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T F Meyer

Publications and source records attributed to T F Meyer.

At least 145 records · Page 8Linked to original sources
PubMed1992

Production of Neisseria gonorrhoeae pili (fimbriae) in Pseudomonas aeruginosa.

Pseudomonas aeruginosa K/2PfS, when transformed with an expression plasmid harboring the pilin gene (pilE1) of Neisseria gonorrhoeae MS11, was able to express and assemble gonococcal pilin monomers into surface-associated pili, as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, immunoblotting, and immunoelectron microscopy. Concomitant with the expression of gonococcal pili in P. aeruginosa was the virtual loss of production of P. aeruginosa K/2PfS pili normally associated with the host cell.

Amino Acid Sequence↗
PubMed1991

Phase variation of the opacity outer membrane protein controls invasion by Neisseria gonorrhoeae into human epithelial cells.

Neisseria gonorrhoeae is a facultative intracellular bacterium capable of penetrating into certain human epithelial cell types. In order to identify gonococcal factors essential for invading Chang human conjunctiva cells, a gentamicin selection assay for the quantification of viable intracellular bacteria was used in conjunction with microscopy. The results demonstrate a correlation between the invasive behaviour of gonococci and the expression of Opa proteins, a family of variable outer membrane proteins present in all pathogenic Neisseria species. However, only particular Opa proteins supported invasion into Chang cells as indicated by the use of two unrelated gonococcal strains. Invasion was sensitive to cytochalasin D, and strong adherence mediated by the Opa proteins appeared to be essential for the internalization of gonococci. In contrast pili, which also conferred binding to Chang conjunctiva cells, did not support cellular invasion but rather were inhibitory.

Bacterial Adhesion↗
PubMed1991

Direction of gaze during vibrotactile choice reaction time tasks.

A vibrotactile choice reaction time (RT) task was used, with the hands in their own hemispace (arms uncrossed), and in their opposite hemispace (arms crossed). Gaze was directed at the stimulated and responding hand, away from it at the other (inactive) hand, or at a central fixation point (a neutral control). Responses were slower in the crossed than the uncrossed condition. Further, in the crossed condition, responses were faster when subjects looked at the stimulated and responding hand, rather than at the inactive hand or at the central fixation point. As RT in the latter two conditions did not differ, there is a benefit when subjects look at the stimulated and responding hand, rather than a cost when they look at the inactive hand. In the look at condition, visual or attentional factors may reduce the response coding conflict which occurs when arms are crossed.

Analysis of Variance↗
PubMed1991

L-pilin variants of Neisseria gonorrhoeae MS11.

Phase- and antigenic variation of pilin expression in Neisseria gonorrhoeae is based on the genetic exchange between silent pilin genes (pilS) and the pilin expression locus (pilE). Similarly, the non-piliated L-variants of strain MS11, which show an increased resistance to certain antibiotics, are the result of recombination with the pilE locus. However, this recombination is atypical in that pilE(L) carries a tandem arrangement of a complete pilin gene and additional partial pilin genes under the control of the same pilE promoter. Since the two pilin gene copies are tandemly arranged and are often in the same translational frame, oversized pilin molecules are produced, which do not assemble into pili. The tandem gene copies introduced in a pilE(L) locus originate from silent loci where they are already joint. Upon reversion to the P+ phenotype the L-variants lose one pilin gene copy from the pilE(L) in a process reminiscent of the deletion events that otherwise lead to the formation of the non-revertible and non-piliated Pn mutants of MS11 gonococci. Thus deletion of pilin genes from pilE can be regarded as a third mechanism of pilin variation in gonococci.

Amino Acid Sequence↗
PubMed1991

The opacity proteins of Neisseria gonorrhoeae strain MS11 are encoded by a family of 11 complete genes.

Variants of Neisseria gonorrhoeae MS11 show distinct colony morphologies because of the expression of a class of surface components called opacity (Opa, PII) proteins. Southern analyses combined with molecular cloning of genomic DNA from a single variant of MS11 has identified 11 opa genes contained in separate loci. These opa genes code for distinct opacity proteins which are distinguishable at their variable domains. The opa gene analyses were also extended to divergent variants of MS11. These studies have shown that, during in vitro and in vivo culture, 10 of the 11 opa genes did not undergo significant change in their primary sequence. However, in these variants, one gene (opaE) underwent non-reciprocal inter-opa recombinations to generate newer Opa variants. Phylogenic analysis of the opa gene sequences suggests that the opa gene family have evolved by a combination of gene duplication, gene replacement and partial inter-opa recombination events.

Amino Acid Sequence↗
PubMed1991

Physical and genetic map of the Neisseria gonorrhoeae strain MS11-N198 chromosome.

A macro-restriction map of the Neisseria gonorrhoeae chromosome was constructed using the enzymes Nhel and Spel. Combinations of one- and two-dimensional electrophoresis of completely or partially digested chromosomal DNA were performed to align the restriction fragments. The chromosome is circular, with an estimated size of 2.33 Mb +/- 35 kb. A genetic map was derived from the physical map; positions of over 60 defined loci were determined by Southern hybridization.

Blotting, Southern↗
PubMed1991

Evasion mechanisms of pathogenic Neisseriae.

The outcome of the early stages of a neisserial infection is determined by receptor-mediated events that culminate in the attachment and invasion of human mucosal tissues. The factors participating in this process, including pili, opacity proteins (Opa), and perhaps lipopolysaccharide (LPS), undergo phase and antigenic variation allowing the pathogens to evade the human immune response. In addition antigenic variation is essential in the modulating pathogen host cell interactions. Likewise the production of distinct Opa proteins allows the bacteria to enter epithelial cells and thereby to escape the humoral host responses. Other mechanisms including antigenic mimicry by capsular polysaccharides and antigenic masquerade by immunoglobulin fragments confer additional resistance to the extracellular life style of these organisms. Finally alpha-protein, a putative hormone-like factor produced by pathogenic Neisseriae, may contribute to the complex evasion-program of these species.

Antigens, Bacterial↗
PubMed1991

Recovery, distribution, and development of Acanthocheilonema viteae third- and early fourth-stage larvae in adult jirds.

Living third- and fourth-stage larvae (L3 and L4) of Acanthocheilonema viteae were recovered quantitatively from adult Meriones unguiculatus within the first 10 days after subcutaneous inoculation of 60 arthropod-derived larvae (mL3). The average recovery of the inoculated larvae was about one third (28.5%), and the majority (87.7%) were found in muscular tissues. Seventy-two hours after inoculation, larvae could be isolated from all body locations, although the majority still was found near the site of inoculation. Morphological and biometrical data indicated that, at least until molting, the development of the larval population was not synchronous, with molting occurring over a period of 48 hr on days 7 and 8 postinoculation. The stomatal rings of postinvasive L3's and L4's were distinguishable structurally and could be used as stage-specific determinants. Immediately after infection, L3's showed a linear growth in diameter; rapid longitudinal growth started after the molt, leading to a doubling in the length of L4's within 4 days. The time course of shedding was reconstructed in detail using isolated L3/L4 intermediates.

Abdomen↗
PubMed1990

Mouse IgA Fc receptor on CD3+ T cells. Molecular forms of IgA that bind to a 38-kDa Fc alpha R protein and development of an anti-Fc alpha R antisera.

Previous studies have shown that splenic T cells from mice that bear IgA myelomas, as well as certain T cell lines, express receptors for the Fc of IgA, and are termed Fc alpha R. In this study, we have isolated and characterized two CD3+ T cell lines derived by fusion of murine Peyer's patch (PP) CD4+ T cells with the BW 5147 lymphoma cell line. These cell lines, designated PPT4-6 and PPT4-16, were shown to bind monomeric or dimeric IgA, whereas the fusion partner did not bind either form of IgA. However, polymeric IgA (m.w. 600,000) bound equally well to all three cell lines. Similar results were also obtained with two known Fc alpha R+ T cell lines, ThHA1 nos. 9 and 10. Immunoprecipitation studies with IgA on PPT4-16 and ThHA1 no. 9 have shown that IgA binds to a 38-kDa protein. A rabbit antiserum was prepared to a 38-kDa fraction of Fc alpha R+ T cell membranes, and heterophilic antibody was removed from the antiserum by adsorption with mouse thymocytes, BW 5147 and R1.1 lymphoma. The antiserum bound to both PPT4-16 and ThHA1 no. 9 as well as to other Fc alpha R+ T cells, but did not bind to thymocytes or to the T lymphomas R1.1 or BW 5147. The antiserum appeared specific for the Fc alpha R, because it failed to block binding of anti-CD3 (145 2C11) or other surface molecule-specific antibodies. Further, competitive inhibition studies with IgA and anti-Fc alpha R (38 kDa) showed that preincubation of Fc alpha R+ T cells with the anti-38-kDa protein completely eliminated IgA binding, whereas IgA partially blocked the binding of the anti-Fc alpha R antibodies to the cell membrane. Immunoisolation with the anti-Fc alpha R antibody of radioiodinated cell membrane proteins from Fc alpha R+ T cells, but not from Fc alpha R- cells, gave a distinct band at 38 kDa. To further test the specificity of this antiserum, we have isolated T cells from spleens of IgA-myeloma bearing mice, and tested the phenotype and IgA binding. A subset consisting of 15 to 20% of CD3+, CD8+ T cells was found that bound monomeric or dimeric IgA. Further, the anti-Fc alpha R antiserum also recognized this CD8+ T cell subset, and preincubation of the cells with antibody resulted in their failure to bind IgA. Our results indicate that the Fc alpha R on T cell lines derived from PP is a 38-kDa protein.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Extracellular transport of cholera toxin B subunit using Neisseria IgA protease beta-domain: conformation-dependent outer membrane translocation.

The beta-domain of the Neisseria IgA protease precursor (Iga) provides the essential transport function for the protease across the outer membrane. To investigate the secretion function of the beta-domain (Iga beta), we engineered hybrid proteins between Iga beta and the non-toxic 12 kd cholera toxin B subunit (CtxB) and examined their targeting behaviour in Salmonella typhimurium. We show that CtxB-Iga beta hybrid proteins integrate into the outer membrane, leading to the exposition of the CtxB moiety on the cell surface. Exposed CtxB can be degraded by externally added proteases like trypsin, but can also be specifically cleaved off from membrane-associated Iga beta by purified IgA protease. We further demonstrate that folding of the CtxB moiety at the periplasmic side of the outer membrane interferes with its translocation. Prevention of disulphide-induced folding in periplasmic CtxB renders the protein moiety competent for outer membrane transport. Iga beta may be of general interest as an export vehicle for even larger proteins from Gram-negative bacteria.

Amino Acid Sequence↗
PubMed1990

Molecular analysis of periodontal pathogens.

Both Bacteroides gingivalis and Actinobacillus actinomycetemcomitans have been implicated in the destruction of periodontal tissues. To understand better the role putative virulence factors from the two bacterial species may play in an infection, the collagenase gene from Bact. gingivalis and the leucotoxin gene from A. actinomycetemcomitans were cloned. As it is intended to generate strains carrying defined mutations in these genes for in vitro and in vivo experiments, extensive restriction mapping and sequence analyses of these clones are being undertaken. Furthermore a conjugation system for Bact. gingivalis and A. actinomycetemcomitans will be established.

Actinobacillus↗
PubMed1990

Active release of surface proteins: a mechanism associated with the immune escape of Acanthocheilonema viteae microfilariae.

Living Acanthocheilonema viteae microfilariae obtained from peripheral blood of parasitised Meriones unguiculatus were surface-labelled with 125I. Four major surface exposed proteins of approximately 14.50, 14.55, 17.5, 19 kDa and one less abundant protein of 40 kDa were identified. Under non-reducing conditions the low-molecular-weight (LMW) proteins were isolated as multimers suggesting the presence of intermolecular disulphide linkages. In gels containing Triton X-100 the labelled epicuticular proteins behaved lipophilically. By cultivation of surface-labelled and metabolically labelled microfilaria in vitro, a continuous shedding of two LMW proteins was demonstrated. These proteins were produced in large amounts and released into the culture supernatant as monomeric and pentameric molecules. Concomitant with this release, one of the proteins appeared to lose its lipophilic character, giving rise to a hydrophilic 14.50-kDa entity. Although most of the extracted surface proteins reacted with sera from patent jirds, these sera failed to recognise the surface of living microfilariae. However, microfilariae pretreated with glutaraldehyde or attenuated with Na-azide could be labelled with surface specific antibodies.

Acanthocephala↗
PubMed1990

Pathogenic neisseriae--a model of bacterial virulence and genetic flexibility.

The outcome of the early stages of a neisserial infection is determined by receptor-mediated events that culminate in the attachment and invasion of human mucosal tissues. The factors participating in this process, including pili, opacity proteins (Opa), and perhaps lipopolysaccharide (LPS), are subject to complex genetic controls that allow these factors to be produced in multiple forms. Antigenic variation allows the pathogenic Neisseriae to evade the human immune response, and facilitates their interaction with a variety of different cells and tissues of the human host. One of the major genetic mechanisms causing antigenic variation is transformation, which allows virulence genes to be exchanged and recombined between independent Neisseria strains within multiply infected individuals. A number of other factors, such as IgA protease, alpha-factor, and the meningococcal capsule are also implicated in pathogenesis and render the pathogenic Neisseriae an excellent model for the investigation of bacterial virulence.

Antigens, Bacterial↗
PubMed1990

Generation of capsule-deficient Neisseria meningitidis strains by homologous recombination.

Capsule-deficient mutants of Neisseria meningitidis serogroup B strain B1940 were constructed by allelic replacement using the plasmids pMF120 and pMF121, which contain the flanking regions of the gene locus for the biosynthesis pathway of the group B meningococcal capsular polysaccharide. Southern blot analysis of chromosomal DNA of the capsule-deficient meningococcal strains confirmed the generation of large deletions in the chromosomal cps gene complex. The same strategy proved useful in constructing meningococcal strains with capsular types A, C, W135, Y and Z.

Alleles↗
PubMed1989

Reassortment of pilin genes in Neisseria gonorrhoeae occurs by two distinct mechanisms.

Phase and antigenic variation of pilin expression in Neisseria gonorrhoeae result from recombination events in which variant sequences from one of the silent loci (pilS) are transferred to the expression locus (pilE). Such rearrangements were originally thought to be gene conversions, but findings showing that phase variation is partially inhibited by DNase I, that piliated (P+) cells are highly competent for DNA uptake and that gonococci readily undergo autolysis in culture, led to the suggestion that pilin variation occurs through transformation by exogenous DNA. We have developed a simple method for the selection of non-piliated (P-) cells and have evaluated naturally occurring P+ to P- transitions. Two primary pathways of pilin variation can be distinguished--transformation-mediated recombination, which is influenced by culture conditions and inhibited by DNase I, and intragenomic reciprocal recombination, which is unaffected by DNase I. Furthermore, we demonstrate that both piliated and revertible P- cells are competent for DNA uptake, an essential prerequisite of the first pathway.

Bacterial Outer Membrane Proteins↗
PubMed1989

Mosaic-like organization of IgA protease genes in Neisseria gonorrhoeae generated by horizontal genetic exchange in vivo.

IgA protease is a putative virulence factor that exists in several allelic forms in Neisseria gonorrhoeae. However, extracellular secretion of these variant IgA proteases occurs by the same pathway involving three steps of autoproteolytic maturation from a large precursor. Two principal precursor types (H1 and H2) can be distinguished with respect to the location of autoproteolytic sites and the sizes of the mature products. By partial DNA sequence analysis, additional variations have been detected which are not unique to one particular gene; rather, otherwise unrelated iga genes often share homology, thus revealing a composite organization. In the context of other gonococcal features, this observation implies that recombination has occurred in vivo between iga genes of different strains, probably via the route of species-specific DNA transformation. This process may be of general significance for the modulation and the natural exchange of virulence properties among pathogenic Neisseriae.

Amino Acid Sequence↗
PubMed1989

Molecular characterization and expression in Escherichia coli of the gene complex encoding the polysaccharide capsule of Neisseria meningitidis group B.

The gene complex encoding all determinants of the biosynthesis pathway of the capsule of group B meningococci (cps) has been cloned in Escherichia coli. A 24-kilobase large chromosomal fragment is necessary for capsule expression on the E. coli surface. By transposon and deletion mutagenesis, two separate steps in transport of the polysaccharide from the cytoplasm to the periplasm and further to the cell surface became evident. Mutants were also isolated that accumulate soluble poly(sialic acid) in the cytoplasm. The cloned cps complex conferred to E. coli strain GC6 sensitivity for E. coli K1-specific phages; phage sensitivity was enhanced in two distinct classes of cps mutants. Southern blot experiments revealed homology to some or all other Neisseria meningitidis capsular types and other Neisseria species, depending on the fragment of the cps complex used as probe.

Cell Membrane↗