MUC13 Cell Surface Mucin Limits Salmonella Typhimurium Infection by Protecting the Mucosal Epithelial Barrier

BACKGROUND & AIMS

MUC13 cell surface mucin is highly expressed on the mucosal surface throughout the intestine, yet its role against bacterial infection is unknown. We investigated how MUC13 impacts Salmonella typhimurium (S Tm) infection and elucidated its mechanisms of action.

METHODS

Muc13-/- and wild-type littermate mice were gavaged with 2 isogenic strains of S Tm after pre-conditioning with streptomycin. We assessed clinical parameters, cecal histology, local and systemic bacterial load, and proinflammatory cytokines after infection. Cecal enteroids and epithelial cell lines were used to evaluate the mechanism of MUC13 activity after infection. The interaction between bacterial SiiE and MUC13 was assessed by using siiE-deficient Salmonella.

RESULTS

S Tm-infected Muc13-/- mice had increased disease activity, histologic damage, and higher local and systemic bacterial loads. Mechanistically, we found that S Tm binds to MUC13 through its giant SiiE adhesin and that MUC13 acts as a pathogen-binding decoy shed from the epithelial cell surface after pathogen engagement, limiting bacterial invasion. In addition, MUC13 reduces epithelial cell death and intestinal barrier breakdown by enhancing nuclear factor kappa B signaling during infection, independent of its decoy function.

CONCLUSIONS

We show for the first time that MUC13 plays a critical role in antimicrobial defense against pathogenic S Tm at the intestinal mucosal surface by both acting as a releasable decoy limiting bacterial invasion and reducing pathogen-induced cell death. This further implicates the cell surface mucin family in mucosal defense from bacterial infection.

Single-cell analyses reveal phosphate availability as critical factor for nutrition of Salmonella enterica within mammalian host cells

Salmonella enterica serovar Typhimurium (STM) is an invasive, facultative intracellular pathogen and acquisition of nutrients from host cells is essential for survival and proliferation of intracellular STM. The nutritional environment of intracellular STM is only partially understood. We deploy bacteria harbouring reporter plasmids to interrogate the environmental cues acting on intracellular STM, and flow cytometry allows analyses on level of single STM. Phosphorus is a macro-element for cellular life, and in STM inorganic phosphate (P_i ), homeostasis is mediated by the two-component regulatory system PhoBR, resulting in expression of the high affinity phosphate transporter pstSCAB-phoU. Using fluorescent protein reporters, we investigated P_i availability for intracellular STM at single-cell level over time. We observed that P_i concentration in the Salmonella-containing vacuole (SCV) is limiting and activates the promoter of pstSCAB-phoU encoding a high affinity phosphate uptake system. Correlation between reporter activation by STM in defined media and in host cells indicates P_i concentration less 10 μM within the SCV. STM proliferating within the SCV experience increasing P_i limitations. Activity of the Salmonella pathogenicity island 2 (SPI2)-encoded type III secretion system (T3SS) is crucial for efficient intracellular proliferation, and SPI2-T3SS-mediated endosomal remodelling also reliefs P_i limitation. STM that are released from SCV to enter the cytosol of epithelial cells did not indicate P_i limitations. Addition of P_i to culture media of infected cells partially relieved P_i limitations in the SCV, as did inhibition of intracellular proliferation. We conclude that availability of P_i is critical for intracellular lifestyle of STM, and P_i acquisition is maintained by multiple mechanisms. Our work demonstrates the use of bacterial pathogens as sensitive single-cell reporters for their environment in host cell or host organisms. TAKE AWAY: Salmonella strains were engineered to report their intracellular niche and the availability of inorganic phosphate (P_i ) on level of single intracellular bacteria Within the Salmonella-containing vacuole (SCV), P_i is limited and limitation increases with bacterial proliferation Salmonella located in host cell cytosol are not limited in P_i availability Remodelling of the host cell endosomal system mediated by T3SS-2 reliefs P_i limitation in the SCV.

Comprehensive Single Cell Analyses of the Nutritional Environment of Intracellular Salmonella enterica

The facultative intracellular pathogen Salmonella enterica Typhimurium (STM) resides in a specific membrane-bound compartment termed the Salmonella-containing vacuole (SCV). STM is able to obtain all nutrients required for rapid proliferation, although being separated from direct access to host cell metabolites. The formation of specific tubular membrane compartments, called Salmonella-induced filaments (SIFs) are known to provides bacterial nutrition by giving STM access to endocytosed material and enabling proliferation. Additionally, STM expresses a range of nutrient uptake system for growth in nutrient limited environments to overcome the nutrition depletion inside the host. By utilizing dual fluorescence reporters, we shed light on the nutritional environment of intracellular STM in various host cells and distinct intracellular niches. We showed that STM uses nutrients of the host cell and adapts uniquely to the different nutrient conditions. In addition, we provide further evidence for improved nutrient supply by SIF formation or presence in the cytosol of epithelial cells, and the correlation of nutrient supply to bacterial proliferation.

Humoral immunity to smallpox vaccines and monkeypox virus challenge: proteomic assessment and clinical correlations

Despite the eradication of smallpox, orthopoxviruses (OPV) remain public health concerns. Efforts to develop new therapeutics and vaccines for smallpox continue through their evaluation in animal models despite limited understanding of the specific correlates of protective immunity. Recent monkeypox virus challenge studies have established the black-tailed prairie dog (Cynomys ludovicianus) as a model of human systemic OPV infections. In this study, we assess the induction of humoral immunity in humans and prairie dogs receiving Dryvax, Acam2000, or Imvamune vaccine and characterize the proteomic profile of immune recognition using enzyme-linked immunosorbent assays (ELISA), neutralization assays, and protein microarrays. We confirm anticipated similarities of antigenic protein targets of smallpox vaccine-induced responses in humans and prairie dogs and identify several differences. Subsequent monkeypox virus intranasal infection of vaccinated prairie dogs resulted in a significant boost in humoral immunity characterized by a shift in reactivity of increased intensity to a broader range of OPV proteins. This work provides evidence of similarities between the vaccine responses in prairie dogs and humans that enhance the value of the prairie dog model system as an OPV vaccination model and offers novel findings that form a framework for examining the humoral immune response induced by systemic orthopoxvirus infection.

Development of improved vectors for DNA-based immunization and other gene therapy applications

Optimizing gene expression and delivery are necessary steps in the production of vectors for DNA-based immunization as well as for other gene therapy applications. A mouse muscle/reporter gene assay system was used to systematically improve a plasmid DNA vector. The optimized vector VR1255 contained: (1) CMV promoter and enhancer; (2) CMV IE Intron A; (3) kanamycin resistance gene; (4) deleted SV40 origin of replication; (5) optimized lux coding region; and (6) a minimal synthetic terminator from the rabbit beta globin gene, mRBG. The vector VR1255 expressed 137 times greater than an earlier prototype RSV-based vector. For plasmid vector delivery into nonmuscle tissues, a recently synthesized cationic lipid, GAP-DLRIE, was found to greatly enhance the uptake and expression of plasmid DNA by 100-fold when instilled into the mouse lung. The time-course of CAT expression with GAP-DLRIE indicated that peak expression occurs 2-5 days after intranasal administration and expression diminished to about one-third the peak value by day 21. This cationic lipid may be useful for immunization by pulmonary and perhaps other nonmuscle routes.

Converting an alcohol to an amine in a cationic lipid dramatically alters the co-lipid requirement, cellular transfection activity and the ultrastructure of DNA-cytofectin complexes

Cytofectins are positively charged lipophilic molecules that readily form complexes with DNA and other anionic polynucleotides. Normally, cytofectins are combined with an activity-augmenting phospholipid such as dioleoylphosphatidylethanolamine (DOPE), and a film of dried, mixed lipid is prepared and hydrated to form cationic liposomes. The liposome solution is then mixed with a plasmid DNA solution to afford cytofectin-DNA complexes which, when presented to living cells, are internalized and the transgene is expressed. One of the most potent cytofectins, dimyristoyl Rosenthal inhibitor ether (DMRIE), is presently being used to deliver transcriptionally active DNA into human tumor tissues. Here we report the remarkable consequences of replacing the alcohol moiety of DMRIE with a primary amine. The resulting cytofectin, called beta-aminoethyl-DMRIE (betaAE-DMRIE), promoted high level transfection over a broad range of DNA and cationic lipid concentrations. A comparison of in vitro transfection activity between DMRIE and betaAE-DMRIE in 10 cell types revealed that betaAE-DMRIE was more active than DMRIE, and that betaAE-DMRIE, unlike DMRIE, was maximally effective in the absence of colipid. The consequences of the alcohol-to-amine conversion on the structure of the cytofectin/DNA complex was also examined by Atomic Force Microscopy. Strikingly dissimilar images were found for plasmid DNA alone and for the plasmid complexes of betaAE-DMRIE and DMRIE/DOPE.

Use of liposome encapsulation in a combined single-liquid reagent for homogeneous enzyme immunoassay

A technique has been developed to permit mutually reactive macromolecular reagents used in immunoassays to be combined without premature reaction. A conjugate of glucose-6-phosphate dehydrogenase (EC 1.1.1.49) and theophylline has been encapsulated in 0.2-micron-diameter bi-lamellar liposomes. Suspensions of these liposomes had excellent stability. Whereas the enzyme activity of the free conjugate is rapidly inhibited by anti-theophylline antibody, a suspension of the encapsulated conjugate in a solution of the antibody and NAD+ (6.0 mmol/L) retained greater than 92% of the initial enzyme activity after standing for one year at 4 degrees C. At higher NAD+ concentrations the liposomes aggregated, and enzyme activity was inhibited by leakage of the NAD+ hydrolysis product, adenosine diphosphoryl 5-ribose (ADP-ribose), into the liposomes. Inhibition by ADP-ribose could be blocked and partly reversed by adding semicarbazide. The liposomes were efficiently lysed by Triton X-100, deoxycholate, or octyl glucoside, the kinetics and extent of lysis being affected by liposome size and correlating with the acid strength of various cholate derivatives. Addition of a serum sample and a solution of buffer, substrate, and detergent to a single reagent containing the liposomes and anti-theophylline antibody provided assay results equivalent to those obtained by conventional two-reagent EMIT homogeneous enzyme immunoassay for theophylline.

Use of liposome encapsulation in a combined single-liquid reagent for homogeneous enzyme immunoassay

A technique has been developed to permit mutually reactive macromolecular reagents used in immunoassays to be combined without premature reaction. A conjugate of glucose-6-phosphate dehydrogenase (EC 1.1.1.49) and theophylline has been encapsulated in 0.2-micron-diameter bi-lamellar liposomes. Suspensions of these liposomes had excellent stability. Whereas the enzyme activity of the free conjugate is rapidly inhibited by anti-theophylline antibody, a suspension of the encapsulated conjugate in a solution of the antibody and NAD+ (6.0 mmol/L) retained greater than 92% of the initial enzyme activity after standing for one year at 4 degrees C. At higher NAD+ concentrations the liposomes aggregated, and enzyme activity was inhibited by leakage of the NAD+ hydrolysis product, adenosine diphosphoryl 5-ribose (ADP-ribose), into the liposomes. Inhibition by ADP-ribose could be blocked and partly reversed by adding semicarbazide. The liposomes were efficiently lysed by Triton X-100, deoxycholate, or octyl glucoside, the kinetics and extent of lysis being affected by liposome size and correlating with the acid strength of various cholate derivatives. Addition of a serum sample and a solution of buffer, substrate, and detergent to a single reagent containing the liposomes and anti-theophylline antibody provided assay results equivalent to those obtained by conventional two-reagent EMIT homogeneous enzyme immunoassay for theophylline.

Quantification of amebae specific antibodies as "Multiple of normal activity (MONA)" with a standardized enzyme immunoassay (EIA)

Sera of 853 returnees from tropical countries, of 24 cases with amebic liver abscess and of 172 nonexposed German individuals were tested for antibodies to E. histolytica in the enzyme immunoassay (EIA). Antibody results were expressed as "multiple of normal activity (MONA)". The qualification of the EIA as a routine screening procedure for amebae specific antibodies was investigated and compared to that of the complement fixation test. Based on the symmetric frequency distribution of results from the 172 non-exposed controls the upper one sided limits for 95% (less than 2.8 MONA) and 99% (less than 4.2 MONA) specificity were determined. Routine results below the 95% specificity limit were considered "inconspicuous", such between both limits "borderline" and all MONA values exceeding the 99% specificity limit "conspicuous". The intention was to thereby secure a high degree of sensitivity for amebae antibody in the test. Cases with clinically confirmed liver abscess revealed a one sided lower 95% sensitivity limit (greater than or equal to 1.2 MONA), far above the onset of the defined sensitivity thresholds for conspicuous MONA values.

Epidemiological studies on the animal reservoir of gambiense sleeping sickness. Part II. Parasitological and immunodiagnostic examination of the human population

The prevalence of the disease was determined in the population (n = 3402) of a highly endemic sleeping sickness area in the Ivory Coast and an area of recent low endemicity in southwestern Upper Volta by using parasitological techniques supplemented by the determination of trypanosome specific antibodies and serum macroglobulins (IgM). 62 cases of trypanosomiasis were diagnosed parasitologically in the sleeping sickness focus in the Ivory Coast. 30 Trypanozoon stocks were established for their behavioural and biochemical characterization. The percentage of specific antibody carriers. 26% and 10% obtained with the enzyme-linked immunosorbent assay (ELISA) in both areas, respectively, was compared to that obtained for raised IgM levels. False negative diagnosis resulted in 24% with the ELISA, 12% with the indirect immunofluorescent test (IFT) and 19% with the radial immunodiffusion (RID). Considering IFT and IgM levels together, the proportion of false negative results fell to 8%. Possible reasons for low sensitivities, especially of the ELISA are discussed.

Fusion of dipalmitoylphosphatidylcholine vesicles

Small unilamellar dipalmitoylphosphatidylcholine vesicles formed by sonication are shown to fuse spontaneously below the phase transition temperature. The ultimate fusion products are unilamellar vesicles about 700 A in diameter, which are stable and provide an intact ionic permeation barrier either above or below the phase transition. The fused vesicles have been characterized by gel chromatography, trapped volume, 31P nuclear magnetic resonance, and negative stain and freeze-fracture electron microscopy.

[Serum antibodies in cystic and alveolar hydatid disease (author's transl)]

Serum samples of 107 patients with cystic and 30 with alveolar hydatid disease were tested for antibodies with hydatid fluid and extract from cyst material of E. alveolaris as antigens. Complement-fixation, indirect haemagglutination and an indirect enzyme immune (ELISA) technique were employed. The results indicate an antibody picture which confirms the value of serum-antibodies in the diagnosis of hydatid disease. Diagnostically insufficient antibody formation was present in seven patients with cystic and two with alveolar hydatid disease. The indirect haemagglutination test with alveolaris antigen proved to be the most sensitive reaction for antibody demonstration of both echinococci, while the same antigen in the ELISA technique gave species-specific results in patients with E. alveolaris.

Antibody activity in stick-ELISA as compared to other quantitative immunological tests in sera of echinococcosis cases

Antibody activity in sera of 43 cases with cystic and 5 cases with alveolar echinococcosis was determined against hydatid fluid and extract of E. alveolaris. The results with Stick-ELISA were compared to those obtained with complement fixation and indirect hemagglutination. Results in ELISA were determined in stepless fashion and expressed as multiple of normal activity (MONA). Sensitivities of the different tests with reference to their respective ranges of nonrelevant activities were 95% in ELISA, 95% in indirect hemagglutination and 90% in complement fixation as determined with sera from cystic echinococcosis cases and their homologous antigen. Employing homologous and heterologous antigens, none of the three immunotests allowed the species specific diagnosis of cystic echinococcosis cases, whereas most cases of alveolar echinococcosis could be recognized by their predominant homologous antibody activity in ELISA and complement fixation.

Stepless antibody determination with the stick-ELISA technique. Results expressed as multiple of normal activity (MONA)

A means is presented whereby results of antibody determination with ELISA (enzyme-linked immunospecific assay) can be expressed as the multiple of normal activity (MONA) contained in a normal serum pool, assessed by an internal standard. The procedure combines the advantage of stepless titration, inherent in the method of ELISA, with the opportunity to provide the clinician with an imaginable antibody result. It is discussed that independent of ELISA with the evolution of serology as an aid for the diagnosis of parasitic disease the clinician is faced with an evergrowing variety of normal antibody titers caused among others by different sensitivities of the methods and techniques employed. To preclude these differences result communications as MONA is suggested.

[Serum antibody findings in trichinosis (author's transl)]

Serum samples of 66 persons who had eaten meat from a wild boar were tested two to three times within 11 months for antibodies against extracts from Trichinella larvae. Watery extract of Trichinella spiralis larvae served as antigen. Complement-fixation was of little use because of its lack of sensitivity. Indirect haemagglutination and the ELISA test (enzyme-linked immunosorbent assay) gave uncertain results only in individual cases. There was a relationship between the clinical picture and the mean antibody concentration, clearer in the ELISA test than the indirect haemagglutination one. A fall in antibody titre was observed within the period of observation in only one third of patients. Results with sera of control subjects were of only limited use in relation to the specificity of the demonstrated antibodies.

A new technique of heterogenous enzyme-linked immunosorbent assay, stick-ELISA. II. Application of stick-ELISA to antigens of various infective agents

Stick-enzyme-linked immunosorbent assay (Stick-ELISA) was applied to antigens of a variety of infective agents. An acceptable reproducibility in a series was reached, the variation coefficient being twelve percent. Preliminary results revealed that ready coated sticks could be stored at 4 degrees C for at least two to three weeks.

A new technique of heterogenous enzyme-linked immunosorbent assay, stick-ELISA. I. Description of the technique

A new quantitative technique is described to perform hererogenous enzyme-linded immunosorbent assay using polysterene sticks as solid phase (Stick-ELISA). Advantage of the technique is a combination of economic antigen and conjugate requirements, rapid and thorough washing procedures, and part adaption to general automation devices present in most hospital laboratories which render the technique equally ideal for small and large series in routine serodiagnosis.

Serologic diagnosis of extraintestinal amebiasis: a comparison of stick-ELISA and other immunological tests

The sera of 37 patients with amebic liver abscess and of 20 healthy donors were tested in Stick-ELISA (enzyme-linked immunosorbent assay), and the results compared to those obtained with complement fixation, indirect hemagglutination, counterelectrophoresis, and latex agglutination. Stick-ELISA results correlated positively with those of complement fixation and indirect hemagglutination at the one percent level.

Some aspects of immunodiagnosis in amebiasis

Antigen from axenically and with crithidia monoxenically grown amebae are compared in complement fixation test and indirect hemagglutination test. While similar reactivity was observed in indirect hemagglutination monoxenic antigen yielded extremely higher titers in complement fixation tests. Transient latex agglutinations of severely ill malaria tropica patients proved to be spontaneous in nature. It is recommended that extra latex is added to the test kits to provide for a check of positive sera for spontaneous agglutination. Glutaraldehyde treated and sensitized sheep red cells were stored under different conditions and their reactivity assessed over various periods of time. No loss of reactivity was found to occur under either condition after the respective times of observation, the longest of which lasted 12 months.

Further studies on the behavior of 2-mercaptoethanol resistant antibody following cholera vaccinations in a nonendemic country

Additional data are presented in support of the earlier observation that in nonendemic countries 2-mercaptoethanol (2-ME) resistant vibriocidal antibodies better reflect antibacterial immunity against cholera following vaccination than does total vibriocidal activity. It can be shown that in more than half of the cases even after at least three subsequent vaccinations in six to eight months intervals 2-ME resistant vibriocidins would not last as long as six months. Following intradermal inocculations of vaccine only one in a group of five demonstrated faint 2-ME resistant antibody response. All sera were tested with and without dialysis following 2-ME treatment revealing corresponding results.