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Biomedical subjects

J Verhoef

Publications and source records attributed to J Verhoef.

At least 199 records · Page 11Linked to original sources
PubMed1997

Mannoproteins of Cryptococcus neoformans induce proliferative response in human peripheral blood mononuclear cells (PBMC) and enhance HIV-1 replication.

To investigate the possible role of Cryptococcus neoformans var. neoformans in HIV disease progression, and to identify the responsible cryptococcal components, an in vitro cell culture model was set up to study the C. neoformans-induced enhancement of HIV replication in HIV-1-infected PBMC. Similar to whole C. neoformans, cell-wall membrane fraction and mannoproteins induced proliferation of PBMC and enhancement of lymphotropic HIV replication in HIV-infected PBMC, while galactoxylomannan did not. MoAbs capable of interfering with MHC class II-mediated antigen presentation prevented the induction of cell proliferation by whole C. neoformans or cryptococcal mannoproteins. MoAb binding to adhesion molecules intercellular adhesion molecule-1 (ICAM-1) and lymphocyte function-associated antigen-1 (LFA-1) also inhibited C. neoformans-induced cell proliferation. In addition, anti-MHC class II MoAb inhibited the enhancement of HIV replication by C. neoformans. The results suggest that: (i) C. neoformans may accelerate HIV disease progression by stimulation of HIV replication through MHC class II-mediated antigen presentation; and (ii) cryptococcal mannoprotein may be one of the responsible components. The ability to enhance HIV replication in PBMC in vitro is not unique for C. neoformans. However, this is the first report to study in detail a yeast-induced enhancement of HIV replication in PBMC.

Antibodies, Monoclonal↗
PubMed1997

Cryptococcus neoformans and cryptococcal glucuronoxylomannan, galactoxylomannan, and mannoprotein induce different levels of tumor necrosis factor alpha in human peripheral blood mononuclear cells.

Tumor necrosis factor alpha (TNF-alpha) release by peripheral blood mononuclear cells (PBMC) during disseminated infection by Cryptococcus neoformans may initiate and amplify the immune response of the host, leading to elimination of the fungus. The ability to induce TNF-alpha in PBMC by four clinical strains of C. neoformans, a laboratory strain (NIH 37), and the purified cryptococcal components glucuronoxylomannan (GXM), galactoxylomannan (GalXM), and mannoproteins (MP1 and MP2) were investigated under different opsonic conditions. In the absence of serum, the levels of TNF-alpha induced by all strains and cryptococcal components were not above background levels. Normal human serum (NHS) enhanced TNF-alpha induction by whole cryptococci and the different cryptococcal components, with MP2 being the most potent TNF-alpha inducer. Inactivation of complement (HI NHS) almost abrogated the ability of whole cryptococci and the GXMs to induce TNF-alpha. In contrast, when MP1, MP2, and GalXM were incubated with HI NHS, 48, 71, and 44%, respectively, of the original TNF-alpha levels remained. MPs incubated with heat-inactivated immunoglobulin G (IgG)-depleted serum still induced 50% of the levels of TNF-alpha induced by components incubated with HI NHS. Both these sera contained the same very low levels of anti-MP IgG antibodies, indicating the opsonic effect of a heat-stable factor other than antibody. Two anti-CD14 monoclonal antibodies (60BCA and 3C10) inhibited the production of TNF-alpha induced by MP2. The results indicate that (i) induction of TNF-alpha by C. neoformans and GXMs strongly depends on complement, (ii) MP1 and MP2 induction of TNF-alpha is facilitated by a heat-stable serum factor other than Ig, and (iii) CD14 may be involved in the induction of TNF-alpha by MP2.

Antibodies↗
PubMed1997

Saturable CD14-dependent binding of fluorescein-labeled lipopolysaccharide to human monocytes.

We used rough lipopolysaccharide (ReLPS) to construct a fluorescein-labeled LPS (FITC-LPS) with a very high labeling efficiency that bound to isolated human monocytes in a CD14-dependent fashion and that in this respect behaved indistinctively from native LPS. The CD14-dependent binding could be inhibited either by a 1,000-fold excess of unlabeled LPS or by polymyxin B, bactericidal/permeability-increasing protein, cationic protein 18, or soluble CD14. Although this FITC-LPS preparation no longer possessed the ability to prime neutrophils for the production of reactive oxygen species or to stimulate human monocytes to produce tumor necrosis factor, activation of the Limulus amoebocyte lysate cascade was comparable to activation by native LPS. Binding to monocytes was enhanced by human pooled serum (HPS) or LPS-binding protein (LBP) for LPS concentrations up to 100 ng/ml and was completely CD14 dependent. For LPS concentrations exceeding 100 ng/ml, binding was still partially CD14 dependent, but not HPS or LBP dependent. CD14-dependent association of LPS with monocytes was shown to be totally saturable. In conclusion, we found an HPS- or LBP-dependent binding of FITC-LPS to monocytes that was CD14 dependent at up to 100 ng of LPS per ml, and saturation of binding was shown.

Animals↗
PubMed1996

Molecular typing of methicillin-resistant Staphylococcus aureus on the basis of protein A gene polymorphism.

The polymorphic X-region of the protein A gene (spa) was used for molecular typing of methicillin-resistant Staphylococcus aureus (MRSA) strains. The X-region is characterized by a variable number (between 3 and 15) of small repeats. DNA sequencing of MRSA strains revealed 25 distinct repeats. Analysis of MRSA strains grown in vitro and in vivo revealed that the X-region was sufficiently stable for epidemiologic typing of MRSA strains. Spa typing of MRSA strains was compared to phage typing and, in general, concordance was found between the two methods. However, spa typing was more sensitive, allowing differentiation of strains within a particular phage type. Results obtained with spa typing suggest that hospital outbreaks may be caused by two or more MRSA strains. Spa typing may be an important tool in unravelling the spread of MRSA strains within and between hospitals.

Bacterial Typing Techniques↗
PubMed1996

Intracellular pathways involved in tumor necrosis factor-alpha release by human monocytes on stimulation with lipopolysaccharide or staphylococcal peptidoglycan are partly similar.

This study compared the effects of intracellular pathway inhibitors on tumor necrosis factor-alpha (TNF-alpha) release from human monocytes. Cells were stimulated with peptidoglycan (PG) from Staphylococcus epidermidis or with Escherichia coli lipopolysaccharide (LPS), both in the presence of 10% human serum. Of 10 substances tested, only the protein tyrosine kinase inhibitor tyrphostin AG 126 discriminated significantly between PG and LPS: TNF-alpha release induced by PG, but not by LPS, was dose-dependently suppressed. The results obtained with other modulatory substances, including different protein kinase and G protein inhibitors, suggest that calmodulin-dependent protein kinase, protein tyrosine kinase, and a cholera-toxin-sensitive G protein are involved in both PG- and LPS-induced TNF-alpha release. Further, drugs such as pentoxifylline, chloroquine, and the antioxidant apocynin similarly inhibited TNF-alpha release by PG- as well as LPS-stimulated cells.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1996

Moraxella catarrhalis in acute laryngitis: infection or colonization?

The complement phenotypes of Moraxella catarrhalis isolates obtained from adult patients with acute laryngitis were investigated using a microliter serum bactericidal assay and compared with those of other donor groups. Laryngitis isolates had a higher proportion (57%) of complement-resistant strains than did carrier strains from healthy 8- to 13-year-old schoolchildren (16%). The difference between these groups was statistically significant (chi2 [3 x 2 table] = 21.55; P < .001). The relatively frequent occurrence of the complement-resistant (virulence-associated) phenotype in adults with acute laryngitis supports the theory of an active role of M. catarrhalis in the pathogenesis of acute laryngitis.

Adolescent↗
PubMed1996

Issues in the adjunct therapy of severe sepsis.

Until recently the concept of immunomodulation in patients with severe sepsis (formerly called sepsis syndrome or septic shock) appeared very promising. Research has focused on the possible therapeutic potential of interfering with cytokine pathways, either by preventing the induction of cytokines, such as TNF-alpha, by neutralization of lipopolysaccharide (LPS), or through the use of agents that attenuate cytokine action. Nowadays research on protein or protein constructs with antibacterial activities such as bacterial/permeability increasing protein (BPI), platelet activating factor receptor antagonists, nitric oxide and cyclo-oxygenase inhibitors, are still being followed. In large clinical trials monoclonal antibodies against core glycolipid (E5, HAIA) were shown to be at best of only marginal benefit, and in some trials results were indecisive. Also, the results with IL-lra, although initially heralded with high expectation, were at the end disappointing and the trials discontinued. Two large trials with monoclonal antibodies against TNF showed some effect in subcategories of patients: a third trial is on its way. Other phase I; II studies include those of soluble TNF receptors and BPI. The area of immunomodulation has now become an area of more realism and the results of early trials has forced investigators to go back the drawing board and to re-investigate the whole concept of immunotherapy and immunoprophylaxis.

Antibodies, Monoclonal↗
PubMed1996

Molecular characterization of the BRO beta-lactamase of Moraxella (Branhamella) catarrhalis.

A rapid increase in the prevalence of beta-lactamase-producing Moraxella (Branhamella) catarrhalis strains has been noticed during the last decades. Today, more than 80% of strains isolated worldwide produce beta-lactamase. To investigate beta-lactamase(s) of M. catarrhalis at the molecular level, the BRO-1 beta-lactamase gene (bla) was isolated as part of a 4,223-bp HindIII fragment. Sequence analysis indicated that bla encodes a polypeptide of 314 amino acid residues. Insertional inactivation of bla in M. catarrhalis resulted in complete abrogation of beta-lactamase production and ampicillin resistance, demonstrating that bla is solely responsible for beta-lactam resistance. Comparison with other beta-lactamases suggested that M. catarrhalis beta-lactamase is a unique enzyme with conserved residues at the active sites. The presence of a signal sequence for lipoproteins suggested that it is lipid modified at its N terminus. In keeping with this assumption was the observation that 10% of beta-lactamase activity was found in the membrane compartment of M. catarrhalis. M. catarrhalis strains produce two types of beta-lactamase, BRO-1 and BRO-2, which differ in their isoelectric points. The BRO-1 and BRO-2 genes from two ATCC strains of M. catarrhalis were sequenced, and only one amino acid difference was found between the predicted products. However, there was a 21-bp deletion in the promoter region of the BRO-2 gene, possibly explaining the lower level of production of BRO-2. The G + C content of bla (31%) was significantly lower than those of the flanking genes (47 and 50%), and the overall G + C content of the M. catarrhalis genome (41%). These results indicate that bla was acquired by horizontal gene transfer from another, still unknown species.

Amino Acid Sequence↗
PubMed1996

Effect of imipenem on monoclonal antibody-mediated protection against Escherichia coli O18K5.

Flow cytometry revealed that the binding of immunoglobulin M monoclonal antibodies (MAbs) to Escherichia coli O18K5 was modulated by exposure of the bacteria to subinhibitory concentrations of imipenem. The binding of anti-K5 MAb was decreased, while the binding of anti-O18 MAb was increased. In addition, anti-lipid A MAbs bound only to imipenem-treated bacteria. The biological effect of MAb binding was investigated in BALB/c mice by determination of the levels of bacteremia, tumor necrosis factor (TNF) in serum and survival after intraperitoneal challenge with bacteria preincubated with MAb. Neither MAb alone (150 micrograms per animal) proved to be protective against untreated bacteria. Anti-lipid A MAb on its own, in contrast to anti-K5 and anti-O18 MAbs, was not protective against imipenem-treated bacteria. Only combinations which included anti-O18 MAb and anti-K5 MAb exerted in mice enhanced protection against smooth E. coli O18K5 as well as imipenem-treated E. coli O18K5. This was reflected by reduced TNF levels in serum and increased survival. The addition of anti-lipid A MAb to the combination of anti-K5 MAb and anti-O18 MAb reduced serum TNF levels in mice, but not significantly.

Animals↗
PubMed1996

A new procedure for the purification of streptococcal pyrogenic exotoxin A from Streptococcus pyogenes supernatant.

An important role in the pathogenesis of invasive group A streptococcal disease has been ascribed to the production of streptococcal pyrogenic exotoxin A. We present a new technique for the purification of streptococcal pyrogenic exotoxin A from Streptococcus pyogenes NY-5 supernate, which is highly efficient with respect to yield (35%), purity (> or = 99%), and time.

Bacterial Proteins↗
PubMed1996

Supernatants from Staphylococcus epidermidis grown in the presence of different antibiotics induce differential release of tumor necrosis factor alpha from human monocytes.

Bacterial products from gram-positive bacteria, such as peptidoglycan, teichoic acid, and toxins, activate mononuclear cells to produce tumor necrosis factor alpha (TNF). The present study evaluated the release of soluble cell wall components from Staphylococcus epidermidis capable of inducing TNF after exposure of the bacteria to various antibiotics. A clinical S. epidermidis isolate (694) was incubated with either penicillin, oxacillin, vancomycin, or clindamycin at five times the MIC. Supernatants of the cultures obtained by filtration were added to plastic adherent monocytes in the absence or presence of human serum. After 18 h of incubation, monocyte supernatants were tested for the presence of TNF by enzyme-linked immunosorbent assay (ELISA). Supernatants from bacteria incubated with beta-lactam antibiotics induced higher TNF levels than those obtained from bacteria incubated with culture medium only (no antibiotics), vancomycin, or clindamycin. Human serum potentiated supernatant-induced TNF release, especially in beta-lactam supernatants. The soluble peptidoglycan and teichoic acid contents of supernatants, as estimated by inhibition ELISA and, for peptidoglycan, also by affinity depletion with vancomycin-Sepharose gel, were proportional to TNF release. Differences in the ability of individual antibiotics to generate TNF-releasing products from S. epidermidis were observed, the most potent antibiotics being penicillin and oxacillin.

Anti-Bacterial Agents↗
PubMed1996

Enhanced protection by use of a combination of anticapsule and antilipopolysaccharide monoclonal antibodies against lethal Escherichia coli O18K5 infection of mice.

To study antibody-mediated protection against Escherichia coli peritonitis in BALB/c mice, monoclonal antibodies (MAbs) were generated against the capsule (K5) and the lipopolysaccharide (O18) of E. coli. Flow cytometric analysis with two selected immunoglobulin M MAbs revealed that bacteria were antigenically heterogeneous. Arbitrarily, three subpopulations in E. coli O18K5 cultures could be distinguished by double immunofluorescence. A subpopulation bound only the anti-K5 MAb, and another subpopulation bound only the anti-O18 MAb. An intermediate subpopulation, however, bound both MAbs. In agreement with this result, combinations of both MAbs enhanced phagocytosis of fluorescein isothiocyanate-labeled bacteria by human polymorphonuclear leukocytes and mouse macrophage J774 cells as well. In protection experiments, combinations of both MAbs, preincubated with 3 50% lethal doses of E. coli O18K5, protected all mice upon intraperitoneal challenge. Relatively high doses of either MAb alone proved to be not fully protective in this infection model. Protection of mice by the combination of MAbs was associated with significantly lower (P < 0.02) tumor necrosis factor levels in serum 90 min after challenge compared with any other treatment group. Similarly, prophylactic administration of MAbs yielded significantly lower (P < 0.01) tumor necrosis factor levels in mice that received the combination of MAbs than in any other treatment group.

Animals↗
PubMed1995

Pneumococcal virulence factors and host immune responses to them.

The principal virulence determinant of most encapsulated bacterial pathogens is the possession of an extracellular capsule. This paper discusses biological aspects of the Streptococcus pneumoniae capsule, putative roles played by accessory virulence factors of this pathogen and prospects for improvement of the currently available pneumococcal vaccine. Even though the interruption of genes encoding selected proteins has been shown to attenuate virulence to some degree, the physical removal of the pneumococcal capsule or the interruption of encapsulation genes completely abolishes virulence in mice. The role of the capsule in pathogenesis is not completely clear, however, since it is not known whether this structure is important in colonization, the obligatory first step in the process. In addition, a number of proteins have been implicated as possible accessory virulence factors. These include pneumolysin, two distinct neuraminidases, an IgA1 protease and two surface proteins, pspA and psaA. While interruption of the expression of some of these proteins examined to date has been shown to attenuate virulence, so far it has not proven possible to completely abolish virulence in this fashion. Proteinaceous accessory virulence factors may prove important to the development of second-generation pneumococcal vaccines, however. Pneumococcal and other proteins conjugated to pneumococcal polysaccharides are currently being evaluated as carriers in attempts to improve the immunogenicity of polysaccharide vaccines, primarily in small children.

Animals↗
PubMed1995

Bacterial and viral removal efficiency, heat and moisture exchange properties of four filtration devices.

Four devices used for filtration of microorganisms and/or for heating and moistening the ventilated air during mechanical ventilation were evaluated. This evaluation included measurement of bacterial and viral removal efficiency, heat and moisture exchange properties, dead space and air flow resistance. The devices included: Pall BB50T and DAR Sterivent (filtration devices); DAR Hygrobac and Gibeck Humid-vent [heat and moisture exchangers (HMEs)]. The two devices which are primarily conceived as filters, had the highest bacterial and viral removal efficiency (titre reduction of 10(5)-10(6) for bacteria and of 10(4)-10(5) for viruses), while removal efficiencies of the HME devices were lower: titre reduction of 10(4) for bacteria and 10(1)-10(3) for viruses. As expected, heat and moisture output of HMEs was better than that of filters. In mechanical ventilation, dead space and air flow resistance are important properties of devices, which might disturb efficient ventilation. There were only minor differences in dead space and air flow resistance. Resistance to airflow in the HMEs was increased by nebulization of medication (mesna) unlike that of the filters.

Airway Resistance↗
PubMed1995

The role of cytokines in gram-positive bacterial shock.

In Gram-positive bacterial shock, little is known about the sequence of events that controls the signalling of monocytes and macrophages that leads to the release of cytokines. Cell-wall components, such as peptidoglycan and teichoic acid, are clearly important in the activation of these cells, but exotoxins may also be involved.

Animals↗
PubMed1995

Interactions of surfactant protein A with influenza A viruses: binding and neutralization.

The interaction of pulmonary surfactant protein A (SP-A) with influenza A H1N1 and H3N2 viruses was investigated. SP-A is a sialated C type lectin with affinity for mannose residues. Flow cytometry showed that binding of fluorescein isothiocyanate (FITC)-labeled SP-A to H3N2 virus-infected cells was specific and time- and concentration-dependent. Oligosaccharides did not affect the binding of FITC-SP-A to the infected cells. Preincubation of H1N1 and H3N2 with SP-A resulted in a dose-dependent reduction of the infectivity of the viruses to cells. Removal of the carbohydrate moiety of SP-A by N-glycosidase F or cleavage of its sialic acid residues by neuraminidase prevented the interactions of SP-A with the viruses. It is concluded that SP-A binds to influenza A viruses via its sialic acid residues and, thereby, neutralizes the virus.

Animals↗