Immune response to plasmid- and chromosome-encoded Yersinia antigens

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.

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.

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.

Defense Against Biological Weapons (Biodefense)

Biological warfare (germ warfare) is defined as the use of any disease-causing organism or toxin(s) found in nature as weapons of war with the intent to destroy an adversary. Though rare, the use of biological weapons has occurred throughout the centuries.

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.

Contribuição para o diagnóstico de peste

Apesar de sua fundamentação clínico-epidemiológica, numerosos casos suspeitos de peste nos focos brasileiros têm sido descartados por serem negativos pelo teste de hemaglutinação para detecção de anticorpos contra o antígeno F1 da Yersinia pestis. A transcendência da peste justifica estudar se tais resultados decorrem da falta de resposta ao F1, e se outras proteínas da Yersinia pestis poderiam ser reconhecidas nos soros suspeitos, sendo desta forma candidatas como alvo diagnóstico alternativo ao F1. Assim sendo, cepas de Yersinia pestis e de Yersinia pseudotuberculosis, uma proteína YopH recombinante e a F1 foram utilizadas para analisar soros de pacientes e soros imunes de coelhos. A F1 e a YopH não foram reconhecidas pelos soros humanos HA- e nenhuma proteína majoritária, comum a todos os soros humanos e coelhos, foi identificada, o que permite concluir que os casos suspeitos devem ser submetidos a uma avaliação clínico-laboratorial mais rigorosa, aprofundando a investigação epidemiológica em busca de outras etiologias.

DNA adenine methylase overproduction in Yersinia pseudotuberculosis alters YopE expression and secretion and host immune responses to infection

Yersinia pseudotuberculosis mutants that overproduce the DNA adenine methylase (Dam) are highly attenuated, confer fully protective immune responses, and secrete several Yersinia virulence proteins (Yersinia outer proteins [Yops]) under conditions that are nonpermissive for secretion in wild-type strains. We examined here the effects of Dam overproduction on Yersinia virulence determinant expression and secretion, as well as the host immune response to Yersinia antigens. Western blot analysis with convalescent antisera identified several low-calcium-responsive antigens whose synthesis was affected by Dam overproduction. One of these antigens was shown to be the type III secretion effector protein, YopE, a cytotoxin involved in antiphagocytosis. Dam overproduction disrupted both the thermal and calcium regulation of YopE synthesis and relaxed the thermal but not the calcium dependence of YopE secretion. Altered expression and/or secretion of Yersinia proteins in Dam-overproducing strains may contribute to the decreased virulence and heightened immunity observed in vaccinated hosts and may provide a means by which to deliver heterologous antigens and/or immune modulators of the inflammatory response.

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

There is limited information concerning the nature and extent of the immune response to the virulence determinants of Yersinia pestis during the course of plague infection. In this study, we evaluated the humoral immune response of mice that survived lethal Y. pestis aerosol challenge after antibiotic treatment. Such a model may replicate the clinical situation in humans and indicate which virulence determinants are expressed in vivo. Immunoglobulin G enzyme-linked immunosorbent assay and immunoblotting were performed by using purified, recombinant antigens including F1, V antigen, YpkA, YopH, YopM, YopB, YopD, YopN, YopE, YopK, plasminogen activator protease (Pla), and pH 6 antigen as well as purified lipopolysaccharide. The major antigens recognized by murine convalescent sera were F1, V antigen, YopH, YopM, YopD, and Pla. Early treatment with antibiotics tended to reduce the immune response and differences between antibiotic treatment regimens were noted. These results may indicate that only some virulence factors are expressed and/or immunogenic during infection. This information may prove useful for selecting potential vaccine candidates and for developing improved serologic diagnostic assays.

Protective efficacy of recombinant Yersinia outer proteins against bubonic plague caused by encapsulated and nonencapsulated Yersinia pestis

To evaluate the role of Yersinia outer proteins (Yops) in conferring protective immunity against plague, six yop loci from Yersinia pestis were individually amplified by PCR, cloned, and expressed in Escherichia coli. The recombinant proteins were purified and injected into mice. Most Yop-vaccinated animals succumbed to infection with either wild-type encapsulated Y. pestis or a virulent, nonencapsulated isogenic variant. Vaccination with YpkA significantly prolonged mean survival time but did not increase overall survival of mice infected with the nonencapsulated strain. The only significant protection against death was observed in YopD-vaccinated mice challenged with the nonencapsulated strain.

Type III protein secretion systems in bacterial pathogens of animals and plants

Various gram-negative animal and plant pathogens use a novel, sec-independent protein secretion system as a basic virulence mechanism. It is becoming increasingly clear that these so-called type III secretion systems inject (translocate) proteins into the cytosol of eukaryotic cells, where the translocated proteins facilitate bacterial pathogenesis by specifically interfering with host cell signal transduction and other cellular processes. Accordingly, some type III secretion systems are activated by bacterial contact with host cell surfaces. Individual type III secretion systems direct the secretion and translocation of a variety of unrelated proteins, which account for species-specific pathogenesis phenotypes. In contrast to the secreted virulence factors, most of the 15 to 20 membrane-associated proteins which constitute the type III secretion apparatus are conserved among different pathogens. Most of the inner membrane components of the type III secretion apparatus show additional homologies to flagellar biosynthetic proteins, while a conserved outer membrane factor is similar to secretins from type II and other secretion pathways. Structurally conserved chaperones which specifically bind to individual secreted proteins play an important role in type III protein secretion, apparently by preventing premature interactions of the secreted factors with other proteins. The genes encoding type III secretion systems are clustered, and various pieces of evidence suggest that these systems have been acquired by horizontal genetic transfer during evolution. Expression of type III secretion systems is coordinately regulated in response to host environmental stimuli by networks of transcription factors. This review comprises a comparison of the structure, function, regulation, and impact on host cells of the type III secretion systems in the animal pathogens Yersinia spp., Pseudomonas aeruginosa, Shigella flexneri, Salmonella typhimurium, enteropathogenic Escherichia coli, and Chlamydia spp. and the plant pathogens Pseudomonas syringae, Erwinia spp., Ralstonia solanacearum, Xanthomonas campestris, and Rhizobium spp.

Surface-exposed antigenic determinants in outer membranes of wild Yersinia pestis isolates

Immunogenic surface exposed envelope proteins of Yersinia pestis strains were investigated with SDS-PAGE and immunoblots with antisera of immunized guinea pigs and convalescent patients. The sarkosyl-insoluble outer membrane proteins (OMPs) of three human isolates and one laboratory strain of Y. pestis grown in different rich media to exponential or stationary phase, and cultivated at 28 degrees C or 37 degrees C, were assayed for the presence of immunogenic peptides. Seven guinea-pig sera immunized with one of the four Y. pestis strains and four human sera from plague-infected patients indicated that at least four outer membrane proteins with molecular weights of 45 KDal, 42 KDal, 21 KDal and 16.5 KDal were strongly recognized by at least one of them. All but one of the guinea-pig serum and one human serum recognized the 45 KDal protein. The 42 KDal was identified only in outer membrane isolated from Y. pestis cells grown at 28 degrees C. All immunogenic OMPs were found in the four strains investigated. Labelling of intact Y. pestis cells with Iodogen and 131I further demonstrated the surface-exposed location of the immunogenic OMPs.

Factors promoting acute and chronic diseases caused by yersiniae

The experimental system constructed with the medically significant yersiniae provides a powerful basic model for comparative study of factors required for expression of acute versus chronic disease. The system exploits the close genetic similarity between Yersinia pestis, the etiological agent of bubonic plague, and enteropathogenic Yersinia pseudotuberculosis and Yersinia enterocolitica. Y. pestis possesses three plasmids, of which one, shared by the enteropathogenic species, mediates a number of virulence factors that directly or indirectly promote survival within macrophages and immunosuppression. The two remaining plasmids are unique and encode functions that promote acute disease by enhancing bacterial dissemination in tissues and resistance to phagocytosis by neutrophils and monocytes. These properties are replaced in the enteropathogenic yersiniae by host cell invasins and an adhesin which promote chronic disease; the latter are cryptic in Y. pestis. Additional distinctions include specific mutational losses in Y. pestis which result in loss of fitness in natural environments plus gain of properties that facilitate transmission and infection via fleabite.

Immunoblot analysis of IgM, IgG, and IgA responses to plasmid encoded released proteins of Yersinia enterocolitica in patients with or without yersinia triggered reactive arthritis

The IgM, IgG, and IgA antibody responses of patients with Yersinia enterocolitica O:3 infection were studied by immunoblotting with plasmid encoded released proteins of Y enterocolitica as the antigens. The results indicate that antibodies of all three classes are most consistently directed against the proteins of molecular weights 25,000 and 36,000. Less than two months after the onset of infection 18 of the 19 patients with yersinia triggered reactive arthritis had IgA class antibodies against the released protein of mol. wt 36,000, whereas only eight of the 17 patients with non-arthritic yersiniosis had these antibodies. The same difference between the arthritic and non-arthritic patients was observed also 8-12 months after the onset of infection.

Humoral immune response to individual Yersinia enterocolitica antigens in patients with and without reactive arthritis

The IgG, IgA and IgM antibody responses to individual Yersinia enterocolitica antigens were analysed by immunoblotting in 10 patients with reactive arthritis and 11 patients with enterocolitis caused by Y. enterocolitica serotype 0:3. The IgG antibody response was directed against partly different antigens compared with IgA. The expression of these antigens varied with bacterial culture conditions. The IgG and IgM antibody responses in the early stages of infection (less than or equal to 3 weeks) were directed against a large number of antigens. The IgA response was more selective, with antibodies against 240, 48 and 34.5 kD antigens dominating. IgA antibodies against eight antigens ranging in molecular weight from 52.5 to 105 kD were seen exclusively among arthritic patients. When following the IgA antibody response in the two groups of patients for up to 993 days, antibodies tended to persist to selective antigens. However, these antigens varied to some extent between patients, but the persistence was seen both among arthritic and non-arthritic patients. Persistent antibodies to 240, 48 and 34.5 kD antigens were most common. IgA antibodies to a 112 kD antigen were more prevalent and persisted longer in patients with arthritis compared to patients with uncomplicated infection.

Expression of the low calcium response in Yersinia pestis

Pathogenic yersiniae undergo an established low calcium response (LCR) at 37 degrees C in Ca2+-deficient media characterized by restricted growth with synthesis of Lcr plasmid-encoded virulence functions. The latter include outer membrane peptides (Yops) known to undergo Pst plasmid-mediated post-translational degradation in Yersinia pestis but not in enteropathogenic yersiniae lacking this plasmid. Salient Yops of Y. pestis are shown here to be either maintained in the steady state or to exist as a stable degradation product (p24 of Yop E). Processing of plague plasminogen activator (p36 to p33), responsible for hydrolysis of Yops, required 2 h. Avirulence of mutants with inserted Mu dl1 (Apr lac) in yopE was verified and shown to occur independently of introduced fusion-dependent peptides. However, avirulence of such yopE mutants but not that of isolates lacking the Lcr plasmid was phenotypically suppressed in mice injected with iron. Appearance of 20,500 and 40,500 Da heat-shock peptides preceded onset of the LCR. Lcr plasmid mediated V antigen (p38) and p20, Pst plasmid-encoded p36, and chromosomally promoted p56 and p70 were synthesized throughout the LCR. Classical antigen 5 was equated with p70 which was shared by Yersinia pseudotuberculosis but not Yersinia enterocolitica.

Analysis of the class-specific immune response to Yersinia enterocolitica virulence-associated antigens in oro-gastrically infected rabbits

The antibody response was analysed in rabbits oro-gastrically infected (i) with virulent-(plasmid-carrying) Yersinia enterocolitica 0:3 (v-rabbits) and (ii) with the avirulent (plasmid-cured) derivative (av-rabbits). In an immunoblot assay with whole cell lysate proteins from the infecting virulent Yersinia strain, a significant IgG response was evident in convalescent-sera of v-rabbits and of av-rabbits, demonstrating that all rabbits seroconverted. However, v-rabbits mounted a stronger immune response to the cell lysate proteins than av-rabbits and the immune response persisted for a longer time. The post-challenge sera also reacted with whole cell lysate proteins of Escherichia coli and Salmonella typhimurium, indicating cross-reactivity between the different members of Enterobacteriaceae. In contrast, the antibody response against plasmid-encoded released proteins (RPs) appeared specific for infection with virulent strains in that the sera of av-rabbits failed to recognize the plasmid-encoded proteins. Six days following challenge with the virulent Yersinia strain all animals mounted a serum IgM and IgA response to RPs, followed by IgG antibodies on day 9. While the IgM and IgA serum antibody response rapidly decreased (within five-seven and eight-ten months, respectively), IgG antibodies to RPs were still present one year after challenge. Fourteen months after the first infection both the av-rabbits and the v-rabbits were reinfected with the virulent Yersinia strain and the antibody response to RPs was monitored. The v-rabbits only responded with a significant increase of IgG antibodies, indicating that they were primed to the RPs whereas the av-rabbits produced IgM, IgA and IgG specific antibodies like those seen in the primary response of v-rabbits. This study indicates that the rabbit model is helpful and adequate to analyse the character and kinetics of the antibody response during Yersinia infection.

In vitro expression of a 22-kilodalton Yersinia pestis polypeptide immunologically related to the 25-kilodalton plasmid-encoded protein of the three pathogenic Yersinia species

Antibodies raised against the 25-kilodalton (p25) plasmid-encoded polypeptide of Yersinia enterocolitica recognized the homologous protein in the three Yersinia species grown in vitro. This polypeptide was recovered from whole cells as well as from the fluid supernatant of bacteria grown at 37 degrees C in a Ca2+-deficient medium. Furthermore, a 22-kilodalton (p22) plasmid-encoded polypeptide immunologically related to p25 was found only in Y. pestis during early growth. After 30 h of culture, the Y. pestis p25 and p22 were completely degraded, whereas the intensity of the Y. enterocolitica p25 was decreased, but the protein was still detectable in the fluid supernatant. This proteolytic activity was independent of the presence of the virulence plasmid. Some disulfide bonds are probably involved in the quaternary structure of the p25 of the three pathogenic species and of the Y. pestis p22.

Identification of encapsulated and non-encapsulated Yersinia pestis by immunofluorescence tests using polyclonal and monoclonal antibodies

Rabbit polyclonal hyperimmune antibodies to Yersinia pestis, and a mouse monoclonal antibody against the capsular antigen fraction 1 (F1) were compared in immunofluorescence (IF) tests. Fluorescent antibody conjugates were prepared from polyclonal antisera to four F1 positive Y. pestis strains; the conjugated antibody to strain A1122 gave the strongest IF staining of F1 positive and F1 negative Y. pestis strains. Indirect assays were rejected in favour of direct assays utilizing polyclonal and monoclonal reagents because the increased background staining reduced the effective contrast of bacterial visualisation. Polyclonal conjugates gave fairly homogeneous staining of Y. pestis bacterial populations, but in monoclonal assays a skew distribution of fluorescence intensity was observed, the majority of bacteria being poorly stained. The proportion of cells stained well by the monoclonal sufficed for easy identification of Y. pestis of the F1 positive phenotype however, and staining was not affected by washing the bacteria or treating them with formaldehyde. Y. pestis strains of the F1 positive genotype reacted with the monoclonal if bacteria were grown at 37 degrees C but not if the growth temperature was reduced to 25 degrees C thus preventing capsule production. The polyclonal conjugate reacted with bacteria of these strains that had been grown at either temperature. Strains of F1 negative genotype grown at either temperature reacted with the polyclonal conjugate but not with the monoclonal. Cross reactions between the polyclonal reagents and Y. enterocolitica biovar 2, serovar O 8 could not be removed by selective absorption; however, the monoclonal antibody gave no cross reaction. The F1 phenotypic status of bacterial preparations was verified by ELISA measurement of the fraction 1 antigen concentration. Antigen levels for F1 positive and F1 negative phenotypes differed by about three logs for suspensions of Y. pestis harvested from solid media. The polyclonal and monoclonal direct IF tests applied to spleen and blood smears of laboratory mice infected with Y. pestis were able to differentiate between lethal infection with an F1 positive strain carrying all four classical virulence determinants, an F1 positive vaccine strain, and an F1 negative strain.

The plasmid-encoded Yop2b protein of Yersinia pseudotuberculosis is a virulence determinant regulated by calcium and temperature at the level of transcription

The basic Yop2b protein, encoded by the virulence plasmid pIBI of Yersinia pseudotuberculosis, is produced under Ca2+-deficient conditions. A mutant deleted for the entire yopH gene, which encodes the Yop2b protein, was found to be avirulent. Virulence could be restored by trans-complementation. The DNA-sequence of yopH predicted a 50 737 D polypeptide lacking a typical signal peptide. Transcription of yopH is regulated by both temperature and Ca2+-concentration. Mutations within the region of the virulence plasmid known to be involved in regulating gene expression in response to Ca2+ abolished transcription of yopH. Other temperature-sensitive mutations in the Ca2+-regulatory locus showed a high level of transcription regardless of Ca2+-concentration. These responses were similar to those of the yopE gene. The promoter region of the yopE and yopH genes were compared and four conserved motifs identified.

Post-translational regulation of Lcr plasmid-mediated peptides in pesticinogenic Yersinia pestis

The low calcium response of wild type Yersinia pestis, the causative agent of bubonic plague, and of enteropathogenic Yersinia pseudotuberculosis and Yersinia enterocolitica is known to be mediated by a shared Lcr plasmid of about 70 kb. At 37 degrees C in Ca2+-deficient medium, this element promotes restriction of growth with concomitant production of virulence functions including the common V antigen and a set of yersiniae outer membrane peptides termed YOPs (Lcr+). The latter are expressed by the enteropathogenic species but not by wild type Y. pestis which possesses a unique 10 kb Pst plasmid associated with pesticinogeny (Pst+). We show in this report that, after pulse with 35S-methionine, peptides with molecular weights corresponding to YOPs of 78, 47, 45, 44, 36, and 26 kDa are synthesized during the low calcium response by both Lcr+, Pst+ and Lcr+, Pst- cells of Y. pestis. Although stable in the latter, radioactivity in YOPs of wild type was rapidly chased into lower molecular weight degradation products. At least four soluble peptides, including V, were also labeled during starvation for Ca2+; these structures were stable in both Lcr+, Pst+ and Lcr+, Pst- yersiniae. These findings suggest that a product encoded by the Pst plasmid of Y. pestis is required for post-translational regulation of outer membrane but not soluble peptides mediated by a second unrelated Lcr plasmid.

Modulation of the low-calcium response in Yersinia pestis via plasmid-plasmid interaction

Virulent cells of Yersinia pestis, Yersinia pseudotuberculosis, and Yersinia enterocolitica are known to exhibit a low-calcium response in vitro characterized by restriction of growth and induction of V antigen at 37 degrees C in Ca2+-deficient media (Lcr+). A shared Lcr plasmid mediates these properties and encodes yersiniae outer membrane peptides (Yops) that are expressed in Lcr+ Y. pseudotuberculosis and Y. enterocolitica but not Y. pestis. We present direct evidence here verifying that synthesis of major Yops in the former two species is, like V, repressed by Ca2+ and that these structures are located primarily in the outer membrane. We also verified that rabbits infected with live Lcr+ Y. pestis can raise antibodies against V and Yops. Similar antisera, however, were recovered after immunization with sterile extracts of Ca2+-starved Lcr+ cells of Y. pestis. Results of immunoblots obtained with these antisera showed that restricted Y. pestis produced Yops of about 46 kDa (YopB) and 44 kDa (YopC) after shiftup by addition of Ca2+ at 37 degrees C or reduction of temperature to 26 degrees C. It is established that virulent cells of Y. pestis also possess a unique plasmid known to mediate pesticinogeny (Pst+). Restricted Lcr+, Pst- Y. pestis expressed YopB and YopC plus additional 76 kDa (YopF), 48 kDa (YopH), 36 kDa (YopD), 32.5 kDa (YopJ), and 27 kDa (YopE) outer membrane structures at concentrations comparable to those in Ca2+-starved Y. pseudotuberculosis and Y. enterocolitica. These findings indicate that carriage of the Pst plasmid prevents expression of the Lcr plasmid-mediated Yops in wild type Y. pestis.

Immunoblotting analysis of human IgM, IgG and IgA response to chromosomally coded antigens of Yersinia enterocolitica 0:3

Human antibody response after Yersinia enterocolitica infection was studied by immunoblotting sequentially collected sera against a whole-cell homogenate of Y. enterocolitica serotype 0:3, grown under conditions restrictive for the plasmid. The antibodies observed were directed against a multitude of chromosomally coded antigens, and a considerable individual heterogeneity was found in the reactions of individual sera. The early (0-2 months) and late (greater than or equal to 11 months) responses were directed against the same antigenic determinants. Antibodies against different bacterial epitopes decreased evenly with time, indicating that several, if not all, antigenic epitopes of the bacteria are responsible for the prolonged antibody production. IgM responses by most patients declined within a few months but were surprisingly strong in some even one year after onset of the infection. IgG antibodies showed a strong reaction against a region corresponding to lipid A and core of the bacterial LPS, whereas IgM and IgA recognized this region less often. No other significant differences between IgM, IgG and IgA responses were observed. Immunoblotting of sera from patients with post-infection complications (arthritis, iritis, erythema nodosum) did not reveal any additional or specifically involved antigens. Altogether, these findings suggest that Yersiniae causing the original infection may hide in some of the patients for prolonged periods.

Proteolysis of V antigen from Yersinia pestis

Lcr-plasmids of yersiniae are known to mediate a unique low calcium response characterised by restriction of growth in vitro with induction of putative virulence factors including yersiniae outer membrane-peptides (YOPs) and V antigen (Lcr+). A medium was developed that permitted expression of high yields of V by Yersinia pestis KIM in large fermenter vessels. Immunoblots of specific precipitates prepared by prior molecular sieving showed that native unaggregated V exists as a monomeric 37,000 dalton peptide. Fractionation by precipitation with (NH4)2SO4 and chromatography on phenyl-Sepharose, DEAE cellulose, Sephacryl S200, calcium hydroxyapatite, and Sephadex G200 yielded highly purified antigen as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of parallel preparations from Lcr+ and Lcr- yersiniae. However, yields of V obtained by this process were unexpectedly low. As determined from immunoblots with monospecific polyclonal and monoclonal anti-V, this loss of activity occurred as a function of evident degradation at every step of purification yielding antigenic fragments of about 36,000, 34,000, 31,000, 30,000, and 28,000 daltons. Neutral or acidic pH favored hydrolysis; insignificant cleavage occurred in viable Lcr+ cells of Y. pestis or in culture supernatant fluids. V in neutral cytoplasm from Yersinia pseudotuberculosis or Yersinia enterocolitica did not undergo comparable degradation.