Comparative roles of the Arg-Gly-Asp sequence present in the Bordetella pertussis adhesins pertactin and filamentous hemagglutinin

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.

Effect of hydromechanical stress on cellular antigens of Bordetella pertussis

Cells of Bordetella pertussis grown in a bioreactor under stirring conditions were studied to investigate the effect of shear stress on cellular-bound filamentous haemagglutinin (FHA). FHA attached to the bacterial surface, unlike extracellular FHA, was not affected at the shear levels tested. Moreover, no other cellular immunogen involved in the whole-cell protective activity seemed to be affected by hydromechanical forces.

The OmpU outer membrane protein, a potential adherence factor of Vibrio cholerae

Expression of the OmpU outer membrane protein of Vibrio cholerae is positively regulated by toxR, which also regulates critical virulence factors such as cholera toxin and the toxin-coregulated pilus colonization factor. In this study, we have characterized the 38-kDa OmpU protein and investigated its role in the adhesion of V. cholerae to mammalian cells. The amino-terminal sequence of OmpU has similarity with the sequences of Haemophilus influenzae HMW1 and HMW2 adhesins, which, in turn, also have similarity with the sequence of Bordetella pertussis filamentous hemagglutinin. A monoclonal antibody directed against FHA recognized both V. cholerae OmpU and Escherichia coli OmpA, and polyclonal anti-OmpU antibodies recognized FHA and E. coli OmpA, suggesting the existence of common epitopes among these proteins. OmpU was strongly recognized by convalescent-phase serum from volunteers experimentally infected with virulent V. cholerae strains, indicating that OmpU is immunogenic and produced in vivo. OmpU selectively bound to fibronectin and to an arginine-glycine-asparagine (RGD) tripeptide but not to other matrix glycoproteins tested such as collagen or laminin. Antibodies directed against OmpU or their F(ab)2 fragments completely inhibited adhesion of several V. cholerae strains to HeLa, HEp-2, Caco-2, and Henle 407 epithelial cells and also inhibited intestinal colonization and conferred protection in newborn mice against both biotypes (El Tor and classical) of V. cholerae O1. Collectively, these data indicate that OmpU has adhesive properties which may play a role in the pathogenesis of cholera.

Tracheal colonization factor: a Bordetella pertussis secreted virulence determinant

We report here the identification of a virulence-associated factor, Tcf, (tracheal colonization factor), produced by strains of Bordetella pertussis but not Bordetella parapertussis or Bordetella bronchiseptica. This protein is encoded by the tcfA gene. When a strain of B. pertussis 18323 lacking this protein is used to infect mice with an aerosol challenge, the number of bacteria isolated from the tracheas is decreased 10-fold when compared with the parent 18323. The derived amino acid sequence of tcfA predicts a 68 kDa RGD-containing, proline-rich protein, which after cleavage of a typical prokaryotic signal sequence would be 64 kDa. Amino acid sequence analysis demonstrates that the C-terminal 30 kDa of this protein shows 50% identity to the 30 kDa C-terminus of another Bordetella protein, the pertactin precursor. The N-terminal 34 kDa region contains the three amino-acid motif RGD and is 16.5% proline. Coupled in vitro transcription and translation analysis indicates that the tcfA gene product migrates as two bands of approximately 90 kDa. A fusion protein of the N-terminal, 34 kDa portion of Tcf to maltose-binding protein migrates, on SDS-PAGE, 30 kDa higher than expected from the combined molecular weights. Polyclonal antisera raised against the unique N-terminal portion of Tcf recognizes 90 kDa and 60 kDa bands in immunoblots of whole-cell lysates of strains of B. pertussis; it does not recognize any protein in whole-cell lysates of B. bronchiseptica or B. parapertussis. Supernatants of cultures of B. pertussis 18323 contain the 60 kDa form of the protein. Southern blot analysis of chromosomal DNA from strains of B. bronchiseptica and B. parapertussis, using a probe derived from tcfA, shows strong hybridization only to B. pertussis DNA. Thus, Tcf appears to be a unique virulence factor of B. pertussis.

Invasion and intracellular survival of Bordetella bronchiseptica in mouse dendritic cells

We have studied the interaction between the respiratory pathogen Bordetella bronchiseptica and murine spleen dendritic cells, important antigen-presenting cells that are found in the airway epithelium. Wild-type B. bronchiseptica 5376 attached very efficiently to dendritic cells, whereas the bvg mutant ATCC 10580, wild-type strain BB7865, and its spontaneous delta bvgS mutant BB7866 bound less efficiently. However, all tested B. bronchiseptica strains were able to invade dendritic cells and survive intracellularly for at least 72 h. These results suggest that bvg-independent or bvg-downregulated products are involved in the uptake and intracellular survival. Transmission electron microscopic analysis revealed that bacteria grew and replicated intracellularly and were present in typical phagosomes, which fused with lysosomes during the initial infection period. However, in later infection stages some bacteria seemed to escape into an unfused endocytic compartment, where individual bacteria were tightly surrounded by a membrane. The in vitro interaction of B. bronchiseptica with dendritic cells reported here may be relevant to natural infections caused by this organism that lead to chronicity or an altered immune response.

Mechanisms involved in uptake of Bordetella bronchiseptica by mouse dendritic cells

The invasion and intracellular survival of Bordetella bronchiseptica in mouse dendritic cells were investigated. The results obtained suggest that B. bronchiseptica binds specifically to glycosylated receptors present on the plasma membrane of dendritic cells, thereby inducing a signal that triggers an actin polymerization-dependent phagocytic process, probably via a protein kinase-dependent transducing phosphorylation signal. The energy required for the uptake process by host cells is provided mainly by the glycolytic pathway. An intact microtubule system and de novo protein synthesis in eukaryotic and prokaryotic cells are essential for efficient uptake and intracellular survival. The interaction of B. bronchiseptica with dendritic cells may be pertinent to natural infections that follow a chronic clinical course and predispose to secondary infections, and to the T-cell response involved in protective immunity following infections caused by Bordetella spp.

Sulfated glycoconjugate receptors for the Bordetella pertussis adhesin filamentous hemagglutinin (FHA) and mapping of the heparin-binding domain on FHA

Filamentous hemagglutinin (FHA) is a major adhesin present on the surface of the gram-negative respiratory pathogen Bordetella pertussis. A number of binding mechanisms have been described for the interaction of FHA with eukaryotic cells. We have focused on its function as a sulfated polysaccharide-binding protein and on identifying potential receptors for FHA on the epithelial cell surface. Using a thin-layer overlay technique, we found that FHA binds specifically to sulfated glycolipids but not to gangliosides or other neutral glycolipids. These results suggest that epithelial cell surface sulfated glycolipids function as receptors for FHA. Further studies demonstrated that a Chinese hamster ovary (CHO) cell strain deficient in glycosaminoglycan expression exhibits greatly diminished attachment to FHA. By FHA-Affi-Gel chromatography, a putative receptor for FHA that has characteristics consistent with a heparan sulfate proteoglycan was isolated from epithelial cell extracts. In addition, by using recombinant FHA fusion proteins, a specific glycosaminoglycan-binding domain located near the N terminus of the FHA molecule was identified. Our results indicate that the B. pertussis adhesin FHA may utilize sulfated glycolipids and proteoglycans commonly found on the surface of human cells and tissues to initiate infection.

Cloning and sequencing of a Bordetella pertussis serum resistance locus

We have characterized a new virulence factor in Bordetella pertussis: serum resistance. Compared with Escherichia coli HB101, wild-type B. pertussis was relatively resistant to classical-pathway, complement-dependent killing by normal human serum. However, a mutant of B. pertussis (BPM2041) which is less virulent in mice and which has Tn5 lac inserted in a previously uncharacterized bvg-regulated gene was found to be at least 10-fold more susceptible to serum killing than the wild type. We have named this locus brk, for Bordetella resistance to killing. We have cloned and sequenced the brk locus, and it encodes two divergently transcribed open reading frames (ORFs), termed BrkA and BrkB. Both ORFs are necessary for serum resistance. Within the 300 bases which separate the two ORFs and upstream of each ORF are putative sites for BvgA binding. BrkA shows 29% identity to pertactin and has two RGD motifs in addition to a conserved proteolytic processing site and an outer membrane targeting signal. Like pertactin, BrkA is involved in adherence and invasion. Despite the similarities, a pertactin mutant was found to be not as sensitive to serum killing as the BrkA or BrkB mutants. BrkB is similar to ORFs in E. coli and Mycobacterium leprae and displays domains of homology to various transporters. On the basis of its hydropathy profile, BrkB is predicted to be a cytoplasmic membrane protein. By Southern blot, brk sequences were found in Bordetella bronchiseptica and Bordetella parapertussis but not in Bordetella avium.

A Haemophilus influenzae IgA protease-like protein promotes intimate interaction with human epithelial cells

Haemophilus influenzae represents a common cause of human disease and an important source of morbidity and mortality. Disease caused by this organism begins with colonization of the upper respiratory tract. Several studies indicate that H. influenzae is capable of binding to and entering cultured human cells, properties which are potentially of relevance to the process of colonization. In the present study, we isolated an H. influenzae gene designated hap, which is associated with the capacity for in vitro attachment and entry. Analysis of the derived amino acid sequence of hap demonstrated significant homology with the serine-type IgA1 proteases expressed by H. influenzae and Neisseria gonorrhoeae. It is notable that the hap product shares the catalytic domain of the IgA1 proteases and appears to be processed and secreted in an analogous manner. We speculate that the hap gene product is an important determinant of colonization, perhaps enabling the organism to evade the local immune response and thereby persist within the respiratory tract.

Epithelial cell invasion and survival of Bordetella bronchiseptica

Wild-type Bordetella bronchiseptica and a bvg mutant strain were used for invasion and survival experiments in human Caco-2 and A549 epithelial cells. Both bacterial strains were able to enter and persist within the host cells for at least a week. A significant proportion of the bacteria from both B. bronchiseptica strains but not from Bordetella pertussis were found free in the cytoplasm, suggesting different invasion and survival strategies of the two species in epithelial cells.

Heparin-inhibitable lectin activity of the filamentous hemagglutinin adhesin of Bordetella pertussis

Bordetella pertussis, the etiologic agent of whooping cough, produces an outer membrane-associated filamentous hemagglutinin (FHA) which is the major adhesin of this organism. FHA exhibits a lectin-like activity for heparin and dextran sulfate. By using in vitro adherence assays to cultured epithelial cells, the attachment of B. pertussis was reduced in the presence of sulfated polysaccharides such as heparin and dextran sulfate but not in the presence of dextran, indicating the crucial role of polysaccharide sulfation. In addition, inhibition of cellular sulfation by chlorate treatment of the cells resulted in a reduction of B. pertussis adherence, suggesting that epithelial cell surface-exposed sulfated glycoconjugates may serve as receptors for the microorganism. B. pertussis mutant strains deficient in FHA production expressed residual adherence that was no longer inhibited by sulfated polysaccharides. In addition, purified FHA displayed heparin-inhibitable binding to epithelial cells. Mapping experiments of the heparin-binding site of FHA indicated that this site is different from the RGD site and the recently proposed carbohydrate-binding site involved in the interaction of FHA with lactosylceramide. This result demonstrates that FHA contains at least three different binding sites, a feature unusual for bacterial adhesions but similar to features of eukaryotic adhesins and extracellular matrix proteins.

Binding and internalization of microorganisms by integrin receptors

Many microbial pathogens bind host-cell integrin receptors. These interactions are promoted either by a host protein binding the microorganism or by a surface-localized ligand encoded by the pathogen. Attachment facilitates extracellular adhesion of the microorganism or internalization by the host cell.

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.

Bordetella pertussis induces apoptosis in macrophages: role of adenylate cyclase-hemolysin

Bordetella pertussis, the causative agent of whooping cough, has been shown recently to enter and survive in epithelial cells and macrophages in vitro. In the present study, we show that B. pertussis is cytotoxic for J774A.1 cells, a monocyte-macrophage cell line, and for murine alveolar macrophages. We demonstrate that cell cytotoxicity mediated by B. pertussis occurred through apoptosis, as shown by changes in nuclear morphology and by host cell DNA fragmentation. Parental strains and a mutant deficient in pertussis toxin expression are able to induce apoptosis, whereas avirulent mutant or adenylate cyclase-hemolysin-deficient mutants are not cytotoxic. Both adenylate cyclase and hemolytic activities are required for programmed cell death. These results show that induction of apoptosis is dependent on the expression of adenylate cyclase-hemolysin. The infection of murine alveolar macrophages in primary culture with B. pertussis leads to apoptosis, suggesting that this process might be relevant in vivo. The ability of B. pertussis to promote cell death may be important for the initiation of infection, bacterial survival, and escape of the host immune response.

Adhesion of Bordetella pertussis to eukaryotic cells requires a time-dependent export and maturation of filamentous hemagglutinin

Bordetella pertussis, the human pathogen of whooping cough, when grown at 22 degrees C is nonvirulent and unable to bind eukaryotic cells. In response to a temperature shift to 37 degrees C, the bacterium acquires the ability to bind eukaryotic cells in a time-dependent fashion. By studying in vitro the temperature-induced transition, from the nonvirulent to the virulent state, we found that binding to CHO cells is mediated by the Arg-Gly-Asp-containing domain of filamentous hemagglutinin (FHA), a protein with multiple binding specificities. This protein is synthesized as a 367-kDa polypeptide within 10 min after temperature shift, but requires 2 hr before it is detected on the bacterial cell surface and starts to bind CHO cells. Mutations affecting the cell surface export of FHA abolish bacterial adhesion to CHO cells, while mutations in the outer membrane protein pertactin strongly reduce binding. This suggests that multiple chaperon proteins are required for a correct function of FHA. Finally, several hours after maximum binding efficiency is achieved, the N-terminal 220-kDa portion of FHA that contains the binding regions is cleaved off, possibly to release the bacteria from the bound cells and facilitate spreading. The different forms of FHA may play different roles during bacterial infection.

The filamentous haemagglutinin, a multifaceted adhesion produced by virulent Bordetella spp

Filamentous haemagglutinin (FHA) is the major attachment factor produced by virulent Bordetella spp. Similar to the other virulence factors, its production is tightly regulated by a two-component system in response to environmental changes. Although of impressive size (c. 220 kDa), it is very efficiently released into the culture supernatant of Bordetella pertussis. Its biogenesis involves complex processing of a larger precursor with a calculated molecular mass of 370 kDa. Export of FHA into the culture medium depends on an outer membrane protein homologous to haemolysin accessory proteins. Purified extracellular FHA is able to increase the adherence of other pathogens to the host, which may contribute to super-infection in whooping cough. Although FHA- mutants colonize lungs as efficiently as the wild-type parent strains, immune responses against FHA appear to protect against colonization. Unlike many other adhesins, FHA expresses at least three different attachment activities, one specific for the CR3 integrins of macrophages, one involving a carbohydrate-binding site, specific for interactions with cilia, and a heparin-binding activity that may be important for interaction of B. pertussis with epithelial cells or extracellular matrices.

Protection of mice against respiratory Bordetella pertussis infection by intranasal immunization with P.69 and FHA

Intranasal immunization of adult female Balb/c mice with the Bordetella pertussis antigens FHA or P.69, greatly enhanced their ability to clear B. pertussis from their lungs following aerosol challenge compared with ovalbumin-immunized controls. Low numbers of lymphocytes secreting antibodies (IgG, IgA and IgM) against the immunizing antigens could be isolated from the lungs of immunized mice. Following aerosol challenge with B. pertussis there was a large increase in the numbers of FHA or P.69-specific antibody-secreting cells in the lungs of mice immunized with these antigens. Intranasal immunization, particularly with FHA, also primed mice to develop a systemic serum anti-pertussis antibody response subsequent to challenge. However, pulmonary clearance of B. pertussis correlated most closely with the local antibody response. A strong anti-FHA response was demonstrated in the lungs of mice that received a booster dose of FHA 9 months after their previous exposure to FHA, demonstrating that long immunological memory can develop in the murine respiratory tract following direct application of pertussis antigens to the respiratory tract mucosa.

Inhibition of Bordetella pertussis filamentous hemagglutinin-mediated cell adherence with monoclonal antibodies

Filamentous hemagglutinin (FHA), a 220-kDa protein located on the surface of Bordetella pertussis, is one of the major cell adhesins of this bacterium. We have produced three hybridoma cell lines that express monoclonal antibodies (mAbs) against FHA: X3C, X3E and X4B. The anti-FHA mAbs X3C and X3E reacted with 220-kDa and 98-kDa FHA protein bands on Western blots. The mAb X4B, which reacted with FHA in ELISA, did not bind to FHA in a Western blot assay. All three mAbs seemed to be directed to the same epitope or to epitopes in close proximity as suggested by competition ELISAs. All three mAbs were able to inhibit the adherence of Chinese hamster ovary cells to purified FHA, and they could also inhibit the FHA-mediated agglutination of goose red blood cells. The attachment of B. pertussis to epithelial cell monolayers was inhibited by the mAb X3C. These antibodies are very useful probes to identify the presence of FHA in bordetellae species and in clinical reagents such as pertussis vaccines, and to characterize the functional domains of this important bacterial adhesin.

Uptake and intracellular survival of Bordetella pertussis in human macrophages

Recent reports have demonstrated that Bordetella pertussis has invasive behavior in vivo and in vitro. In this study, we investigated the ability of a virulent strain, avirulent mutants, and mutants deficient in specific virulence factors to enter and survive intracellularly in human macrophages in vitro. Uptake of virulent B. pertussis was dose dependent and occurred in the absence of serum or specific antibody, with entry occurring via a microfilament-dependent phagocytic process. The virulent wild-type parental strain was internalized and persisted intracellularly over the 3 days of experiments, as determined by transmission electron microscopy and by recovery of viable plate counts. This is the first report of long-term survival of B. pertussis in human macrophages. Avirulent mutants entered macrophages, but at only an average of 1.5% of virulent parental levels, and did not survive intracellularly. Mutants which did not express adenylate cyclase toxin, filamentous hemagglutinin, or pertussis toxin had decreased abilities to enter and to survive inside macrophages. The results suggest that the internalization process, as well as intracellular survival, is virulence dependent and that mutations which inactivate expression of virulence factors may affect both. The ability of B. pertussis to enter and persist inside macrophages may be important not only for survival of the bacteria but also in the pathogenesis of whooping cough.