Pulsed-field gel electrophoresis, pertactin, pertussis toxin S1 subunit polymorphisms, and surfaceome analysis of vaccine and clinical Bordetella pertussis strains

To add new insight to our previous work on the molecular epidemiology of Bordetella pertussis in Argentina, the prn and ptxS1 gene sequences and pulsed-field gel electrophoresis (PFGE) profiles of 57 clinical isolates obtained during two periods, 1969 to 1989 and 1997 to 2006, were analyzed. Non-vaccine-type ptxS1A was detected in isolates obtained since 1969. From 1989 on, a shift of predominance from the vaccine prn1 type to the nonvaccine prn2 type was observed. This was also reflected in a transition of PFGE group IV to group VI. These results show that nonvaccine B. pertussis strains are currently circulating. To analyze whether the observed genomic divergences between vaccine strains and clinical isolates have functional implications, protection assays using the intranasal mouse challenge model were performed. For such experiments, the clinical isolate B. pertussis 106 was selected as representative of circulating bacteria, since it came from the major group of the PFGE dendrogram (PFGE group VI). Groups of mice were immunized either with diphtheria-tetanus-whole-cell pertussis vaccine (ptxS1B prn1) or a vaccine prepared by us containing B. pertussis 106. Immunized mice were then challenged with a B. pertussis vaccine strain (Tohama, harboring ptxS1B and prn1) or the clinical isolate B. pertussis 106 (ptxS1A prn2). An adequate bacterial-elimination rate was observed only when mice were immunized and challenged with the same kind of strain. For further characterization, comparative proteomic profiling of enriched membrane proteins was done using three vaccine strains and the selected B. pertussis 106 clinical isolate. By matrix-assisted laser desorption ionization-time of flight mass spectrometry analysis, a total of 54 proteins were identified. This methodology allowed us to detect differing proteins among the four strains studied and, in particular, to distinguish the three vaccine strains from each other, as well as the vaccine strains from the clinical isolate. The differing proteins observed have cellular roles associated with amino acid and carbohydrate transport and metabolism. Some of them have been proposed as novel vaccine candidate proteins for other pathogens. Overall, the global strategy described here is presented as a good tool for the development of next-generation acellular vaccines.

Adenylate cyclase toxin (ACT) from Bordetella hinzii: characterization and differences from ACT of Bordetella pertussis

Bordetella hinzii is a commensal respiratory microorganism in poultry but is increasingly being recognized as an opportunistic pathogen in immunocompromised humans. Although associated with a variety of disease states, practically nothing is known about the mechanisms employed by this bacterium. In this study, we show by DNA sequencing and reverse transcription-PCR that both commensal and clinical strains of B. hinzii possess and transcriptionally express cyaA, the gene encoding adenylate cyclase toxin (ACT) in other pathogenic Bordetella species. By Western blotting, we also found that B. hinzii produces full-length ACT protein in quantities that are comparable to those made by B. pertussis. In contrast to B. pertussis ACT, however, ACT from B. hinzii is less extractable from whole bacteria, nonhemolytic, has a 50-fold reduction in adenylate cyclase activity, and is unable to elevate cyclic AMP levels in host macrophages (nontoxic). The decrease in enzymatic activity is attributable, at least in part, to a decreased binding affinity of B. hinzii ACT for calmodulin, the eukaryotic activator of B. pertussis ACT. In addition, we demonstrate that the lack of intoxication by B. hinzii ACT may be due to the absence of expression of cyaC, the gene encoding the accessory protein required for the acylation of B. pertussis ACT. These results demonstrate the expression of ACT by B. hinzii and represent the first characterization of a potential virulence factor of this organism.

The use of microcalorimetry to characterize tetanus neurotoxin, pertussis toxin and filamentous haemagglutinin

Tetanus neurotoxin (TeNT), pertussis toxin (PT) and pertussis filamentous haemagglutinin (FHA) are major virulence factors of Clostridium tetani and Bordetella pertussis, which are the causative agents of tetanus and whooping cough respectively. Inactivated forms of these virulence factors are the protein components of vaccines against these diseases. Here we report microcalorimetric studies to characterize these proteins. The microcalorimetric titration curves of TeNT with micelles of gangliosides GD1b, GT1b and GQ1b were biphasic. For these gangliosides a high-affinity binding site (KD 45-277 nM) can be distinguished from a lower-affinity binding event (KD 666-1190 nM). This is direct evidence for multiple binding sites for gangliosides of the 1b series at TeNT as proposed by Emsley et al. [Emsley, Fotinou, Black, Fairweather, Charles, Watts, Hewitt and Isaacs (2000) J. Biol. Chem. 275, 8889-8894]. In agreement with previous reports, no binding was observed for gangliosides GM1, GM2, GM3 and GD2. The thermal denaturation of TeNT was characterized by two unfolding transitions centred around 57.4 and 62.4 degrees C. The conversion of TeNT into the toxoid form by formaldehyde treatment was accompanied by a large increase in Tm (the midpoint of protein unfolding transition, that is, the temperature at which half the protein is denatured and the other half is still present in its native form). Fetuin and asialofetuin bound to PT with similar affinities (KD 420 and 335 nM respectively). Binding was largely enthalpy-driven and counterbalanced by an unfavourable entropy change, indicating a loss of conformational flexibility. The latter could account for the observed inhibition of ATP binding after binding to fetuin. Furthermore, the molecular limits of mature PT subunit S5 were defined by MS and N-terminal peptide sequencing. The differential-scanning-calorimetry thermogram of FHA shows four well-resolved unfolding transitions, a finding consistent with the sequential denaturation of four structural domains.

A quantitative analysis for the ADP-ribosylation activity of pertussis toxin: an enzymatic-HPLC coupled assay applicable to formulated whole cell and acellular pertussis vaccine products

The majority of the biological effects of pertussis toxin (PT) are the result of a toxin-catalyzed transfer of an adenosine diphosphate-ribose (ADP-ribose) moiety from NAD(+)to the alpha-subunits of a subset of signal-transducing guanine-nucleotide-binding proteins (G-proteins). This generally leads to an uncoupling of the modified G-protein from the corresponding receptor and the loss of effector regulation. This assay is based on the PT S1 subunit enzymatic transfer of ADP-ribose from NAD to the cysteine moiety of a fluorescent tagged synthetic peptide homologous to the 20 amino acid residue carboxyl-terminal sequence of the alpha-subunit of the G(i3)protein. The tagged peptide and the ADP-ribosylated product were characterized by HPLC/MS and MS/MS for structure confirmation. Quantitation of this characterized ADP-ribosylated fluorescently tagged peptide was by HPLC fluorescence using Standard Addition methodology. The assay was linear over a five hr incubation period at 20 degrees C at PT concentrations between 0.0625 and 4.0 microg/ml and the sensitivity of the assay could be increased several fold by increasing the incubation time to 24 h. Purified S1 subunit of PT exhibited 68.1+/-10.1% of the activity of the intact toxin on a molar basis, whereas the pertussis toxin B oligomer, the genetically engineered toxoid, (PT-9K/129G), and several of the other components of the Bordetella pertussis organism possessed little (<0.6%) or no detectable ribosylation activity. Commonly used pertussis vaccine reference materials, US PV Lot #11, BRP PV 66/303, and BRP PV 88/522, were assayed by this method against Bordetella pertussis Toxin Standard 90/518 and demonstrated to contain, respectively, 0.323+/-0.007, 0.682+/-0.045, and 0.757+/-0.006 microg PT/ml (Mean+/-SEM) or in terms of microg/vial: 3.63, 4.09 and 4.54, respectively. A survey of several multivalent pertussis vaccine products formulated with both whole cell as well as acellular components indicated that products possessed a wide range of ribosylation activities. The pertussis toxin S1 subunit catalyzed ADP- ribosylation of the FAC-Galpha(i3)C20 peptide substrate and its subsequent quantitation by HPLC was demonstrated to be a sensitive and quantitative method for measuring intrinsic pertussis toxin activity. This methodology not only has the potential to be an alternative physicochemical method to replace existing bioassay methodology, but has the added advantage of being a universal method applicable to the assay of pertussis toxin in both whole cell and acellular vaccines as well as bulk and final formulated vaccine products. Acceptance of this method by regulatory agencies and industry as a credible alternative to existing methods would, however, require validation in an international collaborative study against the widely accepted bioassay methods.

Monitoring of diphtheria, pertussis and tetanus toxoids by circular dichroism, fluorescence spectroscopy and size-exclusion chromatography

A combination of spectroscopic and chromatographic methods has been used to monitor the quality and integrity of diphtheria, pertussis and tetanus toxoids (DTxd, PTxd and TTxd) which have been prepared from the toxins by formaldehyde treatment. Different processes for detoxifying all three toxins have yielded toxoids varying in their molecular size, including oligomers (associated monomers) and aggregates (high molecular weight complexes of non-specifically associated monomers). Changes in the intrinsic fluorescence spectra of the polypeptides have been observed in some sized fractions of DTxd and PTxd. Some physico-chemical changes have been observed to correlate with a loss of antigenicity. Spectroscopic and chromatographic methods are useful not only in monitoring the stability and consistency of vaccine starting materials, but can also be used to dissect heterogeneous toxoid preparations.

[The effect of methylated cyclodextrin on pertussis toxin accumulation in a Bordetella pertussis culture in a bioreactor]

The results obtained in the study of the influence methylated cyclodextrin (beta CD) on the growth of B. pertussis and the accumulation of pertussis toxin in the course of submerged batch cultivation in a bioreactor are presented. As demonstrated by these results, the presence of beta CD in the culture medium in a dose of 0.1 ml/l in the growth deceleration phase causes a tenfold increase in the synthesis of pertussis toxin by microbial cells in comparison with conditions characterized by the absence of beta CD. It cannot by ruled out that beta CD may act as a stressor which influences the synthesis of pertussis toxin, protector protein making it possible for the microbe to survive under new conditions.

Release of outer membrane vesicles from Bordetella pertussis

The aim of the study reported here was to investigate the production of Bordetella pertussis outer membrane vesicles (OMVs). Numerous vesicles released from cells grown in Stainer-Scholte liquid medium were observed. The formation of similar vesicle-like structures could also be artificially induced by sonication of concentrated bacterial suspensions. Immunoblot analysis showed that OMVs contain adenylate cyclase-hemolysin (AC-Hly), among other polypeptides, as well as the lipopolysaccharide (LPS). Experiments carried out employing purified AC-Hly and OMVs isolated from B. pertussis AC-Hly- showed that AC-Hly is an integral component of the vesicles. OMVs reported here contain several protective immunogens and might be considered a possible basic material for the development of acellular pertussis vaccines.

[Evaluation of the usefulness of Bordetella pertussis toxins for serodiagnosis of whooping cough]

The results of serological tests for the detection of antibodies against pertussis toxin by means of the ELISA test, and endotoxin of B. pertussis in the passive haemagglutination test were analysed. The levels of IgG, IgM and IgA antibodies were determined for 95% of serum samples of 108 children in control group (without evidence of respiratory infections) for establishing of the correlation of these with the age of these children. In the light of these data the results were evaluated of testing of 136 serum samples taken from 127 children with suspected whooping-cough. The highest diagnostic importance had the demonstration of high IgA or/and IgG immunoglobulins level against pertussis toxin in ELISA test, or tracing of the rate of rise of antipertussis antibodies in the passive haemagglutination test with B. pertussis endotoxin in children with clinical symptoms of whooping-cough.

Evaluation of an immunoglobulin G enzyme-linked immunosorbent assay for pertussis toxin and filamentous hemagglutinin in diagnosis of pertussis in Senegal

The enzyme-linked immunosorbent assay is widely employed for the serological diagnosis of pertussis. It is generally concluded that a significant increase in specific immunoglobulin G (IgG) or IgA against the pertussis toxin (PT) or against filamentous hemagglutinin (FHA) in paired sera correlates with Bordetella pertussis infection. However, this type of diagnosis of pertussis has mainly been applied to unvaccinated children, with timely sampling of acute- and convalescent-phase sera. In current practice and in epidemiological studies, such criteria are not always fulfilled. The aim of this study was to analyze the significance of decreases in IgG antibody titers against PT and FHA between paired sera observed in suspected cases of pertussis infection. Serological results from paired sera were available for 460 children experiencing at least 8 days of cough. An anti-PT IgG decrease was observed in 25% of the children, more frequently than the anti-FHA IgG decrease. Fourteen percent of the serologic decreases were observed in children with culture-confirmed infection, and 59% of the decreases were observed in children with confirmation criteria according to World Health Organization recommendations. Most of the decreases were observed when serum samples were collected according to a standard recommended schedule. Serologic decreases were observed more frequently among vaccinated children than among unvaccinated children. This difference, which was highly significant (P < 0.00001), was explained by the different kinetics of the antibody responses between vaccinated and unvaccinated children. The importance of the antibody response for the evaluation of vaccine efficacy, namely a bias toward higher absolute vaccine efficacy when this response is not taken into account, is discussed. This study supports an earlier recommendation that a significant decrease in PT or FHA should be added to the diagnostic criteria for pertussis.

Molecular characterization of two Bordetella bronchiseptica strains isolated from children with coughs

During a surveillance program associated with the Italian clinical trial for the evaluation of new acellular pertussis vaccines, two bacterial isolates were obtained in cultures of samples from immunocompetent infants who had episodes of cough. Both clinical isolates were identified as Bordetella bronchiseptica by biochemical criteria, although both strains agglutinated with antisera specific for Bordetella parapertussis, suggesting that the strains exhibited some characteristics of both B. bronchiseptica and B. parapertussis. Both children from whom these strains were isolated exhibited an increase in serum antibody titer to pertussis toxin (PT), a protein that is produced by Bordetella pertussis but that is not thought to be produced by B. bronchiseptica. We therefore examined whether the clinical isolates were capable of producing PT. Neither strain produced PT under laboratory conditions, although both strains appeared to contain a portion of the ptx region that encodes the structural subunits of PT. In order to determine whether the ptx genes may encode functional proteins, we inserted an active promoter directly upstream of the ptx region of one of these strains. Biologically active PT was produced, suggesting that this strain contains the genetic information necessary to encode an active PT molecule. Sequence analysis of the ptx promoter region of both strains indicated that, while they shared homology with the B. bronchiseptica ATCC 4617 sequence, they contained certain sequence motifs that are characteristic of B. parapertussis and certain motifs that are characteristic of B. pertussis. Taken together, these findings suggest that variant strains of B. bronchiseptica exist and might be capable of causing significant illness in humans.

[The expression of Bordetella pertussis protective antigens during bacterial multiplication on a medium with a fixed chemical composition]

The possibility of obtaining native pertussis preparations with high immunobiological activity has been shown. To obtain such preparations, the use of B. pertussis selected strain, its growth under the conditions of static cultivation in a synthetic culture medium and the use of supernatants with the maximum content of protective antigens with the aim of obtaining protective complexes are necessary.

Characterisation of ovine Bordetella parapertussis isolates by analysis of specific endotoxin (lipopolysaccharide) epitopes, filamentous haemagglutinin production, cellular fatty acid composition and antibiotic sensitivity

Isolates of Bordetella parapertussis, recovered from sheep or man, were characterised by reaction with specific anti-Bordetella lipopolysaccharide monoclonal antibodies, production of filamentous haemagglutinin, fatty acid patterns, and antibiotic sensitivity. Generally, the isolates lay within one of four groups, with separation of the ovine isolates into two groups. Reactions with specific monoclonal antibodies against lipopolysaccharide separated the ovine isolates into these two groupings. Analysis of the cellular fatty acid compositions by cluster analysis differentiated between the human and the ovine strains and also showed variation within the ovine isolates. When the production of filamentous haemagglutinin was analysed in an ELISA system, a similar pattern emerged. Varying concentrations of filamentous haemagglutinin (11-429 ng (mg total protein)-1) were extracted from the human isolates and the one group of ovine isolates with no significant protein detected in the other ovine group. These studies demonstrate variation between and within B. parapertussis isolates recovered from two mammalian sources.

Mutations in the bvgA gene of Bordetella pertussis that differentially affect regulation of virulence determinants

By using chemical mutagenesis and genetic mapping, a search was undertaken for previously undescribed genes which may be involved in different regulatory mechanisms governing different virulence factors of Bordetella pertussis. Previous studies have shown that the fha locus encoding filamentous hemagglutinin is regulated directly by the bvgAS two component system, while regulation of ptx encoding pertussis toxin is less direct or occurs by a different mechanism. With a strain containing gene fusions to each of these regulated loci, screening was done for mutations which were defective for ptx expression but maintained normal or nearly normal levels of fha expression. Two mutations which had such a phenotype and were also deficient in adenylate cyclase toxin/hemolysin expression were found and characterized more fully. Both were found to affect residues in the C-terminal portion of the BvgA response regulator protein, a domain which shares sequence similarity with a family of regulatory proteins including FixJ, UhpA, MalT, RcsA, RcsB, and LuxR. The residues affected are within a region which, by extension from studies on the LuxR protein, may be involved in transcriptional activation.

Mimicking of discontinuous epitopes by phage-displayed peptides, II. Selection of clones recognized by a protective monoclonal antibody against the Bordetella pertussis toxin from phage peptide libraries

We have screened phage peptide libraries to establish if clones binding to a monoclonal antibody (mAb), specific for a discontinuous epitope, could be isolated and if the selected phage particles would be able to elicit an in vivo immuno-response against the original antigen. Two phage peptide libraries, consisting of 9 random amino acids inserted in the major coat protein (pVIII), were independently screened with a mAb which is capable of neutralizing the Bordetella pertussis toxin (PTX) in in vitro and in vivo assays. The epitope of PTX recognized by this and other protective mAb has been shown to be discontinuous. Six different positive phage clones were selected; their binding to the mAb could be competed for by PTX, showing that these clones bind to the antigen-binding site of the mAb. Three of the clones were used (alone or as a mixture) to immunize BALB/c mice. The sera showed a good immunoresponse both against the phage bearing the epitopes and against synthetic multiple-antigen peptides of the same sequence. The immune sera, however, showed no detectable signal against PTX and no capacity to neutralize the CHO-cell-clustering activity of the toxin. The results show that the selected recombinant phage are capable of mimicking the discontinuous epitope as far as binding to the corresponding mAb, but they are unable to elicit a detectable production of antibodies specific for the original antigen.

Molecular characterization of an operon required for pertussis toxin secretion

Mutants of Bordetella pertussis which are defective in secretion of pertussis toxin were isolated and characterized. The region of the B. pertussis chromosome identified by mutagenesis as playing a role in transport of pertussis toxin was sequenced. Analysis of this region revealed eight open reading frames, seven of which predict a protein exhibiting homology with one of the VirB proteins of Agrobacterium tumefaciens, which are involved in the transport of the T-DNA molecule across bacterial and plant membranes. Thus a set of accessory proteins are most likely involved in the secretion of pertussis toxin, and these proteins appear to be members of a family of proteins involved in the secretion of macromolecules from bacteria.

[Properties of an acellular preparation of Bordetella pertussis and its analysis after centrifugation in saccharose gradient]

Acellular preparations were studied which were obtained by a method of acidic extraction from culture of strain Tohama of Bordetella pertussis. Obtained preparations EM I and EM II were exhibiting property of leukocytosis stimulation and were respectively of following values: 43.5 and 19 u LPF/mg of protein. They also caused hemagglutination (150 and 19 u HA/mg of protein). Both preparations were exhibiting protective effect in intracerebral test performed on mice. After differentiation of EM I preparation by preparative centrifugation in saccharose gradient two fractions were obtained, of which lighter was exhibiting high hemagglutinating activity and leukocytosis stimulation (198 u LPF/mg of protein). Heaver fraction contained mainly endotoxin. Applied method permitted for partial purification of acellular preparation of B. pertussis; mainly decrease in its content of endotoxin responsible for high reactogenicity of pertussis vaccines.

Quantification of pertussis toxin, filamentous haemagglutinin, 69 kDa outer membrane protein, agglutinogens 2 and 3 and lipopolysaccharide in the Danish whole-cell pertussis vaccine

The amounts of pertussis toxin (PT), filamentous haemagglutinin (FHA), 69 kDa outer membrane protein (69 kDa OMP) and agglutinogens (AGG) 2 and 3 in extracts from the Danish whole-cell pertussis vaccine were studied in quantitative capture ELISA. With the exception of PT, the most effective extraction of these antigens was by heating the bacteria at 60 degrees C for 30 min in 2 M urea followed by sonication for 45 s. Extraction by 1 M sodium chloride prior to sonication resulted in higher levels of antigenic and biologically active PT. On average, a single human dose of pertussis vaccine (approximately 16 opacity units) was found to contain 5520 ng FHA, 63 ng PT, 1061 ng 69 kDa OMP, 397 ng AGG 2, 534 ng AGG 3 and 4840 ng lipopolysaccharide (LPS). The antigen content of one dose of the Danish pertussis vaccine appears to be low compared with the amounts found in the acellular vaccines currently in use. These findings may have important implications for the evaluation of the protective substances and the immunogenicity of whole-cell as opposed to acellular pertussis vaccines.

The melanophore aggregating response of isolated fish scales: a very rapid and sensitive diagnosis of whooping cough

Pertussis toxin (PT) has been found to block noradrenaline-induced pigment aggregation in fish melanophores, and, based on this, a rapid and highly sensitive assay for PT was developed. Some preliminary results have also indicated that it may be possible to detect PT-like activity in saliva samples from patients with clinically suspected pertussis. In the present study the diagnostic value of the fish melanophore method was evaluated in 70 patients suspected of having pertussis; culture, serology and physician diagnosis were used as reference methods. In 60 of the patients, pertussis was verified by at least one of the reference methods. The melanophore test showed PT-like activity in saliva samples from 58 of the patients. Three patients with reference-verified pertussis showed no PT-like activity in the test; among these, one patient had been immunized and had also been treated with erythromycin during 3 days immediately prior to visiting the hospital. The melanophore test has three major advantages: it allows detection of pertussis in the early and curable stage of the disease; it takes only 2 h to perform; and it requires no sophisticated equipment.

Purification and immunological characterization of HPLC-purified pertussis toxin subunits

Pertussis toxin (PT), an oligomeric exotoxin of Bordetella pertussis containing five dissimilar subunits, is considered to be an essential immunogen in acellular and component pertussis vaccines against whooping cough. A rapid single-step procedure for isolating PT subunits was developed using reverse-phase high-performance liquid chromatography. Recoveries of individual subunits were 75% (S1), 70% (S2), greater than 90% (S3), greater than 90% (S4), and 50% (S5), as judged by SDS-PAGE and amino acid analysis. Lyophilized subunits were solubilized in urea followed by step-wise dialysis to remove the urea. All subunits were inactive in histamine sensitization, lymphocytosis, and hemagglutination assays. However, purified S1 retained residual NAD-glycohydrolase and ADP-ribosyltransferase activity. A partially active holotoxin could be generated by mixing the five individual subunits. All subunits were immunogenic in rabbits and mice. Monospecific antisera raised in both animal species were able to neutralize the PT-mediated clustering of Chinese hamster ovary cells, but active immunization of mice with single subunits failed to protect them in the intracerebral challenge assay. These subunit preparations therefore retained neutralizing determinants, but did not contain protective epitopes.

[The phenotypic properties of freshly isolated strains of Bordetella]

As the result of our investigations, newly isolated B. pertussis and B. bronchiseptica strains were studied. The results of these investigations showed that B. pertussis strains isolated under the conditions of immunoprophylaxis were characterized by sufficient stability of the main phenotypical properties which determined their pathogenicity: B. pertussis toxin, fimbrial agglutinogens and filamentous hemagglutinin. At the same time B. bronchiseptica strains isolated from animals proved to be phenotypically variable both in vivo and in the process of in vitro passage.

Hemagglutination activities of purified pertussis toxin and filamentous hemagglutinin against erythrocytes from various animals

The hemagglutinating (HA) activities of purified pertussis toxin (PT) and filamentous hemagglutinin (FHA) were evaluated against unfixed and glutaraldehyde-fixed erythrocytes from ox, goose, horse, monkey, sheep, chicken, and rabbit. Both PT and FHA showed HA activities against fixed and unfixed erythrocytes from all the animals studied. The HA titers of FHA were higher than those of PT. The HA activities of FHA and PT were not destroyed completely even after heating these preparations at 56 C for 30 min. A simple test for the assay of PT in culture supernatants of Bordetella pertussis on the basis of HA activity has been described.

Simultaneous determination of Bordetella pertussis toxin and filamentous haemagglutinin concentrations by hydroxyapatite high-performance liquid chromatography

A simple and rapid method for the simultaneous determination of Bordetella pertussis toxin (PT) and filamentous haemagglutinin (FHA) concentrations in fermentation broths has been developed. The rapid single-step analysis performed by hydroxyapatite high-performance liquid chromatography using a salt gradient with UV detection allows both the separation of PT from FHA and the measurement of their respective concentrations. The assay is highly reproducible. Over 35 lots of acellular B. pertussis vaccine production lots were examined and PT concentrations measured by high-performance liquid chromatography were found to be in good agreement with the values obtained by sodium dodecyl sulphate-polyacrylamide gel electrophoresis densitometry. The chromatographic conditions have been optimized to separate the intact holotoxin from its B-oligomer subunits.

Preliminary X-ray crystallographic analysis of holotoxin from Bordetella pertussis

Pertussis (whooping cough) is a serious infectious disease caused by the bacterium Bordetella pertussis. One of the major virulence factors is a protein known as pertussis toxin, which is composed of six subunits, with a total molecular weight of 106,000. Enzymatic transfer of ADP-ribose from NAD to a family of GTP-binding proteins is effected by the largest subunit (S1 or the A monomer), while binding of host cells and entry of S1 to the interior is a function of the other subunits (the B oligomer). The holotoxin crystallizes in the orthorhombic space group P2(1)2(1)2(1), with unit cell dimensions a = 98.4 A, b = 164.2 A and c = 195.2 A. The crystals are suitable for high-resolution X-ray diffraction analysis.

Quantitation of pertussis toxin in an enzyme linked immunosorbent assay with improved specificity

The quantitation of pertussis toxin (PT) in two sandwich ELISAs was tested for specificity. The detection of the captured PT was obtained by using either polyspecific rabbit anti Bordetella pertussis serum (RaBp-ELISA) or a monoclonal anti-PT antibody (McaPT-ELISA). No major differences in the estimation of PT in highly purified preparations were noted using either ELISA variants. In contrast, the quantitation of PT in crude extracts of B. pertussis cultures by the RaBp-ELISA was found to be over-estimated and showed greater variability when compared to the McaPT-ELISA. Comparison of the distribution of PT in the eluate fractions following partial purification by hydroxylapatite chromatography revealed that the results of the McaPT-ELISA were more specific as judged by SDS-PAGE analysis.

Biochemical and biological activities of recombinant S1 subunit of pertussis toxin

degP-deficient strains of Escherichia coli grown in M-9 medium supplemented with ZnCl2 expressed the recombinant S1 subunit of pertussis toxin (rS1) in a form electrophoretically identical to the authentic S1 subunit. Subcellular fractionation showed that the full-length form of rS1 was membrane associated, while proteolytic fragments of rS1 were present in the periplasm. rS1 was extracted from outer membrane preparations with 8 M urea and purified by gel filtration chromatography. Purified rS1 ADP-ribosylated transducin at a similar molar efficiency relative to authentic pertussis toxin and, when associated with the native B oligomer of pertussis toxin, elicited Chinese hamster ovary cell clustering.

Multiple T and B cell epitopes in the S1 subunit ("A"-monomer) of the pertussis toxin molecule

The immunogenicity and reactogenicity of Bordetella pertussis vaccine are mediated in part by the S1 subunit of pertussis toxin (PT). To identify the immune epitopes in the S1 subunit of PT, synthetic peptides were prepared and tested for their capacity to induce antibodies in mice with different MHC genotypes. In BALB/c mice, peptides corresponding to sequences 1-17, 70-82 and 189-199 generate T cell proliferative responses, induce the production of antibodies capable of neutralization of the toxin in the Chinese hamster ovary-cell assay, and protect mice from a shock-like syndrome caused by alternate injections of BSA and PT. Protection and neutralization correlated with the ability of these peptides to elicit high anti-PT titers. Different B cell epitopes were detected in other inbred mouse strains. The antibody reactivity against synthetic peptides from two infants vaccinated with pertussis vaccine was tested. These infants had antibodies reactive to a variety of epitopes in the S1 subunit, including peptides 1-17, 70-82, 99-112, 135-145, and 189-199. Thus, it appears that there are multiple T and B cell epitopes in the S1 subunit of PT.

Development of a rapid diagnostic test for pertussis: direct detection of pertussis toxin in respiratory secretions

Monoclonal antibodies (MAb) were produced against the specific Bordetella pertussis antigen pertussis toxin (PT). In preliminary studies, one MAb (IB12) was selected and used in an enzyme-linked dot blot immunoassay to evaluate the ability of the method to detect known amounts of PT in control experiments and to test its potential for direct detection of PT in nasopharyngeal secretion (NP) specimens from patients with confirmed cases of whooping cough. The dot blot assay was able to detect PT at levels as low as 10 ng per dot in either buffer or control NP specimens. The assay demonstrated specificity, reacting only with dot blots of whole B. pertussis and not Bordetella bronchiseptica, Bordetella parapertussis, or other bacterial strains. In preliminary studies, NP aspirate, swab, and wash specimens were compared. The specimen of choice was found to be the NP aspirate, for which 100% positive results were found in the assay. These initial studies suggest that the dot blot immunoassay in which a MAb is used for direct detection of PT in NP specimens may be useful as a rapid diagnostic test for pertussis.

The effect of cyclodextrin on lipopolysaccharide production in cultures of Bordetella pertussis

The effect of adding 500 micrograms of (2,6-0-dimethyl) beta-cyclodextrin (Me-beta-CD) per ml of Stainer-Scholte (SS) medium in two-day shaker flask cultures of Bordetella pertussis on the production of lipopolysaccharide (LPS) was investigated. The amount of LPS per 10(9) cells found in the supernatants of these cultures was either somewhat reduced or unaffected by comparison with the amounts in cultures grown in SS-medium alone. In addition, the time course of LPS release from cultures of B. pertussis strain 3843 cells during a 96-h growth period in normal and Me-beta-CD-enriched SS medium is described. By using the enriched medium bacterial growth, the production of filamentous haemagglutinin (FHA) and of pertussis toxin (Pt) and the levels of haemagglutination and lymphocytosis-promoting activity were enhanced to various degrees. Measurements made on sedimented whole and on sonicated B. pertussis cells grown in the two media showed no differences in LPS content. The reasons for the reduced/unaffected LPS production are discussed. It has been suggested that an interaction between hydrophobic cavities of the Me-beta-CD molecules and the 'lipid A' part of LPS reduces the reactivity of LPS in the Limulus Amoebocyte Lysate (LAL) assay. This possibility, however, was rejected as the reactivity of Me-beta-CD-spiked purified B. pertussis strain 3803 LPS, compared with unspiked samples, remained unchanged.

Monoclonal antibodies that define neutralizing epitopes of pertussis toxin: conformational dependence and epitope mapping

The epitope specificities of 13 hybridomas secreting monoclonal antibodies (MAbs) specific for pertussis toxin (PT) is described. Hybridoma lines were derived by the fusion of spleen cells from mice immunized with native PT, Formalin-detoxified PT, or isolated PT subunits (S1 to S5) with the myeloma line X63-Ag8.653. Five MAbs showed a toxin-neutralizing ability, which was demonstrated by use of a Chinese hamster ovary cell assay system and by a NAD glycohydrolase assay. All five toxin-neutralizing MAbs demonstrated high specificities for and reactivities with native PT but were unable to bind to denatured PT. One MAb was able to neutralize the enzymatic activity of PT. The other four neutralizing MAbs inhibited the binding of PT or PT subunits to the surface of Chinese hamster ovary cells, as shown by an immunofluorescence assay. All neutralizing MAbs reacted with purified S2-S4 or S3-S4 dimers but not with S4 alone. Three MAbs which recognized a common epitope shared by S2 and S3 (which are about 70% homologous at the DNA level) and one MAb which recognized S4 were not neutralizing. Isolated S2-S4 and S3-S4 dimers bound to Chinese hamster ovary cells. These results indicate that the majority of critical epitopes which elicit neutralizing antibody are conformation dependent.

Domain-specific bias in arginine/lysine usage by protein toxins

The content of lysine and arginine residues in a number of A-B type protein toxins has been examined. It is found that the A subunit, or its equivalent, often shows a strong bias in the type of basic amino acid residue used tending towards nearly exclusive use of either arginine or lysine rather than use of both, whereas the B subunit or its equivalent shows no such bias. Although arginine codons are GC-rich and lysine codons are AT-rich, the content of GC and AT in the genes coding for the toxins does not adequately explain this bias. Other explanations are discussed, including the possibility that the bias is linked to catalytic function or membrane interaction. Understanding this bias may yield valuable insights into toxin structure and function. Furthermore, identification of bias in sequences may be a useful tool for identifying new toxins and their domains.

[Use of an immunoblotting method for identifying the individual proteins in the antigenic complexes of Bordetella pertussis]

The composition of antigenic complexes isolated from the supernatant fluid of B. pertussis culture has been studied by means of immunoblotting techniques. In preparations obtained from B. pertussis strains 305 and 475 fragments of the molecule of fimbrial hemagglutinin, three subunits of B. pertussis toxin and agglutinogens 2 and 3 have been detected with the use of antisera to B. pertussis protective substances.

[Immunobiologic activity of Bordetella pertussis strains defective in various virulence factors]

The immunobiological properties of mutant strains, selectively deprived of certain antigens (hemagglutinin, B. pertussis toxin, dermonecrotic toxin, hemolysin, adenylate cyclase), have been studied with the aim of finding out the relationship between the presence of certain antigens in microbial strains and their protective properties. The results of these studies suggest that the protective potency of pertussis vaccine may be related to the presence of some antigenic substances, including those not pertaining to the known factors of virulence.

Mapping of linear B-cell epitopes of the S2 subunit of pertussis toxin

The linear immunogenic and antigenic structure of the S2 subunit of pertussis toxin was investigated with synthetic peptides corresponding to regions of the protein sequence predicted to contain surface-exposed hydrophilic beta turns. Five peptides as peptide-bovine serum albumin conjugates were recognized by anti-pertussis toxin antiserum and were thus designated "immunogenic epitopes." Two prominent immunogenic epitopes were specified by peptides corresponding to sequences spanning R107-120 and R186-199, whereas peptides corresponding to residues R35-50 and R91-106 were only bound in low titer. Three peptides as thyroglobulin conjugates elicited antisera in rabbits that bound intact pertussis toxin by enzyme-linked immunosorbent assay and immunoblot. These peptides were designated "antigenic epitopes." The most prominent antigenic determinant was localized to the N-terminal end of the S2 sequence encompassing residue R1-7. Peptides R35-50 and R91-106 represented two minor antigenic epitopes. Antisera to two additional peptides corresponding to residues R134-149 and R186-199 recognized the S2 subunit only by Western blotting (immunoblotting). Only antiserum raised against peptide R91-106 also recognized the S3 subunit by Western blotting, indicating a marked antigenic and probably also structural difference between the two highly homologous subunits.

Studies of the antigenic structure of two cross-reacting proteins, pertussis and cholera toxins, using synthetic peptides

Peptide fragments of pertussis toxin subunit 1 (PT-S1) have been synthesized in order to investigate their antigenic and immunogenic activity, and to evaluate their possible use as components of a new vaccine. Two peptides (sequence 73-82, EAERAGRGTG and sequence 107-116, YVDTYGDNAG) were selected for their predictable exposure on the surface of the molecule, and a third (8-18, YRYDSRPPEDV) for its homology with the sequence 6-16 of cholera toxin subunit A (CT-A 6-16) (YRADSRPPDEI). Antipeptide polyclonal antibodies produced in rabbits, were tested in different immunoassays for their ability to interact with toxin proteins. All of them proved interactive with recombinant PT-S1 (rPT-S1); CT-A interact not only, as expected, with anti 8-18 antibodies, due to the high homology between the two toxins in this region, but also, unexpectedly, with anti 107-116 antibodies, in spite of the lack of homology of this peptide with the entire CT. We also found a direct cross-reactivity between the two toxins: anti PT and anti rPT-S1 antibodies interacted with CT-A, whereas anti CT antibodies did not recognize PT. Antipertussis antibodies also recognized the peptide 8-18, which therefore represents at least a part of an antigenic determinant of the toxin, while no interaction could be evidenced between anti-cholera antibodies and any of the peptides, thus demonstrating important differences in the antigenic structures of the two toxins. None of the antipeptide antibodies examined showed protective activity against the toxins in a Chinese hamster ovary (CHO) cell test.

The quantitative assay of the clustering activity of the lymphocytosis-promoting factor (pertussis toxin) of Bordetella pertussis on Chinese hamster ovary (CHO) cells

An experimental design and a statistical method for the estimation of the clustering-response activity of lymphocytosis-promoting factor (LPF) in Chinese hamster ovary cells growing in wells on a microplate were investigated. The scoring method introduced by Ipsen was adopted to express the grade of the clustering response rather than the end-point method generally used. The scoring method was validated by statistical analyses. The grade of response varied with the location of the wells on a microplate, and thus the expression of the clustering activity of a test sample in terms of the end-point may be inadequate in terms of accuracy and reproducibility. It was shown that the allocation of test samples to individual wells according to a Latin square design minimized the effect of the location of wells on the clustering response. Under such experimental conditions, a fairly precise and reproducible method for the quantification of the clustering activity was developed.

Subunit S1 of pertussis toxin: mapping of the regions essential for ADP-ribosyltransferase activity

The toxicity of pertussis toxin is mediated by the ADP-ribosyltransferase activity of subunit S1. To understand the structure-function relationship of subunit S1 and guide the construction of nontoxic molecules suitable for vaccines, we constructed and expressed in Escherichia coli a series of amino-terminal and carboxyl-terminal deletion mutants as well as a number of molecules containing amino acid substitutions. The shortest peptide still retaining enzymatic activity contains amino acids 2-179. Within this region we identified three mutants in which amino acid substitutions abolish the enzymatic activity. Mutation of amino acids 8 and 9 or 50 and 53, located within the region of the S1 subunit of pertussis toxin homologous to cholera toxin, causes loss of enzymatic activity. Outside this homology region, substitution of Glu-129 with glycine or aspartic acid also eliminates the enzymatic activity of the S1 subunit. In this respect, Glu-129 resembles the glutamic acid that is crucial for the catalytic activity of diphtheria and Pseudomonas toxins. Once introduced into the Bordetella pertussis chromosome, the above mutations should lead to the synthesis of nontoxic pertussis toxin molecules suitable for vaccine production.

Pertussis: the disease and new diagnostic methods

Bordetella pertussis, the causative agent of whooping cough, produces an acute and chronic respiratory infection in infants and young children. B. pertussis is still a major health problem of young children throughout the world even though effective immunization against whooping cough is available. While predominantly a childhood disease, it has been reported also to be a cause of persistent cough in adults. This review discusses the numerous bacterial virulence factors that may play roles in the pathogenesis of pertussis and in immunity to infection. The present problems with pertussis diagnosis, recent advances, and future prospects for new and improved rapid diagnostics tests also are explored.

Dermonecrotic toxin and tracheal cytotoxin, putative virulence factors of Bordetella avium

We examined Bordetella avium for virulence factors common to Bordetella pertussis, including pertussis toxin, filamentous hemagglutinin, adenylate cyclase, dermonecrotic toxin, and tracheal cytotoxin. B. avium produced a dermonecrotic toxin and a tracheal cytotoxin. The dermonecrotic toxin of B. avium is a 155,000-molecular-weight, heat-labile protein which was lethal for mice, guinea pigs, young chickens, and turkey poults and produced dermonecrosis when injected intradermally into guinea pigs, chickens, and turkey poults. High-pressure liquid chromatography of B. avium culture supernatant fluid revealed the presence of a tracheal cytotoxin chemically identical to that produced by B. pertussis. B. avium isolates were negative for B. pertussis-like filamentous hemagglutinin and pertussis toxin when assayed with antibody against B. pertussis filamentous hemagglutinin and pertussis toxin. Furthermore, B. avium failed to induce the clustered CHO cell morphology characteristic of pertussis toxin. Adenylate cyclase assays indicated that B. avium does not produce an extracytoplasmic adenylate cyclase, even after passage through embryonated turkey eggs. Since production of virulence proteins by B. pertussis is regulated by growth in media containing nicotinamide or MgSO4 or by growth at reduced temperatures, we determined the effect of these supplements and growth conditions on production of dermonecrotic toxin by B. avium. Production of dermonecrotic toxin in B. avium was not altered by growth in media containing 100 microM FeSO4 or 500 micrograms of nicotinamide per ml or by growth at 25 or 42 degrees C, but production was significantly decreased by growth in media containing 20 mM MgSO4 and slightly reduced by growth in media containing 500 micrograms of nicotinic acid per ml. These studies revealed that B. avium is similar to B. pertussis in that both species produce a dermonecrotic toxin and a tracheal cytotoxin and production of dermonecrotic toxin is regulated by nicotinamide and MgSO4. The presence of dermonecrotic toxin and tracheal cytotoxin in all Bordetella species indicates that these products may be important virulence factors in bordetellosis.

A sensitive chemiluminescence assay for pertussis toxin and for evaluation of cell-free pertussis toxoids

Pertussis toxin (PT) inhibited luminol-enhanced chemiluminescence induced in rabbit peritoneal neutrophils by N'-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP) at doses as low as 0.8 ng.ml-1, even in the presence of a 10-fold higher concentration of filamentous haemagglutinin (FHA). A cell-free extract of Bordetella pertussis, containing predominantly PT and FHA, suppressed the neutrophil response to fMLP. After toxoiding with carbodiimide, the inhibitory activity of the extract was abolished and an enhancement of neutrophil chemiluminescence was observed due to FHA activity. Abrogation of the chemiluminescent response of neutrophils to fMLP is proposed as a sensitive, in vitro assay for pT, and may be useful for monitoring the residual toxin activity in pertussis toxoids and for determining the anti-toxic effects of anti-PT antibodies.

Immuno-electronmicroscopy of fimbriae-like structures on Bordetella pertussis serotype 1.3

Fimbriae-like filaments were demonstrated on the surface of Bordetella pertussis, serotype 1.3, by negative staining and electronmicroscopy. Immunoelectronmicroscopy with a monoclonal antibody specific for strains possessing agglutinogen 3, and colloidal gold, gave strong labelling of these structures. However, incubation with adsorbed polyclonal anti-agglutinogen 3 serum gave only weak labelling of the distal parts of the filaments and of the bacterial surface. The different binding patterns of the two antisera suggested that the epitopes involved were dissimilar. Thus, agglutinogen 3, as defined by conventional adsorbed sera, appeared to be associated with the fimbriae-like structures but was not necessarily identical to the fimbrial subunit protein. The monoclonal antibody, however was more likely directed against the subunits of the fimbriae-like structures on serotype 1.3 bacteria.

[Development of a method for the quantitative determination of Bordetella pertussis toxin and the prospects of its use for diagnosis]

Two variants of the enzyme immunoassay (EIA) systems for the determination of B. pertussis toxin (BPT), the "double sandwich" system and the competitive assay system, have been developed. For the titration of BPT in B. pertussis antigens the use of fetuin as the affinity base is preferable, and not antibodies from different paired animals. Of the two variants, the competitive EIA is more promising for diagnostic purposes.

The interaction between pertussis toxin and 10 monoclonal antibodies

Data on the epitope specificity of 10 monoclonal hybridoma antibodies (Mabs) that showed positive reaction in enzyme-linked immunosorbent assay (ELISA) towards pertussins toxin (Ptx) are presented. The relative functional affinity of the Mabs was determined in a catching ELISA system. The Mabs were tested for their ability to inhibit the biological activities of this toxin in two in vitro systems, viz. haemagglutination (HA) and Chinese Hamster Ovary cell (CHO) test, and in three in vivo assays: histamine sensitization (HS), leucocytosis-promoting activity (LP) and protection against intra-cerebral challenge (i.c.) with virulent B. pertussis organisms. Four Mabs were found inhibiting HA and three inhibited the effect on CHO cells. Two Mabs showed demonstrable protective effect on mice in i.c. test. The same two Mabs were also able to inhibit HS and LP activity of Ptx. Five of the ten Mabs reacted with Ptx subjected to blotting after separation of the toxin subunits in sodium-dodecyl sulphate polyacrylamide gel electrophoresis. The five Mabs all bound to more than one subunit. The epitopes defined by several of the Mabs might be useful in the context of a third-generation whooping cough vaccine.