgA may be more consistently linked to immune induction in palatine tonsils and adenoids (human NALT), as supported by the homing molecule profile of NALT-derived B cell blasts. Also several other variables influence the levels of antibodies in oral secretions. These include difficulties with reproducibility and standardization of immunoassays, the impact of flow rate, acute or chronic stress, protein loss during sample handling, and uncontrolled admixture of serum-derived IgG and monomeric IgA. Despite such problems, saliva remains an interesting biological fluid with great scientific and clinical potentials.

Cross-talk between probiotic bacteria and the host immune system

Among the numerous purported health benefits attributed to probiotic bacteria, their capacity to interact with the immune system of the host is now supported by an increasing number of in vitro and in vivo experiments. In addition to these, a few well-controlled human intervention trials aimed at preventing chronic immune dysregulation have been reported. Even though the precise molecular mechanisms governing the cross-talk between these beneficial bacteria and the intestinal ecosystem remain to be discovered, a new and fascinating phase of research has been initiated in this area as demonstrated by a series of recent articles. This article summarizes the status and latest progress of the field in selected areas and aims at identifying key questions that remain to be addressed, especially concerning the translocation of ingested bacteria, the identification of major immunomodulatory compounds of probiotics, and specific aspects of the host-microbe cross-talk. The interaction with immunocompetent cells and the role of secretory IgA in gut homeostasis are also evoked. Finally, a brief overview is provided on the potential use of recombinant DNA technology to enhance the health benefits of probiotic strains and to unravel specific mechanisms of the host-microbe interaction.

Biological Functions of IgA

Immunoglobulin A (IgA) is the most enigmatic of immunoglobulins. It is by far the most abundant of human Igs, being present in the blood plasma at concentrations approximating 2–3mg/mL, as well as the dominant isotype in most secretions where its output amounts to some 5–8g/day in adults. Furthermore, its evolutionary origins appear to precede the synapsid– diapsid divergence in tetrapod phylogeny (>300 million years ago) because it is present in both mammals and birds and therefore possibly also in reptiles (reviewed in Peppard et al., 2005); an IgA-like molecule has now been identified in a lizard (Deza et al., 2007).

Influences of animal mucins on lysozyme activity in solution and on hydroxyapatite surfaces

The purpose of this study was to investigate the influence of animal mucins on lysozyme activity in solution and on the surface of hydroxyapatite (HA) beads. The effects of animal mucins on lysozyme activity in solution were examined by incubating porcine gastric mucin (PGM) or bovine submaxillary mucin (BSM) with hen egg-white lysozyme (HEWL) or salivary samples. HA-immobilised animal mucins or lysozyme were used to determine the influence of animal mucins on lysozyme activity on HA surfaces. Lysozyme activity was determined by turbidity measurement of a Micrococcus lysodeikticus substrate suspension. Protein concentration was determined by ninhydrin assay. PGM inhibited the activity of HEWL and salivary lysozyme in solution. The amount of inhibition was dependent on mucin concentration, incubation time and temperature, and the structural integrity of the mucin. The inhibition of salivary lysozyme activity by PGM was greater in submandibular/sublingual saliva than in parotid saliva. The inhibition of lysozyme activity by PGM was markedly dependent on pH. However, BSM did not inhibit the in-solution lysozyme activities of HEWL and clarified saliva. Both PGM and BSM bound to HA surfaces, and HA-adsorbed animal mucins increased the subsequent adsorption of lysozyme. When HA beads were exposed to a mixture of HEWL and PGM or BSM, lysozyme activity on the HA surfaces was significantly increased. The results suggest that animal mucins affect lysozyme activity, and the effects are different on HA surfaces compared with in solution. Further research is needed to determine the effect of animal mucins on lysozyme activity in vivo.

[Expression of antimicrobial peptide MUC7 in kidneys with pyelonephritis]

BACKGROUND

Mucins are glycoproteins secreted by epithelial cells of various organ systems exerting multiple functions. MG2 as the protein transcript of the MUC7 gene has first been described as secreted by serous salivary glands in the oral cavity. We sought to explore changes of MUC7 expression in the kidney stimulated by bacterial infection of the upper urinary tract.

METHODS

We investigated the gene expression of MUC7 by reverse transcriptase-polymerase chain reaction in voided urine specimens from 15 patients with acute pyelonephritis compared to 15 healthy volunteers. Furthermore, the gene and protein expression of MUC7 was studied in 15 renal tissue samples with chronic bacterial pyelonephritis versus 10 normal human kidney samples taken from tumor-bearing organs.

RESULTS

MUC7 gene expression was detected in 5 of 15 voided urine samples of patients with pyelonephritis and in 2 samples from 15 healthy volunteers (Fisher's exact test p=0.39). MUC7 gene expression was detected in 7 of 15 tissue samples of kidneys with chronic pyelonephritis and in none of 10 normal renal tissue samples from tumor bearing organs (p=0.02). Immunohistochemical staining with the monoclonal antibody PANH3 revealed protein expression in 6 of the 15 tissue samples with chronic pyelonephritis, but not in normal tissue samples.

CONCLUSION

Upregulated MUC7 expression in the urinary tract particularly in renal tubular epithelium can occur under inflammatory conditions. This indicates a putative role of MUC7 as an antimicrobial host defense molecule within the urogenital tract.

Polymeric IgR knockout mice are more susceptible to mycobacterial infections in the respiratory tract than wild-type mice

It is generally accepted that cellular, and not humoral immunity, plays the crucial role in defense against intracellular bacteria. However, accumulating data indicate the importance of humoral immunity for the defense against a number of intracellular bacteria, including mycobacteria. We have investigated the role of secretory IgA, the main isotype found in mucosal tissues, in protection against mycobacterial infection, using polymeric IgR (pIgR)-deficient mice. Characterization of the humoral response induced after intra-nasal immunizations with the mycobacterial antigen PstS-1 revealed a loss of antigen-specific IgA response in saliva from the knockout mice. IgA level in the bronchoalveolar lavage of knockout mice was similar to wild-type level, although the IgA antibodies must have reached the lumen by other means than pIgR-mediated transport. Infection with Mycobacterium bovis bacillus Calmette-Guérin (BCG) demonstrated that the immunized pIgR-/- mice were more susceptible to BCG infection than immunized wild-type mice, based on higher bacterial loads in the lungs. This was accompanied by a reduced production of both IFN-gamma and tumor necrosis factor-alpha (TNF-alpha) in the lungs. Additionally, the pIgR-/- mice displayed reduced natural resistance to mycobacterial infection proved by significantly higher bacterial growth in their lungs compared with wild-type mice after infection with virulent Mycobacterium tuberculosis. The knockout mice appeared to have a delayed mycobacteria-induced immune response with reduced expression of protective mediators, such as IFN-gamma, TNF-alpha, inducible nitric oxide synthase and regulated upon activation normal T cell sequence, during early infection. Collectively, our results show that actively secreted IgA plays a role in protection against mycobacterial infections in the respiratory tract, by blocking entrance of bacilli into the lungs, in addition to modulation of the mycobacteria-induced pro-inflammatory response.

Innate secretory antibodies protect against natural Salmonella typhimurium infection

The production of IgA is induced in an antigen-unspecific manner by commensal flora. These secretory antibodies (SAbs) may bind multiple antigens and are thought to eliminate commensal bacteria and self-antigens to avoid systemic recognition. In this study, we addressed the role of "innate" SAbs, i.e., those that are continuously produced in normal individuals, in protection against infection of the gastrointestinal tract. We used polymeric immunoglobulin receptor (pIgR-/-) knock-out mice, which are unable to bind and actively transport dimeric IgA and pentameric IgM to the mucosae, and examined the role of innate SAbs in protection against the invasive pathogen Salmonella typhimurium. In vitro experiments suggested that innate IgA in pIgR-/- serum bound S. typhimurium in a cross-reactive manner which inhibited epithelial cell invasion. Using a "natural" infection model, we demonstrated that pIgR-/- mice are profoundly sensitive to infection with S. typhimurium via the fecal-oral route and, moreover, shed more bacteria that readily infected other animals. These results imply an important evolutionary role for innate SAbs in protecting both the individual and the herd against infections, and suggest that the major role of SAbs may be to prevent the spread of microbial pathogens throughout the population, rather than protection of local mucosal surfaces.

Mucosal immunoglobulins

Due to their vast surface area, the mucosal surfaces of the body represent a major site of potential attack by invading pathogens. The secretions that bathe mucosal surfaces contain significant levels of immunoglobulins (Igs), which play key roles in immune defense of these surfaces. IgA is the predominant antibody class in many external secretions and has many functional attributes, both direct and indirect, that serve to prevent infective agents such as bacteria and viruses from breaching the mucosal barrier. This review details current understanding of the structural and functional characteristics of IgA, including interaction with specific receptors (such as Fc(alpha)RI, Fc(alpha)/microR, and CD71) and presents examples of the means by which certain pathogens circumvent the protective properties of this important Ig.

Immunoglobulin levels and phagocytes in the cervical mucus plug at term of pregnancy

BACKGROUND

To characterize the potential for adaptive immune protection in cervical mucus plugs with respect to immunoglobulin isotypes and effector cells (phagocytes).

METHODS

Thirty-one cervical mucus plugs were collected from healthy women in labor at term. The cervical mucus plugs were allocated either to analysis of immunoglobulins by enzyme-linked immunosorbent assay (ELISA), gel chromatography and Western blotting (n = 20) or to microscopical, including immunocytochemical, analyses. The levels of immunoglobulin in the plugs were compared to the levels in 10 samples of ovulatory cervical mucus from nonpregnant women.

RESULTS

In the cervical mucus plugs, levels of immunoglobulin G (IgG) [median 3270 microg/mL (100-14 500)] and IgA [540 (22-2820)], but not IgM [30.5 (1.0-160)], were significantly elevated compared to cervical mucus from nonpregnant women (p < 0.02 for IgG and IgA). The IgG : IgA ratio in the plugs was also elevated (p < 0.02). The proportion of secretory immunoglobulin A (SIgA) relative to total IgA in the plugs ranged from 16 to 65% (n = 5). IgA and IgG were largely intact. Microscopically, the vagina-proximal part of the cervical mucus plugs contained bacteria and was rich in cells, mainly phagocytes. Conversely, the uterine part contained few cells.

CONCLUSION

The high immunoglobulin levels in combination with the presence of phagocytes suggest a potential for adaptive immune defense in the cervical mucus plug, which, together with innate immune factors, may act as an immunological gatekeeper protecting the fetomaternal unit against infection from the vagina.

A comparative analysis of antibody repertoire against Staphylococcus aureus antigens in patients with deep-seated versus superficial staphylococcal infections

Immunoblot and an enzyme-linked immunosorbent assays were used to evaluate and compare IgG antibodies against S. aureus whole cell lysate, cell wall peptidoglycan and lipoteichoic acid to discriminate between deep-seated and superficial S. aureus infection. Serum samples were examined from patients with deep-seated (n = 25) and superficial (n = 25) S. aureus infections and 15 healthy controls. Patients with deep-seated infections exhibited a large number of immuno-reactive bands in their IgG immunoblot profile as compared to those with superficial infections and healthy controls. Anti-staphylococcal IgG antibodies that reacted with two antigens of apparent molecular weight 110 and 98 kDa were specifically present in 96% (24/25) of patients with deep-seated infections, and were absent in, superficial and control sera. Moreover other Gram-positive and Gram-negative bacteria did not share these two unique antigens. The ELISA assays revealed significantly elevated levels of IgG antibodies to peptidoglycan (PG) in 18 of 25 (72%) patients with deep infection and 15 of 25 (60%) patients with superficial staphylococcal infection. The elevated levels of IgG antibodies to teichoic acid (TA) antigen were detected in all (100%) deep-seated group patients and among 40% (10/25) patients with superficial infection. An increase in levels of antibodies to PG showed a positive correlation trend with levels of IgG antibodies to TA only in deep infection group. Thus immunoblot detection of these two unique antigens as well as detection of elevated antibodies against PG and TA may be useful for the discrimination of staphylococcal deep-seated and superficial infection in humans.

Streptococcus mutans surface alpha-enolase binds salivary mucin MG2 and human plasminogen

Matrix-assisted laser desorption ionization-time of flight mass spectrometry analysis identified enolase as a cell surface component of Streptococcus mutans, which was confirmed by enzyme-linked immunosorbent assay, Western blotting, and transmission electron microscopy. Surface enolase was demonstrated to bind to human plasminogen and salivary mucin MG2. The results suggested a role for enolase in S. mutans attachment, clearance, or breach of the bloodstream barrier.

Neuroendocrine regulation of salivary IgA synthesis and secretion: implications for oral health

Secretory immunoglobulin A (S-IgA) represents the main adaptive immune mechanism in the oral cavity. The regulation of secretion and synthesis of S-IgA is not only dependent on prior antigenic stimulation, but is also under strong neuroendocrine control. Thus, alterations in neuroendocrine functioning (such as induced by stress, exercise, pregnancy, menstrual cycle, and pharmacological interventions) may affect salivary IgA levels. This review deals with the neuroendocrine regulation of synthesis and secretion of salivary IgA and its potential role in the maintenance of oral health.

Human salivary aggregation in Streptococcus intermedius type g strains: relationship with IgA

Bacterial aggregation is an important step in elimination from the human body to protect against infection. Streptococcus intermedius K1K aggregates in human saliva. In this study, the salivary agglutinin was identified. The aggregation level was very strong in sonic-treated saliva and 1-microm filtrate. Preincubation of human saliva with anti-human alpha chain serum or anti-human whole saliva serum completely inhibited aggregation, but preincubation with anti-human micro chain serum or anti-Fc fragment of human IgG serum had no effect. Agglutinin of human saliva that could aggregate the strain K1K was purified using DEAE-Sepharose CL-6B, Phenyl-Sepharose CL-4B and Sephacryl S200HR gel filtration. Purified salivary agglutinin was characterized with electrophoresis and immunological techniques, indicating that purified material was IgA. Bacterial aggregation was dependent on the presence of calcium. Saliva filtrate specimens from eight healthy men and eight women showed different aggregation activities. Three men and one woman had little activity. These data show that the present bacterial aggregation was an immunoreaction between IgA in saliva and the bacteria dependent on the levels of calcium. In addition, the IgA in human saliva related with possible calcium-dependent antigen(s) on the surface of strain K1K.

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.

Adhesion of oral streptococci to experimental bracket pellicles from glandular saliva

The aim of this study was to evaluate the functions of bracket pellicles as the binding receptors for Streptococcus mutans and Streptococcus gordonii. Four different types of orthodontic brackets were used: stainless steel, monocrystalline sapphire, polycrystalline alumina, and plastic. The bracket pellicles were formed by incubating orthodontic brackets with fresh submandibular-sublingual saliva or parotid saliva for 2 hours. The pellicles were extracted, and their components were confirmed by gel electrophoresis, immunodetection, and amino acid composition analysis. The roles of the bracket pellicles in the adhesion of oral streptococci were evaluated by incubating tritium-labeled streptococci with pellicle-transfer blots. The results showed that the salivary components adhered selectively according to type of bracket and glandular saliva. The selective adsorption was also proven by the amino acid composition profiles. Among the several salivary proteins, MG2, alpha-amylase, and the acidic proline-rich proteins provided the binding sites for S gordonii. However, none of these proteins in the bracket pellicles contributed to the adhesion of S mutans. These findings suggest that numerous salivary proteins can adhere selectively to the orthodontic brackets, and some of them contribute to the binding of S gordonii.

MG2 and lactoferrin form a heterotypic complex in salivary secretions

Protein-protein interactions are necessary for homeostasis to be maintained and for biological systems to be integrated. Heterotypic complexes occur in saliva, and a complex between MG2 and SIgA has been suggested to promote microbial clearance from the oral cavity. In this study, we used a peptide display library to investigate previously unrecognized heterotypic complexes involving MG2 and other proteins. The library was panned with MG2 12 times, and analyses of clones identified the sequence Ala-Leu-Leu-Cys-, which occurs in salivary lactoferrin. Blotting experiments confirmed that MG2 and lactoferrin form a heterotypic complex in vitro and in vivo. Periodate treatment of MG2 did not affect the interaction. A synthetic lactoferrin peptide containing the motif Ala-Leu-Leu-Cys-blocked the interaction between MG2 and lactoferrin, confirming the specificity of the interaction identified by panning. This complex may enhance the properties of these salivary components in the oral environment.

Experimental salivary pellicles formed on the surface of self-curing resin

The aim of this study was to identify the salivary components present in the pellicles formed on self-curing resin and to investigate the qualitative variations in adsorbed salivary pellicle compositions according to different exposure time to saliva. Experimental pellicles were formed by the incubation of polymerized resin particles with fresh human parotid or submandibular-sublingual saliva for either 20 min or 2 h. Pellicles were extracted using formic acid and lyophilized, they were then subjected to sodium dodecyl sulphate-polyacrylamide gel electrophoresis and immunoblotting to identify the adsorbed salivary components. The amino acid profiles of the 2 h-pellicles were analysed and compared with those of fresh glandular salivas. There was a difference in the 2 h-pellicle components on the self-curing resin compared with those of other dental materials as well as tooth enamel. The amino acid profiles of the 2 h-pellicles were also different from those of fresh glandular salivas. In the case of submandibular-sublingual saliva, the components of the 2 h-pellicle showed a different pattern compared with those of the 20 min-pellicle. However, there was no significant difference between the components of the 2 h- and 20 min-pellicles in the case of parotid saliva. A distinct difference was found in the surface binding affinities of immunoglobulin (IgA) from different glandular salivas. The findings of this study provide information concerning the initial bacterial adhesion on the surfaces of self-curing resin.

Salivary biochemistry in Buffalo: the legacy of Michael J. Levine

The author pays tribute to the contributions of Michael J. Levine to the field of salivary biochemistry.

Functional domain of bovine milk lactoferrin which inhibits the adherence of Streptococcus mutans cells to a salivary film

The bovine lactoferrin molecule and relatively long lactoferrin fragments containing residues 473 to 538 strongly inhibited adherence of Streptococcus mutans to saliva-coated hydroxyapatite beads. Each cysteine residue in Lf411 (residues 473 to 538) was replaced by a serine residue, and the mutants Lf411-C481S and Lf411-C532S strongly inhibited S. mutans adherence. These results suggest that the functional domain of lactoferrin that binds to a salivary film lies in residues 473 to 538 and that the region might be concealed by disulfide bond formation between Cys481 and Cys532 in the Lf411 fragment.

Structural characterisation of cysteines in a bacterial-binding motif of human salivary mucin MG2

Human salivary mucin MG2 is a 180 kDa glycoprotein secreted by submandibular/sublingual and minor salivary glands. Secreted MG2 contains a domain with the only two cysteines (Cys(45) and Cys(50)) present in the polypeptide backbone; in native and recombinant MG2 this domain is involved in mucin binding to oral microbes. As the reduction and alkylation of MG2 has been shown to abolish binding, the present study was undertaken to determine whether the cysteine residues exist in the dithiol or disulphide form. Electrophoretic analysis under reducing and non-reducing conditions showed that intermolecular disulphide bonds do not occur between MG2 molecules. The same incorporation of radiolabelled iodoacetamide into MG2 was obtained with or without prior reduction. When radiolabelled alkylated MG2 was digested with Endoproteinase Lys-C and the derived peptides were separated by reversed-phase high-performance liquid chromatography (RP-HPLC), radioactivity was found in two fractions. Mass spectral analyses of these fractions showed the presence of peptides Cys-Leu-His-Lys and Arg-Cys-Arg-Pro-Lys, both containing carboxymethylated cysteines. These results show that the cysteines in the structural motif associated with bacterial binding exist in the dithiol form, and suggest the potential use of cysteine-containing peptides as agents to modify interactions of MG2 with microbes and oral surfaces.

Secretory component: a new role in secretory IgA-mediated immune exclusion in vivo

Secretory immunoglobulin (Ig) A (SIgA) is essential in protecting mucosal surfaces. It is composed of at least two monomeric IgA molecules, covalently linked through the J chain, and secretory component (SC). We show here that a dimeric/polymeric IgA (IgA(d/p)) is more efficient when bound to SC in protecting mice against bacterial infection of the respiratory tract. We demonstrate that SC ensures, through its carbohydrate residues, the appropriate tissue localization of SIgA by anchoring the antibody to mucus lining the epithelial surface. This in turn impacts the localization and the subsequent clearance of bacteria. Thus, SC is directly involved in the SIgA function in vivo. Therefore, binding of IgA(d/p) to SC during the course of SIgA-mediated mucosal response constitutes a crucial step in achieving efficient protection of the epithelial barrier by immune exclusion.

Identification and characterization of a nonimmunoglobulin factor in human saliva that inhibits Streptococcus mutans glucosyltransferase

Saliva contains an array of nonimmunoglobulin defense factors which are thought to contribute to the protection of the hard and soft tissue surfaces of the oral cavity by modulating microbial colonization and metabolism. Here we report the discovery of a putative innate defense factor in human saliva that inhibits the glucosyltransferase (GTF) of Streptococcus mutans, a virulence enzyme involved in oral colonization by this pathogen. The GTF-inhibiting factor (GIF) was initially identified as a nonimmunoglobulin salivary component that interfered with detection of antibodies to the glucan-binding region (GLU) of GTF by an enzyme-linked immunosorbent assay. This inhibitory activity was present in whole saliva and submandibular-sublingual saliva, but it was essentially absent from parotid saliva. GIF inhibited the recognition of S. mutans cell surface-associated GTF by specific antibodies but had no effect on antibodies to other cell surface antigens, suggesting that GIF specifically binds to GTF on S. mutans. GIF purified by size exclusion or affinity chromatography was used for biochemical and functional characterization. Analysis of GIF by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a high-molecular-weight glycoprotein after staining with Coomassie blue or Schiff's reagent. Heating and reduction with 2-mercaptoethanol of GIF resulted in the release of a approximately 58-kDa protein that was identified as alpha-amylase by Western blotting using anti-alpha-amylase antibodies. GLU bound blotted alpha-amylase, suggesting that the latter molecule is the GLU-binding component of the GIF complex. The ability of GTF to synthesize extracellular glucans was inhibited by GIF but not by uncomplexed alpha-amylase or an unrelated high-molecular-weight glycoprotein. In conclusion, our findings demonstrate that in human saliva, there is a high-molecular-weight glycoprotein-alpha-amylase complex which is capable of inhibiting GTF and may contribute to control of S. mutans colonization in the oral cavity.

Preventive effect of glutamine on intestinal barrier dysfunction induced by severe trauma

AIM: To investigate the mechanism underlying intestinal barrier function damage after severe trauma and the therapeutic effect of glutamine.

METHODS: Burned patients, and animal models of severe trauma replicated by hemorrhagic shock combined with endotoxin infusion and burn injury, were included in a serial experiment. Effects of oral glutamine on intestinal barrier function were observed in scalded rats. Parameters measured in these experiments were as follows: plasma levels of diamine oxidase (DAO), tumor necrosis factor (TNFα ), endotoxin (LPS), and lactate as well as D-lactate by biochemical methods, lactose/mannitol (L/M) ratio in urine by SP-3400, and pathological examination of intestinal mucosa under light microscopy.

RESULTS: Plasma DAO activity was significantly increased after injury. There was a negative correlation between plasma DAO and intestinal mucosal DAO or pHi (r = -0.93, plasma 0.80 ± 0.93, 2.83 ± 1.71, 1.14 ± 0.64, 2.36 ± 2.06 and 2.49 ± 1.67 vs intestinal 0.52 ± 0.12, 0.34 ± 0.03, 0.45 ± 0.18, 0.37 ± 0.26 and 0.41 ± 0.07; r = -0.533, plasma 0.87 ± 0.75, 1.89 ± 1.13, 1.21 ± 0.23, 3.03 ± 2.61 and 4.70 ± 1.22 vs pHi 7.03 ± 0.05, 7.05 ± 0.06, 7.14 ± 0.096, 7.20 ± 0.08 and 7.05 ± 0.07; P < 0.01-0.05). Positive correlations were found between DAO activity and plasma TNFα , LPS, lactate, L/M and D-lactate (r = 0.817, 0.842, 0.872, and 0.951; plasma DAO 0.87 ± 0.75, 1.89 ± 1.13, 1.21 ± 0.23, 3.03 ± 2.61 and 4.70 ± 1.22 vs TNFα 0.08 ± 0.02, 0.03 ± 0.25, 0.17 ± 0.09, 0.34 ± 0.15 and 0.33 ± 0.18; vs LPS 0.14 ± 0.03, 0.16 ± 0.04, 0.21 ± 0.02, 0.18 ± 0.16 and 0.37 ± 0.10; vs lactate 9.03 ± 2.19, 18.30 ± 2.56, 9.81 ± 2.83, 12.01 ± 6.83, 12.01 ± 6.84 and 43.61 ± 11.27; vs L/M 0.03 ± 0.01, 0.41 ± 0.27, 0.62 ± 0.20, 1.70 ± 0.60; r = 0.774, plasma DAO 1.25 ± 0.41, 2.17 ± 0.71, 2.29 ± 0.87, 1.23 ± 0.55 and 1.11 ± 0.47 vs D-lactate 8.37 ± 2.48, 18.25 ± 6.18, 13.96 ± 4.94, 8.93 ± 3.00 and 12.39 ± 4.94; all P < 0.01), repestively. Damage of intestinal mucosa was found by pathological examination. Intestinal barrier function was improved to a certain extent by oral glutamine in scalded rats.

CONCLUSION: Intestinal barrier function was damaged in the early stage after trauma. Plasma DAO activity, D-lactate content, intestinal pHi and urine L/M may be sensitive markers of intestinal mechanical injury, and glutamine may protect against intestinal barrier dysfunction after severe trauma.

Recombinant immunoglobulin A: powerful tools for fundamental and applied research

The use of monoclonal antibodies has become routine in research and diagnostic laboratories but the potential level of antibodies in use in public health and medical applications is still far from its maximum. From a clinical perspective, topical immunotherapy of mucosal surfaces with monoclonal antibodies can block entry and transmission of bacteria, viruses, fungi and parasites that infect humans, and defeat some key strategies, evolved by many pathogens, to evade the host immune system. The chief antibody at mucosal surfaces is secretory immunoglobulin A (SIgA), a multi-polypeptide complex originating from two cell types. The recent design of heterologous expression systems, coupled with modern biotechnology processes, should form a sound basis for studying the functional properties of SIgAs and evaluate their value as biotherapeutics. Here, we discuss the principles underlying mucosal immunity and review the application of recombinant SIgA to the dissection of mechanisms in passive and active protection at mucosal surfaces.

Lactoferrin, amylase and mucin MUC5B and their relation to the oral microflora in hyposalivation of different origins

There are several reasons for hyposalivation, each affecting the salivary composition in different ways. The aim of this study was to analyze and compare lactoferrin, amylase and mucin MUC5B in stimulated whole saliva collected from subjects with hyposalivation of different origins and to relate the results to the presence of some microbial species associated with oral disorders. Albumin was determined as a marker of serum leakage. The characteristic feature for subjects with radiation-induced hyposalivation was a large increase in lactoferrin, probably due to leakage through inflamed mucosal tissues, while it was a high albumin content for the group with primary Sjögren's syndrome, probably due to disruption of the fragile mucosa. The saliva composition in subjects with hyposalivation of unknown origin or due to medicines was close to that in the healthy controls. All three hyposalivation groups tended to display a decrease in the concentrations of MUC5B and amylase. None of the microbial species analyzed (streptococci, mutans streptococci, Lactobacillus spp., Fusobacterium nucleatum, Prevotella intermedia/Prevotella nigrescens, Candida albicans, Staphylococcus aureus and enterics) correlated with concentration of MUC5B in saliva. The RT group, having the highest concentration of lactoferrin, had the lowest median number of F. nucleatum and was the only group in which median number of P. intermedia/P. nigrescens was zero.

Determinants of Staphylococcus aureus nasal carriage

Nasal carriage of Staphylococcus aureus has been identified as a risk factor for community-acquired and nosocomial infections. We screened 230 donors of diverse ethnic and socioeconomic backgrounds and identified 62 (27%) whose nasal secretions were colonized by S. aureus. In 18 donors in whom the various regions of the nasal luminal surface were separately sampled, the predominant region of S. aureus colonization was the moist squamous epithelium on the septum adjacent to the nasal ostium. Nasal fluid from carriers was defective in killing endogenous S. aureus and nasal carrier isolates of S. aureus but not a laboratory S. aureus strain. Transmission electron microscopy revealed that S. aureus isolates incubated in nasal fluid from carriers for 2 h at 37 degrees C were less damaged than those incubated in noncarrier fluid and were coated with an electron-dense layer. Compared with that from healthy donors and patients with acute rhinitis, nasal fluid from carriers contained elevated concentrations of the neutrophil-derived defensins human neutrophil peptides 1 to 3 (47- and 4-fold increases, respectively), indicative of a neutrophil-mediated inflammatory host response to S. aureus colonization. The concentration of the inducible epithelial antimicrobial peptide human beta-defensin 2 was also highly elevated compared to that in healthy donors, in whom the level was below the detection limit, or patients with acute rhinitis (sixfold increase). Thus, nasal carriage of S. aureus takes hold in nasal fluid that is permissive for colonization and induces a local inflammatory response that fails to clear the colonizing bacteria.

[Nasal carriers of methicillin-resistant Staphylococcus aureus among cuban children attending day-care centers]

BACKGROUND

Recent but scarce reports of methicillin-resistant Staphylococcus aureus strains (MRSA) among children without risk factors associated with its acquisition prompted us to investigate its presence in the community.

PATIENTS AND METHODS

During the September and October months in 1997, nasal and pharyngeal swabs were obtained from 358 children aged less than five years who attended three day-care centers in the Marianao Area, La Habana City, Cuba. The isolated S. aureus strains were characterized for antimicrobial sensitivity using the Kirby-Bauer method. Methicillin resistance was confirmed by te Oxacillin Salt-Agar Screening-Plate method recommended by the National Committee for Clinical Laboratory Standards.

RESULTS

18.7% of children were carriers of S. aureus in the upper respiratory tract; 2.2% of children carried MRSA strains. The highest resistance levels corresponded to erythromycin (50.74%) and tetracycline (29.9%). All tested strains were sensitive to ciprofloxacin.

CONCLUSIONS

Our results provide evidence on the recovery of MRSA strains among healthy children attending day-care centers and are suggestive of a rapid colonization and spread of these microorganisms in the community.

Diffusion of macromolecules and virus-like particles in human cervical mucus

To determine whether or not large macromolecules and viruses can diffuse through mucus, we observed the motion of proteins, microspheres, and viruses in fresh samples of human cervical mucus using fluorescent recovery after photobleaching and multiple image photography. Two capsid virus-like particles, human papilloma virus (55 nm, approximately 20,000 kDa) and Norwalk virus (38 nm, approximately 10,000 kDa), as well as most of the globular proteins tested (15-650 kDa) diffused as rapidly in mucus as in saline. Electron microscopy of cervical mucus confirmed that the mesh spacing between mucin fibers is large enough (20-200 nm) for small viruses to diffuse essentially unhindered through mucus. In contrast, herpes simplex virus (180 nm) colocalized with strands of thick mucus, suggesting that herpes simplex virus, unlike the capsid virus particles, makes low-affinity bonds with mucins. Polystyrene microspheres (59-1000 nm) bound more tightly to mucins, bundling them into thick cables. Although immunoglobulins are too small to be slowed by the mesh spacing between mucins, diffusion by IgM was slowed by mucus. Diffusion by IgM-Fc(5 mu), the Fc pentamer core of an IgM with all 10 Fab moieties removed, was comparably slowed by mucus. This suggests that the Fc moieties of antibodies make low-affinity bonds with mucins.

Mucosal immune network in the gut for the control of infectious diseases

The common mucosal immune system (CMIS) consists of an integrated cross-communication pathway of lymphoid tissues made up of inductive and effector sites for host protection against pathogenic microorganisms. Major effector molecules of the CMIS include IgA antibodies and cytokines, chemokines and their corresponding receptors. Secretory IgA (S-IgA), the major immunoglobulin, is induced by gut-associated lymphoreticular tissue (GALT)-derived B cells with the help of Th1- and Th2-type CD4(+) T lymphocytes. Cytotoxic T lymphocytes (CTLs) in the mucosal epithelium, a subpopulation of intraepithelial lymphocytes (IELs), also help maintain the mucosal barrier. The CMIS is unique in that it can provide both positive and negative signals for the induction and regulation of immune responses in both the mucosal and systemic compartments after oral or nasal antigen exposure. Prevention of infection through mucosal surfaces can be achieved by the CMIS through connections between inductive (e.g. GALT) and effector tissues. When vaccine antigens are enterically administered together with mucosal adjuvants [e.g. cholera toxin (CT), heat-labile toxin produced by Escherichia coli (LT) and IL-12], antigen-specific Th1/Th2 and IgA B cell responses are induced simultaneously in the mucosal effector compartment. Since these antigen-specific immune responses are not generated by oral vaccine without mucosal adjuvant, safe and effective adjuvants for the induction of antigen-specific S-IgA and CTL responses are essential for the development of mucosal vaccines for protection against infectious diseases. Finally, recent findings suggest the presence of a CMIS-independent IgA induction pathway, which also must be considered in the development of mucosal vaccines.