CD4+ T Cells Targeting Dominant and Cryptic Epitopes from Bacillus anthracis Lethal Factor

Anthrax is an endemic infection in many countries, particularly in the developing world. The causative agent, Bacillus anthracis, mediates disease through the secretion of binary exotoxins. Until recently, research into adaptive immunity targeting this bacterial pathogen has largely focused on the humoral response to these toxins. There is, however, growing recognition that cellular immune responses involving IFNγ producing CD4+ T cells also contribute significantly to a protective memory response. An established concept in adaptive immunity to infection is that during infection of host cells, new microbial epitopes may be revealed, leading to immune recognition of so called 'cryptic' or 'subdominant' epitopes. We analyzed the response to both cryptic and immunodominant T cell epitopes derived from the toxin component lethal factor and presented by a range of HLA-DR alleles. Using IFNγ-ELISpot assays we characterized epitopes that elicited a response following immunization with synthetic peptide and the whole protein and tested their capacities to bind purified HLA-DR molecules in vitro. We found that DR1 transgenics demonstrated T cell responses to a greater number of domain III cryptic epitopes than other HLA-DR transgenics, and that this pattern was repeated with the immunodominant epitopes, as a greater proportion of these epitopes induced a T cell response when presented within the context of the whole protein. Immunodominant epitopes LF457-476 and LF467-487 were found to induce a T cell response to the peptide, as well as to the whole native LF protein in DR1 and DR15, but not in DR4 transgenics. The analysis of Domain I revealed the presence of several unique cryptic epitopes all of which showed a strong to moderate relative binding affinity to HLA-DR4 molecules. However, none of the cryptic epitopes from either domain III or I displayed notably high binding affinities across all HLA-DR alleles assayed. These responses were influenced by the specific HLA alleles presenting the peptide, and imply that construction of future epitope string vaccines which are immunogenic across a wide range of HLA alleles could benefit from a combination of both cryptic and immunodominant anthrax epitopes.

Structure of the adenylation domain of an NAD+-dependent DNA ligase

Background: DNA ligases catalyse phosphodiester bond formation between adjacent bases in nicked DNA, thereby sealing the nick. A key step in the catalytic mechanism is the formation of an adenylated DNA intermediate. The adenyl group is derived from either ATP (in eucaryotes and archaea) or NAD+4 (in bacteria). This difference in cofactor specificity suggests that DNA ligase may be a useful antibiotic target.

Results: The crystal structure of the adenylation domain of the NAD+-dependent DNA ligase from Bacillus stearothermophilus has been determined at 2.8 Å resolution. Despite a complete lack of detectable sequence similarity, the fold of the central core of this domain shares homology with the equivalent region of ATP-dependent DNA ligases, providing strong evidence for the location of the NAD+-binding site.

Conclusions: Comparison of the structure of the NAD+4-dependent DNA ligase with that of ATP-dependent ligases and mRNA-capping enzymes demonstrates the manifold utilisation of a conserved nucleotidyltransferase domain within this family of enzymes. Whilst this conserved core domain retains a common mode of nucleotide binding and activation, it is the additional domains at the N terminus and/or the C terminus that provide the alternative specificities and functionalities in the different members of this enzyme superfamily.

Quantitative surface-enhanced Raman spectroscopy of dipicolinic acid - towards rapid anthrax endospore detection

Dipicolinic acid (DPA) is an excellent marker compound for bacterial spores, including those of Bacillus anthracis ( anthrax). Surface-enhanced Raman spectroscopy (SERS) potentially has the sensitivity and discrimination needed for trace DPA analysis, but mixing DPA solutions with citrate-reduced silver colloid only yielded measurable SERS spectra at much higher (> 80 ppm) concentrations than would be desirable for anthrax detection. Aggregation of the colloid with halide salts eliminated even these small DPA bands but aggregation with Na2SO4(aq) resulted in a remarkable increase in the DPA signals. With sulfate aggregation even 1 ppm solutions gave detectable signals with 10 s accumulation times, which is in the sensitivity range required. Addition of CNS- as an internal standard allowed quantitative DPA analysis, plotting the intensity of the strong DPA 1010 cm(-1) band (normalised to the ca. 2120 cm(-1) CNS- band) against DPA concentration gave a linear calibration (R-2 = 0.986) over the range 0 - 50 ppm DPA. The inclusion of thiocyanate also allows false negatives due to accidental deactivation of the enhancing medium to be detected.

Biodegradation and biosorption of acid anthraquinone dye

The acid anthraquinone dye Tectilon Blue (TB4R) is a major coloured component from the aqueous effluent of a carpet printing plant in Northern Ireland. The aerobic biodegradation of TB4R has been investigated experimentally in batch systems, using three strains of bacteria, namely, Bacillus gordonae (NCIMB 12553), Bacillus benzeovorans (NCIMB 12555) and Pseudomonas putida (NCIMB 9776). All three strains successfully decolourised the dye, and results were correlated using Michaelis-Menten kinetic theory. A recalculation of the reaction rate constants, to account for biosorption, gave an accurate simulation of the colour removal over a 24-h period. Up to 19% of the decolorisation was found to be caused by biosorption of the dye onto the biomass, with the majority of the decolorisation caused by utilisation of the dye by the bacteria. The reaction rate was found to be intermediate between zero and first order at dye concentrations of 200-1000 mg/l. (C) 2000 Elsevier Science Ltd. All rights reserved.

Natural Exposure to Cutaneous Anthrax Gives Long-Lasting T Cell Immunity Encompassing Infection-Specific Epitopes

There has been a long history of defining T cell epitopes to track viral immunity and to design rational vaccines, yet few data of this type exist for bacterial infections. Bacillus anthracis, the causative agent of anthrax, is both an endemic pathogen in many regions and a potential biological warfare threat. T cell immunity in naturally infected anthrax patients has not previously been characterized, which is surprising given concern about the ability of anthrax toxins to subvert or ablate adaptive immunity. We investigated CD4 T cell responses in patients from the Kayseri region of Turkey who were previously infected with cutaneous anthrax. Responses to B. anthracis protective Ag and lethal factor (LF) were investigated at the protein, domain, and epitope level. Several years after antibiotic-treated anthrax infection, strong T cell memory was detectable, with no evidence of the expected impairment in specific immunity. Although serological responses to existing anthrax vaccines focus primarily on protective Ag, the major target of T cell immunity in infected individuals and anthrax-vaccinated donors was LF, notably domain IV. Some of these anthrax epitopes showed broad binding to several HLA class alleles, but others were more constrained in their HLA binding patterns. Of specific CD4 T cell epitopes targeted within LF domain IV, one is preferentially seen in the context of bacterial infection, as opposed to vaccination, suggesting that studies of this type will be important in understanding how the human immune system confronts serious bacterial infection.

Can the protein costs of bacterial resistance be offset by altered feeding behaviour?

1. Mounting an immune response is likely to be costly in terms of energy and nutrients, and so it is predicted that dietary intake should change in response to infection to offset these costs. The present study focuses on the interactions between a specialist grass-feeding caterpillar species, the African armyworm Spodoptera exempta, and an opportunist bacterium, Bacillus subtilis.
2. The main aims of the study were (i) to establish the macronutrient costs to the insect host of surviving a systemic bacterial infection, (ii) to determine the relative importance of dietary protein and carbohydrate to immune system functions, and (iii) to determine whether there is an adaptive change in the host's normal feeding behaviour in response to bacterial challenge, such that the nutritional costs of resisting infection are offset.
3. We show that the survival of bacterially infected larvae increased with increasing dietary protein-to-carbohydrate (P:C) ratio, suggesting a protein cost associated with bacterial resistance. As dietary protein levels increased, there was an increase in antibacterial activity, phenoloxidase (PO) activity and protein levels in the haemolymph, providing a potential source for this protein cost. However, there was also evidence for a physiological trade-off between antibacterial activity and phenoloxidase activity, as larvae whose antibacterial activity levels were elevated in response to immune activation had reduced PO activity.
4. When given a choice between two diets varying in their P:C ratios, larvae injected with a sub-lethal dose of bacteria increased their protein intake relative to control larvae whilst maintaining similar carbohydrate intake levels. These results are consistent with the notion that S. exempta larvae alter their feeding behaviour in response to bacterial infection in a manner that is likely to enhance the levels of protein available for producing the immune system components and other factors required to resist bacterial infections (‘self-medication’).

A microtitre plate assay for the detection of antibiotics in porcine urine

Techniques for screening porcine samples for antimicrobial residues in the EU usually involve analysis of samples taken post slaughter, and are either time consuming or expensive. Some of the positive test results at this screening stage could be avoided by allowing the animal sufficient withdrawal time following drug treatment. A method is described that can detect the presence of five major antibiotics in porcine urine at concentrations below 1 mu g ml(-1) for each of the compounds. The test uses Bacillus subtilis, which is already widely employed in antimicrobial inhibition assays, and when combined with a colorimetric substrate, p-nitrophenyl-beta-D-glucopyranoside, can detect inhibitory substances within an assay time of four and a half hours. The method, which uses microtitre plate technology, could be developed into a convenient test kit for use at farm level to determine whether animals were still excreting antimicrobials in their urine prior to their submission for slaughter.

PHYSICAL FACTORS AFFECTING THE SPORICIDAL ACTIVITY OF CHLORHEXIDINE GLUCONATE

The effects of pH and indirect ultrasonication on the cidal activity of aqueous and alcoholic solutions of chlorhexidine gluconate against Bacillus subtilis spores were examined. At moderately elevated temperatures, increasing pH enhanced sporicidal activity. pH markedly enhanced the sporicidal activity between indirect ultrasound and chlorhexidine. 'Alcoholic' chlorhexidine gluconate was more sporicidal than its aqueous counterpart.

Application of atmospheric pressure nonthermal plasma for the in vitro eradication of bacterial biofilms

The use of atmospheric pressure nonthermal plasma represents an interesting and novel approach for the decontamination of surfaces colonized with microbial biofilms that exhibit enhanced tolerance to antimicrobial challenge. In this study, the influence of an atmospheric pressure nonthermal plasma jet, operated in a helium and oxygen gas mixture under ambient pressure, was evaluated against biofilms of Bacillus cereus,Staphylococcus aureus,Escherichia coli and Pseudomonas aeruginosa. Within <4 min of plasma exposure, complete eradication of the two Gram-positive bacterial biofilms was achieved. Although Gram-negative biofilms required longer treatment time, their complete eradication was still possible with 10 min of exposure. Whilst this study provides useful proof of concept data on the use of atmospheric pressure plasmas for the eradication of bacterial biofilms in vitro, it also demonstrates the critical need for improved understanding of the mechanisms and kinetics related to such a potentially significant approach. © 2012 Federation of European Microbiological Societies.

Characterization of SodC, a periplasmic superoxide dismutase from Burkholderia cenocepacia

Burkholderia cenocepacia is a gram-negative, non-spore-forming bacillus and a member of the Burkholderia cepacia complex. B. cenocepacia can survive intracellularly in phagocytic cells and can produce at least one superoxide dismutase (SOD). The inability of O2- to cross the cytoplasmic membrane, coupled with the periplasmic location of Cu,ZnSODs, suggests that periplasmic SODs protect bacteria from superoxide that has an exogenous origin (for example, when cells are faced with reactive oxygen intermediates generated by host cells in response to infection). In this study, we identified the sodC gene encoding a Cu,ZnSOD in B. cenocepacia and demonstrated that a sodC null mutant was not sensitive to a H2O2, 3-morpholinosydnonimine, or paraquat challenge but was killed by exogenous superoxide generated by the xanthine/xanthine oxidase method. The sodC mutant also exhibited a growth defect in liquid medium compared to the parental strain, which could be complemented in trans. The mutant was killed more rapidly than the parental strain was killed in murine macrophage-like cell line RAW 264.7, but killing was eliminated when macrophages were treated with an NADPH oxidase inhibitor. We also confirmed that SodC is periplasmic and identified the metal cofactor. B. cenocepacia SodC was resistant to inhibition by H2O2 and was unusually resistant to KCN for a Cu,ZnSOD. Together, these observations establish that B. cenocepacia produces a periplasmic Cu,ZnSOD that protects this bacterium from exogenously generated O2- and contributes to intracellular survival of this bacterium in macrophages.

A quorum-quenching approach to investigate the conservation of quorum-sensing-regulated functions within the Burkholderia cepacia complex

Taxonomic studies of the past few years have shown that the Burkholderia cepacia complex, a heterogeneous group of B. cepacia-like organisms, consists of at least nine species. B. cepacia complex strains are ubiquitously distributed in nature and have been used for biocontrol, bioremediation, and plant growth promotion purposes. At the same time, B. cepacia complex strains have emerged as important opportunistic pathogens of humans, particularly those with cystic fibrosis. All B. cepacia complex species investigated thus far use quorum-sensing (QS) systems that rely on N-acylhomoserine lactone (AHL) signal molecules to express certain functions, including the production of extracellular proteases, swarming motility, biofilm formation, and pathogenicity, in a population-density-dependent manner. In this study we constructed a broad-host-range plasmid that allowed the heterologous expression of the Bacillus sp. strain 240B1 AiiA lactonase, which hydrolyzes the lactone ring of various AHL signal molecules, in all described B. cepacia complex species. We show that expression of AiiA abolished or greatly reduced the accumulation of AHL molecules in the culture supernatants of all tested B. cepacia complex strains. Phenotypic characterization of wild-type and transgenic strains revealed that protease production, swarming motility, biofilm formation, and Caenorhabditis elegans killing efficiency was regulated by AHL in the large majority of strains investigated.

Anthrax lethal toxin and the induction of CD4 T cell immunity

Bacillus anthracis secretes exotoxins which act through several mechanisms including those that can subvert adaptive immunity with respect both to antigen presenting cell and T cell function. The combination of Protective Antigen (PA) and Lethal Factor (LF) forming Lethal Toxin (LT), acts within host cells to down-regulate the mitogen activated protein kinase (MAPK) signaling cascade. Until recently the MAPK kinases were the only known substrate for LT; over the past few years it has become evident that LT also cleaves Nlrp1, leading to inflammasome activation and macrophage death. The predicted downstream consequences of subverting these important cellular pathways are impaired antigen presentation and adaptive immunity. In contrast to this, recent work has indicated that robust memory T cell responses to B. anthracis antigens can be identified following natural anthrax infection. We discuss how LT affects the adaptive immune response and specifically the identification of B. anthracis epitopes that are both immunogenic and protective with the potential for inclusion in protein sub-unit based vaccines.

CHARACTERISATION OF THE HUMAN ANTIBODY RESPONSE TO THE UK ANTHRAX VACCINE

Potential Cellular Targets and Antibacterial Efficacy of Atmospheric Pressure Non-Thermal Plasma

Atmospheric pressure non-thermal plasma (APNTP) has been gaining increasing interest as a new alternative antibacterial approach. Although this approach has demonstrated promising antibacterial activity, its exact mechanism of action remains unclear. Mechanistic elucidation of the antimicrobial activity will facilitate development and rational optimisation of this approach for potential medical applications. In this study, the antibacterial efficacy of an in-house-built APNTP jet was evaluated alongside an investigation of the interactions between APNTP and major cellular components in order to identify the potential cellular targets involved in plasma-mediated bacterial destruction mechanisms. The investigated plasma jet exhibited excellent, rapid antibacterial activity against a selected panel of clinically significant bacterial species including Bacillus cereus, meticillin-resistant Staphylococcus aureus (MRSA), Escherichia coli and Pseudomonas aeruginosa, all of which were completely inactivated within 2 min of plasma exposure. Plasma-mediated damaging effects were observed, to varying degrees, on all of the investigated cellular components including DNA, a model protein enzyme, and lipid membrane integrity and permeability. The antibacterial efficacy of APNTP appears to involve a multiple-target mechanism, which potentially reduces the likelihood of emergence of microbial resistance towards this promising antimicrobial approach. However, cellular membrane damage and resulting permeability perturbation was found to be the most likely rate-determining step in this mechanism. Crown Copyright © 2013.

Anthrax Lethal Factor as an Immune Target in Humans and Transgenic Mice and the Impact of HLA Polymorphism on CD4+ T Cell Immunity

Bacillus anthracis produces a binary toxin composed of protective antigen (PA) and one of two subunits, lethal factor (LF) or edema factor (EF). Most studies have concentrated on induction of toxin-specific antibodies as the correlate of protective immunity, in contrast to which understanding of cellular immunity to these toxins and its impact on infection is limited. We characterized CD4+ T cell immunity to LF in a panel of humanized HLA-DR and DQ transgenic mice and in naturally exposed patients. As the variation in antigen presentation governed by HLA polymorphism has a major impact on protective immunity to specific epitopes, we examined relative binding affinities of LF peptides to purified HLA class II molecules, identifying those regions likely to be of broad applicability to human immune studies through their ability to bind multiple alleles. Transgenics differing only in their expression of human HLA class II alleles showed a marked hierarchy of immunity to LF. Immunogenicity in HLA transgenics was primarily restricted to epitopes from domains II and IV of LF and promiscuous, dominant epitopes, common to all HLA types, were identified in domain II. The relevance of this model was further demonstrated by the fact that a number of the immunodominant epitopes identified in mice were recognized by T cells from humans previously infected with cutaneous anthrax and from vaccinated individuals. The ability of the identified epitopes to confer protective immunity was demonstrated by lethal anthrax challenge of HLA transgenic mice immunized with a peptide subunit vaccine comprising the immunodominant epitopes that we identified.