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Biomedical subjects

A Weyer

Publications and source records attributed to A Weyer.

At least 19 recordsLinked to original sources
PubMed2003

Morphological development and neurochemical differentiation of cerebellar inhibitory interneurons in microexplant cultures.

The cerebellar cortex comprises a rather limited variety of interneurons, prominently among them inhibitory basket and stellate cells and Golgi neurons. To identify mechanisms subserving the positioning, morphogenesis, and neurochemical maturation of these inhibitory interneurons, we analyzed their development in primary microexplant cultures of the early postnatal cerebellar cortex. These provide a well-defined, patterned lattice within which the development of individual cells is readily accessible to experimental manipulation and observation. Pax-2-positive precursors of inhibitory interneurons were found to effectively segregate from granule cell perikarya. They emigrate from the core explant and avoid the vicinity of granule cells, which also emigrate and aggregate into small clusters around the explant proper. This contrasts with the behavior of Purkinje neurons, which remain within the explant proper. During migration, a subset of Pax-2-positive cells gradually acquires a GABAergic phenotype, and subsequently also expresses the type 2 metabotropic receptor for glutamate, or parvalbumin, markers for Golgi neurons and basket or stellate cells, respectively. The latter eventually orient their dendrites such that they take a preferentially perpendicular orientation relative to granule cell axons. Both the neurochemical maturation of basket/stellate cells and the specific orientation of their dendrites are independent of their continuous contact with radially oriented glia or Purkinje cell dendrites projecting from the core explant. Numbers of parvalbumin-positive basket/stellate cells and the prevalence of glutamate-positive neurites, which form a dense network preferentially within cell clusters containing granule cell perikarya and their dendrites, are subject to regulation by chronic depolarization. In contrast, brain-derived neurotrophic factor results in a drastic decrease of numbers of basket/stellate cells. These findings document that granule cell axons (parallel fibers) are the major determinant of basket/stellate cell dendritic orientation. They also show that the neurochemical maturation of cerebellar interneurons is sensitive to regulation by activity and neurotrophic factors.

Animals↗
PubMed2003

Human serum IgE-mediated mast cell degranulation shows poor correlation to allergen-specific IgE content.

BACKGROUND: Although allergen-specific IgE content in serum can be determined immunochemically, little is known about the relationship between this parameter and the strength of the degranulation response upon allergen triggering. OBJECTIVES: Analyse the degranulation capacity of immunochemically defined purified and serum IgE after challenge with anti-IgE or allergen using a rat mast cell line (RBL) transfected with the alpha-chain of the human high-affinity IgE receptor (FcepsilonRI). METHODS: Purified IgE specific for 4-hydroxy-3nitrophenylacetyl, purified IgE of unknown specificity, and sera from allergic patients sensitive to Dermatophagoides pteronyssinus and Dactylis glomerata were assessed. Degranulation was measured by a beta-hexosaminidase release assay after anti-IgE or allergen-specific challenge. RESULTS: For purified monoclonal IgE a significant correlation (r = 0.97) was found between the proportion of bound allergen-specific IgE and the strength of the degranulation response. In contrast, no correlation (r = 0.27) was detected after sensitization with serum IgE. CONCLUSION: Our studies demonstrate that mast cell activation mediated through IgE from allergic patients is a result of complex relationships that are not only dependent on allergen-specific IgE content but also relate to the capacity to efficiently sensitize and trigger the signalling responses that lead to degranulation.

Allergens↗
PubMed2002

Expression and localization of heat shock proteins in rat basophilic leukemia cells: differential modulation by degranulation, thermal or oxidative stress.

BACKGROUND: Rat basophilic leukemia (RBL-2H3) cells are well characterized in terms of morphological and biochemical changes upon activation, and have been extensively used as a model system for studying the mechanisms of the immediate hypersensitivity reaction. To investigate whether overexpression of heat shock/stress proteins (HSP) is involved in the mast cell-dependent reactivity, we examined the adaptive responses of RBL-2H3 cells to classical stress conditions such as heat shock or oxidative injury produced by an aqueous extract of tobacco smoke. METHODS: HSP were determined by flow cytometry and immunocytochemistry. Degranulation was confirmed as the release of beta-hexosaminidase, determined spectrophotometrically, and by electron microscopy experiments. RESULTS: We found that RBL-2H3 cells respond to heat shock or oxidative injury by the synthesis of both the inducible 72 kDa HSP (Hsp70), and the oxidation-specific 32 kDa heme oxygenase (HO)-1. Heat shock induced mainly Hsp70 in a cell growth-dependent manner, whereas oxidative stress induced mainly HO-1 in a cell growth-independent manner. However, heat shock or oxidative stress had no significant effects on degranulation. CONCLUSION: Stress-mediated synthesis of HSP was not associated with RBL-2H3 degranulation and likewise, degranulation did not induce HSP.

Animals↗
PubMed2000

Molecular characterization of human IgG monoclonal antibodies specific for the major birch pollen allergen Bet v 1. Anti-allergen IgG can enhance the anaphylactic reaction.

We report the molecular characterization of five human monoclonal antibodies, BAB1-5 (BAB1: IgG(1); BAB4: IgG(2); BAB2, 3, 5: IgG(4)), with specificity for the major birch pollen allergen, Bet v 1. BAB1-5 were obtained after immunotherapy and contained a high degree of somatic mutations indicative of an antigen-driven affinity maturation process. While BAB1 inhibited the binding of patients IgE to Bet v 1, BAB2 increased IgE recognition of Bet v 1, and, even as Escherichia coli-expressed Fab, augmented Bet v 1-induced immediate type skin reactions. The demonstration that IgG antibodies can enhance allergen-induced allergic reactions is likely to explain the unpredictability of specific immunotherapy.

Allergens↗
PubMed2000

Inhibitory effect of wheat germ agglutinin on mouse mast cell adhesion to fibronectin.

BACKGROUND: Mast cells play a critical role in allergic and inflammatory responses. The interactions between these cells and extracellular matrix components influence the distribution of mast cells in tissues and their biological responsiveness. It has been reported that the lectin wheat germ agglutinin (WGA) inhibits mast cell mediator release. We decided to investigate whether adhesion to fibronectin (FN), another mast cell function, which is upregulated following FcepsilonRI cross-linking, is also inhibited by WGA. METHODS: Mouse bone-marrow-derived mast cell line MCP5/L was used. For FcepsilonRI-dependent mast cell activation, MCP5/L cells were sensitized with mouse IgE antibodies. WGA was added to cell suspensions simultaneously with a challenging agent and, after an appropriate incubation period, beta-hexosaminidase release and adhesion to FN were determined. RESULTS: Both FcepsilonRI cross-linking-dependent mast cell adhesion to FN and mediator release were dose-dependently inhibited by WGA; however, the lectin concentrations required to induce maximum inhibition of adhesion were significantly lower. Furthermore, WGA inhibited phorbol-myristate-acetate- and A-23187-mediated mast cell adhesion to FN, i.e. processes that do not engage FcepsilonRI. The effect of WGA on FcepsilonRI-mediated secretion was reversed by GlcNAc. In contrast, combination of GlcNAc and NeuNAc or N, N'-diacetylchitobiose was required to reverse the inhibitory effect of WGA on mast cell adhesion. CONCLUSION: The characteristics of WGA-mediated inhibition of MCP5/L mast cell adhesion to FN suggest that mast cell integrins are targets of the inhibitory action of WGA and the sugar moieties on these receptors might be important for receptor function.

Acetylglucosamine↗
PubMed1998

Fc epsilonRI-mediated induction of TNF-alpha gene expression in the RBL-2H3 mast cell line: regulation by a novel NF-kappaB-like nuclear binding complex.

Using rat basophilic leukemia (RBL-2H3) cells as a model, we investigated how aggregation of the high affinity receptor for IgE (Fc epsilonRI) regulates TNF-alpha gene expression. Antigenic stimulation of RBL-2H3 cells led to an increase in newly synthesized TNF-alpha mRNA that was dependent on continuous receptor aggregation and did not require de novo protein synthesis. Kinetic analysis showed that maximal levels were achieved at 60 min and waned by 180 min of stimulation. Concomitant with the transcriptional activation of the TNF-alpha gene, the rapid appearance and disappearance of a previously uncharacterized nuclear NF-kappaB DNA binding activity, comprised of two distinct protein complexes, were observed. These protein complexes bound to NF-kappaB sites within the TNF-alpha gene and contained novel proteins (three species of Mr between 90,000-110,000) distinct from the classical proteins in NF-kappaB complexes. The induced NF-kappaB binding activity required continuous receptor stimulation and induced NF-kappaB-dependent reporter gene expression. Consistent with a role for the novel NF-kappaB nuclear binding activity in TNF-alpha gene expression, deletion of several 5' kappaB elements in the TNF-alpha promoter abolished all measurable Fc epsilonRI-dependent induction of a reporter construct. Pharmacologic agents that inhibited the NF-kappaB binding activity also inhibited TNF-alpha mRNA expression. Our results demonstrate that a novel NF-kappaB-like nuclear binding activity plays an important role in regulation of the rapid and transient transcriptional activation of the TNF-alpha gene via Fc epsilonRI.

Animals↗
PubMed1998

Specific signaling pathways in the regulation of TNF-alpha mRNA synthesis and TNF-alpha secretion in RBL-2H3 mast cells stimulated through the high affinity IgE receptor.

OBJECTIVE: In the present study, we investigated signal transduction pathways involved in TNF-alpha gene expression and TNF-alpha secretion by mast cells stimulated through the high affinity IgE receptor (FcepsilonRI). MATERIALS AND METHODS: TNF-alpha mRNA steady state levels and TNF-alpha secretion in the presence of specific pharmacological agents were monitored using rat basophilic leukemia cells (RBL-2H3) stimulated through FcepsilonRI. Relative amounts of TNF-alpha mRNA versus beta-actin levels were quantified by RNase protection and RT-PCR assays. TNF-alpha secretion was measured by a current ELISA test. RESULTS: We show that EGTA (5 mM) prevented TNF-alpha mRNA expression and TNF-alpha secretion in antigen-stimulated cells. The protein kinase C (PKC) inhibitor bisindolylmaleimide I substantially blocked TNF-alpha secretion at 2 microM but had only a marginal effect on TNF-alpha mRNA expression. The results were similar when PKC isoforms were depleted by long-term exposure to 100 nM phorbol ester (PMA). The PI 3-kinase inhibitor wortmannin blocked TNF-alpha secretion at low doses (EC50= 13 nM), but only partially affected mRNA expression. CONCLUSIONS: Our results show that in FcepsilonRI-stimulated RBL-2H3 cells calcium mobilization, activation of PKC and PI 3-kinase are necessary for TNF-alpha secretion while for the increased TNF-alpha mRNA expression PKC activity is dispensable and PI 3-kinase activity only partially required.

Androstadienes↗
PubMed1998

Mapping of Dermatophagoides farinae mite allergens by two-dimensional immunoblotting.

BACKGROUND: Allergens from the house dust mite Dermatophagoides farinae are responsible for frequent respiratory allergic disorders, but only 3 groups of these allergens are well characterized. OBJECTIVE: This study was performed to complete the repertoire of D farinae allergens using two-dimensional (2-D) electrophoresis. METHODS: D farinae mite allergens, extracted from whole cultures in the presence of a mild detergent, were separated by 2-D electrophoresis with subsequent immunoblotting. IgE-binding proteins were detected with individual mite-sensitive patient sera and the anti-D pteronyssinus human serum pool. Allergens were identified by an inhibition immunoblot test, by means of specific mAbs, or by biochemical characterization. The internal peptides of 2 allergens were microsequenced. RESULTS: 2-D immunoblotting with individual patient sera showed a marked heterogeneity in the isoelectric point of the allergens, as well as differences in the individual IgE-binding patterns. In addition to identification of allergens Der f 1, Der f 2, and Der f 3, new allergens have been characterized as Der f 4, Der f 5, and 2 high molecular mass allergens. Microsequencing of peptides from the latter allergens revealed significant homologies with allergen Mag 3 from D farinae and with a chitinase from prawn Penaeus japonicus. CONCLUSION: 2-D electrophoresis with subsequent immunoblotting and protein microsequencing allowed characterization of a more complete repertoire of D farinae allergens and their multiple isoforms, and identification of six new allergens.

Allergens↗
PubMed1997

Immunologic characterization of monoclonal antibodies that modulate human IgE binding to the major birch pollen allergen Bet v 1.

BACKGROUND: Bet v 1 and homologous proteins represent major allergens for almost 95% of patients allergic to tree pollen and approximately 70% of those allergic to fruits and vegetables. As yet, no continuous (sequential) IgE epitopes have been determined for Bet v 1, and evidence has accumulated that Bet v 1 IgE epitopes belong to the conformational (discontinuous) type. OBJECTIVE: A panel of 85 mouse monoclonal anti-Bet v 1 antibodies was raised as a tool with which to study the interaction of human IgE antibodies with Bet v 1. METHODS: The epitopes of selected monoclonal antibodies (mAbs) were characterized by mapping with synthetic overlapping peptides and by cross-competition experiments. Cross-reactivity of Bet v 1-specific mAbs with tree and plant food allergens was investigated by Western blotting. The influence of Bet v 1-specific mAbs on the IgE-Bet v 1 interaction was studied by competition assays with immobilized purified recombinant Bet v 1 and by basophil histamine release experiments. RESULTS: Antibodies that increased the IgE binding to Bet v 1 up to fivefold could be defined, whereas others inhibited IgE binding to Bet v 1 up to 99% and competed with the Bet v 1-induced histamine release from patients' basophils. CONCLUSION: The activity of the enhancing antibodies is interpreted as a stabilization of Bet v 1 states/IgE epitopes, which are either more accessible for certain IgE antibodies or are recognized with higher affinity. Those mAbs that competed with the Bet v 1-IgE interaction, if humanized or produced as recombinant antibody fragments, might be considered as potential tools for local allergy therapy.

Allergens↗
PubMed1996

Human IgG monoclonal antibodies that modulate the binding of specific IgE to birch pollen Bet v 1.

Birch pollen allergy is a very frequent pathology in Europe and North America. More than 95% of the tree pollen allergic patients display IgE reactivity against Bet v 1, the major birch pollen allergen. Starting with PBL from a patient desensitized by immunotherapy, we have generated five B cell lines (BAB1 to BAB5) that secrete human IgG mAbs of high affinity for Bet v 1. Although competition studies indicated that these human IgG mAb recognized different epitopes, broad cross-reactivity was found with Bet v 1 homologous allergens present in tree pollens and plant-derived foods. When tested for interference with allergic patients' IgE, BAB1 inhibited (by 80-100%) the binding of IgE to nitrocellulose-blotted Bet v 1, while BAB2 enhanced it. The biologic significance of the ability of BAB1 to interfere with patients' IgE binding is indicated by the finding that BAB1 completely inhibited Bet v 1-induced histamine release from allergic patients' basophils. Allergen-specific human IgG mAbs such as BAB1, which presents high blocking activity in both immunochemical and cellular IgE competition experiments, might have therapeutical application.

Adjuvants, Immunologic↗
PubMed1996

Cloning, sequencing and immunological characterization of Dac g 3, a major allergen from Dactylis glomerata pollen.

Preliminary work showed that a 14-kDa allergen with a pI of 9 was recognized by more than 60% of sera from Dactylis glomerata (Dac g) pollen-allergic individuals. The N-terminal amino acid sequence of this Dac g allergen was determined by Edman degradation and compared with that of Lol p 3, a major allergen of Lolium perenne. A sequence identity of 65% was found, suggesting that the Dac g allergen could be the homologue of Lol p 3 and therefore named Dac g 3. We report the cloning and sequence analysis of a cDNA encoding the Dac g 3 pollen allergen. The recombinant allergen (rDac g 3) expressed in plasmid vector pGEX-2T contained IgE-reactive epitopes found in its natural counterpart, and induced histamine release from basophils of Dac g-allergic individuals, confirming that the recombinant protein has biological properties similar to the pollen extracted allergen. Computer analyses showed that, in spite of a high degree of sequence homology, even closely related allergens such as Dac g 3 and Lol p 3 have dissimilar predictive secondary structures and potential different antigenicity. Because it possesses the properties of the native counterpart, rDac g 3 could be a relevant tool for molecular studies in allergy.

Allergens↗
PubMed1996

Isotypic analysis of grass pollen-specific antibodies in human plasma. 4. Biological activity of allergen-specific and autoanti-IgE antibody fractions on basophil histamine release.

BACKGROUND: Blocking antibodies are defined as antibodies that compete with IgE for binding to allergens due to their specificity for those allergens. Thus, they may inhibit allergen-induced basophil and mast cell IgE-dependent mediator release both in vivo and in vitro. OBJECTIVE: The present study was designed to evaluate the ability of antibodies isolated from human plasma samples on a Dactylis glomerata (Cocksfoot) pollen affinity-column to inhibit the Dactylis pollen-induced histamine release from human basophils (BHR) in vitro. METHODS: Antibodies from Ig pools containing either high or low IgG4 anti-Dactylis pollen were purified on a Dactylis pollen affinity-column and then separated on an antihuman IgE column. Obtained Ig fractions were incubated for 30 min with Dactylis pollen allergens prior to incubation with basophils from Dactylis pollen-allergic donors. Cell supernatants were assessed for histamine content and the inhibition of BHR was calculated. RESULTS: Unlike control non-isolated Igs, the antibodies isolated on the Dactylis pollen column were able to inhibit efficiently and in a dose-dependent manner Dactylis pollen-induced BHR. The inhibitory activity was increased in isolated antibody samples that had high IgG4 levels. Antibodies isolated on the Dactylis pollen column, however, consisted not only of true allergen-specific (potentially blocking) antibodies but also of autoanti-IgE binding to allergen-specific IgE and mistaken for allergen-specific antibodies thus opening to question the involvement of the true allergen-specific antibodies in the BHR-inhibitory activity. Unlike the true allergen-specific antibodies, the autoanti-IgE were retained on and eluted from the anti-IgE column. Results showed that both the autoanti-IgE-depleted and the autoanti-IgE-containing fractions accounted for the inhibition observed with the related non-depleted sample that had been isolated on the Dactylis pollen column. CONCLUSION: For the first time, the true blocking activity of allergen-specific antibodies is demonstrated, that is, in the absence of the autoanti-IgE which can also inhibit BHR.

Allergens↗
PubMed1995

Human auto-anti-idiotypic antibodies to mite-specific IgE can degranulate human basophils in vitro.

BACKGROUND: Anti-idiotypic antibodies (anti-Ids) to specific IgE antibodies are formed spontaneously during an anti-allergen immune response and can be induced by immunotherapy. Although anti-Ids can down-regulate the production of IgE antibodies, at least in experimental models, their possible role in the modulation of target cell reactivity remains ill-defined. OBJECTIVE: The capacity of human anti-Ids to modulate the release of histamine was examined in an in vitro system of human basophil degranulation. Anti-Ids were prepared from the serum of six Dermatophagoides pteronyssinus (Dp)-hypersensitive patients suffering from atopic dermatitis and who had never been desensitized. Basophils were obtained from the blood of atopic donors. The extent of histamine release was determined using a fluorometric assay. RESULTS: We show that: anti-Ids trigger the release of histamine in an allergen-specific, dose- and IgE-dependent manner; the release is not due to the presence of allergen and/or anti-IgE antibodies; and that the degranulating activity can be removed by absorption with affinity-purified anti-Dp antibodies of the corresponding patient. CONCLUSION: These results indicate that spontaneously produced human anti-Ids can modulate the reactivity of human basophils.

Allergens↗
PubMed1994

In vitro inhibition, by loratadine and descarboxyethoxyloratadine, of histamine release from human basophils, and of histamine release and intracellular calcium fluxes in rat basophilic leukemia cells (RBL-2H3).

The effect of the H1-antihistamine drug loratadine and its active metabolite descarboxyethoxyloratadine upon histamine release was examined on anti-immunoglobulin E (IgE) triggered human basophils and 2,4-dinitrophenyl (DNP) triggered rat basophilic leukemia (RBL-2H3) cells. In both experimental systems, dose-dependent inhibition of histamine release was observed at descarboxyethoxyloratadine and loratadine doses above 2 and 7 microM, respectively. In the RBL-2H3 experimental system, inhibition by loratadine increased when the concentration of extracellular Ca2+ was reduced from 1.8 to 0.45 mM. We further investigated the effect of loratadine and descarboxyethoxyloratadine on the increase in cytosolic calcium concentration (Ca2+)i, an early step in biochemical events leading to exocytosis. The effect of these two drugs upon (Ca2+)i changes was measured using the fluorescent probe fura-2 loaded into RBL-2H3 cells passively sensitized with DNP-specific IgE. Both drugs inhibited, in a dose-dependent manner (2.5-25 microM), the (Ca2+)i rise induced by DNP-BSA challenge in sensitized RBL cells, a process observed in both the presence and absence of extracellular Ca2+. Loratadine also inhibited the Mn2+ influx into these cells, thus reflecting the Ca2+ influx. These results suggest that loratadine and descarboxyethoxyloratadine impair the increase in (Ca2+)i following cell activation by decreasing both the influx of extracellular Ca2+ and the release of Ca2+ from intracellular stores.

Animals↗
PubMed1993

Immunoglobulin-G-dependent stimulation of guinea pig lung mast cells and macrophages.

Alveolar macrophages and mast cells isolated from guinea pig lung were passively sensitized with IgG1, IgG2, or serum obtained from guinea pigs actively sensitized with ovalbumin. The release of histamine by mast cells and of thromboxane A2 by alveolar macrophages upon ovalbumin challenge indicated that both antibodies and serum were capable of sensitizing these cells with similar effectiveness. Heating the serum at 56 degrees C for 4 h to inactivate IgE did not modify the antigen-dependent response of lung cells. These results suggest a predominant role for IgG in the allergic response of the guinea pig through the activation of different cell types such as lung mast cells and alveolar macrophages.

Animals↗
PubMed1993

Mite-allergen exposure and spontaneous histamine release in monosensitive and polysensitive mite-allergic patients.

Forty-three patients allergic to mites and suffering mainly from asthma were recruited: 25 were mite-monosensitive and 18 were polysensitive, as determined by skin tests and specific serum IgE determinations with various allergens. In vitro spontaneous histamine release (SHR) by washed blood basophils was measured once or several times for each patient. Throughout this study, the mean periods of high and low mite-allergen exposure were defined on the basis of relative indoor humidity and temperature data. For the mite-monosensitive patients, there was a significant increase in mean SHR during the season of high mite-allergen exposure as compared to the months of lower mite-allergen presence (P < 0.002). No significant difference between mean SHR values was observed when comparing the monosensitive group during the season of high mite-allergen exposure with polysensitive patients (allergic to mite and pollen) during the period of exposure to both allergens. Differences in mean SHR reported here emphasize the positive relationship between intense allergen exposure and the in vitro SHR increase in blood basophils of mite-allergic patients.

Adult↗