Immune response to Yersinia outer proteins and other Yersinia pestis antigens after experimental plague infection in mice

Secretory System Components as Potential Prophylactic Targets for Bacterial Pathogens

Bacterial secretory systems are essential for virulence in human pathogens. The systems have become a target of alternative antibacterial strategies based on small molecules and antibodies. Strategies to use components of the systems to design prophylactics have been less publicized despite vaccines being the preferred solution to dealing with bacterial infections. In the current review, strategies to design vaccines against selected pathogens are presented and connected to the biology of the system. The examples are given for Y. pestis, S. enterica, B. anthracis, S. flexneri, and other human pathogens, and discussed in terms of effectiveness and long-term protection.

The Use of an Organo-Selenium Peptide to Develop New Antimicrobials That Target a Specific Bacteria

This study examines the use of a covalently selenium-bonded peptide and phage that binds to the Yersinia pestis F1 antigen for the targeting and killing of E. coli expressing this surface antigen. Using a Ph.D.-12 phage-display library for affinity selection of the phage which would bind the F1 antigen of Y. pestis, a phage displaying a peptide that binds the F1 antigen with high affinity and specificity was identified. Selenium was then covalently attached to the display phage and the corresponding F1-antigen-binding peptide. Both the phage and peptides with selenium covalently attached retained their binding specificity for the Y. pestis F1 antigen. The phage or peptide not labeled with selenium did not kill the targeted bacteria, while the phage or peptide labeled with selenium did. In addition, the seleno-peptide, expressing the F1 targeting sequence only, killed cells expressing the F1 antigen but not the parent strain that did not express the F1 antigen. Specifically, the seleno-peptide could kill eight logs of bacteria in less than two hours at a 10-µM concentration. These results demonstrate a novel approach for the development of an antibacterial agent that can target a specific bacterial pathogen for destruction through the use of covalently attached selenium and will not affect other bacteria.

Yersinia Outer Membrane Vesicles as Potential Vaccine Candidates in Protecting against Plague

Despite the relatively low incidence of plague, its etiological agent, Yersinia pestis, is an exceptional epidemic danger due to the high infectivity and mortality of this infectious disease. Reports on the isolation of drug-resistant Y. pestis strains indicate the advisability of using asymmetric responses, such as phage therapy and vaccine prophylaxis in the fight against this problem. The current relatively effective live plague vaccine is not approved for use in most countries because of its ability to cause heavy local and system reactions and even a generalized infectious process in people with a repressed immune status or metabolic disorders, as well as lethal infection in some species of nonhuman primates. Therefore, developing alternative vaccines is of high priority and importance. However, until now, work on the development of plague vaccines has mainly focused on screening for the potential immunogens. Several investigators have identified the protective potency of bacterial outer membrane vesicles (OMVs) as a promising basis for bacterial vaccine candidates. This review is aimed at presenting these candidates of plague vaccine and the results of their analysis in animal models.

Yersinia pestis Antigen F1 but Not LcrV Induced Humoral and Cellular Immune Responses in Humans Immunized with Live Plague Vaccine-Comparison of Immunoinformatic and Immunological Approaches

The recent progress in immunoinformatics provided the basis for an accelerated development of target-specific peptide vaccines as an alternative to the traditional vaccine concept. However, there is still limited information on whether the in silico predicted immunoreactive epitopes correspond to those obtained from the actual experiments. Here, humoral and cellular immune responses to two major Yersinia pestis protective antigens, F1 and LcrV, were studied in human donors immunized with the live plague vaccine (LPV) based on the attenuated Y. pestis strain EV line NIIEG. The F1 antigen provided modest specific cellular (mixed T helper 1 (Th1)/Th2 type) and humoral immune responses in vaccinees irrespective of the amount of annual vaccinations and duration of the post-vaccination period. The probing of the F1 overlapping peptide library with the F1-positive sera revealed the presence of seven linear B cell epitopes, which were all also predicted by in silico assay. The immunoinformatics study evaluated their antigenicity, toxicity, and allergenic properties. The epitope TSQDGNNH was mostly recognized by the sera from recently vaccinated donors rather than antibodies from those immunized decades ago, suggesting the usefulness of this peptide for differentiation between recent and long-term vaccinations. The in silico analysis predicted nine linear LcrV-specific B-cell epitopes; however, weak antibody and cellular immune responses prevented their experimental evaluation, indicating that LcrV is a poor marker of successful vaccination. No specific Th17 immune response to either F1 or LcrV was detected, and there were no detectable serum levels of F1-specific immunoglobulin A (IgA) in vaccinees. Overall, the general approach validated in the LPV model could be valuable for the rational design of vaccines against other neglected and novel emerging infections with high pandemic potency.

Yersinia pestis Plasminogen Activator

The Gram-negative bacterium Yersinia pestis causes plague, a fatal flea-borne anthropozoonosis, which can progress to aerosol-transmitted pneumonia. Y. pestis overcomes the innate immunity of its host thanks to many pathogenicity factors, including plasminogen activator, Pla. This factor is a broad-spectrum outer membrane protease also acting as adhesin and invasin. Y. pestis uses Pla adhesion and proteolytic capacity to manipulate the fibrinolytic cascade and immune system to produce bacteremia necessary for pathogen transmission via fleabite or aerosols. Because of microevolution, Y. pestis invasiveness has increased significantly after a single amino-acid substitution (I259T) in Pla of one of the oldest Y. pestis phylogenetic groups. This mutation caused a better ability to activate plasminogen. In paradox with its fibrinolytic activity, Pla cleaves and inactivates the tissue factor pathway inhibitor (TFPI), a key inhibitor of the coagulation cascade. This function in the plague remains enigmatic. Pla (or pla) had been used as a specific marker of Y. pestis, but its solitary detection is no longer valid as this gene is present in other species of Enterobacteriaceae. Though recovering hosts generate anti-Pla antibodies, Pla is not a good subunit vaccine. However, its deletion increases the safety of attenuated Y. pestis strains, providing a means to generate a safe live plague vaccine.

New Promising Targets for Synthetic Omptin-Based Peptide Vaccine against Gram-Negative Pathogens

Omptins represent a family of proteases commonly found in various Gram-negative pathogens. These proteins play an important role in host-pathogen interaction and have been recognized as key virulence factors, highlighting the possibility of developing an omptin-based broad-spectrum vaccine. The prototypical omptin, His-tagged recombinant Pla, was used as a model target antigen. In total, 46 linear and 24 conformational epitopes for the omptin family were predicted by the use of ElliPro service. Among these we selected highly conserved, antigenic, non-allergenic, and immunogenic B-cell epitopes. Five epitopes (2, 6, 8, 10, and 11 corresponding to Pla regions 52-60, 146-150, 231-234, 286-295, and 306-311, respectively) could be the first choice for the development of the new generation of target-peptide-based vaccine against plague. The partial residues of omptin epitopes 6, 8, and 10 (regions 136-145, 227-230, and 274-285) could be promising targets for the multi-pathogen vaccine against a group of enterobacterial infections. The comparative analysis and 3D modeling of amino acid sequences of several omptin family proteases, such as Pla (Yersinia pestis), PgtE (Salmonella enterica), SopA (Shigella flexneri), OmpT, and OmpP (Escherichia coli), confirmed their high cross-homology with respect to the identified epitope clusters and possible involvement of individual epitopes in host-pathogen interaction.

A Combined YopB and LcrV Subunit Vaccine Elicits Protective Immunity against Yersinia Infection in Adult and Infant Mice

Yersinia enterocolitica causes a severe enteric infection in infants and young children. There is no vaccine approved for use in humans. We investigated the immunogenicity and protective capacity of Yersinia YopB, a conserved type III secretion system protein, alone or combined with LcrV in adult mice immunized intranasally. YopB or LcrV (5 μg) administered with the Escherichia coli double mutant heat-labile toxin (dmLT) adjuvant afforded modest (10-30%) protection against lethal Y. enterocolitica oral infection. The combination of YopB and LcrV (5 μg each) dramatically improved vaccine efficacy (70-80%). Additionally, it afforded complete protection against Y. pestis pulmonary infection. Immunization with YopB/LcrV+dmLT resulted in Ag-specific serum IgG, systemic and mucosal Ab-secreting cells, as well as IFN-γ, TNF-α, IL-2, IL-6, IL-17A, and KC production by spleen cells. Serum Abs elicited by YopB/LcrV+dmLT had enhanced bactericidal and opsonophagocytic killing activity. After Y. enterocolitica challenge, YopB/LcrV+dmLT-vaccinated mice exhibited intact intestinal tissue, active germinal centers in mesenteric lymph nodes, IgG+ and IgA+ plasmablasts in the lamina propria, and Abs in intestinal fluid. On the contrary, complete tissue destruction and abscesses were seen in placebo recipients that succumbed to infection. Mice immunized as infants with YopB+dmLT or LcrV+dmLT achieved 60% protection against lethal Y. enterocolitica infection, and vaccine efficacy increased to 90-100% when they received YopB/LcrV+dmLT. YopB+dmLT also afforded substantial (60%) protection when administered intradermally to infant mice. YopB/LcrV+dmLT is a promising subunit vaccine candidate with the potential to elicit broad protection against Yersinia spp.

Humoral and cellular immune responses to Yersinia pestis Pla antigen in humans immunized with live plague vaccine

Background

To establish correlates of human immunity to the live plague vaccine (LPV), we analyzed parameters of cellular and antibody response to the plasminogen activator Pla of Y. pestis. This outer membrane protease is an essential virulence factor that is steadily expressed by Y. pestis.

Methodology/Principal findings

PBMCs and sera were obtained from a cohort of naïve (n = 17) and LPV-vaccinated (n = 34) donors. Anti-Pla antibodies of different classes and IgG subclasses were determined by ELISA and immunoblotting. The analysis of antibody response was complicated with a strong reactivity of Pla with normal human sera. The linear Pla B-cell epitopes were mapped using a library of 15-mer overlapping peptides. Twelve peptides that reacted specifically with sera of vaccinated donors were found together with a major cross-reacting peptide IPNISPDSFTVAAST located at the N-terminus. PBMCs were stimulated with recombinant Pla followed by proliferative analysis and cytokine profiling. The T-cell recall response was pronounced in vaccinees less than a year post-immunization, and became Th17-polarized over time after many rounds of vaccination.

Conclusions/Significance

The Pla protein can serve as a biomarker of successful vaccination with LPV. The diagnostic use of Pla will require elimination of cross-reactive parts of the antigen.

Yersinia pestis, the causative agent of plague, has been recognized as one of the most devastating pathogen experienced by mankind. It remains endemic in many parts of the world, and is considered emerging pathogen. A live attenuated Y. pestis strain EV line NIIEG has been used for decades in the former Soviet Union for human vaccination and has proven effective against all forms of plague. We began characterizing the Y. pestis-specific antibody and T cell-mediated immune responses in people immunized with live plague vaccine. The long term goal of our research is to understand the protective mechanisms underlying immunity to plague in humans and to discover novel protective antigens for their incorporation into a subunit vaccine. Here, we describe our study on immune responses in vaccinees to one of the essential virulence factors of Y. pestis, namely Pla antigen. The results of the study shed light on the development of the optimal markers to assess the correlation with vaccine-induced protection.

A Replication-Defective Human Type 5 Adenovirus-Based Trivalent Vaccine Confers Complete Protection against Plague in Mice and Nonhuman Primates

Currently, no plague vaccine exists in the United States for human use. The capsular antigen (Caf1 or F1) and two type 3 secretion system (T3SS) components, the low-calcium-response V antigen (LcrV) and the needle protein YscF, represent protective antigens of Yersinia pestis We used a replication-defective human type 5 adenovirus (Ad5) vector and constructed recombinant monovalent and trivalent vaccines (rAd5-LcrV and rAd5-YFV) that expressed either the codon-optimized lcrV or the fusion gene designated YFV (consisting of ycsF, caf1, and lcrV). Immunization of mice with the trivalent rAd5-YFV vaccine by either the intramuscular (i.m.) or the intranasal (i.n.) route provided protection superior to that with the monovalent rAd5-LcrV vaccine against bubonic and pneumonic plague when animals were challenged with Y. pestis CO92. Preexisting adenoviral immunity did not diminish the protective response, and the protection was always higher when mice were administered one i.n. dose of the trivalent vaccine (priming) followed by a single i.m. booster dose of the purified YFV antigen. Immunization of cynomolgus macaques with the trivalent rAd5-YFV vaccine by the prime-boost strategy provided 100% protection against a stringent aerosol challenge dose of CO92 to animals that had preexisting adenoviral immunity. The vaccinated and challenged macaques had no signs of disease, and the invading pathogen rapidly cleared with no histopathological lesions. This is the first report showing the efficacy of an adenovirus-vectored trivalent vaccine against pneumonic plague in mouse and nonhuman primate (NHP) models.

Expression and Association of the Yersinia pestis Translocon Proteins, YopB and YopD, Are Facilitated by Nanolipoprotein Particles

Yersinia pestis enters host cells and evades host defenses, in part, through interactions between Yersinia pestis proteins and host membranes. One such interaction is through the type III secretion system, which uses a highly conserved and ordered complex for Yersinia pestis outer membrane effector protein translocation called the injectisome. The portion of the injectisome that interacts directly with host cell membranes is referred to as the translocon. The translocon is believed to form a pore allowing effector molecules to enter host cells. To facilitate mechanistic studies of the translocon, we have developed a cell-free approach for expressing translocon pore proteins as a complex supported in a bilayer membrane mimetic nano-scaffold known as a nanolipoprotein particle (NLP) Initial results show cell-free expression of Yersinia pestis outer membrane proteins YopB and YopD was enhanced in the presence of liposomes. However, these complexes tended to aggregate and precipitate. With the addition of co-expressed (NLP) forming components, the YopB and/or YopD complex was rendered soluble, increasing the yield of protein for biophysical studies. Biophysical methods such as Atomic Force Microscopy and Fluorescence Correlation Spectroscopy were used to confirm that the soluble YopB/D complex was associated with NLPs. An interaction between the YopB/D complex and NLP was validated by immunoprecipitation. The YopB/D translocon complex embedded in a NLP provides a platform for protein interaction studies between pathogen and host proteins. These studies will help elucidate the poorly understood mechanism which enables this pathogen to inject effector proteins into host cells, thus evading host defenses.

Plague Vaccines: Status and Future

Three major plague pandemics caused by the gram-negative bacterium Yersinia pestis have killed nearly 200 million people in human history. Due to its extreme virulence and the ease of its transmission, Y. pestis has been used purposefully for biowarfare in the past. Currently, plague epidemics are still breaking out sporadically in most of parts of the world, including the United States. Approximately 2000 cases of plague are reported each year to the World Health Organization. However, the potential use of the bacteria in modern times as an agent of bioterrorism and the emergence of a Y. pestis strain resistant to eight antibiotics bring out severe public health concerns. Therefore, prophylactic vaccination against this disease holds the brightest prospect for its long-term prevention. Here, we summarize the progress of the current vaccine development for counteracting plague.

Immunization with a DNA adenine methylase over-producing Yersinia pseudotuberculosis vaccine confers robust cross-protection against heterologous pathogenic serotypes

Yersinia pseudotuberculosis is a foodborne pathogen that can cause serious human illness. Although the source and route of transmission often remain obscure, livestock have been implicated in some cases. The diversity of yersiniae present on farms and their widespread distribution in animal and environmental reservoirs necessitates the use of broad prophylactic strategies that are efficacious against many serotypes simultaneously. Herein, immunization of mice with a modified, live attenuated Y. pseudotuberculosis vaccine that overproduces the DNA adenine methylase (Dam(OP)) conferred robust protection against virulent challenge (150-fold LD50) with homologous and heterologous serotypes that have been associated with human disease (O:1, O:1a, O:3). Further, the dam gene was shown to be essential for cell viability in all (7 of 7) Y. pseudotuberculosis strains tested. Direct selection for the inheritance of dam mutant alleles in Y. pseudotuberculosis resulted in dam strain variants that contained compensatory (second-site suppressor) mutations in genes encoding methyl-directed mismatch repair proteins (mutHLS) that are involved in suppression of the non-viable cell phenotype in all (19/19) strains tested. Such dam mutH variants exhibited a significant increase in virulence and spontaneous mutation frequency relative to that of a Dam(OP) vaccine strain. These studies indicate that Y. pseudotuberculosis Dam(OP) strains conferred potent cross-protective efficacy as well as decreased virulence and spontaneous mutation frequency relative to those that lack Dam, which have compensatory mutations in mutHLS loci. These data suggest that development of yersiniae livestock vaccines based on Dam overproduction is a viable mitigation strategy to reduce these potential foodborne contaminants.

Protecting against plague: towards a next-generation vaccine

The causative organism of plague is the bacterium Yersinia pestis. Advances in understanding the complex pathogenesis of plague infection have led to the identification of the F1- and V-antigens as key components of a next-generation vaccine for plague, which have the potential to be effective against all forms of the disease. Here we review the roles of F1- and V-antigens in the context of the range of virulence mechanisms deployed by Y. pestis, in order to develop a greater understanding of the protective immune responses required to protect against plague.

LcrV mutants that abolish Yersinia type III injectisome function

LcrV, the type III needle cap protein of pathogenic Yersinia, has been proposed to function as a tether between YscF, the needle protein, and YopB-YopD to constitute the injectisome, a conduit for the translocation of effector proteins into host cells. Further, insertion of LcrV-capped needles from a calcium-rich environment into host cells may trigger the low-calcium signal for effector translocation. Here, we used a genetic approach to test the hypothesis that the needle cap responds to the low-calcium signal by promoting injectisome assembly. Growth restriction of Yersinia pestis in the absence of calcium (low-calcium response [LCR(+)] phenotype) was exploited to isolate dominant negative lcrV alleles with missense mutations in its amber stop codon (lcrV(*327)). The addition of at least four amino acids or the eight-residue Strep tag to the C terminus was sufficient to generate an LCR(-) phenotype, with variant LcrV capping type III needles that cannot assemble the YopD injectisome component. The C-terminal Strep tag appears buried within the cap structure, blocking effector transport even in Y. pestis yscF variants that are otherwise calcium blind, a constitutive type III secretion phenotype. Thus, LcrV(*327) mutants arrest the needle cap in a state in which it cannot respond to the low-calcium signal with either injectisome assembly or the activation of type III secretion. Insertion of the Strep tag at other positions of LcrV produced variants with wild-type LCR(+), LCR(-), or dominant negative LCR(-) phenotypes, thereby allowing us to identify discrete sites within LcrV as essential for its attributes as a secretion substrate, needle cap, and injectisome assembly factor.

Detection and Isolation of Yersinia pestis Without Fraction 1 Antigen by Monoclonal Antibody in Foods and Water

Most available immunoassays for Yersinia pestis are based on the detection of fraction 1 antigen (F1) when yersiniae are grown at 37°C. A monoclonal antibody (MAb) was developed based on the detection of surface antigens that are not F1. F1-deficient Y. pestis cells were induced and used to immunize BALB/c mice from which MAb (immunoglobulin G1), which specifically recognizes Y. pestis, with or without F1, was obtained. This MAb (6B5) did not cross-react with enteric bacteria, including Yersinia enterocolitica. Enzyme-linked immunosorbent assay results revealed that MAb 6B5 is specific for Y. pestis, with the exception of a minor cross-reaction with Yersinia pseudotuberculosis. Western immunoblot analysis revealed that MAb 6B5 recognizes a Y. pestis outer membrane protein of ca. 30 kDa. Magnetic beads that were coated with MAb 6B5 were compared with beads coated with polyclonal antibody (PAb; rabbit) against Y. pestis for the isolation of Y. pestis in food and water samples by using a PATHATRIX cell concentration apparatus. Enrichment cultures of Y. pestis in different foods by using two different times (6 and 24 h) in brain heart infusion broth at 37°C were evaluated. Results revealed MAb 6B5–coated magnetic beads were equivalent to magnetic beads coated with PAb against Y. pestis A1122 whole cells in concentrating Y. pestis for isolation, especially when samples were enriched for 6 h. However, the selectivity for Y. pestis of the magnetic beads coated with MAb 6B5 was greater than that coated with PAb.

Immune responses to plague infection in wild Rattus rattus, in Madagascar: a role in foci persistence?

Background

Plague is endemic within the central highlands of Madagascar, where its main reservoir is the black rat, Rattus rattus. Typically this species is considered susceptible to plague, rapidly dying after infection inducing the spread of infected fleas and, therefore, dissemination of the disease to humans. However, persistence of transmission foci in the same area from year to year, supposes mechanisms of maintenance among which rat immune responses could play a major role. Immunity against plague and subsequent rat survival could play an important role in the stabilization of the foci. In this study, we aimed to investigate serological responses to plague in wild black rats from endemic areas of Madagascar. In addition, we evaluate the use of a recently developed rapid serological diagnostic test to investigate the immune response of potential reservoir hosts in plague foci.

Methodology/Principal Findings

We experimentally infected wild rats with Yersinia pestis to investigate short and long-term antibody responses. Anti-F1 IgM and IgG were detected to evaluate this antibody response. High levels of anti-F1 IgM and IgG were found in rats one and three weeks respectively after challenge, with responses greatly differing between villages. Plateau in anti-F1 IgM and IgG responses were reached for as few as 500 and 1500 colony forming units (cfu) inoculated respectively. More than 10% of rats were able to maintain anti-F1 responses for more than one year. This anti-F1 response was conveniently followed using dipsticks.

Conclusion/Significance

Inoculation of very few bacteria is sufficient to induce high immune response in wild rats, allowing their survival after infection. A great heterogeneity of rat immune responses was found within and between villages which could heavily impact on plague epidemiology. In addition, results indicate that, in the field, anti-F1 dipsticks are efficient to investigate plague outbreaks several months after transmission.

A novel post-exposure medical countermeasure L-97-1 improves survival and acute lung injury following intratracheal infection with Yersinia pestis

Yersinia pestis, a Gram-negative bacillus causing plague and Centers for Disease Control and Prevention (CDC) classified Category A pathogen, has high potential as a bioweapon. Lipopolysaccharide, a virulence factor for Y. pestis, binds to and activates A(1) adenosine receptor (AR)s and, in animals, A(1)AR antagonists block induced acute lung injury (ALI) and increase survival following cecal ligation and perforation. In this study, rats were infected intratracheally with viable Y. pestis [CO99 (pCD1( + )/Δpgm) 1 × 10( 8 ) CFU/animal] and treated daily for 3 d with ciprofloxacin (cipro), the A(1)AR antagonist L-97-1, or cipro plus L-97-1 starting at 0, 6, 24, 48, or 72 h post-Y. pestis. At 72 h post-Y. pestis, cipro plus L-97-1 significantly improved 6-d survival to 60-70% vs 28% for cipro plus H(2)O and 33% for untreated Y. pestis controls (P = 0.02, logrank test). Lung edema, hemorrhage and leukocyte infiltration index (LII) were evaluated histologically to produce ALI scores. Cipro plus L-97-1 significantly reduced lung edema, as well as aggregate lung injury scores vs controls or cipro plus H(2)O, and LII vs controls (P < 0.05, Student's unpaired t test). These results support efficacy for L-97-1 as a post-exposure medical countermeasure, adjunctive therapy to antibiotics for Y. pestis.

A Yersinia pestis YscN ATPase mutant functions as a live attenuated vaccine against bubonic plague in mice

Yersinia pestis is the causative agent responsible for bubonic and pneumonic plague. The bacterium uses the pLcr plasmid-encoded type III secretion system to deliver virulence factors into host cells. Delivery requires ATP hydrolysis by the YscN ATPase encoded by the yscN gene also on pLcr. A yscN mutant was constructed in the fully virulent CO92 strain containing a nonpolar, in-frame internal deletion within the gene. We demonstrate that CO92 with a yscN mutation was not able to secrete the LcrV protein (V-Antigen) and attenuated in a subcutaneous model of plague demonstrating that the YscN ATPase was essential for virulence. However, if the yscN mutant was complemented with a functional yscN gene in trans, virulence was restored. To evaluate the mutant as a live vaccine, Swiss-Webster mice were vaccinated twice with the ΔyscN mutant at varying doses and were protected against bubonic plague in a dose-dependent manner. Antibodies to F1 capsule but not to LcrV were detected in sera from the vaccinated mice. These preliminary results suggest a proof-of-concept for an attenuated, genetically engineered, live vaccine effective against bubonic plague.

The natural history and incidence of Yersinia pestis and prospects for vaccination

Plague is an ancient, serious, infectious disease which is still endemic in regions of the modern world and is a potential biothreat agent. This paper discusses the natural history of the bacterium and its evolution into a flea-vectored bacterium able to transmit bubonic plague. It reviews the incidence of plague in the modern world and charts the history of vaccines which have been used to protect against the flea-vectored disease, which erupts as bubonic plague. Current approaches to vaccine development to protect against pneumonic, as well as bubonic, plague are also reviewed. The considerable challenges in achieving a vaccine which is licensed for human use and which will comprehensively protect against this serious human pathogen are assessed.

Humoral and cellular immune responses to Yersinia pestis infection in long-term recovered plague patients

Plague is one of the most dangerous diseases and is caused by Yersinia pestis. Effective vaccine development requires understanding of immune protective mechanisms against the bacterium in humans. In this study, the humoral and memory cellular immune responses in plague patients (n = 65) recovered from Y. pestis infection during the past 16 years were investigated using a protein microarray and an enzyme-linked immunosorbent spot assay (ELISpot). The seroprevalence to the F1 antigen in all recovered patients is 78.5%. In patients infected more than a decade ago, the antibody-positive rate still remains 69.5%. There is no difference in the antibody presence between gender, age, and infected years, but it seems to be associated with the F1 antibody titers during infection (r = 0.821; P < 0.05). Except F1 antibody, the antibodies against LcrV and YopD were detected in most of the patients, suggesting they could be the potential diagnostic markers for detecting the infection of F1-negative strains. Regarding cellular immunity, the cell number producing gamma interferon (IFN-γ), stimulated by F1 and LcrV, respectively, in vitro to the peripheral blood mononuclear cells of 7 plague patients and 4 negative controls, showed no significant difference, indicating F1 and LcrV are not dominant T cell antigens against plague for a longer time in humans. Our findings have direct implications for the future design and development of effective vaccines against Y. pestis infection and the development of new target-based diagnostics.

[Immunobiological properties of Yersinia pestis antigens]

The present review contains information concerning immunobiological properties of plague microbe antigens. All of the identified antigens are evaluated in relation to pathogenicity of Yersinia pestis namely a resistance to phagocytosis, toxicity, adhesiveness etc. as well as persistence ability and adaptation to variable environment. In addition, the role of antigens in immunogenicity of living plague microbe for experimental animals is considered. The data concerning mechanisms of antigenic contribution to the development of adaptive immunity are presented.

Use of protein microarray to identify gene expression changes ofYersinia pestisat different temperatures

Yersinia pestis is a bacterium that is transmitted between fleas, which have a body temperature of 26 °C, and mammalian hosts, which have a body temperature of 37 °C. To adapt to the temperature shift, phenotype variations, including virulence, occur. In this study, an antigen microarray including 218 proteins of Y. pestis was used to evaluate antibody responses in a pooled plague serum that was unadsorbed, adsorbed by Y. pestis cultivated at 26 °C, or adsorbed by Y. pestis cultivated at 26 and 37 °C to identify protein expression changes during the temperature shift. We identified 12 proteins as being expressed at 37 °C but not at 26 °C, or expressed at significantly higher levels at 37 °C than at 26 °C. The antibodies against 7 proteins in the serum adsorbed by Y. pestis cultivated at 26 and 37 °C remained positive, suggesting that they were not expressed on the surface of Y. pestis in LB broth in vitro or specifically expressed in vivo. This study proved that protein microarray and antibody profiling comprise a promising technique for monitoring gene expression at the protein level and for better understanding pathogenicity, to find new vaccine targets against plague.

Transgenic carrot tap roots expressing an immunogenic F1-V fusion protein from Yersinia pestis are immunogenic in mice

Expression of the protective F1 and V antigens of Yersinia pestis, as a fusion protein, in carrot was pursued in an effort to develop an alternative vaccine production system against the serious plague disease. Transgenic carrot plants carrying the F1-V encoding gene were developed via Agrobacterium-mediated transformation. Presence, integration, and expression of the F1-V encoding gene were confirmed by polymerase chain reaction (PCR), DNA gel blot analysis, and reverse-transcriptase (RT)-PCR analyses, respectively. An ELISA assay confirmed the antigenicity of the plant-derived F1-V fusion protein. Immunogenicity was evaluated subcutaneously in mice using a soluble protein extract of freeze-dried transgenic carrot. Significant antibody levels were detected following immunization. These results demonstrated that the F1-V protein could be expressed in carrot tap roots, and that the carrot F1-V recombinant protein retained its antigenicity and immunogenicity.

The many faces of the YopM effector from plague causative bacterium Yersinia pestis and its implications for host immune modulation

The Yersinia outer protein (Yop) M effector from the Yersinia pestis bacterium is well-known for being a critical virulence determinant; however, structural insight vis-à-vis its role in Y. pestis pathogenesis has been elusive. Here, we investigate the intact sequence of the YopM protein through our recently developed fold identification and homology modeling tools, and analyze the immune modulatory potential of its constituent domains. We identify a putative novel E3 ligase (NEL) domain towards the C-terminal tail of YopM and characterize its active site, to show that YopM could function as an autoregulated bacterial type E3 ubiquitin ligase. We further identify unreported NEL domains in several other bacteria and note remarkable similarity in sequence, structure, surface, and electrostatics for the family of NEL-containing bacterial effectors that suggests conserved function and potentially similar host targets for these proteins. Based on these observations and recent empirical evidence for degradation of the human proteins HLA-DR, thioredoxin, and NEMO/IKKγ by other members of the NEL-containing bacterial family, we discuss the potential for YopM to modulate a wide spectrum of immune signal transduction pathways. The key immune modulatory effects highlighted are suppression of MHC class II antigen presentation, dampening of nuclear factor (NF)-κB mediated inflammatory response, and intonation of mitogen-activated protein kinase (MAPK) signaling. Additionally, our analysis of the modeled YopM LRR domain reveals structural features akin to the Toll-like receptor 4 (TLR4) LRR motif. We propose that YopM LRR could be a 'molecular mimic' of TLR4 LRR, permitting reduced immunogenicity and potentially mitigating bacterial lipopolysaccharide surveillance of the innate immune system. Our identification and characterization of the YopM NEL domain, taken together with our analysis of the YopM LRR domain, provides plausible insight into subversion of host immunity by Y. pestis YopM and perhaps could set the stage for design of new therapeutic opportunities.

Efficacy and safety of a modified vaccinia Ankara (MVA) vectored plague vaccine in mice

The efficacy and safety of plague vaccines based on the modified vaccinia Ankara (MVA) viral vector was evaluated. MVA recombinants were constructed expressing Yersinia pestis antigens under the translational control of the encephalomyocarditis virus (EMCV) internal ribosomal entry site (IRES) and/or fused to the tissue plasminogen activator (tPA) secretory signal. A MVA/Y. pestis recombinant that expressed a truncated version of the low-calcium response V antigen (MVA/IRES/tPA/V(307)), conferred significant protection (87.5-100%) against intranasal or intraperitoneal challenge with CO92 (encapsulated) or Java 9 (non-encapsulated) strains of Y. pestis, respectively. In contrast, a MVA/Y. pestis recombinant that expressed the full-length V antigen provided only 37.5% protection against challenge with CO92 or Java 9 strains, respectively. Interestingly, a MVA/Y. pestis recombinant that expressed the capsular protein (F1) did not elicit significant antibody titers but still conferred 50% and 25% protection against CO92 or Java 9 challenge, respectively. The MVA/Y. pestis recombinant viruses did not demonstrate any mortality or morbidity in SCID mice. Based on their safety and efficacy in mice, these MVA/Y. pestis recombinants are candidates for further development as biodefense and public health vaccines.

Protection against pneumonic plague following oral immunization with a non-replicating vaccine

Yersinia pestis is a dangerous bacterial pathogen that when inhaled can rapidly induce fatal pneumonic plague. Thus, there is a need for stable, safe, and easily administered mucosal vaccines capable of eliciting effective protection against pulmonary Y. pestis infections. Cationic liposome-nucleic acid complexes (CLDC) have been shown previously to be effective vaccine adjuvants for parenteral immunization, but have not been previously evaluated for use in oral immunization. Therefore, we investigated the ability of an orally administered CLDC adjuvanted vaccine to elicit protective immunity against lethal pneumonic plague. C57Bl/6 mice were vaccinated orally or subcutaneously using 10mug Y. pestis F1 antigen combined with CLDC and immune responses and protection from challenge was assessed. We found that oral immunization elicited high titers of anti-F1 antibodies, equivalent to those generated by parenteral immunization. Importantly, orally immunized mice were protected from lethal pulmonary challenge with virulent Y. pestis for up to 18 weeks following vaccination. Vaccine-induced protection following oral immunization was found to be dependent primarily on CD4+ T cells, with a partial contribution from CD8+ T cells. Thus, CLDC adjuvanted vaccines represent a new type of orally administered, non-replicating vaccine capable of generating effective protection against pulmonary infection with virulent Y. pestis.

Establishing Efficacy of Human Products Using Animals

In 2002, the US Food and Drug Administration issued regulations to allow the approval of human drugs and biological products based on animal efficacy studies when human efficacy studies would be unethical or not feasible. These regulations are intended to assist in the approval process for products aimed at preventing or treating human diseases caused by nuclear, radiological, biological, and chemical agents that have the potential to harm a significant percentage of the US population. This article discusses the criteria that must be met to use the Animal Rule to demonstrate efficacy in place of human clinical trials.

Prospects for new plague vaccines

The potential application of Yersinia pestis for bioterrorism emphasizes the urgent need to develop more effective vaccines against airborne infection. The current status of plague vaccines has been reviewed. The present emphasis is on subunit vaccines based on the F1 and LcrV antigens. These provide good protection in animal models but may not protect against F1 strains with modifications to the type III secretion system. The duration of protection against pneumonic infection is also uncertain. Other strategies under investigation include defined live-attenuated vaccines, DNA vaccines, mucosal delivery systems and heterologous immunization. The live-attenuated strain Y. pestis EV NIIEG protects against aerosol challenge in animal models and, with further modification to reduce residual virulence and to optimize respiratory protection, it could provide a shortcut to improved vaccines. The regulatory problems inherent in licensing vaccines for which efficacy data are unavailable and their possible solutions are discussed herein.

The smpB-ssrA mutant of Yersinia pestis functions as a live attenuated vaccine to protect mice against pulmonary plague infection

The bacterial SmpB-SsrA system is a highly conserved translational quality control mechanism that helps maintain the translational machinery at full capacity. Here we present evidence to demonstrate that the smpB-ssrA genes are required for pathogenesis of Yersinia pestis, the causative agent of plague. We found that disruption of the smpB-ssrA genes leads to reduction in secretion of the type III secretion-related proteins YopB, YopD, and LcrV, which are essential for virulence. Consistent with these observations, the smpB-ssrA mutant of Y. pestis was severely attenuated in a mouse model of infection via both the intranasal and intravenous routes. Most significantly, intranasal vaccination of mice with the smpB-ssrA mutant strain of Y. pestis induced a strong antibody response. The vaccinated animals were well protected against subsequent lethal intranasal challenges with virulent Y. pestis. Taken together, our results indicate that the smpB-ssrA mutant of Y. pestis possesses the desired qualities for a live attenuated cell-based vaccine against pneumonic plague.

Identification of in vivo-induced conserved sequences from Yersinia pestis during experimental plague infection in the rabbit

In an effort to identify the novel virulence determinants of Yersinia pestis, we applied the gene "discovery" methodology, in vivo-induced (IVI) antigen technology, to detect genes upregulated during infection in a laboratory rabbit model for bubonic plague. After screening over 70,000 Escherichia coli clones of Y. pestis DNA expression libraries, products from 25 loci were identified as being seroreactive to reductively adsorbed, pooled immune serum. Upon sequence analysis of the predicted IVI gene products, more frequently encountered conserved protein functional categories have emerged, to include type-V autotransporters and components of more complex secretion systems including types III and VI. The recombinant products from eight selected clones were subsequently immunoblotted against pooled immune serum from two naturally infected host species: the prairie dog, and a species refractory to lethal disease, the coyote. Immune prairie dog serum recognized 2-3 of the rabbit-reactive antigens, suggesting at least some overlap in the pathogen's in vivo survival mechanisms between these two hosts. Although the coyote serum failed to recognize most of the IVI antigens, LepA was universally reactive with all three host sera. Collectively, the profiles/patterns of IVI conserved sequences (IVICS) may represent immune "signatures" among different host species, possessing the potential for use as a diagnostic tool for plague. Further, the antigenic nature of IVICS makes them ideal for further evaluation as novel subunit vaccine candidates. The gathering of additional data and analysis of the intact IVI genes and the expressed IVICS products should provide insight into the unique biologic processes of Y. pestis during infection and reveal the genetic patterns of the pathogen's survival strategy in different hosts.

Plague

Killed whole cell vaccines for plague were first produced as long ago as the late 1890s and modified versions of these are still used, with evidence that they are efficacious against bubonic plague. Renewed efforts with modern technology have yielded new candidate vaccines which are less reactogenic, can be produced in a conventional pharmaceutical manufacturing plant and are protective against the life-threatening pneumonic form of the disease. This paper reviews the progress towards an improved vaccine for plague and assesses the likely impact of a prophylactic vaccine for bubonic and pneumonic plague.

High-throughput identification of new protective antigens from a Yersinia pestis live vaccine by enzyme-linked immunospot assay

Yersinia pestis, the plague pathogen, is a facultative intracellular bacterium. Cellular immunity plays important roles in defense against infections. The identification of T-cell targets is critical for the development of effective vaccines against intracellular bacteria; however, the function of cellular immunity in protection from plague was not clearly understood. In this study, 261 genes from Y. pestis were selected on the basis of bioinformatics analysis and previous research results for expression in Escherichia coli BL21(DE3). After purification, 101 proteins were qualified for examination of their abilities to induce the production of gamma interferon in mice immunized with live vaccine EV76 by enzyme-linked immunospot assay. Thirty-four proteins were found to stimulate strong T-cell responses. The protective efficiencies for 24 of them were preliminarily evaluated using a mouse plague model. In addition to LcrV, nine proteins (YPO0606, YPO1914, YPO0612, YPO3119, YPO3047, YPO1377, YPCD1.05c, YPO0420, and YPO3720) may provide partial protection against challenge with a low dose (20 times the 50% lethal dose [20x LD(50)]) of Y. pestis, but only YPO0606 could partially protect mice from infection with Y. pestis at a higher challenge dosage (200x LD(50)). These proteins would be the potential components for Y. pestis vaccine development.

Transcriptional profiling of a mice plague model: insights into interaction between Yersinia pestis and its host

Despite the importance of pneumonic plague caused by Yersinia pestis, a few is known about the interaction between Y. pestis and its host at the molecular level during the pneumonic plague development. In this study, we employed an intranasally challenged plague model in mice for investigating the kinetics of the disease progression by transcriptional profiling of Y. pestis and mice using qRT-PCR and microarray, respectively. The increasing transcription of important virulence genes of Y. pestis and of mice genes involving in immune and inflammatory defensive responses, and responses to stimuli, presents an overview of interaction between Y. pestis and mice during development of pneumonic plague. The early and persisting up-regulation of caf 1, psa A and lcr V in vivo indicated their role in resisting the host innate immune responses. The up-regulation of fur, ybt A and hms H in vivo reflected the ability of Y. pestis for acquiring iron. The transcription regulators, including pho P, oxy R and omp R, were up-regulated during plague development, suggesting their roles in interaction between Y. pestis and mice. Many genes encoding cytokines, such as IL2, IL-1B, CXCL2, CXCL5, CCL20, CD14 and TNFRSF13B, were up-regulated during the infection, confirming the report that they are important mediators to activate host responses to invading pathogens. The up-regulation of some genes encoding important virulent factors of Y. pestis and expression alterations of some genes encoding cytokines in the host reflect the interaction between the pathogen and the host, which will help us better understand plague pathogenesis.

Vapour-phase hydrogen peroxide inactivates Yersinia pestis dried on polymers, steel, and glass surfaces

AIMS

This study evaluated the inactivation of virulent Yersinia pestis dried on polymers, steel, and glass surfaces using vapour-phase hydrogen peroxide.

METHODS AND RESULTS

A suspension of Y. pestis CO92 (1.70 x 10(8) CFU) was dried on 10 different types of test surfaces and exposed to vapour-phase hydrogen peroxide fumigation for a contact time of 2 h. A significant reduction in the log10 CFU of Y. pestis on all 10 materials was observed between the controls evaluated after a 1 h drying time and unexposed controls evaluated after the decontamination run. Qualitative growth assessment showed that vapour-phase hydrogen peroxide exposure inactivated Y. pestis on all replicates of the 10 test materials as well as biological indicators up to 7 days postexposure.

CONCLUSIONS

Virulent Y. pestis CO92 is inactivated on polymers, steel, and glass surfaces when exposed to vapour-phase hydrogen peroxide without observable physical damage to the test materials.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study provides information for using vapour-phase hydrogen peroxide as a practical process for the decontamination of virulent Y. pestis in circumstances where time-dependent attenuation/inactivation orliquid/heat decontamination may not be the most suitable approach.

Single-dose, virus-vectored vaccine protection against Yersinia pestis challenge: CD4+ cells are required at the time of challenge for optimal protection

We have developed an experimental recombinant vesicular stomatitis virus (VSV) vectored plague vaccine expressing a secreted form of Yersinia pestis low calcium response protein V (LcrV) from the first position of the VSV genome. This vector, given intramuscularly in a single dose, induced high-level antibody titers to LcrV and gave 90-100% protection against pneumonic plague challenge in mice. This single-dose protection was significantly better than that generated by VSV expressing the non-secreted LcrV protein. Increased protection correlated with increased anti-LcrV antibody and a bias toward IgG2a and away from IgG1 isotypes. We also found that the depletion of CD4+ cells, but not CD8+ cells, at the time of challenge resulted in reduced vaccine protection, indicating a role for cellular immunity in protection.

Effective plague vaccination via oral delivery of plant cells expressing F1-V antigens in chloroplasts

The chloroplast bioreactor is an alternative to fermentation-based systems for production of vaccine antigens and biopharmaceuticals. We report here expression of the plague F1-V fusion antigen in chloroplasts. Site-specific transgene integration and homoplasmy were confirmed by PCR and Southern blotting. Mature leaves showed the highest level of transgene expression on the third day of continuous illumination, with a maximum level of 14.8% of the total soluble protein. Swiss Webster mice were primed with adjuvant-containing subcutaneous (s.c.) doses of F1-V and then boosted with either adjuvanted s.c. doses (s.c. F1-V mice) or unadjuvanted oral doses (oral F1-V mice). Oral F1-V mice had higher prechallenge serum immunoglobulin G1 (IgG1) titers than s.c. F1-V mice. The corresponding serum levels of antigen-specific IgG2a and IgA were 2 and 3 orders of magnitude lower, respectively. After vaccination, mice were exposed to an inhaled dose of 1.02 x 10(6) CFU of aerosolized Yersinia pestis CO92 (50% lethal dose, 6.8 x 10(4) CFU). All control animals died within 3 days. F1-V given s.c. (with adjuvant) protected 33% of the immunized mice, while 88% of the oral F1-V mice survived aerosolized Y. pestis challenge. A comparison of splenic Y. pestis CFU counts showed that there was a 7- to 10-log reduction in the mean bacterial burden in survivors. Taken together, these data indicate that oral booster doses effectively elicit protective immune responses in vivo. In addition, this is the first report of a plant-derived oral vaccine that protected animals from live Y. pestis challenge, bringing the likelihood of lower-cost vaccines closer to reality.

Relative immunogenicity and protection potential of candidate Yersinia Pestis antigens against lethal mucosal plague challenge in Balb/C mice

Yersinia Pestis outer proteins, plasminogen activator protease and Yop secretion protein F are necessary for the full virulence of Yesinia pestis and have been proposed as potential protective antigens for vaccines against plague. In the current study, we used DNA immunization as a tool to study the relative protective immunity of these proteins with a standardized intranasal challenge system in mice. While the natural full-length gene sequences for most of these Y. pestis proteins did not display a good level of protein expression in vitro when delivered by a DNA vaccine vector, the overall immunogenicity of these wild type gene DNA vaccines was low in eliciting antigen-specific antibody responses and gene sequence modifications improved both of these parameters. However, even modified YopD, YopO and YscF antigens were only able to partially protect immunized mice at various levels against lethal challenge with Y. pestis KIM 1001 strain while no protection was observed with either the YopB or Pla antigens. These results demonstrate that DNA immunization is effective in screening, optimizing and comparing optimal antigen designs and immunogenicity of candidate antigens for the development of a subunit-based plague vaccine.

Antibody profiling in plague patients by protein microarray

A protein microarray containing 144 known or putative virulence-related proteins of Yersinia pestis was used to evaluate the antibody responses of plague patients. Forty-two proteins were found to be expressed in vivo and antibodies against 14 of them were detected in all patients analyzed, providing potential candidates for novel protective antigens and novel serodiagnostic markers in Y. pestis. Moreover, the lack of antibody to LcrV in the five patients in Focus F might be a challenge to our understanding of the pathogenesis of Y. pestis.

Pathogen proteins eliciting antibodies do not share epitopes with host proteins: a bioinformatics approach

The best way to prevent diseases caused by pathogens is by the use of vaccines. The advent of genomics enables genome-wide searches of new vaccine candidates, called reverse vaccinology. The most common strategy to apply reverse vaccinology is by designing subunit recombinant vaccines, which usually generate an humoral immune response due to B-cell epitopes in proteins. A major problem for this strategy is the identification of protective immunogenic proteins from the surfome of the pathogen. Epitope mimicry may lead to auto-immune phenomena related to several human diseases. A sequence-based computational analysis has been carried out applying the BLASTP algorithm. Therefore, two huge databases have been created, one with the most complete and current linear B-cell epitopes, and the other one with the surface-protein sequences of the main human respiratory bacterial pathogens. We found that none of the 7353 linear B-cell epitopes analysed shares any sequence identity region with human proteins capable of generating antibodies, and that only 1% of the 2175 exposed proteins analysed contain a stretch of shared sequence with the human proteome. These findings suggest the existence of a mechanism to avoid autoimmunity. We also propose a strategy for corroborating or warning about the viability of a protein linear B-cell epitope as a putative vaccine candidate in a reverse vaccinology study; so, epitopes without any sequence identity with human proteins should be very good vaccine candidates, and the other way around.

Magnetic biosensor for the detection of Yersinia pestis

A novel type of magnetic-beads based magnetic biosensor is described for the detection of Yersinia pestis. Experiments were performed with the antigen fraction F1 of these bacteria. The magnetic sensor platform offers easy and reliable detection of Y. pestis by the use of magnetic beads for labelling and quantification in a single step due to their paramagnetic features. The system uses antiYPF1 antibodies as capture element on ABICAP columns as core element of the magnetic sensor. Several immobilization methods for antibodies on polyethylene were exploited. The established biosensor has a linear detection range of 25-300 ng/ml Y. pestis antigen F1 and a detection limit of 2.5 ng/ml in buffer and human blood serum. The presented sensor system is small, simple, portable and therefore usable as off-lab detection unit for medical and warfare analytes.

Protective immunity against plague

Plague, an infectious disease that reached catastrophic proportions during three pandemics, continues to be a legitimate public health concern worldwide. Although antibiotic therapy for the causative agent Yersinia pestis is available, pharmaceutical supply limitations, multi-drug resistance from natural selection as well as malicious bioengineering are a reality. Consequently, plague vaccinology is a priority for biodefense research. Development of a multi-subunit vaccine with Fraction 1 and LcrV as protective antigens seems to be receiving the most attention. However, LcrV has been shown to cause immune suppression and Y. pestis mutants lacking F1 expression are thought to be fully virulent in nature and in animal experiments. The LcrV variant, rV10, retains the well documented protective antigenic properties of LcrV but with diminished inhibitory effects on the immune system. More research is required to examine the molecular mechanisms of vaccine protection afforded by surface protein antigens and to decipher the host mechanisms responsible for vaccine success.

Altered Ca(2+) regulation of Yop secretion in Yersinia enterocolitica after DNA adenine methyltransferase overproduction is mediated by Clp-dependent degradation of LcrG

DNA methylation by the DNA adenine methyltransferase (Dam) interferes with the coordinated expression of virulence functions in an increasing number of pathogens. While analyzing the effect of Dam on the virulence of the human pathogen Yersinia enterocolitica, we observed type III secretion of Yop effector proteins under nonpermissive conditions. Dam alters the Ca(2+) regulation of Yop secretion but does not affect the temperature regulation of Yop/Ysc expression. The phenotype is different from that of classical "Ca(2+)-blind" mutants of Yersinia, as Dam-overproducing (Dam(OP)) strains still translocate Yops polarly into eukaryotic cells. Although transcription of the lcrGV and yopN-tyeA operons is slightly upregulated, LcrG is absent from lysates of Dam(OP) bacteria, while the amounts of YopN and TyeA are not changed. We present evidence that clpXP expression increases after Dam overproduction and that the ClpP protease then degrades LcrG, thereby releasing a block in type III secretion. This is the first example of posttranslational regulation of type III secretion by the Clp protease and adds a new flavor to the complex regulatory mechanisms underlying the controlled release of effector proteins from bacterial cells.

YopM of Yersinia enterocolitica specifically interacts with alpha1-antitrypsin without affecting the anti-protease activity

It was previously shown that alpha1-antitrypsin (AAT) interacts with the type III secreted (T3S) EspB and EspD proteins of enteropathogenic Escherichia coli (EPEC), resulting in reduced functionality of the proteins. To determine if AAT is also able to interact with T3S proteins of other pathogens, the binding of AAT to Yop proteins of Yersinia enterocolitica was analysed. AAT did not interact with YopB or YopD, which have functions in type III translocation similar to EspB and EspD in EPEC, but specifically interacts with YopM, a member of the leucine-rich repeat (LRR) family of proteins, in overlay and pull-down assays. To determine regions of YopM involved in AAT binding, various N- and C-terminally truncated versions of YopM were recombinantly expressed, and their ability to interact with AAT analysed. All versions tested were able to bind AAT, indicating that at least eight LRR of YopM are sufficient for AAT interaction. The main physiological role of AAT is to inhibit neutrophil elastase; however, elastase was efficiently inhibited by AAT in the presence and absence of YopM, indicating that YopM does not interfere with the anti-protease inhibition activity of AAT, and that the domain of AAT interacting with YopM is not identical to AAT's protease interaction domain. Furthermore, it was shown that elastase efficiently degrades YopM and other Yop proteins. The data suggest that AAT has additional functions in the host response against bacterial infections that are not related to its anti-protease activity.