Long-lived respiratory immune response to filamentous hemagglutinin following Bordetella pertussis infection

Highly attenuated Bordetella pertussis strain BPZE1 as a potential live vehicle for delivery of heterologous vaccine candidates

Bordetella pertussis, the causative agent of whooping cough, is a promising and attractive candidate for vaccine delivery via the nasal route, provided that suitable attenuation of this pathogen has been obtained. Recently, the highly attenuated B. pertussis BPZE1 strain has been described as a potential live pertussis vaccine for humans. We investigated here the use of BPZE1 as a live vehicle for heterologous vaccine candidates. Previous studies have reported the filamentous hemagglutinin (FHA), a major B. pertussis adhesin, as a carrier to express foreign antigens in B. pertussis. In this study, we also examined the BrkA autotransporter as a surface display system. Three copies of the neutralizing peptide SP70 from enterovirus 71 (EV71) were fused to FHA or in the passenger domain of BrkA, and each chimera was expressed in BPZE1. The FHA-(SP70)3 and BrkA-(SP70)3 chimeras were successfully secreted and exposed at the bacterial surface, respectively. Nasal administration of the live recombinant strains triggered a strong and sustained systemic anti-SP70 antibody response in mice, although the titers and neutralizing activities against EV71 were significantly higher in the sera of mice immunized with the BrkA-(SP70)3-producing strain. These data indicate that the highly attenuated BPZE1 strain is a potential candidate for vaccine delivery via the nasal route with the BrkA autotransporter as an alternative to FHA for the presentation of the heterologous vaccine antigens.

Genome rearrangements, deletions, and amplifications in the natural population of Bartonella henselae

Cats are the natural host for Bartonella henselae, an opportunistic human pathogen and the agent of cat scratch disease. Here, we have analyzed the natural variation in gene content and genome structure of 38 Bartonella henselae strains isolated from cats and humans by comparative genome hybridizations to microarrays and probe hybridizations to pulsed-field gel electrophoresis (PFGE) blots. The variation in gene content was modest and confined to the prophage and the genomic islands, whereas the PFGE analyses indicated extensive rearrangements across the terminus of replication with breakpoints in areas of the genomic islands. We observed no difference in gene content or structure between feline and human strains. Rather, the results suggest multiple sources of human infection from feline B. henselae strains of diverse genotypes. Additionally, the microarray hybridizations revealed DNA amplification in some strains in the so-called chromosome II-like region. The amplified segments were centered at a position corresponding to a putative phage replication initiation site and increased in size with the duration of cultivation. We hypothesize that the variable gene pool in the B. henselae population plays an important role in the establishment of long-term persistent infection in the natural host by promoting antigenic variation and escape from the host immune response.

Production of nontypeable Haemophilus influenzae HtrA by recombinant Bordetella pertussis with the use of filamentous hemagglutinin as a carrier

Bordetella pertussis, the etiologic agent of whooping cough, is a highly infectious human pathogen capable of inducing mucosal and systemic immune responses upon a single intranasal administration. In an attenuated, pertussis toxin (PTX)-deficient recombinant form, it may therefore constitute an efficient bacterial vector that is particularly well adapted for the delivery of heterologous antigens to the respiratory mucosa. Filamentous hemagglutinin (FHA) has been used as a carrier to present foreign antigens at the bacterial surface, thereby inducing local, systemic, and protective immune responses to these antigens in mice. Both full-length and truncated (Fha44) forms of FHA have been used for antigen presentation. To investigate the effect of the carrier (FHA or Fha44) on antibody responses to passenger antigens, we genetically fused the HtrA protein of nontypeable Haemophilus influenzae to either FHA form. The fha-htrA and Fha44 gene-htrA hybrids were expressed as single copies inserted into the chromosome of PTX-deficient B. pertussis. Both chimeras were secreted into the culture supernatants of the recombinant strains and were recognized by anti-FHA and anti-HtrA antibodies. Intranasal infection with the strain producing the FHA-HtrA hybrid led to significantly higher anti-HtrA and anti-FHA antibody titers than those obtained in mice infected with the Fha44-HtrA-producing strain. Interestingly, the B. pertussis strain producing the Fha44-HtrA chimera colonized the mouse lungs more efficiently than the parental, Fha44-producing strain and gave rise to higher anti-FHA antibody titers than those induced by the parental strain.

Molecular characterization of Bordetella bronchiseptica filamentous haemagglutinin and its secretion machinery

Two closely related pathogens, Bordetella pertussis and Bordetella bronchiseptica, share a number of virulence factors. Filamentous haemagglutinin (FHA) is widely regarded as the dominant adhesin of B. pertussis, and its multiple binding activities have been well characterized. This large protein is produced and secreted at high levels by B. pertussis and significantly lower levels by B. bronchiseptica strains. FHA secretion is mediated by a single outer-membrane accessory protein, FhaC. The genes encoding FHA and FhaC in B. bronchiseptica were characterized by sequencing and functional analyses and are highly similar to those of B. pertussis. The most distinctive feature of B. bronchiseptica FHA is additional repeats in the N-terminal portion of the predicted protein. Interestingly, a point mutation in the fhaB promoter region of the B. bronchiseptica GP1 isolate, relative to other isolates, was found to be detrimental to promoter activity and to FHA production. FhaC and the N-terminal secretion domain of FHA of B. bronchiseptica were fully functional for secretion in B. pertussis. Thus, the different levels of FHA secretion by these Bordetella species might reflect differences in physiology, composition and structure of cell envelope, or differential protein degradation. Characterization of FHA expression and function may provide clues as to the basis of host species tropism, tissue localization and receptor recognition.

Genital antibody responses in mice after intranasal infection with an attenuated candidate vector strain of Bordetella pertussis

Intranasal administration of live attenuated Bordetella pertussis, from which the pertussis toxin gene has been deleted, has previously been shown to give rise to high levels of serum immunoglobulin G (IgG) antibodies against both the protective antigen filamentous hemagglutinin (FHA) and heterologous antigens genetically fused to FHA. Here, we extend these results by demonstrating that anti-FHA IgA and IgG antibodies are also produced in the genital tract of mice, both in the vagina and in the uterus, after a single intranasal administration of B. pertussis. By comparing the immune responses induced after infection with wild-type virulent B. pertussis with that induced by infection with an attenuated pertussis toxin-deficient strain, we conclude that pertussis toxin produced by the virulent bacteria does not modify antibody production to FHA in the genital tract of B. pertussis-infected mice. The intranasal infection with either the attenuated or the virulent B. pertussis strain also led to the development of immunologic memory that could be efficiently boosted with purified FHA administered either intranasally or intravaginally to give rise to a significant increase in the levels of specific IgA and IgG produced locally in the genital tract, as well as of specific antibodies in the serum. These observations suggest that attenuated B. pertussis could be a promising vector for intranasal administration to induce antibody responses against antigens from sexually transmitted pathogens fused to FHA.

Detection of Bordetella bronchiseptica by the polymerase chain reaction

Polymerase chain reaction (PCR) assays were developed that enabled not only discriminative detection of three Bordetella species, B. pertussis, B. parapertussis, and B. bronchiseptica (Bspp PCR), but also specific detection of B. bronchiseptica (Bb PCR). An upstream sequence of the flagellin gene was used as a target DNA region. This sequence contained differences in B. pertussis, B. parapertussis, and B. bronchiseptica DNA. These species could then be differentiated using two different sets of primers, Bspp and Bb. When oligonucleotide Bspp primers were used, PCR products were obtained from the three species of Bordetella. A fragment of the expected size (164 bp) was amplified using B. bronchiseptica and B. parapertussis DNA, but a fragment with a distinct molecular weight was amplified with B. pertussis DNA (195 bp). This Bspp PCR was specific and sensitive, but it could not differentiate between B. parapertussis and B. bronchiseptica. When Bb primers were used, a 237-bp PCR product was detected only from B. bronchiseptica DNA. No PCR products were identified after Bb PCR amplification of DNAs either from B. parapertussis isolates or B. pertussis isolates, nor from other respiratory pathogen DNAs tested. This second PCR assay had a sensitivity limit of less than 10 organisms of B. bronchiseptica after detection with a specific probe. The specificity and the sensitivity of the fla PCR assay were evaluated with purified DNA, as was its capacity for detecting the bacteria in human clinical samples and in lungs of infected mice.

Intranasal priming with recombinant Bordetella pertussis for the induction of a systemic immune response against a heterologous antigen

One of the current goals in vaccine development is the noninvasive administration of protective antigens via mucosal surfaces. In this context, the gut-associated lymphoid tissues have already been extensively explored. Vaccination via the nasal route has only recently been the focus of intensive investigation, and no live vector specifically designed for the respiratory mucosa is yet available. In this study we show that intranasal administration of the recombinant Bordetella pertussis BPGR60, producing the Schistosoma mansoni 28-kDa glutathione S-transferase (Sm28GST) protective antigen fused to filamentous hemagglutinin, induces priming in mice for the production of serum antibodies. In addition to significant levels of anti-Sm28GST immunoglobulin A (IgA) antibodies, high levels of anti-Sm28GST serum antibodies were obtained after intranasal boost with the purified antigen or infection with S. mansoni following intranasal priming with BPGR60. These antibodies were of the IgG1, IgG2a, and IgG2b isotypes, suggesting a mixed immune response. No priming was observed in animals that had received nonrecombinant B. pertussis or purified Sm28GST, indicating specific priming by BPGR60. This priming was also evident in immune protection against S. mansoni challenge. Significant protection against worm burden and egg output was obtained in mice primed with BPGR60 and intranasally boosted with purified Sm28GST. A lower but still significant degree of protection against egg output was also obtained in mice infected with a single dose of BPGR60. These results indicate that intranasal administration of recombinant B. pertussis can prime for serum antibody responses against a foreign antigen and for heterologous protection.

Restricted B-cell responses to microbial challenge of the respiratory tract

The local B-cell response in the respiratory tract to infectious challenge has been analyzed in pigs and calves using two techniques: flow cytometry and antibody secreting cell (ASC) probes. Pneumonia in pigs caused by experimental infection with Mycoplasma hyopneumoniae resulted in a 25-fold increase in the B-cell population in BAL and lung parenchyma 28 days post infection. ASC probes revealed that the B-cell response of immune pigs to a large challenge infection was localized to lung parenchyma and tracheobronchal lymph nodes. Naive calves infected with Pasteurella multocida had a 5-fold increase in the B-cell blast population in lung parenchyma and BAL, and a greater than 60-fold increase in the draining lymph node at 9 days post infection. The ASC probes prepared post challenge from immune calves showed the response to be localized to the draining lymph nodes, with little response in lung parenchyma. A major finding was that ASC probes prepared from lung parenchyma and from pulmonary lymph nodes of both calves and pigs recognized a restricted range of bacterial antigens, particularly compared to the range of antigens recognized by concurrently circulating sera. The use of ASC probes demonstrates that there is a restricted B-cell repertoire in the respiratory tract.

Pertussis antigens that abrogate bacterial adherence and elicit immunity

Infectious disease processes follow the initial steps of adherence of the organism to host tissues and subsequent colonization of the target tissues that can occur through specific adhesion-receptor systems. Bordetella pertussis, the human pathogen that causes whooping cough, has evolved a genetically controlled system whereby adhesins are expressed when they enter the human host. Two adhesins, filamentous hemagglutinin (FHA) and pertactin, mediate the adherence of the bacterium to eukaryotic cells through varied attachment mechanisms, including lectin-like binding sites that interact with sulfated sugars on cell surface glycoconjugates and the ARG-GLY-ASP binding sequence, which recognizes a family of integrins found on the cell surface. The differential expression of relevant receptors by various eukaryotic cells likely plays a role in the pathogenesis and immune response to the bacterium by the host, directing the organism to specific cell types and to specific tissue sites. Substantial evidence exists that the B. pertussis adhesins, FHA and pertactin, elicit immune responses that are protective in animal models for the disease, including serum antibody production and local immune responses in the respiratory tract following nasal administration of encapsulated antigens. Both of these adhesins are components of new acellular pertussis vaccines that have proven safe and highly effective for prevention of serious disease in infants.

Induction of mucosal immune responses against a heterologous antigen fused to filamentous hemagglutinin after intranasal immunization with recombinant Bordetella pertussis

Live vaccine vectors are usually very effective and generally elicit immune responses of higher magnitude and longer duration than nonliving vectors. Consequently, much attention has been turned to the engineering of oral pathogens for the delivery of foreign antigens to the gut-associated lymphoid tissues. However, no bacterial vector has yet been designed to specifically take advantage of the nasal route of mucosal vaccination. Herein we describe a genetic system for the expression of heterologous antigens fused to the filamentous hemagglutinin (FHA) in Bordetella pertussis. The Schistosoma mansoni glutathione S-transferase (Sm28GST) fused to FHA was detected at the cell surface and in the culture supernatants of recombinant B. pertussis. The mouse colonization capacity and autoagglutination of the recombinant microorganism were indistinguishable from those of the wild-type strain. In addition, and in contrast to the wild-type strain, a single intranasal administration of the recombinant strain induced both IgA and IgG antibodies against Sm28GST and against FHA in the bronchoalveolar lavage fluids. No anti-Sm28GST antibodies were detected in the serum, strongly suggesting that the observed immune response was of mucosal origin. This demonstrates, to our knowledge, for the first time that recombinant respiratory pathogens can induce mucosal immune responses against heterologous antigens, and this may constitute a first step toward the development of combined live vaccines administrable via the respiratory route.

Virulence of Bordetella bronchiseptica: role of adenylate cyclase-hemolysin

Bordetella bronchiseptica is a pathogen of laboratory, domestic, and wild animals and sometimes of humans. In the present study some characteristics of the virulence of B. bronchiseptica isolates of different origin were studied. All isolates had similar phenotypes, similar bacteriological characters, and synthesized adenylate cyclase-hemolysin, filamentous hemagglutinin and pertactin but not pertussis toxin. These isolates, however, differed in their ability to express dermonecrotic toxin and to cause a lethal infection, but no correlation was found with the human or animal origin of the isolates. The fact that the most virulent isolate did not express dermonecrotic toxin suggests that this toxin does not play an important role in the virulence of the bacteria in the murine model. After infection with virulent B. bronchiseptica a very early synthesis and a persistence of anti-adenylate cyclase-hemolysin and anti-filamentous hemagglutinin antibodies were observed in the sera of infected mice, suggesting a persistence of the bacteria or of its antigens. B. bronchiseptica adenylate cyclase-hemolysin was purified and was shown to be a major protective antigen against B. bronchiseptica infection. Furthermore, we showed that its immunological and protective properties were different from that of B. pertussis adenylate cyclase-hemolysin, confirming that Bordetella species are immunologically different.