Characterization of murine lung inflammation after infection with parental Bordetella pertussis and mutants deficient in adhesins or toxins.

Bordetella pertussis expresses factors such as filamentous hemagglutinin, agglutinogens, pertactin, and pertussis toxin, which participate in bacterial adhesion; pertussis toxin, dermonecrotic toxin, lipopolysaccharide, and tracheal cytotoxin, which are responsible for toxic effects; and adenylate cyclase-hemolysin, which is required to initiate infection. By using a murine respiratory model, we showed that the RGD sequences of filamentous hemagglutinin and pertactin are important for bacterial persistence. However, mutants deficient in filamentous hemagglutinin and agglutinogens or in pertactin and the RGD sequence of filamentous hemagglutinin behaved as did wild-type B. pertussis, i.e., induced bronchopneumonia, alveolitis, and an influx of macrophages, lymphocytes, and polymorphonuclear leukocytes into bronchoalveolar lavage fluids. These results suggest that these adhesins are not involved in the induction of pulmonary lesions following infection. The intensity of inflammation was markedly reduced after infection with mutants deficient in either hemolytic activity or pertussis toxin expression, whereas a mutant devoid of adenylate cyclase activity behaved as did the avirulent mutant. Pertussis toxin and adenylate cyclase-hemolysin may act indirectly by altering immune cell functions and thus allowing other factors, such as filamentous hemagglutinin, agglutinogens, and pertactin, to trigger adhesion and lipopolysaccharide, dermonecrotic toxin, and tracheal cytotoxin to induce their toxic effects. However, it is possible that pertussis toxin is also responsible for the induction of some pulmonary alterations.     

Western blot analysis of antibody responses of young infants to pertussis infection

Western blot and agglutination techniques were used to analyze the antibody responses toBordetella pertussis in 27 infants less than six month of age with presumed pertussis infection. The antibody response to theBordetella pertussis adhesins filamentous hemagglutinin, pertactin and agglutinogens, and to theBordetella pertussis toxins pertussis toxin and adenylate cyclase-hemolysin were compared. Infection induced intense antibody responses to filamentous hemagglutinin, pertussis toxin and adenylate cyclase-hemolysin. Antibodies to agglutinogens were never detected, and antibodies to pertactin were rarely detected in infected infants' sera. Therefore, determination of anti-agglutinogens levels only is not suitable for the serological diagnosis of pertussis in young infants. Use of purified filamentous hemagglutinin, pertussis toxin and adenylate cyclase-hemolysin in Western blot analysis may improve the serodiagnosis ofBordetella infections. However, care must be exercised in distinguishing between the antibody response in young infants and maternally derived antibodies.     

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.     

Long-term human serum antibody responses after immunization with whole-cell pertussis vaccine in France.

Three hundred sixty children were tested for pertussis serology 0.5 to 1.58 months after complete whole-cell pertussis vaccination. An immunoblot assay was used to detect serum antibodies to pertussis toxin, filamentous hemagglutinin, adenylate cyclase-hemolysin, and pertactin, and agglutination was used for detection of anti-agglutinogen antibodies. Antibodies against pertussis toxin, pertactin, and agglutinogens decreased rapidly after vaccination but increased secondarily, suggesting exposure to infected persons. In contrast, anti-filamentous hemagglutinin antibodies persisted and anti-adenylate cyclase-hemolysin antibodies increased continuously, suggesting either cross-reaction with non-Bordetella antigens or exposure to Bordetella isolates expressing these two antigens, including Bordetella pertussis. These data suggest that unrecognized pertussis is common in France despite massive and sustained immunization in infants and that vaccinated children become susceptible to infection more than 6 years after their last vaccination.     

The Virulence Factors of Bordetella pertussis: Talented Modulators of Host Immune Response

Approximately 40 million whooping cough cases and between 200,000 and 400,000 pertussis-linked deaths are recorded each year. Although several types of vaccines are licensed and widely used, Bordetella pertussis continues to circulate in populations with high vaccine coverage of infants and children due to the waning of protection induced by the vaccination. B. pertussis typically expresses a wide array of virulence factors which promote bacterial adhesion and invasion by altering the local environment, including pertussis toxin, tracheal cytotoxin, adenylate cyclase toxin, filamentous hemagglutinin, and the lipooligosaccharide. The virulence factors of B. pertussis also possess immunomodulatory properties, exerted through their enzymatic and receptor-binding activities. Both pro- and anti-inflammatory effects are mediated, that can subvert host innate and adaptive immunity and favor the onset of a long-term infection. This review describes the capacities of B. pertussis virulence factors to modulate host immune responses and the mechanisms employed, which have been the subject of extensive research in the recent years, both in murine and human experimental systems. Knowledge of these mechanisms is gaining increasing importance, since it could provide in the near future the basis for the identification of therapeutic agents for modulating the immune system as well as novel molecular targets to treat pertussis.     

Filamentous Hemagglutinin of Bordetella bronchiseptica Is Required for Efficient Establishment of Tracheal Colonization

Adherence to ciliated respiratory epithelial cells is considered a critical early step in Bordetella pathogenesis. For Bordetella pertussis, the etiologic agent of whooping cough, several factors have been shown to mediate adherence to cells and cell lines in vitro. These putative adhesins include filamentous hemagglutinin (FHA), fimbriae, pertactin, and pertussis toxin. Determining the precise roles of each of these factors in vivo, however, has been difficult, due in part to the lack of natural-host animal models for use with B. pertussis. Using the closely related species Bordetella bronchiseptica, and by constructing both deletion mutation and ectopic expression mutants, we have shown that FHA is both necessary and sufficient for mediating adherence to a rat lung epithelial (L2) cell line. Using a rat model of respiratory infection, we have shown that FHA is absolutely required, but not sufficient, for tracheal colonization in healthy, unanesthetized animals. FHA was not required for initial tracheal colonization in anesthetized animals, however, suggesting that its role in establishment may be dedicated to overcoming the clearance action of the mucociliary escalator.     

Substantial gaps in knowledge of Bordetella pertussis antibody and T cell epitopes relevant for natural immunity and vaccine efficacy

The recent increase in whooping cough in vaccinated populations has been attributed to waning immunity associated with the acellular vaccine. The Immune Epitope Database (IEDB) is a repository of immune epitope data from the published literature and includes T cell and antibody epitopes for human pathogens. The IEDB conducted a review of the epitope literature, which revealed 300 Bordetella pertussis-related epitopes from 39 references. Epitope data are currently available for six virulence factors of B. pertussis: pertussis toxin, pertactin, fimbrial 2, fimbrial 3, adenylate cyclase and filamentous hemagglutinin. The majority of epitopes were defined for antibody reactivity; fewer T cell determinants were reported. Analysis of available protective correlates data revealed a number of candidate epitopes; however few are defined in humans and few have been shown to be protective. Moreover, there are a limited number of studies defining epitopes from natural infection versus whole cell or acellular/subunit vaccines. The relationship between epitope location and structural features, as well as antigenic drift (SNP analysis) was also investigated. We conclude that the cumulative data is yet insufficient to address many fundamental questions related to vaccine failure and this underscores the need for further investigation of B. pertussis immunity at the molecular level.     

Bordetella adenylate cyclase is a virulence associated factor and an immunoprotective antigen

Bordetella pertussis and Bordetella parapertussis are both causative agents of whooping cough outbreaks. Although not expressing the pertussis toxin, B. parapertussis induces, in a murine model, an acute hemorrhagic edematous alveolitis, similar to that observed with B. pertussis. These data suggest that the pertussis toxin may only play an accessory role in the acute pulmonary syndrome observed during Bordetella infection. Both with B. pertussis and B. parapertussis, the ability to induce lethal pulmonary lesions is associated with enhanced in vitro adenylate cyclase expression and activity. We also demonstrate that passive immunization with specific anti-B. pertussis adenylate cyclase antibodies or active immunization with purified B. pertussis secreted adenylate cyclase protect mice against a lethal respiratory challenge with B. pertussis or B. parapertussis. Our results suggest that adenylate cyclase might be the primary cytotoxin responsible for mouse pulmonary lesions during respiratory tract infection with B. pertussis or with the related species B. parapertussis and is a protective antigen of B. pertussis.     

Role of pertussis toxin in causing symptoms ofBordetella parapertussis infection

Whooping cough can be caused by eitherBordetella pertussis orBordetella parapertussis. Although the two species share an almost complete DNA identity,Bordetella parapertussis does not produce pertussis toxin, which is thought to be the main virulence factor ofBordetella pertussis. In order to elucidate the role of pertussis toxin in causing the typical symptoms of whooping cough, clinical information from 33 patients with culture-positiveBordetella parapertussis infection was collected and compared to that from 331 patients with infection caused byBordetella pertussis. Isolated strains ofBordetella parapertussis lacked pertussis toxin expression, as was demonstrated by negative tests for histamine sensitization. This was further substantiated in vivo by a significantly lower leukocyte count in the parapertussis group as compared to the pertussis group. Frequencies of typical symptoms of whooping cough, such as paroxysmal coughing, whooping and vomiting, were almost identical in the two groups. Nocturnal coughing and contact anamnesis were noted more often in theBordetella pertussis group. Children in the parapertussis group were significantly more often vaccinated with whole-cell pertussis vaccine than children infected withBordetella pertussis. The results indicate that pertussis toxin may not play a decisive role in causing the typical symptoms of whooping cough, such as paroxysmal coughing, whooping and vomiting.     

Analysis of <Emphasis Type="Italic">Bordetella pertussis</Emphasis> clinical isolates circulating in European countries during the period 1998–2012

Despite more than 50 years of vaccination, pertussis is still an endemic disease, with regular epidemic outbreaks. With the exception of Poland, European countries have replaced whole-cell vaccines (WCVs) by acellular vaccines (ACVs) in the 1990s. Worldwide, antigenic divergence in vaccine antigens has been found between vaccine strains and circulating strains. In this work, 466 Bordetella pertussis isolates collected in the period 1998–2012 from 13 European countries were characterised by multi-locus antigen sequence typing (MAST) of the pertussis toxin promoter (ptxP) and of the genes coding for proteins used in the ACVs: pertussis toxin (Ptx), pertactin (Prn), type 2 fimbriae (Fim2) and type 3 fimbriae (Fim3). Isolates were further characterised by fimbrial serotyping, multi-locus variable-number tandem repeat analysis (MLVA) and pulsed-field gel electrophoresis (PFGE). The results showed a very similar B. pertussis population for 12 countries using ACVs, while Poland, which uses a WCV, was quite distinct, suggesting that ACVs and WCVs select for different B. pertussis populations. This study forms a baseline for future studies on the effect of vaccination programmes on B. pertussis populations.     

Bordetella pertussis virulence factors affect phagocytosis by human neutrophils

The interaction between human neutrophils and wild-type Bordetella pertussis or mutants expressing altered lipopolysaccharide or lacking virulence factors-pertussis toxin, adenylate cyclase toxin, dermonecrotic toxin, filamentous hemagglutinin (FHA), pertactin, or BrkA-was examined. In the absence of antibodies, the wild-type strain and the mutants, with the exception of mutants lacking FHA, attached efficiently to neutrophils. The addition of opsonizing antibodies caused a significant reduction (approximately 50%) in attachment of the wild-type strain and most of the mutants expressing FHA, suggesting that bacterium-mediated attachment is more efficient than Fc-mediated attachment. Phagocytosis was also examined. In the absence of antibodies, about 12% of the wild-type bacteria were phagocytosed. Opsonization caused a statistically significant reduction in phagocytosis (to 3%), possibly a consequence of reduced attachment. Phagocytosis of most of the mutants was similar to that of the wild type, with the exception of the mutants lacking adenylate cyclase toxin. About 70% of the adenylate cyclase toxin mutants were phagocytosed, but only in the presence of opsonizing antibody, suggesting that Fc receptor-mediated signaling may be needed for phagocytosis. These studies indicate that FHA mediates attachment of B. pertussis to neutrophils, but adenylate cyclase toxin blocks phagocytosis.     

T-Cell Immune Response Assessment as a Complement to Serology and Intranasal Protection Assays in Determining the Protective Immunity Induced by Acellular Pertussis Vaccines in Mice

The relative value of antibodies and/or T-cell immune responses to Bordetella pertussis antigens in the immunity induced by acellular pertussis (aP) vaccines is still an open issue, probably due to the incomplete knowledge on the mechanisms of protective immunity to pertussis. The relevance of T-cell immune responses in protection from pertussis has been demonstrated in murine and human models of infection; thus, in this study, the ability of different vaccine preparations of three component (pertussis toxin, filamentous hemagglutinin, and pertactin) aP vaccines to induce T-cell responses was investigated in mice. All vaccine preparations examined passed the immunogenicity control test, based on antibody titer assessment, according to European Pharmacopoeia standards, and protected mice from B. pertussis intranasal challenge, but not all preparations were able to prime T cells to pertussis toxin, the specific B. pertussis antigen. In particular, one vaccine preparation was unable to induce proliferation and gamma interferon (IFN-γ) production while the other two gave borderline results. The evaluation of T-cell responses to pertussis toxin antigen may provide information on the protective immunity induced by aP vaccines in animal models. Considering the critical role of the axis interleukin-12-IFN-γ for protection from pertussis, our results suggest that testing the induction of a key protective cytokine such as IFN-γ could be an additional tool for the evaluation of the immune response induced by aP vaccines.     

Bordetella pertussis and Bordetella parapertussis: two immunologically distinct species.

Bordetella pertussis and Bordetella parapertussis are closely related species. Both are responsible for outbreaks of whooping cough in humans and produce similar virulence factors, with the exception of pertussis toxin, specific to B. pertussis. Current pertussis whole-cell vaccine will soon be replaced by acellular vaccines containing major adhesins (filamentous hemagglutinin and pertactin) and major toxin (pertussis toxin). All of these factors are antigens that stimulate a protective immune response in the murine respiratory model and in clinical assays. In the present study, we examined the protective efficacies of these factors, and that of adenylate cyclase-hemolysin, another B. pertussis toxin, against B. parapertussis infection in a murine respiratory model. As expected, pertussis toxin did not protect against B. parapertussis infection, since this bacterium did not express this protein, but the surprising result was that none of the other factors were protective against B. parapertussis infection. Furthermore, B. parapertussis adenylate cyclase-hemolysin, although it protected against B. parapertussis infection, did not protect against B. pertussis infection. Despite a high degree of homology between both B. pertussis and B. parapertussis species, no cross-protection was observed. Our results outline the fact that, as in other gram-negative bacteria, Bordetella surface proteins vary immunologically.     

Tn5-induced mutations affecting virulence factors of Bordetella pertussis.

Transposon Tn5 was used to isolate mutants of Bordetella pertussis. Strains with Tn5 insertions were screened for loss of virulence-associated factors, including filamentous hemagglutinin, hemolysin, and pertussis toxin. Several mutants deficient for hemolysin production were obtained. All produced dermonecrotic toxin, pertussis toxin, and filamentous hemagglutinin, but were found to vary with respect to adenylate cyclase production. One hemolysin mutant had no detectable adenylate cyclase activity; others had 0.6% or 16% wild-type activity, whereas a fourth seemed to be unaffected in terms of adenylate cyclase activity. Mutants deficient in the ability to hemagglutinate sheep erythrocytes were also isolated. These mutants either failed to synthesize or produced reduced amounts of three protein species of 200,000, 130,000, and 100,000 daltons, all of which reacted with antiserum to filamentous hemagglutinin. Pertussis toxin mutants were identified by screening culture supernatants for failure to induce a clustered growth pattern in Chinese hamster ovary cells, and identification was confirmed by the standard histamine-sensitizing assay in mice. These mutants will be useful to determine the relative contribution of each virulence factor to pathogenicity as well as to determine the identity of the antigens important in protective immunity.     

Immunogenicity and protective efficacy of a newly developed tri-component diphtheria,tetanus, and acellular pertussis vaccine in a murine model

Background/Purpose

Although assessing the immunogenicity and protective efficacy of acellular pertussis (aP) vaccines via murine model studies faces limitations, preliminary assessments have been achieved by evaluating respiratory challenge and humoral and cellular immunity.

Immune Responses to Pertussis Antigens in Infants and Toddlers after Immunization with Multicomponent Acellular Pertussis Vaccine

Given the resurgence of pertussis despite high rates of vaccination with the diphtheria-tetanus-acellular pertussis (DTaP) vaccine, a better understanding of vaccine-induced immune responses to Bordetella pertussis is needed. We investigated the antibody, cell-mediated, and cytokine responses to B. pertussis antigens in children who received the primary vaccination series (at 2, 4, and 6 months) and first booster vaccination (at 15 to 18 months) with 5-component acellular pertussis (aP) vaccine. The majority of subjects demonstrated a 4-fold increase in antibody titer to all four pertussis antigens (pertussis toxin [PT], pertactin [PRN], filamentous hemagglutinin [FHA], and fimbriae [FIM]) following the primary series and booster vaccination. Following the primary vaccine series, the majority of subjects (52 to 67%) mounted a positive T cell proliferative response (stimulation index of ≥3) to the PT and PRN antigens, while few subjects (7 to 12%) mounted positive proliferative responses to FHA and FIM. One month after booster vaccination (age 16 to 19 months), our study revealed significant increase in gamma interferon (IFN-γ) production in response to the PT and FIM antigens, a significant increase in IL-2 production with the PT, FHA, and PRN antigens, and a lack of significant interleukin-4 (IL-4) secretion with any of the antigens. While previous reports documented a mixed Th1/Th2 or Th2-skewed response to DTaP vaccine in children, our data suggest that following the first DTaP booster, children aged 16 to 19 months have a cytokine profile consistent with a Th1 response, which is known to be essential for clearance of pertussis infection. To better define aP-induced immune responses following the booster vaccine, further studies are needed to assess cytokine responses pre- and postbooster in DTaP recipients.     

Role of Bordetella pertussis virulence factors in adherence to epithelial cell lines derived from the human respiratory tract

During colonization of the respiratory tract by Bordetella pertussis, virulence factors contribute to adherence of the bacterium to the respiratory tract epithelium. In the present study, we examined the roles of the virulence factors filamentous hemagglutinin (FHA), fimbriae, pertactin (Prn), and pertussis toxin (PT) in the adherence of B. pertussis to cells of the human bronchial epithelial cell line NCI-H292 and of the laryngeal epithelial cell line HEp-2. Using B. pertussis mutant strains and purified FHA, fimbriae, Prn, and PT, we demonstrated that both fimbriae and FHA are involved in the adhesion of B. pertussis to laryngeal epithelial cells, whereas only FHA is involved in the adherence to bronchial epithelial cells. For PT and Prn, no role as adhesion factor was found. However, purified PT bound to both bronchial and laryngeal cells and as such reduced the adherence of B. pertussis to these cells. These data may imply that fimbriae play a role in infection of only the laryngeal mucosa, while FHA is the major factor in colonization of the entire respiratory tract.     

Detection ofBordetella pertussis by determination of adenylate cyclase activity

The adenylate cyclase activity ofBordetella pertussis in clinical isolates was measured in calmodulin-supplemented Stainer-Scholte broth by the rate of conversion of ATP to cyclic AMP. Analysis of 250 stock strains ofBordetella pertussis showed that measurable adenylate cyclase activity was produced by all strains. In clinical testsBordetella pertussis was isolated from 135 (22 %) of 605 swab samples. Increased adenylate cyclase activity was detected in 124 (92 %) Stainer-Scholte broth cultures of these samples. A total of 475 swabs contained other bacteria or had no growth; only one of the Stainer-Scholte broth cultures of these swab samples contained measurable adenylate cyclase activity. The results indicate that testing for adenylate cyclase activity provides a specific and sensitive means for detectingBordetella pertussis in clinical specimens.     

Purification and characterisation of a fimbrial haemagglutinin from Bordetella pertussis for use in an enzyme-linked immunosorbent assay

The fimbrial haemagglutinin (F-HA) of Bordetella pertussis grown on solid medium was extracted with 1M sodium acetate for 72 h at 20 degree C, and partially purified by Sephacryl S-300 gel chromatography. A pooled fraction with fimbrial haemmagglutinating activity was shown to contain fimbriae haemagglutinating activity was shown to contain fimbriae of the expected morphology by electron microscopy. Chemical and biological assays showed that the F-HA fraction contained some heat-labile agglutinogen and lipopolysaccharide but no measureable lymphocytosis-promoting factor or heat-labile toxin. The F-HA fraction used as antigen in an enzyme-linked immunosorbent assay (ELISA) permitted the detection of antibodies in convalescent serum from a patient with whooping cough. The impurities, heat-labile agglutinogens and lipopolysaccharide, did not contribute to the ELISA activity. The method for preparation of the F-HA antigen is simple, reproducible and gives a high yield.     

Adenylate cyclase toxin is critical for colonization and pertussis toxin is critical for lethal infection by Bordetella pertussis in infant mice.

Proliferation of Bordetella pertussis in the lungs of infant mice challenged by the intranasal route was examined. The bacteria rapidly proliferated in the lungs of mice challenged with a sublethal dose of a wild-type strain (BP338) or a filamentous hemagglutinin mutant (BPM409) from 500 at day 0 to 10(7) at day 15. The infection cleared in about 40 days. Pertussis toxin-deficient mutant BP357 gave a similar profile; however, the number of bacteria recovered was slightly reduced, suggesting that pertussis toxin is not essential for bacterial growth in the lungs. In contrast, adenylate cyclase toxin mutant BP348 was rapidly cleared from the lungs, with no viable bacteria remaining 10 days postchallenge, suggesting that the adenylate cyclase toxin is a colonization factor required for the bacteria to initiate infection.