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At least 19 recordsLinked to original sources
PubMed1994

IgE receptors, IgE content and secretory response of mast cells in athymic rats.

Athymic, nude (Lewis rnu/rnu) and normal (Lewis +/+) rats were used to study the T-cell dependence of the regulation of IgE receptors and IgE content on mast cells in vivo. We estimated the number of IgE receptors and the IgE content on peritoneal mast cells using a cytofluorometric technique. The secretory capacity of the mast cells was measured in terms of histamine release as a function of anti-IgE concentration by incubation with antibodies in vitro. Two groups of rats, aged 6 and 13 weeks, were examined. The mast cells of the rats belonging to the older age group (both normal and athymic) had a higher total protein (equivalent to dry mass or size) and mediator content (heparin, histamine and 5-hydroxytryptamine) in accordance with previous findings. Mast cells of the athymic rats of both age groups contained similar levels of IgE receptors and IgE and did not differ in these respects from those of the normal rats. Of the IgE receptors available for binding, about 80% were occupied by IgE in mast cells of normal and of athymic rats in both age groups. The anti-IgE-induced histamine release of the mast cells was, however, significantly lower in athymic rats compared to the normal controls. A change in housing from barrier-maintained to conventional conditions for 2 weeks enhanced the IgE-receptor and IgE content, as well as the releasability of histamine of the mast cells of both athymic and normal rats. The basal level of IgE occupancy of the receptors on mast cells was therefore not impaired in the athymic rats, as might be inferred from previous findings of a T-cell dependence of the IgE immune response. The results further indicate that T-lymphocyte-derived cytokines appear not to be required for either the expression of IgE receptors or for their ability to acquire IgE on mast cells, but such factors seem to enhance the release of histamine following the cross-linkage of the IgE receptor on mast cells in normal conditions.

Aging↗
PubMedDate not supplied

Surface expression of IgE receptors, IgE occupancy and histamine releasability of mast cells: influence of genetic and T cell factors.

IgE receptor density and IgE occupancy were quantified on individual peritoneal mast cells using cytofluorometry. The secretory capacity of the mast cells was analysed in terms of histamine release as a function of anti-IgE challenge. Histamine releasability was found to be largely a function of the number of IgE molecules on the mast cells. The genetic background influenced IgE receptor expression but also, independently, histamine releasability. Both IgE receptor density and IgE occupancy on the mast cells appeared to be T cell independent under normal conditions. Up-regulated IgE receptor expression and an increased IgE occupancy on the mast cells could be obtained in athymic rats in response to a Nippostrongylus brasiliensis infection, although it was not as pronounced as in euthymic rats. The secretory response was diminished in athymic rats, suggesting that T cell factor(s) enhance secretory signal transduction in the mast cells in vivo.

Animals↗
PubMed1996

Immune responses to a Nippostrongylus brasiliensis infection in athymic and euthymic rats: surface expression of IgE receptors, IgE occupancy and secretory ability of mast cells.

The significance of T cells in an allergy-related immune response was investigated. Athymic, nude (Lewis rnu/rnu) rats lacking T lymphocytes and euthymic (Lewis+/+) rats were infected with the nematode Nippostrongylus brasiliensis. The density and occupancy of IgE receptors on peritoneal mast cells were quantified using a cytofluorometric method. The secretory ability of the mast cells as a function of anti-IgE challenge was evaluated in terms of histamine releasability in vitro. It was found that the IgE receptors were markedly up-regulated and the IgE occupancy increased on the mast cells of both athymic and euthymic rats during the parasite infection. However, at its peak, IgE occupancy was significantly higher in euthymic rats than in athymic ones. To our knowledge, this is the first proof of the possibility of a T-cell-independent IgE response in vivo. The IgE-mediated histamine releasability of mast cells was significantly enhanced 1 week after the infection in euthymic rats but not in athymic ones. These results thus indicate that the IgE immune response can occur in the absence of, but is augmented by, T cells. They also suggest that the concept of the IgE response should be widened to comprise not only increased IgE production but also an up-regulation of Ig receptors and an increase in IgE occupancy on mast cells, as well as an increase in the secretory ability of these cells. The latter is T cell dependent, although it is not directly related to the density of IgE-receptor complexes on the mast cells but is more likely due to a stimulation of the post-receptor signal transduction mechanism.

Animals↗
PubMed2001

IgE receptors.

IgE receptors are implicated as important components of the immunological pathway in allergic and inflammatory diseases. Recent investigations have begun to unravel the structure, signal transduction and function of IgE receptors from different cell types in rodent and human systems. Studies of the mechanisms involved might provide opportunities for therapeutic intervention strategies in the treatment of allergic and hypersensitivity reactions.

Animals↗
PubMed2000

Regulation of IgE-receptor expression, IgE occupancy and secretory capacity of mast cells.

Mast cells play an important role in initiating and modulating allergic and inflammatory reactions. Their responsiveness is determined by three important factors: the expression of IgE receptors on the cell surface, the IgE occupancy of these receptors, and the intrinsic secretory capacity of the cells. In this review, we will summarise some findings relevant to these three aspects of mast cell function, and discuss possible regulatory mechanisms. It appears that the genetic background as well as environmental factors influence all three of these components of the response. T cells appear to play an important role in regulating the IgE-receptor expression and also, independently, the intrinsic secretory capacity of mast cells via an unidentified route, possibly involving the secretory signal transduction chain directly. IgE itself appears to have an important role in the regulation of IgE-receptor expression, as indicated by the upregulation of receptors in vitro in the presence of IgE, and the absence of IgE-binding capacity of mast cells in IL-4 gene knockout mice, lacking IgE production. The IgE-receptors of mast cells are saturated to a high degree under different normal conditions, without an obvious relation to antigenic stimulation, also in athymic animals. We have suggested that this basal IgE content on mast cells may be the result of an antigen-independent production of IgE directed by the mast cells themselves and serving regulatory purposes, modifying the secretory response and preventing a massive possibly harmful degranulation.

Animals↗
PubMed1976

Characterization of the target cell receptor for IgE. II. Polyacrylamide gel analysis of the surface IgE receptor from normal rat mast cells and from rat basophilic leukemia cells.

Purified rat peritoneal mast cells (RMC) and cultured rat basophilic leukemia (RBL) cells were surface labeled with 125I by using lactoperoxidase, incubated with unlabeled rat monoclonal IgE and subjected to solubilization by treatment with Nonidet P-40 (NP-40). With both cell types significant amounts of radioiodinated material could be specifically precipitated by a "sandwich" system consisting of rabbit anti-rat epsilon-chain and goat anti-rabbit Ig. The precipitates were dissociated with sodium dodecyl sulfate (SDS) and urea and subsequently analyzed by SDS-polyacrylamide gel electrophoresis. With RMC three radioactive bands were seen. One corresponded to IgE present on the RMC at the time of isolation. A small band migrating in the region of light chain was seen with both sepcific (anti-IgE) and control precipitates. It showed no demonstrable relationship to IgE. The major radioactive band corresponded to a m.w. of 62,000. This band was dependent upon the presence of IgE and was not found when non-IgE binding control cells were used. With RBL cells, only the IgE-dependent 62,000 dalton peak was present. Saturation of the IgE receptor sites of the RMC or RBL cells before lactoperoxidase labeling almost totally eliminated this radioactive band, indicating that cell-bound IgE rendered this membrane component inaccessible to the radiolabel. These results strongly suggest that this cellular component is identical, at least in part, with the target cell surface receptor for reaginic antibody. The data also further support the hypothesis that the neoplastic RBL cells have a normal surface receptor for IgE.

Animals↗
PubMed1994

Recombinant soluble form of the human high-affinity immunoglobulin E (IgE) receptor inhibits IgE production through its specific binding to IgE-bearing B cells.

A recombinant soluble form of the alpha subunit of the human high-affinity receptor for IgE (rsFc epsilon RI alpha), one of the potent IgE-binding molecules, was tested for its ability to regulate IL-4-induced IgE synthesis by human lymphocytes. Addition of rsFc epsilon RI alpha to cultures induced a dose-dependent inhibition of the T cell-dependent and independent synthesis of IgE. The suppression of IgE synthesis was observed at the protein and the mRNA levels, and it was IgE class specific. By flow cytometry, specific binding of rsFc epsilon RI alpha was detected on surface IgE-bearing B cells as well as on U266 cells, and it was completely blocked by preincubation with IgE. rsFc epsilon RI alpha bound to the cell surface IgE could be effectively dissociated not only by a large excess of IgE, but also by an anti-rsFc epsilon RI alpha mAb that competes with IgE for the binding to rsFc epsilon RI alpha. This mAb abolished the rsFc epsilon RI alpha-mediated suppression of IgE synthesis. These data suggest that rsFc epsilon RI alpha may have a function in selectively suppressing IgE synthesis through its interaction with the membrane-bound form of IgE.

Adult↗
PubMed1988

Augmentation of IgE receptor expression and IgE receptor-mediated phagocytosis of rat bone marrow-derived macrophages by murine interferons.

Receptors for IgE (Fc epsilon R) on rat bone marrow-derived macrophages (BMDM phi) were demonstrated by a rosette assay employing trinitrophenyl-coated ox erythrocytes (EoTNP) sensitized with mouse IgE anti-dinitrophenyl monoclonal antibody (EoTNP-IgE). Virtually all BMDM phi emerging from bone marrow cells cultured for 1 week in the presence of mouse L929 cell supernatant, with partially purified murine CSF-1 or recombinant murine GM-CSF, formed IgE rosettes. To study the effect of interferons (IFNs) on Fc epsilon R expression, 1-week-old rat BMDM phi were incubated with murine recombinant IFN-gamma, purified IFN-alpha or IFN-beta, and were tested for their capacity to bind and ingest EoTNP sensitized suboptimally with IgE. A marked increase in the percentage of cells forming IgE rosettes or phagocytosing EoTNP-IgE was noted after 8-72 hr incubation of BMDM phi with 0.1-1000 U/ml of IFNs. At similar concentrations IFN-gamma and IFN-beta triggered EoTNP-IgE binding or ingestion more efficiently than IFN-alpha. The enhancing effect was blocked by the respective anti-IFN antibodies, cycloheximide or actinomycin D but not by mitomycin C. The IgE rosette formation and IgE-mediated phagocytosis were dose-dependently inhibited by native rat IgE but not by heat-denaturated IgE myeloma protein IR162 or monomeric rabbit IgG. Our results demonstrate that rat BMDM phi express constitutively Fc epsilon R, and that murine IFNs augment Fc epsilon R-mediated binding and ingestion in a time- and dose-dependent manner. This effect probably reflects an increase in the number of Fc epsilon R per cell, as a result of de novo synthesis of Fc epsilon R.

Animals↗
PubMed1993

Effects of subunit mutation on the localization to coated pits and internalization of cross-linked IgE-receptor complexes.

IgE receptors of mast cells, Fc epsilon RI, localize to coated pits and internalize after cross-linking. We investigated whether any one of the receptor's four distinctive cytoplasmic domains regulates these phenomena. COS cells, which lack Fc epsilon RI entirely, and P815 mouse mastocytoma cells that lack the alpha and beta subunits of the tetrameric Fc epsilon RI (alpha beta gamma 2), were transfected with wild-type, incomplete, or variant Fc epsilon RI. IgE-receptor complexes were observed by electron microscopy. Before cross-linking with anti-IgE gold particles, receptors were not preferentially localized to coated pits, which occupy approximately 1% of the cell surface. After cross-linking, up to 10 to 20% of the wild-type and most other receptor variants were in coated pits in transfected P815 cells at any one time. beta-less variants localized normally but, surprisingly, receptors containing a variant beta subunit showed reduced localization. "Receptors" consisting simply of the lipid-anchored ectodomains of the human alpha subunit failed to localize to coated pits. In general, cross-linked receptors that localized to coated pits were progressively internalized, whereas receptors that failed to accumulate in coated pits were not. We conclude that no single cytoplasmic domain of the Fc epsilon RI uniquely controls its ligand-induced localization to coated pits and internalization.

Amino Acid Sequence↗
PubMed1986

IgE receptors on human lymphocytes. II. Detection of cells bearing IgE receptors in unstimulated mononuclear cells by means of a monoclonal antibody.

A monoclonal antibody (mAb) specific for lymphocyte IgE receptors (ER) was employed in a rosette assay for the detection of cells bearing IgE receptors (Fc epsilon R). The specificity of the assay was documented by inhibition studies with soluble immunoglobulins (Ig) and anti-Ig antibodies. Moreover, similar results were obtained by employing the F(ab')2 fragment of mAbER instead of intact molecule. Circulating mononuclear cells isolated from normal or allergic adults and from umbilical cord blood contained approximately 8% of Fc epsilon R-bearing cells with values ranging from 0.3 to 17%. Tonsillar lymphocytes contained about 30% of Fc epsilon R+ cells. After the removal of adherent cells, there was a small but significant reduction of the proportion of Fc epsilon R+ cells. When mononuclear cells were separated into T and B cell fractions by two-cycle rosetting with 2-aminoethylisothiouronium bromide hydrobromide-treated sheep red blood cells, most of the Fc epsilon R+ cells were in the B cell fraction; however, a small proportion of Fc epsilon R+ was also found in the enriched T cells and double-labeling experiments confirmed that these cells were indeed T lymphocytes. Fc epsilon R+ cells were purified by rosetting with mAbER-coated erythrocytes and their phenotype was compared to that of Fc epsilon R- cells; Fc epsilon R+ cells contained about 90% of B cells (B1+) together with a small proportion of OKT3+, Leu 7+ and Mo2+ cells. The bulk of T cells, macrophages and natural killer (NK) cells was found in the Fc epsilon R- cells which contained fewer B cells than the fraction of Fc epsilon R+ cells. These data thus indicated that the great majority of Fc epsilon R-bearing cells are B cells but that a small proportion of NK cells, macrophages and T lymphocytes also express Fc epsilon R. Upon incubation at 37 degrees C, B cells lost their Fc epsilon R and this phenomenon was selectively inhibited by IgE; however, purified T cells seemed to express more Fc epsilon R after overnight incubation at 37 degrees C and this was not influenced by IgE. It is finally shown that the expression of Fc epsilon R is cyclic and that Fc epsilon R-bearing B cells do not represent a functionally distinct subpopulation of B lymphocytes.

Adult↗
PubMed1991

Immobilization and internalization of mutated IgE receptors in transfected cells.

Earlier studies have shown that the mast cell receptor IgE (Fc epsilon RI) for is expressed on COS-7 cells transfected with the cDNA for each of the three types of subunits that form the tetrameric, alpha beta gamma 2, receptor. Although such transfected COS cells fail to exhibit some of the early biochemical perturbations initiated by aggregation of the receptor on normal mast cells and related tumor lines, we show here that other characteristics of the endogenous Fc epsilon RI are retained. Thus, the unaggregated transfected wild-type receptors were found to have a restricted translational diffusion similar to that observed for endogenous receptors on mast cells as assessed by fluorescence photobleaching and recovery. Similarly, as with endogenous receptors the mobility of transfected receptors was sharply reduced when the receptors were aggregated by reaction with small oligomers of IgE. In addition, aggregation of the transfected Fc epsilon RI caused them to be internalized by the COS cells by a cytochalasin-sensitive mechanism, albeit at a considerably slower rate than was seen with endogenous receptors on mast cells or with transfected receptors in a line of receptor-deficient mast cells. We also examined the mobility and internalization before and after aggregation, of some 13 different combinations of receptor subunit mutants in which one or more of the five cytoplasmic domains of the receptor had been truncated. Our results show that whatever interactions between the receptor and cellular components may account for the phenomena we studied, such interactions do not critically depend upon the bulk of the cytoplasmic domains of the receptor.

Amino Acid Sequence↗
PubMed1986

IgE receptors on human lymphocytes. III. Expression of IgE receptors on mitogen-stimulated human mononuclear cells.

Human peripheral blood mononuclear cells (PBMC) were tested for the expression of Fc epsilon-receptor (Fc epsilon R) after stimulation with various mitogens in the absence of IgE. Fc epsilon R were found on virtually all the cells from 19 Epstein-Barr virus-transformed B cell lines including those derived from cord blood, from one agamma-globulinemic patient and VDS-0 pre-B cells. Hence, the data clearly indicate that Fc epsilon R may be expressed on very immature B cells. PBMC cultures stimulated with either pokeweed mitogen (PWM), phytohemagglutinin (PHA) or concanavalin A displayed an early increase of their content in Fc epsilon R-bearing cells followed by a decrease to levels below those of control cultures. After fractionation of the PWM-stimulated cultures into T and B cell-enriched preparations, most of the Fc epsilon R+ cells were in the in the B cell fractions and the same low levels of Fc epsilon R+ cells were found in the T cell fractions isolated from the PWM-stimulated and from the control cultures. Double-labeling experiments, employing biotinylated F(ab')2 monoclonal antibody to FcR and either fluorescein isothiocyanate-conjugated B1 or Mo2 monoclonal antibodies, indicated that PWM mainly exerted its effect on B cells and on monocytes. This effect was T cell dependent and it was mediated by soluble factors of T cell origin. At the peak of the PHA or concanavalin A response, most of the Fc epsilon R-bearing cells were found in the B cell fraction but the T cells isolated from mitogen-stimulated cultures contained significant more Fc epsilon R+ cells than those from the control cultures, suggesting that T cell mitogens had increased the expression of Fc epsilon R on some T cells. This view was supported by the finding of a higher proportion of Fc epsilon R+ cells in PHA-stimulated than in control cultures of highly purified T cells with a maximum response at the end of the culture period. Double-labeling experiments at the peak (day 2) of the peripheral blood mononuclear cell response indicated that the expression of Fc epsilon R was increased on B cells (B1+) and on monocytes (Mo2+). By using the same approach at the peak of the T cell response (day 7), it was found that T cells isolated from PHA-stimulated cultures expressed more Fc epsilon R than those isolated from control cultures.(ABSTRACT TRUNCATED AT 400 WORDS)

Cell Line↗
PubMedDate not supplied

IgE receptors and serum IgE in pollinosis. The influence of season and action of ketotifen.

In the present study we have analyzed the correlation between bound and free IgE in two groups of patients with sensitization to grass pollen; 15 of these patients only presented symptoms of rhinitis, while the other 17 patients had symptoms associated with bronchial asthma. The study was carried out after, and during the pollen season. We observed that no correlation existed between bound and free IgE in the rhinitic group after pollen season, while there was correlation with the same group of patients during the pollen season. On the contrary, the asthmatic group obtained a good correlation between bound and free IgE after the pollen season, rather than within the pollinization period. In view of these results, we can affirm that the relationship which exists between free and membrane-associated IgE varies, depending on the type of individual and the seasonal period at the time the measurements were carried out. At the same time and in order to analyze the dynamics of action of ketotifen, we studied the effect of this drug on the amount of membrane-associated IgE, for which we employed an enriched population of basophils maintained in culture. From the results obtained we deduced that in no way does ketotifen affect the receptor expression for IgE. Therefore, the possible mechanism of action of ketotifen could be directed toward the interior of, rather than the exterior of the plasmatic membrane.

Asthma↗
PubMed2001

Human eosinophils and human high affinity IgE receptor transgenic mouse eosinophils express low levels of high affinity IgE receptor, but release IL-10 upon receptor activation.

FcepsilonRI expressed by human eosinophils is involved in IgE-mediated cytotoxicity reactions toward the parasite Schistosoma mansoni in vitro. However, because receptor expression is low on these cells, its functional role is still controversial. In this study, we have measured surface and intracellular expression of FcepsilonRI by blood eosinophils from hypereosinophilic patients and normal donors. The number of unoccupied receptors corresponded to approximately 4,500 Ab binding sites per cell, whereas 50,000 Ab binding sites per cell were detected intracellularly. Eosinophils from patients displayed significantly more unoccupied receptors than cells from normal donors. This number correlated to both serum IgE concentrations and to membrane-bound IgE. The lack of FcepsilonRI expression by mouse eosinophils has hampered further studies. To overcome this fact and experimentally confirm our findings on human eosinophils, we engineered IL-5 x hFcepsilonRIalpha double-transgenic mice, whose bone marrow, blood, spleen, and peritoneal eosinophils expressed FcepsilonRI levels similar to levels of human eosinophils, after 4 days culture with IgE in the presence of IL-5. Both human and mouse eosinophils were able to secrete IL-10 upon FcepsilonRI engagement. Thus, comparative analysis of cells from patients and from a relevant animal model allowed us to clearly demonstrate that FcepsilonRI-mediated eosinophil activation leads to IL-10 secretion. Through FcepsilonRI expression, these cells are able to contribute to both the regulation of the immune response and to its effector mechanisms.

Animals↗
PubMed1981

Functional and partial chemical characterization of the carbohydrate moieties of the IgE receptor on rat basophilic leukemia cells and rat mast cells.

The role of the carbohydrate portion of the receptor for IgE in the interaction with IgE was investigated. Membrane carbohydrates of rat basophilic leukemia (RBL) cells and rat mast cells (RMC) were labeled by treating the cells with galactose oxidase followed by [3H]-NaBH4. IgE receptors were separated from detergent solubilized membranes and examined by SDS-polyacrylamide gel electrophoresis (SDS-PAGE). Pretreatment with neuraminidase markedly increased the incorporation of 3H into both the total membrane extract and into the IgE receptors. SDS-PAGE analysis demonstrated the presence of galactose in all IgE-binding components of 2 RBL cell lines and the presence of sialic acid on the major IgE-binding component. Prior saturation of the cells with IgE did not prevent the carbohydrate labeling of the receptor, although it did block the labeling of its protein part, indicating that carbohydrates are not located in the binding site. Removal of terminal sialic acid residues with neuraminidase increased the affinity of the receptor for IgE without appreciably affecting the number of receptors per cell. In order to more drastically modify the receptor carbohydrates, RBL cells were grown in the presence of Tunicamycin (TN). TN was shown to markedly inhibit the incorporation of [3H]-glucosamine into the receptor. RBL cells grown in the presence of TN expressed fewer receptors at the cell surface, as judged both by ligand binding studies and external labeling procedures. These data cumulatively suggest that the carbohydrate moieties of the receptor are not directly located in the binding site of the IgE receptor; however, the TN studies suggest that receptor carbohydrate may play a role in transport of the receptor to the plasma membrane or in its orientation thereafter.

Animals↗