Characterisation of protein co-extracted together with LPS in Escherichia coli, Salmonella minnesota and Yersinia enterocolitica

Lipopolysaccharide of the Yersinia pseudotuberculosis Complex

Lipopolysaccharide (LPS), localized in the outer leaflet of the outer membrane, serves as the major surface component of the Gram-negative bacterial cell envelope responsible for the activation of the host's innate immune system. Variations of the LPS structure utilized by Gram-negative bacteria promote survival by providing resistance to components of the innate immune system and preventing recognition by TLR4. This review summarizes studies of the biosynthesis of Yersinia pseudotuberculosis complex LPSs, and the roles of their structural components in molecular mechanisms of yersiniae pathogenesis and immunogenesis.

Localized incorporation of outer membrane components in the pathogen Brucella abortus

The zoonotic pathogen Brucella abortus is part of the Rhizobiales, which are alpha-proteobacteria displaying unipolar growth. Here, we show that this bacterium exhibits heterogeneity in its outer membrane composition, with clusters of rough lipopolysaccharide co-localizing with the essential outer membrane porin Omp2b, which is proposed to allow facilitated diffusion of solutes through the porin. We also show that the major outer membrane protein Omp25 and peptidoglycan are incorporated at the new pole and the division site, the expected growth sites. Interestingly, lipopolysaccharide is also inserted at the same growth sites. The absence of long-range diffusion of main components of the outer membrane could explain the apparent immobility of the Omp2b clusters, as well as unipolar and mid-cell localizations of newly incorporated outer membrane proteins and lipopolysaccharide. Unipolar growth and limited mobility of surface structures also suggest that new surface variants could arise in a few generations without the need of diluting pre-existing surface antigens.

Elimination of trace endotoxin protein from rough chemotype LPS

The phenol-chloroform-petroleum ether (PCP) extraction is the method of choice for isolating LPS chemotypes from rough mutant bacteria. However, we have observed that a high percentage of PCP-purified LPS preparations contain trace levels of protein contaminants, and these protein contaminants may exhibit endotoxin-like activity. To obtain protein-free rough LPS, a modified phenol-water extraction procedure was developed for use as a final step to follow PCP extraction. Using this procedure, Salmonella minnesota Ra, Rc, Rd and Re LPS were recovered in yields of 82-100% from the original PCP-extracted preparations. Yields were determined by recovery of KDO and supported by analysis of silver stained SDS-PAGE gels. Although the original PCP-purified chemotypes were contaminated by major 41, 38.5, 29.5, 23, 17 and 14 kDa proteins (detected by Western blotting and gold staining), the repurified LPS contained no detectable protein. The repurified LPS retained all of its original bioactivity as defined by the ability to stimulate normal C3H/OuJ macrophages to secrete TNF. The importance of utilizing repurified LPS in biologic studies was illustrated by the loss of > 99% of activity when repurified LPS was used to stimulate TNF secretion by LPS 'hyporesponsive' C3H/HeJ macrophages.

Defective immunogenic cell death of HMGB1-deficient tumors: compensatory therapy with TLR4 agonists

Immunogenic cell death induced by anticancer chemotherapy is characterized by a series of molecular hallmarks that include the exodus of high-mobility group box 1 protein (HMGB1) from dying cells. HMGB1 is a nuclear nonhistone chromatin-binding protein. It is secreted at the late stages of cellular demise and engages Toll-like receptor4 (TLR4) on dendritic cells (DCs) to accelerate the processing of phagocytic cargo in the DC and to facilitate antigen presentation by DC to T cells. The absence of HMGB1 expression by dying tumor cells exposed to anthracyclines or oxaliplatin compromises DC-dependent T-cell priming by tumor-associated antigens. Here, we show that transplantable tumors exhibiting weak expression of nuclear HMGB1 respond to chemotherapy more effectively if the treatment is combined with the local or systemic administration of a highly purified and physiochemically defined and standardized lipopolysaccharide solution, which acts as a high-potency and exclusive TLR4 agonist, called Dendrophilin (DEN). The synergistic antitumor effects mediated by the combination of chemotherapy and immunotherapy relied upon the presence of the MyD88 (myeloid differentiation primary response gene) adapter of TLR4 (but not that of the TIR-domain-containing adapter-inducing interferon-β adapter), in line with the well-characterized action of DEN on the MyD88 signaling pathway. DEN and anthracyclines synergized to induce intratumoral accumulation of interferon-γ-producing CD4(+) and CD8(+) T lymphocytes. Moreover, DEN could restore the immunogenicity of dying tumor cells from which HMGB1 had been depleted by RNA interference. These findings underscore the potential clinical utility of combination regimens involving immunogenic chemotherapy and certain TLR4 agonists in advanced HMGB1-deficient cancers.

Receptors, mediators, and mechanisms involved in bacterial sepsis and septic shock

Bacterial sepsis and septic shock result from the overproduction of inflammatory mediators as a consequence of the interaction of the immune system with bacteria and bacterial wall constituents in the body. Bacterial cell wall constituents such as lipopolysaccharide, peptidoglycans, and lipoteichoic acid are particularly responsible for the deleterious effects of bacteria. These constituents interact in the body with a large number of proteins and receptors, and this interaction determines the eventual inflammatory effect of the compounds. Within the circulation bacterial constituents interact with proteins such as plasma lipoproteins and lipopolysaccharide binding protein. The interaction of the bacterial constituents with receptors on the surface of mononuclear cells is mainly responsible for the induction of proinflammatory mediators by the bacterial constituents. The role of individual receptors such as the toll-like receptors and CD14 in the induction of proinflammatory cytokines and adhesion molecules is discussed in detail. In addition, the roles of a number of other receptors that bind bacterial compounds such as scavenger receptors and their modulating role in inflammation are described. Finally, the therapies for the treatment of bacterial sepsis and septic shock are discussed in relation to the action of the aforementioned receptors and proteins.

Pasteurella haemolytica lipopolysaccharide-associated protein induces pulmonary inflammation after bronchoscopic deposition in calves and sheep

The lipopolysaccharide (LPS)-associated protein (LAP) was extracted from Pasteurella haemolytica serotype A1 strains L101 (bovine origin) and 82-25 (ovine origin). Extracts contained 0.017% total LPS and appeared as only two bands at 14 and 16.6 kDa after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. To determine the extent of pulmonary inflammation induced by LAP and its possible role in the pathogenesis of pneumonic pasteurellosis, LAP (500 micrograms in pyrogen-free saline [PFS]) was deposited by fiber-optic bronchoscopy into the dorsum of the caudal portion of the cranial lobe of the right lung of calves (strain L101 LAP) and sheep (strain 82-25 LAP). LPS (500 micrograms in PFS), 3-h P. haemolytica cultures (1.6 x 10(8) to 1.9 x 10(8) CFU in PFS), and PFS alone were deposited similarly as controls. At necropsy, 24 h after deposition, gross and histologic pulmonary lesions of calves and sheep given LAP, LPS, and P. haemolytica were similar and consisted of various degrees of acute bronchopneumonia (relative severities of lesions induced: LAP < LPS < live organisms). By subjective histologic interpretation and semiquantitative morphometry, animals given LAP had the highest percentage of macrophages per alveolar lumen and the lowest percentage of neutrophils. The lesions from animals given LPS were more severe than those given LAP, but the morphometric cell counts were similar. In contrast, animals inoculated with P. haemolytica had lesions typical of this agent, consisting of many neutrophils, proteinaceous exudate, and a few macrophages. Morphometrically, these lesions had the highest numbers of neutrophils and the lowest numbers of macrophages. These studies show that LAP can induce an inflammatory response in the alveolar lumens and may play a role in the pathogenesis of pneumonic pasteurellosis.

Reactivity of the human antiendotoxin immunoglobulin M monoclonal antibody HA-1A with lipopolysaccharides from rough and smooth gram-negative organisms

Clinical data suggest that the human immunoglobulin M antiendotoxin antibody HA-1A reduced mortality in patients diagnosed with gram-negative bacteremia and bacteremia with shock. Previous studies have demonstrated that HA-1A binds to the lipid A domain of lipopolysaccharide (LPS). The present study evaluated the ability of HA-1A to interact with LPs isolated from various strains of gram-negative bacteria by using liquid-phase rate nephelometry and solid-phase immunoblotting assays. HA-1A formed immune complexes in solution with LPSs isolated from both rough and smooth gram-negative organisms. Western blot (immunoblot) analysis of these LPS preparations revealed that HA-1A bound to LPS isolated from rough gram-negative organisms and to a rough LPS-like component present in smooth LPS. HA-1A also bound to LPS-protein complexes found in certain commercial rough LPS preparations. Preincubation of HA-1A with lipid A completely blocked subsequent binding of HA-1A to LPS in both liquid- and solid-phase assay formats, suggesting that the interaction of HA-1A with LPS is through the lipid A domain. Evidence that the binding of HA-1A to LPS was mediated through the antigen-combining (Fv) region of the antibody was provided by the finding that a murine anti-idiotypic antibody to HA-1A inhibited binding. These findings suggested that the broad antiendotoxin reactivity exhibited by HA-1A appeared to be due to the ability of HA-1A to bind to the conserved lipid A moiety of LPSs derived from both smooth- and rough-phenotype gram-negative bacterial strains.

Purification and immunological characterization of a major low-molecular-weight lipoprotein from Borrelia burgdorferi

Borrelia burgdorferi resembles gram-negative bacteria in having both cellular and outer membranes. We previously showed that a lipopolysaccharide (LPS)-like material could be extracted from B. burgdorferi with phenol-chloroform-petroleum ether (PCP). The PCP extract of B. burgdorferi exhibited biological activity in several in vitro assays (e.g., mitogenicity, pyrogenicity, and cytokine release). These activities suggested the presence of endotoxin. The PCP extract of B. burgdorferi, however, also contained a small amount of protein. Preliminary studies showed that monoclonal antibody prepared against this protein inhibited the mitogenic activity of the PCP extract toward murine spleen cells. The current study was therefore undertaken to characterize this protein and to establish methods for its separation from the LPS. The PCP-extracted protein consisted of a single, low-molecular-weight lipoprotein (apparent M(r), 10,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis) (SDS-PAGE). By protein analysis, it accounted for 2% of the dry weight of defatted cells, thus making it a major constituent of the spirochete. It was purified from the LPS by initial extraction into 10% Triton X-100 followed by immunoaffinity chromatography in the presence of detergent. On removal of the LPS, the purified lipoprotein formed aggregates stable to SDS-PAGE which were detectable on Western blots (immunoblots) probed with either the monoclonal antibody or polyclonal antiserum. From a plot of the aggregate molecular weight versus aggregate size, a monomer molecular weight of 7,500 was obtained. Indirect immunofluorescence with the monoclonal antibody showed that the lipoprotein was exposed at the surface of the spirochete in only a small percentage of cells. The lipoprotein was present in several strains of B. burgdorferi but absent in other Borrelia spp., treponemes, and gram-negative human pathogens, indicating species specificity.

Analysis of LPS released from Salmonella abortus equi in human serum

We investigated in which form lipopolysaccharide (LPS) is released from live bacteria incubated with human serum and whether the released LPS can interact with high density lipoprotein (HDL), the main transport protein for purified LPS in circulation. Live biotinylated Salmonella abortus equi bacteria were incubated with fresh serum (37 degrees C; 2 h). The released LPS was isolated by immunoprecipitation or immunoabsorption using specific anti-O antibodies. It was analysed and compared with purified LPS, also incubated with serum under identical conditions. Immunoprecipitation led to a 35% recovery and immunoabsorption to quantitative recovery of released or purified LPS. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and subsequent immunoblot analysis revealed that all molecular species present in the purified LPS were present in the released LPS. The rough fraction, which was co-isolated from serum together with the true smooth (O-polysaccharide-containing) molecules, exhibited S. minnesota rough mutant Rb antigenic specificity. In the immunoprecipitated material two forms of released LPS were identified. One represented LPS associated with a biotinylated bacterial component with an apparent molecular mass of 35-36 kDa, which was identified as OmpA, a major outer membrane protein. The OmpA-associated LPS was free of HDL. Another part of the released LPS was free of biotinylated bacterial components. This portion of LPS was associated with HDL, indicating that the interaction with HDL may also proceed with a part of LPS released from bacteria.

Associations of Escherichia coli K-12 OmpF trimers with rough and smooth lipopolysaccharides

The associations of both rough and smooth lipopolysaccharides (LPS) with the OmpF porin of Escherichia coli K-12 were examined in galE strains deleted for ompC. Transformation with pSS37 and growth with galactose conferred the ability to assemble a Shigella dysenteriae O antigen onto the core oligosaccharide of E. coli K-12 LPS. The association of LPS with OmpF trimers was assessed by staining, autoradiography of LPS specifically labeled with [1-14C]galactose, and Western immunoblotting with a monoclonal antibody specific for OmpF trimers. These techniques revealed that the migration distances and multiple banding patterns of OmpF porin trimers in sodium dodecyl sulfate-polyacrylamide gels were dictated by the chemotype of associated LPS. Expression of smooth LPS caused almost all of the trimeric OmpF to run in gels with a slower mobility than trimers from rough strains. The LPS associated with trimers from a smooth strain differed from the bulk-phase LPS by consisting almost exclusively of molecules with O antigen.

Immunological approach of assembly and topology of OmpF, an outer membrane protein of Escherichia coli

Various monoclonal antibodies (MoF) directed against cell-surface-exposed epitopes of OmpF, one major outer membrane pore protein of Escherichia coli B and K-12, have been used to study the assembly and the topology of the protein. This paper firstly describes the characterization of the OmpF epitopes recognized by the various monoclonal antibodies. A comparison between OmpC, OmpF and PhoE porins with respect to their primary amino acid sequence and their cell-surface exposed regions allows us to propose a rough model including 2 antigenic sites. The second part is focused on the assembly of the OmpF protein in the outer membrane. Various forms, precursor, unassembled monomer, metastable oligomer (pre-trimer) and trimer are detected with immunological probes directed against OmpF during a kinetic analysis of the process. The requirement for a concomitant lipid synthesis during the trimerization has been demonstrated by investigating the presence of a specific native epitope. The role of lipopolysaccharide during the stabilization of the conformation is discussed with regard to the various steps of assembly.

Immunological analysis of porin polymorphism in Escherichia coli B and K-12

Two sets of monoclonal antibodies (MoF type I and MoF type II) directed against the OmpF protein were used to analyze the immunological reactivity of the major outer membrane porins of E. coli B and K-12. All these antibodies present a specificity to the native OmpF protein. In addition, among the type II antibodies, MoF 18, 19 and 20 could recognize an epitope present on both monomeric and trimeric forms of the porin as demonstrated by immunoblotting analyses. The use of two different screening methods led to the isolation of two different sets of MoF, one specific for a native conformation accessible only on E. coli B strain and the second directed against epitopes present on OmpF of the two strains, B and K-12. These various responses are discussed in relation to the lipopolysaccharide binding to OmpF and with respect to the screening test used.

Comparison of the biological responses induced by lipopolysaccharide and endotoxin of Treponema hyodysenteriae and Treponema innocens

The chemical composition and classical biologic activities of lipopolysaccharide (LPS; phenol-water) and endotoxin (butanol-water) preparations from virulent Treponema hyodysenteriae and avirulent Treponema innocens were examined. The LPS and endotoxin preparations from T. hyodysenteriae B204 contained approximately 80.9 and 35.2% hexose, 0.12 and 0.45% thiobarbituric acid-reactive compound, and less than 1 and 11.3% protein, respectively. The LPS and endotoxin preparations of T. innocens B1555a contained approximately 56.3 and 37.8% hexose, 0.45 and 0.4% thiobarbituric acid-reactive compound, and less than 1 and 26% protein, respectively. A silver-stained 7.5 to 15% sodium dodecyl sulfate-polyacrylamide gel showed four bands for the T. hyodysenteriae preparations, while the T. innocens preparations failed to resolve into discrete bands on electrophoresis. We determined by the Limulus amebocyte lysate assay that the treponemal preparations had comparable amounts of endotoxin activity when Escherichia coli LPS was used as a standard. The 50% lethal doses of LPS and endotoxin from T. hyodysenteriae for BALB/cByJ mice were 380 and 80 micrograms, respectively. The treponemal preparations were poor adjuvants, failed to induce a dermal Shwartzman reaction, and were not pyrogenic. The treponemal LPS preparations, unlike the endotoxin preparations, were not mitogenic for murine spleen cells. Differences in virulence between the two treponemal species could not be associated with the biologic activities of the respective LPS or endotoxin moieties, but the endotoxin preparations were consistently more active than the purified LPS preparations.

Characterization of the major outer membrane antigens of Treponema hyodysenteriae

Outer membrane extracts of Treponema hyodysenteriae were used to evaluate the antibody responses in immunized or convalescent pigs. Western blot (immunoblot) analysis identified antibodies in sera reactive with 14- to 19-kilodalton (kDa) antigens. Reactivity against these antigens could be removed only by absorption of sera with butanol-water-extracted endotoxin from the homologous strain of T. hyodysenteriae. Treatment of the outer membrane extracts with 0.1 M sodium meta-periodate, but not with proteinase K, abolished reactivity with both outer membrane and endotoxin antigens (14 and 19 kDa). These results indicate that swine vaccinated with the outer membrane extract of T. hyodysenteriae develop antibody responses to outer membrane antigens qualitatively similar to those of swine convalescing from active infection, especially antibodies against low-molecular-mass antigens. The nature of the 14- to 19-kDa antigens appears consistent with that of treponemal endotoxin and lipopolysaccharide.

Molecular cloning and characterisation of the genes for a non-fimbrial adhesin from Escherichia coli

A non-fimbrial adhesin (NFA-1) from the uropathogenic Escherichia coli strain 827 responsible for agglutination of human erythrocytes was cloned using the cos 4 cosmid vector. A clone was isolated which promoted haemagglutination and showed the same biological properties as the adhesin produced by the wild type strain. Both express adhesin at 37 degrees C, but not 18 degrees C nor in the presence of 1% glucose. Adhesin purified from the clone formed high molecular weight aggregates which were resolved to the 21 K dalton subunit protein seen in the wild type strain on denaturation. Binding to human kidney cells by the clone and the wild type E. coli, from which the genes were cloned, were compared in an ELISA assay and shown to be the same. The genes for the adhesin were isolated on a 15.5 kilobase BamHI-EcoRI fragment which was subjected to gamma delta mutagenesis. The NFA-1 operon was localised to a 6.5kb region of this fragment.

Synergistic effect of detergents and aluminium phosphate on the humoral immune response to bacterial and viral membrane proteins

The influence of detergents on the immunogenic activity of the major outer membrane protein of Neisseria gonorrhoeae was investigated. Most detergents tested were found to enhance the immune response. This effect was synergistic with the adjuvant activity of AlPO4. The combination of detergent and AlPO4 showed a stronger adjuvant activity than Freund's complete adjuvant. The adjuvant effect was only observed with protein preparations with very low lipopolysaccharide content. The immunostimulating effect of detergents was also observed with meningococcal group C polysaccharide conjugated to a Haemophilus influenzae type b outer membrane protein and with the fusion protein of measles virus. The influence of some detergent parameters (critical micelle concentration, hydrophile-lipophile balance, charge) was investigated.

Lipopolysaccharide tightly bound to porin monomers and trimers from Escherichia coli K-12

Lipopolysaccharide (LPS) bound to isolated porin was detected on polyacrylamide gels by using a carbohydrate-specific silver stain and on Western blots by using anti-lipid A monoclonal antibodies. Porin was isolated from Escherichia coli JF733 (Ra chemotype) and D21f2 (Re chemotype). Isolated porin was separated from loosely associated LPS by polyacrylamide gel electrophoresis (PAGE) in sodium dodecyl sulfate (SDS). Unheated porin traveled on gels as aggregates, presumably trimers, with an apparent molecular weight of 78,000 to 83,000. After heating to 100 degrees C for 2 min in SDS, the porin traveled as a monomer with a molecular weight of 36,000. The unheated, high-molecular-weight trimer band reacted in the gel with the carbohydrate-specific silver stain, while the heated monomer band showed no staining. In contrast, lipid A-specific monoclonal antibodies showed reactivity on Western blots to the 36,000-molecular-weight band but not to the trimer. Finally, both monomer and trimer bands were isolated from gels and rerun by SDS-PAGE. LPS was released from the trimer preparation when the sample was heated, but the monomer band that was formed by heating the trimer isolate still reacted with anti-lipid A antibodies. Quantitative Limulus amebocyte lysate analysis revealed an approximately equal molar ratio of LPS to protein in the electroeluted porin monomer. Thus, some but not all of the LPS could be released from trimer complexes by boiling in SDS. The isolated monomer did not release more LPS on boiling in SDS a second time but still had LPS tightly bound, as detected by lipid A-specific monoclonal antibodies.