lipid-a and Salmonella-Infections--Animal

Gram-negative bacteria have an outer membrane containing LPS. LPS is constituted of an oligosaccharide portion and a lipid-A moiety that embeds this molecule within the outer membrane. LPS is a pathogen-associated molecular pattern, and several pathogens modify their lipid-A as a stealth strategy to avoid recognition by the innate immune system and gain resistance to host factors that disrupt the bacterial cell envelope. An essential feature of Salmonella enterica Typhimurium pathogenesis is its ability to replicate within vacuoles in professional macrophages. S. Typhimurium modifies its lipid-A by hydroxylation by the Fe2+/α-ketoglutarate-dependent dioxygenase enzyme (LpxO). Here, we show that a periplasmic protein of the bacterial oligonucleotide/oligosaccharide-binding fold family, herein named virulence and stress-related periplasmic protein (VisP), on binding to the sugar moiety of peptidoglycan interacts with LpxO. This interaction inhibits LpxO function, leading to decreased LpxO-dependent lipid-A modifications and increasing resistance to stressors within the vacuole environment during intramacrophage replication promoting systemic disease. Consequently, ΔvisP is avirulent in systemic murine infections, where VisP acts through LpxO. Several Gram-negative pathogens harbor both VisP and LpxO, suggesting that this VisP-LpxO mechanism of lipid-A modifications has broader implications in bacterial pathogenesis. Bacterial species devoid of LpxO (e.g., Escherichia coli) have no lipid-A phenotypes associated with the lack of VisP; however, VisP also controls LpxO-independent phenotypes. VisP and LpxO act independently in the S. Typhimurium murine colitis model, with both mutants being attenuated for diverging reasons; ΔvisP is less resistant to cationic antimicrobial peptides, whereas ΔlpxO is deficient for epithelial cell invasion. VisP converges bacterial cell wall homeostasis, stress responses, and pathogenicity.

Topics: Amino Acid Sequence; Animals; Bacterial Proteins; Cell Line; Female; Genes, Bacterial; HeLa Cells; Host-Pathogen Interactions; Humans; Lipid A; Macrophages; Mice; Mice, Inbred BALB C; Models, Molecular; Molecular Sequence Data; Mutagenesis, Site-Directed; Periplasmic Proteins; Regulon; Salmonella Infections, Animal; Salmonella typhimurium; Sequence Homology, Amino Acid; Virulence; Virulence Factors

Although lipopolysaccharide (LPS) stimulation through the Toll-like receptor (TLR)-4/MD-2 receptor complex activates host defense against Gram-negative bacterial pathogens, how species-specific differences in LPS recognition impact host defense remains undefined. Herein, we establish how temperature dependent shifts in the lipid A of Yersinia pestis LPS that differentially impact recognition by mouse versus human TLR4/MD-2 dictate infection susceptibility. When grown at 37°C, Y. pestis LPS is hypo-acylated and less stimulatory to human compared with murine TLR4/MD-2. By contrast, when grown at reduced temperatures, Y. pestis LPS is more acylated, and stimulates cells equally via human and mouse TLR4/MD-2. To investigate how these temperature dependent shifts in LPS impact infection susceptibility, transgenic mice expressing human rather than mouse TLR4/MD-2 were generated. We found the increased susceptibility to Y. pestis for "humanized" TLR4/MD-2 mice directly paralleled blunted inflammatory cytokine production in response to stimulation with purified LPS. By contrast, for other Gram-negative pathogens with highly acylated lipid A including Salmonella enterica or Escherichia coli, infection susceptibility and the response after stimulation with LPS were indistinguishable between mice expressing human or mouse TLR4/MD-2. Thus, Y. pestis exploits temperature-dependent shifts in LPS acylation to selectively evade recognition by human TLR4/MD-2 uncovered with "humanized" TLR4/MD-2 transgenic mice.

Topics: Acylation; Animals; Cell Line; Chromosomes, Artificial, Bacterial; Cytokines; Escherichia coli; Escherichia coli Infections; HEK293 Cells; Humans; Lipid A; Lipopolysaccharides; Lymphocyte Antigen 96; Mice; Mice, Inbred C57BL; Mice, Transgenic; Plague; Salmonella enterica; Salmonella Infections, Animal; Signal Transduction; Temperature; Toll-Like Receptor 4; Yersinia pestis

Galectin-3 is a beta-galactoside-binding lectin that plays an important role in inflammatory diseases. It also interacts with the surface carbohydrates of many pathogens, including LPS. However, its role in infection is not fully understood. Data presented herein demonstrate for the first time that galectin-3 is a negative regulator of LPS-induced inflammation. Galectin-3 is constitutively produced by macrophages and directly binds to LPS. Galectin-3-deficient macrophages had markedly elevated LPS-induced signaling and inflammatory cytokine production compared with wild-type cells, which was specifically inhibited by the addition of recombinant galectin-3 protein. In contrast, blocking galectin-3 binding sites by using a neutralizing Ab or its ligand, beta-lactose, enhanced LPS-induced inflammatory cytokine expression by wild-type macrophages. In vivo, mice lacking galectin-3 were more susceptible to LPS shock associated with excessive induction of inflammatory cytokines and NO production. However, these changes conferred greater resistance to Salmonella infection. Thus, galectin-3 is a previously unrecognized, naturally occurring, negative regulator of LPS function, which protects the host from endotoxin shock but, conversely, favors Salmonella survival.

Topics: Animals; Cells, Cultured; Down-Regulation; Female; Galectin 3; Gene Expression Regulation; Immunity, Innate; Inflammation Mediators; Lipid A; Lipopolysaccharide Receptors; Lipopolysaccharides; Macrophages; Mice; Mice, Inbred C57BL; Mice, Knockout; Salmonella Infections, Animal; Shock, Septic; Toll-Like Receptor 4

Salmonella enterica serovar Typhimurium encounters antimicrobial peptides (AP) within the phagosomes of professional phagocytes and at intestinal mucosal surfaces. Salmonella serovar Typhimurium utilizes the two-component regulatory system PmrA-PmrB, which is activated in response to the environmental conditions encountered in vivo, to regulate resistance to several AP, including polymyxin B (PM). Random MudJ transposon mutagenesis was used to identify PmrA-PmrB-regulated genes, as well as genetic loci necessary for PM resistance. Three different phenotypic classes of genes were identified: those necessary for PM resistance and regulated by PmrA, those necessary for PM resistance and not regulated by PmrA, and PmrA-regulated genes not required for PM resistance. Loci identified as necessary for PM resistance showed between 6- and 192-fold increased sensitivities to PM, and transposon insertion sites include surA, tolB, and gnd. PmrA-regulated loci identified included dgoA and yibD and demonstrated 500- and 2,500-fold activation by PmrA, respectively. The role of the identified loci in aminoarabinose modification of lipid A was determined by paper chromatography. The gnd mutant demonstrated a loss of aminoarabinose from lipid A, which was suggested to be due to a polar effect on the downstream gene pmrE. The remaining PM(s) mutants (surA and tolB), as well as the two PmrA-regulated gene (yibD and dgoA) mutants, retained aminoarabinose on lipid A. yibD, dgoA, and gnd (likely affecting pmrE) played no role in PmrA-regulated resistance to high iron concentrations, while surA and tolB mutations grew poorly on high iron media. All PM(s) mutants identified in this study demonstrated a defect in virulence compared to wild-type Salmonella serovar Typhimurium when administered orally to mice, while the PmrA-regulated gene (yibD and dgoA) mutants showed normal virulence in mice. These data broaden our understanding of in vivo gene regulation, lipopolysaccharide modification, and mechanisms of resistance to AP in enteric bacteria.

Topics: Animals; Anti-Bacterial Agents; Bacterial Proteins; Base Sequence; DNA Transposable Elements; Drug Resistance, Bacterial; Female; Gene Expression Regulation, Bacterial; Lipid A; Mice; Mice, Inbred BALB C; Microbial Sensitivity Tests; Molecular Sequence Data; Mutagenesis, Insertional; Mutation; Polymyxin B; Salmonella Infections, Animal; Salmonella typhimurium; Transcription, Genetic; Virulence

Systemically administered tumor-targeted Salmonella has been developed as an anticancer agent, although its use could be limited by the potential induction of tumor necrosis factor alpha (TNFalpha)-mediated septic shock stimulated by lipid A. Genetic modifications of tumor-targeting Salmonella that alter lipid A and increase safety must, however, retain the useful properties of this bacteria. We report here that disruption of the Salmonella msbB gene reduces TNFalpha induction and increases the LD50 of this pathogenic bacteria by 10,000-fold. Notwithstanding this enormous difference, Salmonella retains its tumor-targeting properties, exhibiting tumor accumulation ratios in excess of 1000:1 compared with normal tissues. Administration of this bacteria to mice bearing melanoma results in tumors that are less than 6% the size of tumors in untreated controls at day 18. Thus, the antitumor activity previously demonstrated using tumor-targeting Salmonella with normal lipid A is retained. Lipid modification of tumor-specific bacterial vectors provides a means for reducing septic shock and further suggests that the antitumor activity of these bacteria may be independent of TNFalpha.

Topics: Acyltransferases; Animals; Bacterial Proteins; Cell Survival; Escherichia coli Proteins; Humans; Lipid A; Liver; Macrophages; Melanoma, Experimental; Mice; Mice, Inbred Strains; Neoplasm Transplantation; Respiration; Salmonella; Salmonella Infections, Animal; Sequence Deletion; Shock, Septic; Skin Neoplasms; Swine; Tumor Necrosis Factor-alpha; Virulence

Salmonella infections in naturally susceptible mice grow rapidly, with death occurring only after bacterial numbers in vivo have reached a high threshold level, commonly called the lethal load. Despite much speculation, no direct evidence has been available to substantiate a role for any candidate bacterial components in causing death. One of the most likely candidates for the lethal toxin in salmonellosis is endotoxin, specifically the lipid A domain of the lipopolysaccharide (LPS) molecule. Consequently, we have constructed a Salmonella mutant with a deletion-insertion in its waaN gene, which encodes the enzyme that catalyses one of the two secondary acylation reactions that complete lipid A biosynthesis. The mutant biosynthesizes a lipid A molecule lacking a single fatty acyl chain and is consequently less able to induce cytokine and inducible nitric oxide synthase (iNOS) responses both in vivo and in vitro. The mutant bacteria appear healthy, are not sensitive to increased growth temperature and synthesize a full-length O-antigen-containing LPS molecule lacking only the expected secondary acyl chain. On intravenous inoculation into susceptible BALB/c mice, wild-type salmonellae grew at the expected rate of approximately 10-fold per day in livers and spleens and caused the death of the infected mice when lethal loads of approximately 10(8) were attained in these organs. Somewhat unexpectedly, waaN mutant bacteria grew at exactly the same rate as wild-type bacteria in BALB/c mice but, when counts reached 10(8) per organ, mice infected with mutant bacteria survived. Bacterial growth continued until unprecedentedly high counts of 10(9) per organ were attained, when approximately 10% of the mice died. Most of the animals carrying these high bacterial loads survived, and the bacteria were slowly cleared from the organs. These experiments provide the first direct evidence that death in a mouse typhoid infection is directly dependent on the toxicity of lipid A and suggest that this may be mediated via pro-inflammatory cytokine and/or iNOS responses.

Topics: Acyltransferases; Animals; Escherichia coli Proteins; Interleukin-1; Lipid A; Mice; Mice, Inbred BALB C; Mutation; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Phenotype; Salmonella Infections, Animal; Salmonella typhimurium; Tumor Necrosis Factor-alpha; Virulence

Investigations were undertaken to characterize the protective immunity induced by porin-lipopolysaccharide (LPS) against Salmonella typhimurium infection in mice. Mice immunized with porin-LPS showed higher levels of antiporin immunoglobulin G than mice which received porin alone. Further, T cells from porin-LPS-immunized mice showed an augmented proliferative response to porin in vitro compared with the response of T cells from porin-injected animals. The passive transfer of anti-LPS antibodies conferred significant protection (17%), while antiporin serum failed to protect mice against lethal challenge, indicating the protective ability of anti-LPS antibodies. However, the transfer of serum obtained from porin-LPS-immunized mice resulted in better protection (30%) than did anti-LPS or antiporin antibodies alone. In contrast to LPS, monophosphoryl lipid A completely failed to induce protection against lethal infection. However, comparable to the effect of LPS, injection of porin with monophosphoryl lipid A enhanced antibody response and the protective ability of porin (81.25%). The transfer of T cells from porin-LPS-immunized mice provided higher levels of protection (47%) against lethal challenge than did T cells from porin-immunized mice (23%). The combination of T cells and serum from porin-immunized mice transferred 36% protection. However, a combination of T cells and serum from porin-LPS-immunized mice conferred the highest level of protection (92%), which was reflected by the number of survivors (100%) in the porin-LPS-immunized group. These results demonstrate that besides the protective effect of anti-LPS antibodies, the ability of LPS to augment humoral and cell-mediated immune responses to porin confers effective protection against Salmonella infection.

Topics: Animals; Antibodies, Bacterial; Bacterial Outer Membrane Proteins; Female; Immune Sera; Immunization; Immunization, Passive; Immunoglobulin G; Immunoglobulin M; Lipid A; Lipopolysaccharides; Lymphocyte Activation; Male; Mice; Mice, Inbred BALB C; Porins; Salmonella Infections, Animal; T-Lymphocytes

The ability of DT-5461, a chemically synthetic low-toxic lipid A analogue, to activate anti-Salmonella activity in C3H/HeN mice was examined. Previous intraperitoneal (i.p.) injection of DT-5461 (100 micrograms or more/mouse) significantly hindered the bacterial growth in the peritoneal cavities of the mice after the i.p. infection with Salmonella typhimurium LT2 strain. The effect was the maximum when DT-5461 was given 6 h before the challenge. The injection of DT-5461 6 h in advance could also confer protection against the infection. Bactericidal activity enhancement was also seen in mice that had been injected with a small amount of recombinant murine IFN-gamma (10(3) U per mouse) and non-effective dose (10 micrograms) of DT-5461 together 6 h before the challenge. Bactericidal effect enhancement was seen in mice that had been injected with IFN-gamma at 6 h and DT-5461 at 3 h before the challenge, while it could be hardly seen in mice injected with them in a reversed order. The i.p. injection of DT-5461 recruits the exudate cells into the peritoneal cavities, and the phagocytic and bactericidal abilities of the macrophages in the exudate cells are apparently elevated. The mechanisms of non-specific resistance enhancement induced by DT-5461 were discussed.

Topics: Adjuvants, Immunologic; Animals; Disaccharides; Exudates and Transudates; Female; Immunity, Innate; Interferon-gamma; Lipid A; Male; Mice; Mice, Inbred C3H; Phagocytosis; Salmonella Infections, Animal

LPS is the major surface glycolipid on gram-negative bacteria. In this work, we have idiotypically characterized the antibody response against LPS in different species. To do this, we have produced mAb against LPS. Binding of many of these antibodies to LPS could be inhibited by LPS and lipid A, indicating that the monoclonals are specific for lipid A, the toxic moiety of the LPS molecule. One anti-lipid A antibody, IC9, proved protective against gram-negative bacteremia and endotoxic shock in murine protection models. We generated anti-idiotypic antibodies against IC9. The binding of several of these anti-Id to IC9 was specifically inhibited by lipid A. We used these anti-Id to characterize the anti-LPS response, and the results revealed that the IC9 Id is conserved in different species. The importance of an interspecies cross-reactive Id in the response to endotoxin and its relevance in vaccine development for septic shock are discussed.

Topics: Animals; Antibodies, Anti-Idiotypic; Antibodies, Monoclonal; Antibody Specificity; Bacterial Vaccines; Binding Sites, Antibody; Chickens; Cross Reactions; Immunization, Passive; Immunoglobulin Idiotypes; Lipid A; Lipopolysaccharides; Mice; Mice, Inbred Strains; Rabbits; Salmonella Infections, Animal; Salmonella typhimurium; Shock, Septic

We have earlier demonstrated that the C3H/HeJ Salmonella hypersusceptible mouse can be protected against infection with this organism by prior immunization with lipopolysaccharide (LPS)-lipid A-associated protein (LAP) complexes, but not with LPS alone. In the current studies, protection has been shown to correlate with the induction of LPS-specific antibody in immunized mice. LPS was demonstrated to be a relevant target antigen for Salmonella immunity since C3H/HeJ mice were afforded higher survival rates when they were challenged with Salmonella that shared the same LPS O-antigen as the vaccine. Although low levels of LPS-specific antibody can be detected 14 days after immunization with LAP-LPS, significant antibody is present only after 21-28 days. In addition, anti-LAP specific antibodies can be detected after 14 days of immunization with LAP-LPS. Adoptive transfer of either day 28 anti-LAP-LPS immune serum or day 28 LAP-LPS immune splenocytes alone to naive recipients affords mice minimal, if any, survival against lethal S. typhimurium LT2 challenge. In contrast, transfer of day 28 anti-LAP-LPS immune serum and day 28 LAP-LPS immune splenocytes together is able to transfer Salmonella immunity to naive C3H/HeJ mice. Further, equivalent transfer of only day 28 anti-LAP-LPS immune serum to C3H/HeJ mice immunized 7 days previously with LAP-LPS provides protection similar to that found in mice adoptively transferred with immune cells and serum. These results suggest that a host cellular factor or factors responsive to LAP-LPS, in addition to day 28 anti-LAP-LPS immune serum, may contribute to the protection afforded C3H/HeJ mice following immunization with LAP-LPS.

Topics: Animals; Immunity, Cellular; Immunization; Immunization, Passive; Immunoglobulin G; Immunoglobulin M; Lipid A; Lipopolysaccharides; Macrophages; Mice; Mice, Inbred C3H; Salmonella Infections, Animal; Spleen; T-Lymphocytes

The capacity of lipid A, a structure common to the lipopolysaccharide cores of all gram-negative bacteria, to serve as an active immunizing agent in mice and to protect these animals against gram-negative infections was investigated. Active immunization experiments were also performed with the Re mutant of Salmonella minnesota 595 which carries a lipopolysaccharide composed of lipid A and three residues of ketodeoxyoctonic acid. Single injections of lipid A complexed to acid-hydrolyzed bacteria as carriers failed to induce specific protection against subsequent challenge infections with E. coli O4 and S. breslau. Repeated injections of lipid A resulted in good protection against intraperitoneal challenge with S. breslau and partial protection against intravenous challenge with the same organism but did not alter the sensitivity of mice to challenge infections with E. coli or Pasteurella multocida. Whole antisera or serum fractions from rabbits in which high titers against lipid A had been attained by repeated intravenous injections of the antigen did not protect mice against challenge infections with E. coli O4. In contrast a single injection of the Re mutant of S. minnesota antigen in combination with incomplete Freund's adjuvant provided substantial protection against an otherwise lethal intraperitoneal infection with S. breslau over a period of at least 45 days. Repeated application of the Re antigen resulted in partial protection against experimental infections with E. coli O4, S. breslau and Pasteurella multocida. Injections of S. minnesota Re 595 antiserum provided better protection against an E. coli O4 infection than lipid A sera or antibodies of the IgG or IgM type directed against this antigen.

Topics: Animals; Antigens, Bacterial; Bacterial Infections; Escherichia coli Infections; Female; Freund's Adjuvant; Immunity, Active; Immunity, Maternally-Acquired; Immunization; Immunization, Passive; Lipid A; Lipopolysaccharides; Male; Mice; Pasteurella Infections; Rabbits; Salmonella; Salmonella Infections, Animal