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J T Poolman

Publications and source records attributed to J T Poolman.

At least 55 records · Page 3Linked to original sources
PubMed1993

Meningococcal disease in The Netherlands, 1958-1990: a steady increase in the incidence since 1982 partially caused by new serotypes and subtypes of Neisseria meningitidis.

In order to explain a threefold increase in the incidence of meningococcal disease in the Netherlands during the 1980s, we serotyped and subtyped Neisseria meningitidis isolates recovered between 1958 and 1990 from > 3,000 patients with systemic disease. No single strain could be held responsible for the increase. Apart from the newly introduced strain B:4:P1.4, which became the most prevalent phenotype in 1990 (21% of all isolates), the majority of the cases in 1990 were caused by many different strains that were already present in the Netherlands before 1980. For the period 1980-1990, a shift in the age distribution of patients with meningococcal disease from younger to older age categories was found, particularly with regard to cases due to meningococci of serogroup B; this shift is explained by the changing distribution of serotypes and subtypes within serogroup B. A polyvalent group B, class 1 outer-membrane-protein vaccine of a stable composition could theoretically have prevented approximately 80% of all group B meningococcal infections in the Netherlands during the past 30 years.

Adolescent↗
PubMed1993

Expression of an inaccessible P1.7 subtype epitope on meningococcal class 1 proteins.

Dot-blot analysis of whole-cell suspensions of meningococci showed that 81% of B:15:P1.16 strains from patients reacted with a monoclonal antibody (MAb) against subtype P1.7. The remaining strains, which did not react on dot-blots or in ELISA, demonstrated the P1.7 subtype epitope on immunoblots after denaturation of the cells with sodium dodecyl sulphate. The monomeric class 1 proteins of the two P1.16 subtype variants had slightly different mol. wts, but bound the P1.7 antibody equally well. These results were explained by a deletion of three codons in the gene encoding the first variable region of the P1.16 class 1 protein. The deletion accounted for the non-exposure of the P1.7 epitope on native cells. Other patient strains, with subtypes P1.3, P1.9 or without any known subtype, also showed a binding site for the P1.7 MAb, which became available only after denaturation. Demonstration of inaccessible epitopes may have consequences for subtype designations and vaccine development.

Amino Acid Sequence↗
PubMed1993

Meningococcal lipopolysaccharide (LPS)-derived oligosaccharide-protein conjugates evoke outer membrane protein- but not LPS-specific bactericidal antibodies in mice: influence of adjuvants.

Meningococcal lipopolysaccharide (LPS)-derived oligosaccharides (OS) were coupled to tetanus toxoid (TT) and purified P1.7,16 outer membrane proteins (OMP). The immunogenicities of the conjugates with and without the addition of the adjuvant Quil A or the nonionic block polymer L121 were studied in mice. Immunotype L2 and L3,7,9 OS-TT conjugates induced immunoglobulin G (IgG) responses that were strongly augmented by Quil A and L121. These adjuvants not only enhanced the amount of IgG evoked but also shifted the IgG subclass distribution from mainly IgG1 toward the complement-activating subclasses IgG2a and IgG2b. The antibodies induced were directed against the OS part of meningococcal LPS. They were not bactericidal for group B meningococci. Both the L3,7,9 OS-P1.7,16 OMP conjugate and purified P1.7,16 OMP evoked a strong IgG response against the P1.7,16 OMP but not against the L3,7,9 LPS. These anti-OMP IgG responses were comparable to the IgG OMP-specific responses induced by the H44/76 or HIII-5 outer membrane vesicles but still did not lyse group B meningococcal strains. The IgG response evoked with OS-OMP or purified OMP consisted mainly of the IgG1 subclass, whereas the H44/76 or HIII-5 outer membrane vesicles induced high amounts of bactericidal IgG2a and IgG2b antibodies next to the IgG1 antibodies. The addition of the adjuvant Quil A or L121 to OS-OMP or OMP resulted in the induction of high levels of bactericidal anti-P1.7,16-specific OMP antibodies, as reflected by the presence of substantial amounts of IgG2a and IgG2b antibodies. These results indicate that (i) mouse anti-LPS antibodies evoked by LPS-derived OS-protein conjugates are not bactericidal for group B meningococci, (ii) extensive purification of P1.7,16 OMP can lead to the loss of the intrinsic adjuvant properties of outer membrane vesicle preparations, and (iii) the addition of suitable adjuvants restores the ability of these purified P1.7,16 OMP to induce bactericidal antibodies.

Adjuvants, Immunologic↗
PubMed1993

Use of transformation to construct antigenic hybrids of the class 1 outer membrane protein in Neisseria meningitidis.

The class 1 protein of Neisseria meningitidis is an important component of candidate outer membrane vaccines against meningococcal meningitis. This porin protein contains two variable regions which determine subtype specificity and provide binding sites for bactericidal monoclonal antibodies. To determine the contribution of each of these variable regions in the induction of bactericidal antibodies, a set of isogenic strains differing only in their class 1 epitopes was constructed. This was done by transformation of meningococcal strain H44/76 with cloned class 1 genes and selection of the desired epitope combinations in a colony blot with subtype-specific monoclonal antibodies. When used for the immunization of mice, outer membrane complexes induced bactericidal antibodies only against meningococcal strains sharing at least one of their class 1 epitopes. The results demonstrate that the P1.2 and P1.16 epitopes, normally located in the fourth exposed loop of the protein, efficiently induce bactericidal antibodies independently of the particular sequence in the first variable region. The P1.5 and P1.7 epitopes, normally located in the first exposed loop, were found to induce lower bactericidal titers. Hybrid class 1 outer membrane proteins were constructed by inserting oligonucleotides encoding the P1.7 and P1.16 epitopes into the porA gene. In this way, we obtained a set of strains which carry the P1.5 epitope in loop 1, P1.2 in loop 4, and P1.7 and P1.16 (separately or in combination) in either loop 5 or loop 6. The additional epitopes were found to be exposed at the cell surface. Outer membrane complexes from several of these strains were found to induce a bactericidal response in mice against the inserted epitopes. These results demonstrate that it is feasible to construct meningococcal strains carrying multivalent class 1 proteins in which multiple subtype-specific epitopes are present in different cell surface-exposed loops.

Amino Acid Sequence↗
PubMed1993

Molecular characterization of the 98-kilodalton iron-regulated outer membrane protein of Neisseria meningitidis.

When grown under iron limitation, Neisseria meningitidis expresses several additional outer membrane proteins (OMPs), which were studied to assess their vaccine potential. Two monoclonal antibodies were obtained against a 98-kDa OMP of strain 2996 (B:2b:P1.2). Cross-reactivity studies revealed that the two antibodies reacted with 44 and 42 of 74 meningococcal strains, respectively. The antibodies did not block the binding of transferrin or lactoferrin to intact cells. The structural gene for the protein, tentatively designated iroA, was isolated and sequenced. Computer analysis revealed homology to the ferric siderophore receptors in the outer membrane of Escherichia coli and to gonococcal transferrin-binding protein 1 (TbpA). The high degree of cross-reactivity and the results of Southern blot analyses, which showed that the iroA gene is also present in strains that did not react with the monoclonal antibodies, suggest that the 98-kDa OMP is well conserved among meningococci and that it is a suitable vaccine candidate. However, the antibodies were not bactericidal in an in vitro assay with human complement.

Amino Acid Sequence↗
PubMed1993

Meningococcal lipopolysaccharides: virulence factor and potential vaccine component.

Lipopolysaccharides (LPS) are surface components of the outer membrane of Neisseria meningitidis. Today, 12 different types of meningococcal LPS (immunotypes) are known, of which 3 are prevalent in the western world. The differences between these immunotypes are in the oligosaccharide part of the LPS molecule and consist of small differences in the oligosaccharide structure, the amount and location of phosphoethanolamine groups, and the degree of O acetylation of individual monosaccharides. Although the differences between the various immunotypes are small, they have a profound influence on the immunochemical and immunological properties of these molecules. Furthermore, each individual strain synthesizes a number of different LPS molecules. The expression of the various components (protective epitopes) is influenced by growth conditions and growth phase. Meningococci can endogenously sialyate their LPS, which constitutes one of the mechanisms by which N. meningitidis can evade the response of the human host. Meningococcal LPS play a key role in the induction of septic shock and can probably enhance the invasiveness of meningococcal strains and shield protective epitopes. Therefore, incorporation of (detoxified) LPS or oligosaccharide components derived therefrom might be very beneficial for the efficacy of a vaccine against group B meningococci. An overview of the development of vaccines against group B meningococci is given, and the status and potential of meningococcal LPS-derived (synthetic) oligosaccharide-protein conjugate vaccines are discussed.

Bacterial Outer Membrane Proteins↗
PubMed1993

Cloning and molecular analysis of the galE gene of Neisseria meningitidis and its role in lipopolysaccharide biosynthesis.

The galE gene from Haemophilus influenzae was used as a hybridization probe for the galE gene of Neisseria meningitidis Group B, identifying two different homologous loci. Each of the loci was cloned and nucleotide sequence analysis revealed that both loci contained sequences similar to galE. One contained a functional galE gene and mapped to the capsule biosynthetic locus. The second contained only a partial galE-coding sequence, which did not express a functional gene product. A galE mutant meningococcal strain was constructed by transformation with an inactivated galE gene. Analysis of the LPS from the galE mutant strain revealed an apparent reduction in molecular weight and a loss of reactivity with monoclonal antibodies specific for structures known to contain galactose. These results are consistent with an essential role for galE in the incorporation of galactose into meningococcal lipopolysaccharide.

Amino Acid Sequence↗
PubMed1992

Identification of T cell epitopes occurring in a meningococcal class 1 outer membrane protein using overlapping peptides assembled with simultaneous multiple peptide synthesis.

The meningococcal class 1 outer membrane protein (OMP) plays an important role in the development of protective immunity against meningococcal infection, and is therefore considered to be a promising candidate antigen (Ag) for a meningococcal vaccine. The induction of an effective antibody response entirely depends upon T helper cells. To identify T cell epitopes of the OMP, we prepared 45 overlapping synthetic peptides representing the entire sequence of the class 1 protein of reference strain H44/76. Fully automated simultaneous multiple peptide synthesis (SMPS) was used to assemble the 45 twenty mer which overlapped by 12 amino acid residues on a 12 mumol scale. The peptides were tested for recognition by peripheral blood mononuclear cells (PBMC) obtained from 34 volunteers. Surprisingly, all synthetic peptides induced proliferative responses of PBMC isolated from one or more human histocompatibility leukocyte antigen (HLA)-typed immune adults. With PBMC from seven nonimmune donors, no proliferative response was observed. Immunodominant regions were found, recognized by PBMC from many volunteers, irrespective of their HLA type. Most of the immunodominant T cell epitopes are located outside the variable regions and, thus, will be conserved among different meningococcal (and gonococcal) strains. Furthermore, the overlapping peptides could be used to identify the epitopes recognized by OMP-specific T cell clones with known HLA restriction. It is interesting that the epitopes defined with the clones occur in highly conserved areas, shared by all neisserial porin proteins. In summary, this analysis of the T cell response to the meningococcal class 1 OMP constitutes a complete study of reactivity to a foreign protein, and illustrates some important features of Ag recognition by T cells. Our data demonstrate unexpected diversity in the T cell recognition of the OMP, and imply that the T cell repertoire against foreign Ag may be greater than previously assumed. This observation is supported by recent data on the interaction of peptide and major histocompatibility complex (MHC) class II, the latter being much less selective than MHC class I. Finally, a comparative analysis pointed out the limitations of algorithms predicting T cell determinants, and the importance of the empirical methodology provided by SMPS.

Adult↗
PubMed1992

Immunogenicity of a Streptococcus pneumoniae type 4 polysaccharide--protein conjugate vaccine is decreased by admixture of high doses of free saccharide.

In this study we report that the priming capacity of a Streptococcus pneumoniae type 4 polysaccharide-protein conjugate to booster immunizations with the native capsular polysaccharide is dose dependent. Furthermore, it is shown by admixture experiments that simultaneous administration of high doses of free saccharide (0.5-25 micrograms) of different chain lengths (varying from M(r) 1.6-120 kDa) decreases the anti-polysaccharide antibody response. Presence of low doses of saccharide (up to 10%), which are usually present in conjugates prepared by the carbodiimide coupling procedure, did not influence the anti-polysaccharide antibody response in adult and neonatal mice.

Animals↗
PubMed1992

The lipooligosaccharide immunotype as a virulence determinant in Neisseria meningitidis.

We have studied the antigenic (immunotype) and physical characteristics of the lipooligosaccharide (LOS) of epidemiologically related Neisseria meningitidis case (36) and carrier (76) isolates associated with a virulent clone of meningococci (ET-5 complex). LOS immunotypes were determined by dot blotting using immunotype specific monoclonal antibodies and physical characteristics were determined from silver stained SDS-PAGE following proteinase K digestion. The genetic similarity of the different isolates was confirmed by analysis of the restriction fragment length polymorphisms. An association between LOS immunotype expression and invasive disease was found; 97% of case isolates expressed the L3,7,9 immunotype, of which 13% additionally expressed the L1,8,10 determinant. The LOS immunotypes of carrier strains were much more heterogeneous. The predominant immunotype was L1,8,10 (70%) and only 24% expressed L3,7,9 alone. Genotypically related case isolates from Norway (6) and Austria (18) expressed the L3,7,9 immunotype with similar frequency to the U.K. isolates. The combination of LOS immunotype and capsule expression appears to be related to the virulence of these meningococcal strains.

Antibodies, Bacterial↗
PubMed1992

Preparation, antigenicity, and immunogenicity of synthetic ribosylribitol phosphate oligomer-protein conjugates and their potential use for vaccination against Haemophilus influenzae type b disease.

Synthetically prepared ribosylribitol phosphate dimer and trimer analogous to fragments of the capsular polysaccharide of Haemophilus influenzae type b, containing either an amino- or a (masked) thiol-functionalized spacer, were conjugated to protein by two different methods. The thiol-containing carbohydrates were conjugated to tetanus toxoid or H. influenzae outer membrane protein using N-succinimidyl 3-(2-pyridyldithio)propionate. Glutaric dialdehyde was used to conjugate the amino-containing carbohydrates with tetanus toxoid. All conjugates were able to bind antibodies raised against the native bacterial polysaccharide, as determined by competition ELISA. The glutaric dialdehyde conjugate prepared from ribosylribitol phosphate trimer and tetanus toxoid induced a strong polysaccharide-specific antibody response in mice and rabbits.

Animals↗
PubMed1992

In vitro activation of human T lymphocytes by Haemophilus influenzae type b capsular polysaccharides.

Polyribosilribitolphosphate (PRP), the capsular polysaccharide from Haemophilus influenzae type b, is a T-cell-independent type 2 antigen. In vitro culture of adult peripheral blood T cells with 15 micrograms/ml PRP leads to induction of interleukin-2 receptor (IL-2R) expression on up to 10% of T cells. These cells are CD4+ and carry the alpha beta T-cell receptor. PRP, at concentrations above 1-5 micrograms/ml, can also induce in vitro proliferation of both adult and neonatal T cells. We conclude that PRP acts as a human T-cell mitogen. The in vitro proliferative response as well as IL-2R expression was studied in T cells derived from adults after vaccination with native PRP, with PRP conjugated to a carrier protein, or with diphtheria toxoid. Vaccination with conjugated PRP decreased the doses of PRP required for in vitro induction of IL-2R expression and T-cell proliferation. This indicates that vaccination with PRP conjugated to a carrier protein improves the in vitro T-cell response to PRP activation.

Adult↗
PubMed1992

Antibodies to meningococcal class 1 outer membrane proteins in South African complement-deficient and complement-sufficient subjects.

Inhibition assays were used to investigate human serum antibodies to the meningococcal class 1 outer membrane proteins. We adapted the whole-cell enzyme-linked immunosorbent assay technique to determine the ability of sera to inhibit the binding of murine subtyping monoclonal antibodies. Serum samples from 33 South African subjects with a deficiency in the sixth component of complement as well as serum samples from various groups of complement-sufficient subjects were investigated. Subjects were subdivided according to whether they were (i) convalescent from Neisseria meningitidis infections, (ii) nonconvalescent, or (iii) controls. Preliminary subtyping investigations had shown that P1.2 was present on 36% of meningococcal clinical isolates from Cape Province, South Africa. Assays with the anti-P1.2 antibodies showed the presence of high antibody levels in many deficient sera and moderately elevated levels in some sera from the complement-sufficient convalescent patients. P1.2, P1.4, P1.15, and P1.16 are epitopes situated on loop 4 of the class 1 outer membrane proteins, whereas P1.7 is on loop 1. Inhibition assays showed that human sera that inhibited binding by P1.2 monoclonal antibodies tended to inhibit the other monoclonal antibodies directed to loop 4 epitopes. This suggests that the epitopes recognized by the human antibodies are not exactly the same as the epitopes recognized by the murine monoclonal antibodies and raises the possibility of the importance of other epitopes.

Antibodies, Bacterial↗
PubMed1992

Interaction of pertussis toxin with human T lymphocytes.

The binding of pertussis toxin (PT) to the human T-cell line Jurkat was examined by using flow cytometry. Fluorescein isothiocyanate (FITC)-labeled PT bound rapidly to the cells in a specific manner as determined by blocking experiments with unlabeled toxin, B oligomer, and the S2-S4 and S3-S4 dimers. Monoclonal antibodies against the S3 subunit of the toxin also significantly inhibited the binding of FITC-PT. Sialidase treatment of the cells resulted in decreased binding of FITC-PT, indicating that sialic acid residues are involved in the binding process. In addition, we studied the effect of PT binding on the expression of cell surface molecules. On binding of PT to the cell surface, a rapid down-regulation of the T-cell receptor (TCR)-CD3 complex was observed. The modulation of the TCR-CD3 complex was independent of the toxin's enzymatic activity, as the B oligomer and a nonenzymatic toxin mutant induced modulation comparable to that caused by the native holotoxin. Isolated dimers did not cause down-regulation. Stimulation of the TCR-CD3 complex, leading to reduced cell surface expression of this complex, provides a possible explanation for the second messenger production associated with the interaction of PT or B oligomer with T lymphocytes. We therefore conclude that PT activates T cells by divalent binding to the TCR-CD3 complex itself or by binding a structure closely associated with it.

Antibodies, Monoclonal↗
PubMed1992

Clonal and antigenic analysis of serogroup A Neisseria meningitidis with particular reference to epidemiological features of epidemic meningitis in the People's Republic of China.

Representative strains of serogroup A Neisseria meningitidis were chosen from all major meningitis epidemics worldwide since 1960 and subjected to analysis for the electrophoretic variation of 15 cytoplasmic allozymes and four outer membrane proteins. The 290 strains defined 84 unique electrophoretic types which were classified in nine subgroups. Tests with monoclonal antibodies specific for conserved pilin epitopes showed that the class I, IIa, and IIb epitopes were uniform within the subgroups. Similarly, the subgroups were uniform for expression of different variable regions of class 1 outer membrane protein, with a few minor exceptions. Many of the bacteria tested were isolated in the People's Republic of China, and the epidemiology of Chinese epidemics of meningococcal meningitis is described. The analysis approaches a global description of epidemic meningitis caused by serogroup A meningococci in the past 30 years.

Animals↗
PubMed1992

Synthetic trimer and tetramer of 3-beta-D-ribose-(1-1)-D-ribitol-5-phosphate conjugated to protein induce antibody responses to Haemophilus influenzae type b capsular polysaccharide in mice and monkeys.

Synthetic oligosaccharides derived from the capsular polysaccharide (PRP) of Haemophilus influenzae type b were conjugated to carrier proteins via a thioether linkage. Conjugates were made of trimeric and tetrameric ribose-ribitol-phosphate and tetanus toxoid or diphtheria toxin. All conjugates elicited anti-PRP antibody responses with an increasing immunoglobulin G/immunoglobulin M ratio in adult mice and monkeys. Trimer conjugates elicited lower anti-PRP antibody responses compared with tetramer conjugates. Adult monkeys responded equally well to the tetrameric oligosaccharide-tetanus toxoid conjugate as to the oligosaccharide-CRM197 conjugate (HbOC), which elicits protective levels of serum antibodies in human infants after two or three injections.

Animals↗
PubMed1992

Construction of a multivalent meningococcal vaccine strain based on the class 1 outer membrane protein.

Outer membrane complexes (OMCs) are promising vaccine candidates for protection against meningococcal disease. However, a major obstacle to this approach is the fact that the protective antibodies induced are generally type specific. In an attempt to overcome this problem, we have investigated the possibility of constructing a multivalent vaccine strain by insertion of an additional class 1 outer membrane protein-encoding gene. Starting with a derivative of strain H44/76 deficient in class 3 outer membrane protein, a second class 1 gene was inserted into the chromosome, through homologous recombination with a suicide plasmid carrying the class 1 gene from strain 2996 placed within a class 5 gene. In this way, a strain was obtained in which a class 3 protein was in effect replaced by a class 1 protein from another subtype, i.e. P1.5,2 in addition to the P1.7,16 protein of H44/76. Immunization of mice with such OMCs resulted in high bactericidal titers against both H44/76 and 2996, where normally only strain-specific antibodies are induced. Mutational removal of class 3 protein from the immunizing OMCs had no detectable effect on the bactericidal titer against H44/76, whereas removal of class 1 protein led to a strong reduction. These results demonstrate the dominant role of the subtype-specific sequences of class 1 protein in the induction of bactericidal antibodies and show that construction of a multivalent OMC-based vaccine should be feasible.

Animals↗