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The genome of Mycobacterium tuberculosis , the bacterium responsible for the disease tuberculosis, contains an unusual family of abundant antigens (PE/PPEs). To date, certain members of this multigene family occur only in mycobacteria that cause disease. It is possible that the numerous proteins encoded by these mycobacterial genes dictate the immune pathogenesis of this bacterial pathogen. There is also evidence that some of these antigens are present at the cell surface and that they affect the pathology and immunology of the organism in many ways. Also, they elicit both antibodies and T cells, they may be involved in antigenic variation, and they may be good candidates for vaccines and drugs. However, since they are plentiful and extremely homologous, these PE/PPEs are very challenging to study, and it is difficult to be certain what role(s) they have in the pathogenesis of tuberculosis. Consequently, how to develop treatments like vaccines using these antigens as candidates is complex., (Copyright © 2017 Brennan.)

Infection of mice with Mycobacterium avium or immunization with a novel PE gene expressed by M. avium (MaPE) showed that a dominant T-cell immune response was elicited. Immunization with an MaPE DNA vaccine protected mice against an aerosol challenge with Mycobacterium tuberculosis, suggesting that mycobacteria express PE antigens with cross-protective T-cell epitopes.

The heparin-binding hemagglutinin (HBHA) of Mycobacterium tuberculosis is a surface-expressed adhesin that can affect binding to host cells via a unique, methylated, carboxyl-terminal, lysine-, alanine-, and proline-rich repeat region. It has been implicated in extrapulmonary dissemination of M. tuberculosis from the lung following the initial infection of the host. To assess the vaccine potential of this protein, purified preparations of HBHA were emulsified in a dimethyldioctadecylammonium bromide-monophosphoryl lipid A adjuvant and tested for the ability to reduce M. tuberculosis infection in the mouse aerosol challenge model for tuberculosis. The HBHA-containing vaccine gave a approximately 0.7-log reduction in CFU in both mouse lungs and spleens compared to adjuvant controls 28 days following challenge. Although a notable level of serum antibody to HBHA was elicited after three immunizations and the antibodies were able to bind to the surface of M. tuberculosis, passive immunization with monoclonal antibodies directed against HBHA did not protect in the challenge model. Compared to adjuvant controls, an elevated gamma interferon response was generated by splenic and lymph node-derived T cells from immunized mice in the presence of macrophages pulsed with purified HBHA or infected with live M. tuberculosis, suggesting that the effective immunity may be cell mediated. Efforts to construct effective recombinant HBHA vaccines in fast-growing Mycobacterium smegmatis have been unsuccessful so far, which indicates that distinctive posttranslational modifications present in the HBHA protein expressed by M. tuberculosis are critical for generating effective host immune responses. The vaccine studies described here demonstrate that HBHA is a promising new vaccine candidate for tuberculosis.

The elucidation of the genomic sequence of Mycobacterium tuberculosis revealed the presence of a novel multigene family designated PE/PE_PGRS that encodes numerous, highly related proteins of unknown function. In this study, we demonstrate that a transposon insertion in a PE_PGRS gene (1818(PE_PGRS)) found in Mycobacterium bovis BCG Pasteur, which is the BCG homologue of the M. tuberculosis H37Rv gene Rv1818c, introduces new phenotypic properties to this BCG strain. These properties include dispersed growth in liquid medium and reduced infection of macrophages. Complementation of the 1818(PE_PGRS)::Tn5367 mutant with the wild-type gene restores both aggregative growth (clumping) in liquid medium and reestablishes infectivity of macrophages to levels equivalent to those for the parent BCG strain. Western blot analysis using antisera raised against the 1818(PE_PGRS) protein shows that PE_PGRS proteins are found in cell lysates of BCG and M. tuberculosis H37Ra and in the cell wall fraction of M. tuberculosis H37Rv. Moreover, immunofluorescent labeling of mycobacteria indicates that certain PE_PGRS proteins are localized at the cell surface of BCG and M. tuberculosis. Together these results suggest that certain PE_PGRS proteins may be found at the surface of mycobacteria and influence both cell surface interactions among mycobacteria as well as the interactions of mycobacteria with macrophages.

Sequencing of the entire genome of Mycobacterium tuberculosis identified a novel multigene family composed of two closely related subfamilies designated PE and PE_PGRS. The major difference between these two families is the presence of a domain containing numerous Gly-Ala repeats extending to the C terminus of the PE_PGRS genes. We have used a representative PE_PGRS gene from M. tuberculosis, Rv1818c (1818PE_PGRS), and its amino-terminal PE region (1818PE), to investigate the immunological response to these proteins during experimental tuberculosis and following immunization with DNA constructs. During infection of mice with M. tuberculosis, a significant humoral immune response was observed against recombinant 1818PE_PGRS but not toward the 1818PE protein. Similarly, immunization with a 1818PE_PGRS DNA construct induced antibodies directed against 1818PE_PGRS but not against 1818PE proteins, and no humoral response was induced by 1818PE DNA. These results suggest that certain PE_PGRS genes are expressed during infection of the host with M. tuberculosis and that an antibody response is directed solely against the Gly-Ala-rich PGRS domain. Conversely, splenocytes from 1818PE-vaccinated mice but not mice immunized with 1818PE_PGRS secreted gamma interferon following in vitro restimulation and demonstrated protection in the mouse tuberculosis challenge model. These results suggest that the PE vaccine can elicit an effective cellular immune response and that immune recognition of the PE antigen is influenced by the Gly-Ala-rich PGRS domain.

Recognition of receptors on sialidase-treated polymorphonuclear leukocytes (PMNs) by the Gal/GalNAc lectin associated with the type 2 fimbriae of certain strains of actinomyces results in activation of the PMNs, phagocytosis, and destruction of the bacteria. In the present study, plant lectins were utilized as probes to identify putative PMN receptors for the actinomyces lectin. The Gal-reactive lectin from Ricinus communis (RCAI), the Gal/GalNAc-reactive lectins from R. communis (RCAII) and Bauhinia purpurea (BPA), as well as the Gal beta 1-3GalNAc-specific lectins from Arachis hypogaea (PNA) and Agaricus bisporus (ABA) inhibited killing of Actinomyces naeslundii WVU45 by sialidase-treated PMNs. These five lectins detected a 130-kDa surface-labeled glycoprotein on nitrocellulose transfers of PMN extracts separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This glycoprotein was revealed only after treatment of the transfers with sialidase, a condition analogous to the sialidase dependence of the lectin-mediated biological responses of the PMNs to the actinomyces. The mannose-reactive lectin concanavalin A did not inhibit killing of the actinomyces and failed to detect the 130-kDa glycoprotein but did block PMN-dependent killing of Escherichia coli B, a bacterium that possesses mannose-sensitive fimbriae. Therefore, the PMN glycoprotein receptor for A. naeslundii is clearly distinct from those recognized by E. coli. Two major putative glycolipid receptors were also identified by actinomyces and RCAI overlays on sialidase-treated thin-layer chromatograms of PMN gangliosides. Thus, both a 130-kDa glycoprotein and certain gangliosides are implicated in the attachment of the actinomyces to PMNs.

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.

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.

Pertactin and filamentous hemagglutinin (FHA), proteins present on the surface of the gram-negative organism Bordetella pertussis, have been shown to contain the putative cell-binding sequence arginine-glycine-aspartic acid (RGD) and to promote eukaryotic cell attachment. The attachment of epithelial cells to purified pertactin and the entry of B. pertussis into human HeLa cells are both inhibited by an RGD-containing peptide derived from the pertactin sequence. In contrast, an RGD-containing peptide derived from the FHA sequence has no effect on either the attachment of epithelial cells to purified FHA or the entry of B. pertussis into HeLa cells. Staphylococcus aureus organisms coated with pertactin or FHA, purified from B. pertussis, enter HeLa cells more efficiently than S. aureus cells coated with bovine serum albumin. The pertactin-enhanced entry of S. aureus is inhibited by 75% in the presence of the RGD peptide from pertactin, whereas the RGD peptide derived from FHA has no effect on the increased entry promoted by the pertactin-coated or by the FHA-coated S. aureus. These results indicate that the active uptake of B. pertussis by certain mammalian cells may be mediated by the interaction of the RGD site found in pertactin with eukaryotic cell surface receptors.

Phagocytosis of Actinomyces viscosus T14V and A. naeslundii WVU45 by human polymorphonuclear leukocytes in the absence of antibody or complement was mediated by the lectin associated with the type 2 fimbriae of these bacteria. This effect was markedly enhanced by exogenous sialidase, an enzyme also secreted by these actinomyces. Since sialidase treatment of the bacteria did not result in increased phagocytosis, this enzyme presumably acts by unmasking receptors for the fimbrial lectin on phagocytic cells. The viability of A. viscosus T14V, which possesses type 1 and type 2 fimbriae (1+ 2+), and A. naeslundii WVU45, which possesses only type 2 fimbriae (2+), was decreased by at least 98% following incubation with polymorphonuclear leukocytes in the presence of sialidase. Entirely analogous findings were obtained with a 1- 2+ mutant of A. viscosus T14V. In contrast, the phagocytosis of 1+ 2- and 1- 2- mutants of A. viscosus T14V and a 2- mutant of A. naeslundii WVU45 was minimal or absent. Lactose and beta-methylgalactoside inhibited the destruction of the bacteria, whereas cellobiose and alpha-methylgalactoside were ineffective. Thus, the type 2 fimbriae of the oral actinomyces recognize galactose-containing receptors on polymorphonuclear leukocytes which have been exposed by the removal of sialic acid, an interaction that is followed by internalization and subsequent killing of the bacteria.

Cells of Bordetella pertussis BP353, a nonfimbriated Eldering serotype 1.3 strain, were used as an immunogen to produce three monoclonal antibodies, BPE3, BPD8, and BPE8, that agglutinated the immunizing cells, as well as certain other nonfimbriated and fimbriated serotype 3-containing B. pertussis strains. The antibodies did not agglutinate serotype 1 or nontypable B. pertussis cells. These monoclonal antibodies specifically detected a 69-kilodalton (kDa) band on Western blots (immunoblots) containing whole B. pertussis cell lysates of Eldering agglutinogen serotypes 1.3, 1.3.6, 1.2.3.4, and 1.2.3.4.6. This 69-kDa antigen was released from the bacteria by cell incubation for 60 min at 60 degrees C, and it was purified by affinity chromatography with a BPE3-agarose affinity matrix. Purified material was used to produce a polyclonal antiserum that agglutinated all nonfimbriated and fimbriated B. pertussis cells containing serotype 3 agglutinogen. Immunogold electron microscopy and indirect immunofluorescence studies demonstrated that it is an outer membrane constituent but nonfimbrial in appearance. BPE3 did not detect purified fimbriae on Western blots, and antibodies to these fimbriae did not bind to the 69-kDa component. Although B. bronchiseptica and B. parapertussis cells were not agglutinated by the monoclonal antibodies, antigenically similar proteins were detected in extracts of the bacteria. These results identify the 69-kDa protein as a nonfimbrial agglutinogen present on all virulent strains of B. pertussis. The monoclonal antibodies described here should be useful for further studies on the structure and function of this protein.

Monoclonal antibodies that specifically agglutinate strains of Bordetella pertussis having serotype 1 agglutinogen were uniquely reactive with the electrophoretically slow-migrating A form of lipooligosaccharide. These monoclonal antibodies should be useful for the structural analysis of B. pertussis lipooligosaccharide and for the establishment of a better-defined serogroup for Bordetella species.

Two types of fimbriae have been identified on the pathogenic gram-negative organism Bordetella pertussis. Monoclonal antibodies to these fimbriae were produced to better understand the role of fimbriae as serotype-specific agglutinogens and to investigate the antigenic relationship between these fimbriae. Three monoclonal antibodies were identified that specifically agglutinated B. pertussis cells containing the U.S. Reference Factor 2 agglutinogen, and six monoclonal antibodies were produced that agglutinated only those strains containing the U.S. Reference Factor 6 agglutinogen. Indirect immunofluorescence studies and immunogold electron microscopy demonstrated that these monoclonal antibodies bind to an outer membrane component on serotype-specific strains of B. pertussis. All of the monoclonal antibodies reacted with native or partially assembled type-specific fimbriae but not with monomeric fimbrial subunits as indicated by Western blot (immunoblot) analysis. The fimbrial agglutinogens recognized by the monoclonal antibodies were also uniquely reactive with either U.S. Reference Factor 2 or 6 antiserum (Eldering agglutinogen 2 or 6 polyclonal antiserum) in an indirect ELISA. No cross-reactivity of the monoclonal antibodies with the unrelated fimbriae was observed in any of the comparative immunological studies. Some of the monoclonal antibodies agglutinated certain strains of B. bronchiseptica, suggesting that this closely related species can contain antigenically similar fimbriae. These monoclonal antibodies should prove useful for further structural and functional analysis of Bordetella fimbriae and for studies on the role that these antigens play in prevention of infection and disease.

The type 2 fimbrial lectin of Actinomyces naeslundii WVU45 mediated the binding of this bacterium to glycosphingolipids chromatographed on thin-layer silica gel plates. Radioiodinated bacteria attached to GM1, GD1b, and globoside. After chromatograms were treated with sialidase, the bacteria also bound to GD1a and GT1b. The actinomyces lectin apparently recognized the Gal beta 3GalNAc termini of these gangliosides and the GalNAc beta 3Gal terminus of globoside, suggesting that glycolipids containing these sequences may serve as receptors for A. naeslundii on mammalian cells.

The adherence of Actinomyces naeslundii to human epithelial (KB) cells is mediated by the interaction of a fimbrial lectin on this oral bacterium with epithelial cell receptors exposed by sialidase. The D-galactose- and N-acetyl-D-galactosamine-reactive plant lectins from peanut and from Bauhinia purpurea inhibit this interaction. This report describes the partial purification and characterization of a 160-kilodalton (kDa) cell surface glycoprotein which is the principal receptor for these lectins. Radioiodinated lectins detected a band of 160 kDa on sialidase-treated Western blots of epithelial cell extracts but did not detect bands on nontreated filters. However, wheat germ agglutinin was reactive with the 160-kDa band on filters that were not treated with sialidase, suggesting that this lectin recognizes the sialic acid residues of this molecule. The 160-kDa component was partially purified from n-octylglucoside extracts of the epithelial cells by wheat germ agglutinin affinity chromatography. This molecule was metabolically labeled with D-[14C]glucosamine and labeled at the cell surface by lactoperoxidase-catalyzed iodination or periodate oxidation followed by sodium borotritide reduction. Incubation of epithelial cells with sialidase before extraction resulted in the loss of the 160-kDa band and the appearance of a band at 200 kDa which was directly reactive with 125I-labeled peanut agglutinin. These results indicate that the 160-kDa glycoprotein on the surface of the epithelial cell serves as a receptor for the agglutinins from the peanut and B. purpurea and presumably the fimbrial lectin of actinomyces.

The adherence of Actinomyces naeslundii WVU45 to monolayer cultures of human epithelial cell lines was mediated by the lactose-sensitive fimbriae (type 2) of strain WVU45. The attachment of Actinomyces viscosus T14V, which has both types 1 and 2 fimbriae, was approximately half that of A. naeslundii, and only minimal attachment of A. naeslundii and A. viscosus mutants lacking type 2 fimbriae was detected. The adherence of strain WVU45 was enhanced two- to threefold by neuraminidase treatment of the epithelial cells. The Fab fragments of antibodies which recognize the type 2 fimbriae inhibited the adherence of A. naeslundii WVU45 to the epithelial cells. The bacterial interaction with epithelial cells was inhibited by lactose, methyl-beta-D-galactoside, and N-acetyl-D-galactosamine, but not by methyl-alpha-D-galactoside, cellobiose, N-acetyl-D-glucosamine, L-fucose, or D-mannose. To further characterize the epithelial cell receptors for the bacterial lectin, we utilized several plant and invertebrate lectins as potential inhibitors of bacterial adherence. Lectins from Bauhinia purpurea and Arachis hypogaea which recognize N-acetyl-D-galactosamine, D-galactose, and D-galactose-beta-(1----3)-N-acetyl-D-galactosamine inhibited bacterial attachment, and binding of these lectins to epithelial cells was enhanced by the addition of neuraminidase. Lectins reacting with alpha-linked D-galactose, alpha-linked N-acetyl-D-galactosamine, D-mannose, or sialic acid were not inhibitory. Under similar assay conditions, adherence of a mannose-sensitive strain of Escherichia coli was inhibited by concanavalin A but not by the lectin from Bauhinia purpurea. These results indicate that certain plant lectins have specificities similar to that of the actinomyces fimbrial lectin and are, therefore, useful probes for identifying receptors on epithelial cells for certain bacteria.

The binding of pertussis toxin and its subunits to cell surface receptors and purified glycoproteins was examined. The interaction of pertussis toxin with components of two variant Chinese hamster ovary (CHO) cell lines was studied. These cell lines are deficient in either sialic acid residues (LEC 2) or sialic acid and galactose residues (LEC 8) on cell surface macromolecules. The binding of pertussis toxin to components of these cells differed from the binding of the toxin to wild-type components. Although the toxin bound to a 165,000-dalton glycoprotein found in N-octylglucoside extracts of wild-type cells, it did not bind to components found in extracts of LEC 2 cells. In contrast, the toxin bound to components found in extracts of LEC 8 cells, which are variant cells that contain increased amounts of terminal N-acetylglucosamine residues on cell surface macromolecules. These results suggest that the receptor for pertussis toxin on CHO cells contains terminal acetamido-containing sugars. The cytopathic effect of the toxin on both types of variant cells was much reduced compared with its effects on wild-type cells. Thus, optimal functional binding of pertussis toxin appears to require a complete sialyllactosamine (NeuAc----Gal beta 4GlcNAc) sequence on surface macromolecules. In addition to studying the nature of the eucaryotic receptor for pertussis toxin, we examined corresponding binding sites for glycoproteins on the toxin molecule. Binding of both S2-S4 and S3-S4 dimers of the toxin to cellular components and purified glycoproteins was observed. The two dimers bound to a number of glycoproteins containing N-linked oligosaccharides but not O-linked oligosaccharides, and differences in the binding of the two dimers to some glycoproteins was noted. These data indicate that the holotoxin molecule contains at least two glycoprotein-binding sites which may have slightly different specificities for glycoproteins.