Role of the putative "link" glycopeptide of intestinal mucin in binding of piliated Escherichia coli serotype O157:H7 strain CL-49

Role of the Intestinal Epithelium and Its Interaction With the Microbiota in Food Allergy

The intestinal epithelial tract forms a dynamic lining of the digestive system consisting of a range of epithelial cell sub-types with diverse functions fulfilling specific niches. The intestinal epithelium is more than just a physical barrier regulating nutrient uptake, rather it plays a critical role in homeostasis through its intrinsic innate immune function, pivotal regulation of antigen sensitization, and a bi-directional interplay with the microbiota that evolves with age. In this review we will discuss these functions of the epithelium in the context of food allergy.

The effects of mucosal media on some pathogenic traits of Crohn's disease-associated Escherichia coli LF82

Aim: Adherent-invasive Escherichia coli (AIEC) pathovar has been identified in intestinal mucosa of patients with Crohn's disease. Our aim was to compare the impact of sterile mucosal media (Muc-M) originated from different parts of the intestine on some pathogenic traits of AIEC LF82 strain. Materials & methods: Muc-M composed of certain rates of cell culture medium or M63 minimal medium and mucosal contents obtained from different part of intestine were designed for cell-infection experiments and biofilm-formation assays. Results: The results showed that Muc-M reduced usually pathogenic properties of AIEC LF82. However, LF82 adhesion, invasion and specific biofilm formations were markedly higher in Muc-MCR than those in Muc-MIR . Conclusion: In this context, the findings of present study could help the endeavors related to determining molecular targets for AIEC bacteria.

Colonic MUC2 mucin regulates the expression and antimicrobial activity of β-defensin 2

In this study we identified mechanisms at the colonic mucosa by which MUC2 mucin regulated the production of β-defensin in a proinflammatory milieu but functionally protected susceptible bacteria from its antimicrobial effects. The regulator role of MUC2 on production of β-defensin 2 in combination with the proinflammatory cytokine interleukin-1β (IL-1β) was confirmed using purified human colonic MUC2 mucin and colonic goblet cells short hairpin RNA (shRNA) silenced for MUC2. In vivo, Muc2(-/-) mice showed impaired β-defensin mRNA expression and peptide localization in the colon as compared with Muc2(+/-) and Muc2(+/+) littermates. Importantly, purified MUC2 mucin abrogated the antimicrobial activity of β-defensin 2 against nonpathogenic and enteropathogenic Escherichia coli. Sodium metaperiodate oxidation of MUC2 removed the capacity of MUC2 to stimulate β-defensin production and MUC2's inhibition of defensin antimicrobial activity. This study highlights that a defective MUC2 mucin barrier, typical in inflammatory bowel diseases, may lead to deficient stimulation of β-defensin 2 and an unbalanced microbiota that favor the growth of β-defensin-resistant microbes such as Clostridium difficile.

Comparison of performance and intestinal morphology of broilers using step-down supplementation with a mannan-rich fraction versus bacitracin methylene disalicylate

Two experiments were conducted to compare effects of utilising step-down dosing of a mannan-rich fraction (MRF) of yeast cell wall or the antimicrobial growth promoter (AGP) bacitracin methylene disalicylate (BMD) when chicks were raised on built-up litter. Chicks were randomly assigned to one of three treatment groups (12 pen replicates; 50 birds per pen): basal diet (control) or basal diet plus MRF (Actigen™; Alltech Inc., Nicholasville, KY) or BMD (Alpharma Inc., Fort Lee, NJ). In experiment two, intestinal morphology and litter scores were determined on d 42. In experiment one, MRF and BMD increased BW gain at d 21 and d 42 compared with control (P ≤ 0.05) and d 42 BW was greater in BMD birds than controls (P ≤ 0.05). Adjusted FCRs were lower in MRF and BMD birds from d 0 to d 42 (P = 0.06). In experiment two, there was no effect of treatment on d 21 BW, but MRF and BMD improved adjusted FCR (P = 0.02) compared with control. By d 35, both MRF and BMD birds had greater BWs than controls (P = 0.04). At d 42, MRF-supplemented birds had greater BW than controls (P ≤ 0.05). D 35 and d 42 FCR improved with MRF or BMD compared with control (P ≤ 0.01). Litter conditions improved (P ≤ 0.05) when birds were fed diets with BMD and MRF compared with control-fed birds. Jejunal morphology, including villi height (P ≤ 0.05), villi height: crypt depth ratio (P ≤ 0.05), and goblet cell numbers (P ≤ 0.05) improved with MRF and BMD compared with control. Both MRF and BMD improved broiler performance, potentially related to the improvements observed in intestinal morphology. In conclusion, step-down supplementation with MRF may offer a potential alternative to AGP to improve performance in broilers raised in commercial settings.

Association of Lactobacillus acidophilus with mice Peyer's patches

OBJECTIVE

To clarify the adhesion mechanism of Lactobacillus acidophilus to Peyer's patches.

METHODS

Adhesion of L. acidophilus FN001 to mice Peyer's patches was studied in vitro using a fluorescent quantization method. The nature of adhesion mediator was studied by the differing effects of physical, chemical, and enzymatic pre-treatments of the bacteria and the inhibitory effects of sugars on the adhesion. The presence of lectin-like proteins on the cell surface was determined by hemagglutination assay. The effect of L. acidophilus FN001 on the inhibition of adhesion of pathogens to Peyer's patches was also studied.

RESULTS

The adhesion of L. acidophilus FN001 was strongly inhibited in the presence of D-mannose and methyl-α-D-mannoside. Pretreatment of L. acidophilus FN001 with pepsin and trypsin decreased the adhesive capacity indicating that some cell surface proteins might be involved in the adhesion. L. acidophilus FN001 showed agglutinating activity toward the rabbit red cells in a mannose specific manner, which was decreased after protease pretreatment, suggesting possible occurrence of mannose specific lectin(s) on the L. acidophilus FN001 surface. In adhesion inhibition assay, L. acidophilus NF001, when applied to Peyer's patches first or at the same time with pathogen, significantly inhibited adhesion of Escherichia coli ATCC25922 to Peyer's patches.

CONCLUSION

L. acidophilus FN001 contains some mannose-specific protein(s) on its surface that mediates its adhesion to the Peyer's patches. FN001 inhibits the adhesion of E. coli, which also contains mannose specific lectin.

Oligosaccharide-mediated inhibition of the adhesion of pathogenic Escherichia coli strains to human gut epithelial cells in vitro

The aim of the study was to investigate the ability of pectic oligosaccharides (POS) to inhibit adhesion of three strains of verotoxigenic Escherichia coli, three strains of enteropathogenic E. coli, and one nonclinical strain of Desulfovibrio desulfuricans to human intestinal epithelial cell cultures. Lactobacillus acidophilus and Lactobacillus gasseri were included for comparison. Attachment was determined in the human HT29 cell line by viable count of adherent bacteria. POS in buffer at pH 7.2 were antiadhesive at a dose of 2.5 mg ml(-1), reducing adhesion of enteropathogenic E. coil and verotoxigenic E. coli strains to less than 30% of control values. Concentrations resulting in 50% inhibition ranged from 0.15 to 0.46 mg ml(-1). L. acidophilus was not significantly affected, but adhesion of L. gasseri was reduced to 29% of the control value. POS reduced the adhesion of D. desulfuricans to 0.33% of the control value. POS also had a protective effect against E. coli verocytotoxins VT1 and VT2 at concentrations of 0.01 and 1 microg ml(-1), respectively.

Factors involved in binding of Lactobacillus plantarum Lp6 to rat small intestinal mucus

AIM

To investigate the adhesion determinants of Lactobacillus plantarum Lp6, a dairy isolate.

METHODS AND RESULTS

Small intestinal mucus extracted from rats was used as a substrate for adhesion. Adhesion determinants were studied by physical, chemical and enzymatic pretreatments of the bacteria, and adhesion inhibition assay. The mannose-specific adhesins were explored by studying the effect of d-mannose on adhesion and the yeast-agglutinating ability of the bacteria. It was found that adhesion decreased after bacteria were treated with sodium metaperiodate, protease K, trypsin, lithium chloride and trichloroacetic acid. However, adhesion did not decrease after trypsin-treated bacteria were incubated with cell surface protein extract. Cell surface bound exopolysaccharides were found to inhibit the adhesion. D-mannose inhibited the adhesion in a dose-dependent manner. The bacteria could significantly agglutinate yeast and lost this ability after protease K treatment.

CONCLUSIONS

Adhesion was mainly mediated by the mannose specific adhesins, which might be proteins that reversibly bind to the cell surface components. Cell surface-bound exopolysaccharides were also involved in adhesion.

SIGNIFICANCE AND IMPACT OF THE STUDY

The mannose-specific adhesion of Lact. plantarum Lp6 to rat mucus might be important for competing with pathogens-binding sites in gut, which may be used to resist the colonization of the pathogens.

Development of a sensitive and reliable ELISA for quantification of wheat germ agglutinin

Among others, lectin-mediated drug delivery is currently discussed as a promising strategy towards improved bioavailability of biotech drugs. For quantitative determination of the lectin from wheat germ (WGA), a sandwich ELISA relying on capture of the lectin by pig gastric mucin coated wells and detection of bound WGA by a lectin specific first antibody followed by peroxidase-labelled second antibody was elaborated. The stepwise optimised protocol allows quantification over the range from 10 to 1000 ng/ml WGA with a coefficient of determination of 0.9991. The day to day variation was +/-0.09 OD at 500 ng/ml WGA. Additionally, the presented ELISA-protocol allows determination of WGA in serum with the same sensitivity and reliability as in buffer. Lectins with different carbohydrate specificity such as those from jack beans and peanuts exhibited no cross-reactivity. Among the lectins with the same carbohydrate specificity that from potatoes interfered with the assay, whereas that from tomatoes was not recognised by the first antibody. Since the potato lectin is fully degraded in the intestine, no cross-reactivity with WGA is expected in serum samples. Following on from these results, the absorption rate of WGA in biologically active form might be determined as a basis for further steps towards improved drug delivery systems.

Mucin and Toll-like receptors in host defense against intestinal parasites

Gastrointestinal mucin is a constituent of luminal barrier function and is the first line of host defense against invading pathogens. Mucin carbohydrates and amino acids, as well as trapped soluble host defense molecules, serve as substrates for colonization and control or deter pathogen invasion to the underlying mucosal epithelial cells. Toll-like receptors on the surface of epithelial cells act as sensors for invading pathogens, and the ensuing host response limits parasite invasion and leads to adaptive immunity. The latest work in the field and the use of parasite model systems to illustrate the delicate host-parasite interaction at the mucosal surface of the gut are discussed here.

The effect of tissue molecules on bacterial invasion of dentine

Bacterial invasion of dentinal tubules is a critical step in the pathogenesis of dental caries and pulp and periapical disease. The purpose of this study was to determine the effect some molecules commonly found in saliva and dentinal tubule fluid may have on the bacterial invasion of dentine. The results showed that invasion of Streptococcus gordonii or Enterococcus faecalis cells was inhibited when the bacterial cells were in solution with mucin, immunoglobulin G (IgG) and serum, and this was related to bacterial cell aggregation, as a result of interaction with agglutinins, and/or inhibition of collagen binding. When dentine was soaked in growth media containing fibrinogen, IgG, albumin or serum prior to inoculation, bacterial invasion was inhibited. It is suggested that this may be due to reduced dentine permeability as a consequence of the deposition of the compounds within dentinal tubules.

Understanding mucosal responsiveness: lessons from enteric bacterial pathogens

Mucosal immune responses must discriminate between commensal flora within the lumen and potential pathogens. These responses are highly adapted to induce protection without excessive inflammation. The balances that regulate mucosal immune and inflammatory responses have to be understood if effective mucosal immunity is to be induced through local immunization. This review will summarize some of the lessons learnt from studies of antigens derived from enteric bacterial pathogens and discuss how the gastrointestinal epithelia can 'fight back' when it encounters pathogens.

Interaction of bladder glycoprotein GP51 with uropathogenic bacteria

PURPOSE

A major component of bladder surface mucin is a glycoprotein GP51 (molecular weight 51 kD.). GP51, which has previously been isolated from rabbit mucosa, appears to function as part of the defense mechanism in an in vivo infection model. GP51 coats the epithelium and is secreted into the urine, as detected by immunohistochemical testing and enzyme-linked immunosorbent assay (ELISA). Increased urinary GP51 occurs during urinary tract infection. To elucidate the role of GP51 as a component of the primary defense mechanism we studied interactions with uropathogenic bacterial isolates and urine from symptomatic patients with urinary tract infection.

MATERIALS AND METHODS

ELISA was performed to demonstrate the binding of GP51 and various uropathogens. Immunochemical studies were done using monoclonal antibodies to GP51 to determine the interaction of GP51 with certain uropathogenic isolates, including Escherichia coli, Enterobacter cloacae, Klebsiella pneumoniae, Proteus vulgaris, Pseudomonas aeruginosa, Serratia marcescens, Staphylococcus aureus, S. epidermidis and Streptococcus faecalis. Infected urinary sediments and uropathogenic bacterial cultures were examined by immunocytochemical testing to localize GP51. Antigen inhibition ELISA was done to quantitate urinary GP51 in the urine of 17 normal controls and 19 patients with urinary tract infection.

RESULTS

ELISA revealed that GP51 binds to a wide spectrum of gram-positive and gram-negative uropathogens in semiquantitative fashion. Immunochemical methods confirmed that purified GP51 binds to bacteria, encapsulating and aggregating the bacteria. Clinical specimens showed GP51 localized to bacteria and uroepithelial cells. We observed a significant increase in urinary GP51 in urinary tract infection compared to uninfected urine (p = 0.0003).

CONCLUSIONS

These studies suggest that GP51, a component of bladder mucin, may be a strategic factor in the primary defense mechanism of the bladder.

Glycocalyx on rabbit intestinal M cells displays carbohydrate epitopes from Muc2

It is essential to investigate the apical surface properties of both M cells and dome enterocytes to understand the mechanisms involved in the binding of pathogens to M cells. In rabbit appendix tissue, monoclonal antibodies (MAbs) highlight differences between M cells (MAb 58) and dome enterocytes (MAb 214). Such antibodies ultimately recognized intestinal mucin-related epitopes. To further characterize these differences, the labeling patterns obtained with these MAbs were compared to those obtained with other antibodies to intestinal mucins on dissected domes from all gut-associated lymphoid tissues. A glycoprotein recognized by MAb 58 was purified on a CsCl isopycnic density gradient and microsequenced, and its mRNA expression was localized by in situ hybridization. It was identified as the rabbit homologue of human Muc2, i.e., the major mucin secreted in intestine tissue. Two other Muc2 carbohydrate epitopes were also expressed on M cells, although Muc2 mRNA was not detected. All results indicated that M cells express, on their apical membrane, glycoconjugates bearing at least three glycosidic epitopes from Muc2. MAb 214 and MAb 6G2, which recognized a partially characterized mucin expressed on dome enterocytes, were negative markers for M cells in rabbit gut-associated lymphoid tissues. We propose that the presence, on the surface of M cells, of carbohydrates also expressed on Muc2, together with the absence of an enterocyte-associated mucin, could favor pathogen attachment and accessibility to the M-cell luminal membrane.

Characterization of binding of Candida albicans to small intestinal mucin and its role in adherence to mucosal epithelial cells

In order to approximate and adhere to mucosal epithelial cells, Candida must traverse the overlying mucus layer. Interactions of Candida species with mucin and human buccal epithelial cells (BECs) were thus investigated in vitro. Binding of the Candida species to purified small intestinal mucin showed a close correlation with their hierarchy of virulence. Significant differences (P < 0.05) were found among three categories of Candida species adhering highly (C. dubliniensis, C. tropicalis, and C. albicans), moderately (C. parapsilosis and C. lusitaniae) or weakly (C. krusei and C. glabrata) to mucin. Adherence of C. albicans to BECs was quantitatively inhibited by graded concentrations of mucin. However, inhibition of adherence was reversed by pretreatment of mucin with pronase or C. albicans secretory aspartyl proteinase Sap2p but not with sodium periodate. Saturable concentration- and time-dependent binding of mucin to C. albicans was abrogated by pronase or Sap2p treatment of mucin but was unaffected by beta-mercaptoethanol, sodium periodate, neuraminidase, lectins, or potentially inhibitory sugars. Probing of membrane blots of the mucin with C. albicans revealed binding of the yeast to the 66-kDa cleavage product of the 118-kDa C-terminal glycopeptide of mucin. Although no evidence was found for the participation of C. albicans cell surface mannoproteins in specific receptor-ligand binding to mucin, inhibition of binding by p-nitrophenol (1 mM) and tetramethylurea (0.36 M) revealed that hydrophobic interactions are involved in adherence of C. albicans to mucin. These results suggest that C. albicans may both adhere to and enzymatically degrade mucins by the action of Saps, and that both properties may act to modulate Candida populations in the oral cavity and gastrointestinal tract.

Intestinal mucins: the binding sites for Salmonella typhimurium

Mucus-bacterial interactions in the gastrointestinal tract and their impact on subsequent enteric infections are poorly delineated. In the present study, we have examined the binding of Salmonella typhimurium to rat intestinal mucus and characterized a mucus protein (Mucus-Rs) which specifically binds to S. typhimurium. Both virulent (1402/84), and avirulent (SF 1835) S. typhimurium were observed to bind to crude mucus, however, the virulent strain showed 6 fold more binding as compared to avirulent strain. Fractionation of crude mucus on sepharose CL-6B resolved it into three major peaks. Maximal bacterial binding was observed with a high mol. wt. glycoprotein corresponding to neutral mucin. SDS-PAGE of purified protein (termed Mucus-Rs) under non reducing conditions showed it to be a homogenous glycoprotein (mol. wt. 250 kDa), while under reducing conditions, three bands corresponding to mol. wt. of 118,75 and 60 kDa were observed. Pretreatment of Mucus-Rs with pronase, trypsin and sodium metaperiodate markedly inhibited bacterial binding. GLC analysis of Mucus-Rs showed it to contain Mannose, Glucose, Galactose, Glucosamine, Galactosamine and Sialic acid as main sugars. Competitive binding in the presence of various sugars and lectins indicated the involvement of mannose in the mucus-bacterial interactions. The Mucus-Rs binding was highly specific for S. typhimurium; no significant binding was seen with E. coli and V. cholerae. Thus, we conclude that S. typhimurium specifically binds to a 250 kDa neutral mucin of intestinal tract. This binding appears to occur via specific adhesin-receptor interactions involving bacterial pili and mannose of neutral mucin.

Innate mechanisms of epithelial host defense: spotlight on intestine

The single layer of epithelial cells lining the intestinal tract is charged with a most difficult task: protecting the underlying biological compartments from both the normal commensal flora that reside within the intestinal lumen as well as the uninvited pathogens. To such an end, the intestinal epithelial cells are equipped with a panoply of defense mechanisms, both constitutive and inducible. This review focuses only on those defense mechanisms that are initiated and executed by the intestinal epithelial cell. Fitting these strict criteria are three major categories of epithelial host defense: enhanced salt and water secretion, expression of antimicrobial proteins and peptides, and production of intestinal mucins. Each of these areas is discussed in this review.

Probiotics inhibit enteropathogenic E. coli adherence in vitro by inducing intestinal mucin gene expression

Probiotic agents, live microorganisms with beneficial effects for the host, may offer an alternative to conventional antimicrobials in the treatment and prevention of enteric infections. The probiotic agents Lactobacillus plantarum 299v and Lactobacillus rhamnosus GG quantitatively inhibited the adherence of an attaching and effacing pathogenic Escherichia coli to HT-29 intestinal epithelial cells but did not inhibit adherence to nonintestinal HEp-2 cells. HT-29 cells were grown under conditions that induced high levels of either MUC2 or MUC3 mRNA, but HEp-2 cells expressed only minimal levels of MUC2 and no MUC3 mRNA. Media enriched for MUC2 and MUC3 mucin were added exogenously to binding assays and were shown to be capable of inhibiting enteropathogen adherence to HEp-2 cells. Incubation of L. plantarum 299v with HT-29 cells increased MUC2 and MUC3 mRNA expression levels. From these in vitro studies, we propose the hypothesis that the ability of probiotic agents to inhibit adherence of attaching and effacing organisms to intestinal epithelial cells is mediated through their ability to increase expression of MUC2 and MUC3 intestinal mucins.

Binding of Shigella to rat and human intestinal mucin

Invasion of epithelial cells by Shigella is an early step in their pathogenesis. Adherence is generally presumed to be a prerequisite for invasion. This study examined the possibility of intestinal mucins serving as initial binding sites for clinical isolates of S. boydii and S. sonnei. The interactions of Shigella with rat and human small intestinal and colonic mucin were investigated. In solid phase binding assays, [35S] labelled Shigella did not show any preferential binding to rat/human small intestinal mucin or to rat colonic mucin. On the other hand, Shigella bound specifically to human colonic mucin in a concentration-dependent manner. This specific binding to human colonic mucin was not by weak hydrophobic interactions and could not be attributed to the presence of contaminating glycolipids in the mucin preparation. The human colonic mucin receptor was sensitive to periodate treatment suggesting the involvement of the carbohydrate portion of the mucin. Reduction and alkylation of mucin enhanced adherence probably by exposing buried binding sites. The monosaccharides present in mucins were ineffective as hapten inhibitors as was the lectin wheat germ agglutinin suggesting that the mucin receptor is a more complex one. This study identifies, for the first time, the presence of a specific Shigella-binding site on the carbohydrate portion of human colonic mucin, which is not present in rat colonic mucin or in rat/human small intestinal mucin.

Adhesion of human enterotoxigenic Escherichia coli to human mucus secreting HT-29 cell subpopulations in culture

Enterotoxigenic Escherichia coli (ETEC) bearing the fimbrial colonisation factor antigens CFA/I, CFA/II, CFA/III, and the non-fimbrial antigen 2230 were tested for their ability to adhere to two cultured human intestinal HT-29 mucus secreting cell subpopulations. These populations are referred to as HT29-MTX and HT29-FU, which differ in the amount of secreted mucins and in their gastric or colonic mucin immunoreactivity respectively. Adherence of radiolabelled bacteria to cell monolayers infected apically was assessed. All ETEC strains adhered to the mucus secreting HT29-FU subpopulation, which secretes mucins of colonic immunoreactivity. Visualisation of bacteria by scanning electron microscopy showed that ETEC bound to the HT29-FU cells possessing a brush border, but not to the mucus and that ETEC binding developed as a function of cell differentiation. The adhesion of ETEC to cells possessing a brush border and to mucus secreting cells was also analysed by indirect immunofluorescence in HT29-MTX cells, which secrete mucins of gastric immunoreactivity. Fluorescein isothiocyanate labelling using specific anti-CFA/I antibody was used to show ETEC; rhodamine isothiocyanate labelling using a monoclonal antibody (designated M1) against purified human gastric mucus was used to detect secreted mucins, and rhodamine isothiocyanate labelling using a monoclonal antibody (designated 4H3) against human dipeptidylpeptidase IV was used to show cells possessing a brush border. Binding of bacteria colocalised with dipeptidylpeptidase IV of enterocytes and not with mucins.

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.

Binding of Yersinia enterocolitica to purified, native small intestinal mucins from rabbits and humans involves interactions with the mucin carbohydrate moiety

Plasmid-bearing (but not plasmid-cured) Yersinia enterocolitica is known to bind to purified small intestinal mucins from rabbits and humans. This study examined which region(s) of the mucin molecule is important for bacterial adherence. Pronase digestion of mucin and removal of nonglycosylated or poorly glycosylated peptide regions had no effect on bacterial binding, suggesting that plasmid-bearing Y. enterocolitica interacts with mucin carbohydrate. Periodate oxidation also did not alter bacterial adherence, indicating that vicinal hydroxyl groups in the mucin sugars are not important for binding. Boiling of mucin, depolymerization by reduction of disulfide bonds, or removal of noncovalently associated lipid actually enhanced bacterial adherence, suggesting that plasmid-bearing Y. enterocolitica can interact with additional domains in the mucin molecule revealed by these treatments. These domains were destroyed by pronase digestion. In delipidated mucin (but not in reduced or boiled mucin), binding to these domains appeared to be hydrophobic since it could be prevented by treatment of bacteria with tetramethyl urea. Oligosaccharides obtained from both human and rabbit small intestinal mucins were capable of inhibiting attachment of plasmid-bearing (but not plasmid-cured) Y. enterocolitica to mucin. After removal of terminal and backbone sugar residues by treatment of mucin with trifluoromethanesulfonic acid, binding of plasmid-bearing bacteria increased significantly when N-acetylgalactosamine, either alone or with galactose attached, was revealed, indicating that core regions of the sugar side chains are involved in bacterial binding. Adherence of plasmid-cured organisms was unaffected by trifluoromethanesulfonic acid treatment of mucin. We concluded that virulent Y. enterocolitica interacts with the carbohydrate moiety of native small intestinal mucin through a plasmid-mediated process. When mucin becomes denatured, binding of the organism can increase through hydrophobic and nonhydrophobic interactions with (most likely) the mucin protein.

Characterization of quail intestinal mucin as a ligand for endogenous quail lectin

The S-type lectins have been shown to be components of mucosal scrapings, and in avian systems these lectins have been localized immunohistochemically to the mucosal surface and goblet cells of the intestine. The interaction of lectin specifically with purified mucin has not, however, been established. Quail intestinal mucin was purified by two subsequent isopycnic density-gradient centrifugations in CsCl and chromatography on Sepharose Cl-2B. Purified mucin, obtained from the void volume of the Sepharose column, was characterized by SDS/PAGE, amino acid and carbohydrate analyses, sensitivity to thiol reduction, and cross-reactivity with antibody preparations to rat and human intestinal mucins on Western blots. Antibody raised against purified quail mucin partially cross-reacts with purified rat, rabbit and human intestinal mucins, and specifically labels the mucosal surface and goblet cells of quail intestine by the immunoperoxidase technique. Protein eluted by lactose from an affinity matrix composed of quail intestinal mucin possessed the same molecular mass on SDS/PAGE as intestinal lectin and reacted on Western blots with a lectin-specific antibody. The data clearly demonstrate the co-localization of lectin and mucin in the quail intestine and also the ability of the lectin to specifically interact with the purified mucin, raising the question of the role of endogenous lectins in secretions.

Human tracheobronchial mucin: purification and binding to Pseudomonas aeruginosa

Colonization of the respiratory tract with Pseudomonas aeruginosa is a serious problem in cystic fibrosis and seriously ill hospitalized patients. Human tracheobronchial mucin (HTBM), the major glycoprotein of human tracheobronchial secretions, is known to interact with this pathogen, which may then be cleared by mucociliary action. However, the mechanism of interaction is not known. To understand this process, pure HTBM was isolated from tracheobronchial secretions of a laryngectomee. Following initial fractionation on Sepharose CL-2B, the HTBM-containing fraction was subjected to reductive methylation and then gel filtration. Pure HTBM was employed in an overlay binding assay to identify the bacterial adhesin(s) and mucin receptors that participate in mucin-P. aeruginosa interactions. An approximately 16-kDa nonpilus protein component(s) of P. aeruginosa was found to be the adhesin(s) for HTBM. The mucin receptor for the 16-kDa component(s) was found in the peptide moiety. This study confirms that P. aeruginosa utilizes the nonpilus adhesin(s) to bind to HTBM. Identification of the specificity of the HTBM-P. aeruginosa interactions can lead to a better understanding of the predominance of P. aeruginosa colonization in individuals with cystic fibrosis.

Identity of mucin's "118-kDa link protein" with fibronectin fragment

Human and rat intestinal mucin was purified by equilibrium density gradient centrifugation and Sepharose 2B chromatography according to M. Mantle, D. Mantle, and A. Allen (1981, Biochem. J. 195, 277-285) and analyzed using mucin, DNA, and fibronectin-specific antibodies in dot-blot, ELISA, and Western blotting. The 118-kDa component of the mucins and the 118-kDa fragment of fibronectin from the same source displayed affinity for concanavalin A and immunoreacted with fibronectin antibodies. The amino acid and carbohydrate compositions of the 118-kDa peptide electroeluted by gel electrophoresis of mucin and fibronectin preparations were identical within each pair of glycopeptides and closely resembled the "link protein component" of human and rat intestinal mucin preparations of R. E. F. Fahim, R. D. Specian, G. G. Forstner, and J. F. Forstner (1987, Biochem. J. 243, 631-640) and M. Mantle and G. Stewart (1989, Biochem. J. 259, 631-640). We therefore conclude that the "link protein" claimed to be an integral part of mucus glycoproteins in actuality is the 118-kDa fragment of fibronectin.

Mucin isolated from rabbit colon inhibits in vitro binding of Escherichia coli RDEC-1

The rabbit enteric pathogen Escherichia coli RDEC-1 (serotype O15:H-) mediates attaching and effacing binding to colonic epithelium in a manner morphologically identical to that observed in both human enteropathogenic E. coli and enterohemorrhagic E. coli infections. The aim of this study was to determine if colonic mucus and its constituents, including mucin derived from goblet cells, inhibited RDEC-1 adherence in vitro. Crude mucus was prepared from mucosal scrapings of rabbit colon and separated by buoyant density into eight fractions. Purified mucin was characterized by gel electrophoresis, dot immunoblotting, indirect immunofluorescence, and amino acid composition. RDEC-1 bacteria were grown to promote and suppress the expression of mannose-resistant, hydrophobic pili. A nonpiliated mutant, strain M34, was also used as a negative control. Binding of radiolabeled RDEC-1 expressing pili was quantitated in the presence of crude mucus, purified mucin, and nonmucin fractions. Binding of piliated RDEC-1 to hydrophobic polystyrene wells was greater than for both nonpiliated RDEC-1 and strain M34 (P less than 0.05). Both crude mucus and purified mucin mediated a concentration-dependent inhibition of piliated-RDEC-1 binding. Fractions of mucus without immunoreactive mucin did not inhibit the binding of RDEC-1 expressing hydrophobic pili. We conclude that colonic goblet cell-derived mucin mediates inhibition of piliated RDEC-1 attachment in vitro. Inhibition of bacterial adherence could prevent access of attaching and effacing E. coli enteric pathogens to the colonic mucosa in vivo.

The interaction between intestinal mucus glycoproteins and enteric infections

Adherence of pathogenic enteric organisms to specific receptors on mucosal surfaces is widely recognized as an important first step in the initiation of infectious diseases. The specific interactions whereby parasites and bacteria exploit mucus substrates for colonization, and the host uses them as a nonimmunological defense mechanism, is only now being unravelled. In this review, Sil-King Tse and Kris Chadee discuss various hypothetical models for interaction, including the role of the immune system in the regulation of mucus secretion.

Characteristics of binding of Escherichia coli serotype O157:H7 strain CL-49 to purified intestinal mucin

Purified rat intestinal mucin was used as a model mucin to study the binding of Escherichia coli serotype O157:H7, a human pathogen associated with outbreaks of hemorrhagic colitis and hemolytic uremic syndrome. Of six O157:H7 strains, only one strain (designated CL-49) bound to rat (and other) intestinal mucins by a specific and saturable process. Binding was observed only after the bacteria were serially passaged to promote the expression of type 1 pili (fimbriae). Several other type 1-piliated E. coli strains, however, did not bind to mucin. Binding of E. coli CL-49 was inhibited by D-mannose and short oligomannosyl derivatives, particularly Man-alpha-1,3-Man, Man-alpha-1,2-Man, and Man-alpha-1,3-Man-beta-1,4-N-acetylglucosamine. Other inhibitors of binding included p-nitrophenol (10(-4) M), heating at 60 degrees C (to remove pili), an antibody to type 1 pili, and purified type 1 pili of E. coli CL-49 used as hapten inhibitors. A comparison of the hydrophobicity of piliated E. coli CL-49 with other type 1-piliated E. coli strains indicated that the former strain was much more hydrophobic than the others. These findings indicate that highly purified intestinal mucins possess specific mannosyl receptor sites for bacterial type 1 pili on E. coli CL-49, but that strong hydrophobic interactions between the mucin and the pili stabilize the mannose-dependent binding process. We speculate that the mucin receptors for type 1 pili reside in oligosaccharides of the 118-kilodalton "link" glycopeptide, since this is the only mucin component known to contain mannose.