Low-affinity IgE Receptor Research Articles

Il-4 enhances transepithelial antigen transport by stimulating CD23/Fe∈RII (low affinity IgE receptor) expression on enterocytes of sensitized mice

Il-4 enhances transepithelial antigen transport by stimulating CD23/Fe∈RII (low affinity IgE receptor) expression on enterocytes of sensitized mice

CD23/Fc epsilon RII (low affinity IgE receptor) is expressed on human epithelial cells and upregulated by IL-4 and LPS

CD23/Fc epsilon RII (low affinity IgE receptor) is expressed on human epithelial cells and upregulated by IL-4 and LPS

Il-4 enhances transepithelial antigen transport by stimulating CD23/Fe∈RII (low affinity IgE receptor) expression on enterocytes of sensitized mice

Il-4 enhances transepithelial antigen transport by stimulating CD23/Fe∈RII (low affinity IgE receptor) expression on enterocytes of sensitized mice

CD23/Fc epsilon RII (low affinity IgE receptor) is expressed on human epithelial cells and upregulated by IL-4 and LPS

CD23/Fc epsilon RII (low affinity IgE receptor) is expressed on human epithelial cells and upregulated by IL-4 and LPS

Mechanism of cooperative effects of rhinovirus and atopic sensitization on airway responsiveness.

To elucidate the mechanistic interplay between rhinovirus (RV) exposure and atopic sensitization in regulating airway smooth muscle (ASM) responsiveness, isolated rabbit ASM tissue and cultured human ASM cells were passively sensitized with sera from atopic asthmatic or nonatopic nonasthmatic (control) subjects in the absence and presence of inoculation with RV serotype 16. Relative to control subjects, atopic asthmatic serum-sensitized and RV-inoculated ASM exhibited significantly increased contractility to acetylcholine, impaired relaxation to isoproterenol, and enhanced release of the proinflammatory cytokine interleukin-1beta. These effects were potentiated in atopic asthmatic serum-sensitized ASM concomitantly inoculated with RV and inhibited by pretreating the tissues with monoclonal blocking antibodies against intercellular adhesion molecule (ICAM)-1 (CD54), the host receptor for RV serotype 16, or lymphocyte function-associated antigen (LFA)-1 (CD11a/CD18), the endogenous counterreceptor for ICAM-1. Moreover, RV inoculation was found to potentiate the induction of mRNA and surface protein expression of FcepsilonRII (CD23), the low-affinity receptor for IgE, in atopic asthmatic serum-sensitized ASM. Collectively, these observations provide new evidence demonstrating that 1) RV exposure and atopic sensitization act cooperatively to potentiate induction of proasthmatic changes in ASM responsiveness in association with upregulated proinflammatory cytokine release and FcepsilonRII expression and 2) the effects of RV exposure and atopic sensitization are mediated by cooperative ICAM-1-coupled LFA-1 signaling in the ASM itself.

Molecular mechanisms of atopy.

Production of specific immunoglobulin (Ig)E is the characteristic abnormality of atopy. IgE is produced by B lymphocytes under the influence of interleukin (IL)4 and IL-13. IgE binds to high-affinity IgE receptors (Fc«RI) on mast cells to induce degranulation and mediator synthesis. IL-4 enhances the activation of Fc«RI to augment the production of cytokines and lipid mediators. These receptors may also be expressed on other cells such as basophils, monocytes and eosinophils. IgE may also activate low-affinity IgE receptors (Fc«RII or CD23) that are expressed on B lymphocytes, T lymphocytes, macrophages and airway smooth muscle cells. CD23 expression is enhanced by IL-4. Recently, a humanised murine monoclonal antibody (E25) directed against IgE has demonstrated a reduction in early and late responses to inhaled allergen and eosinophil counts in induced sputum, and reduced airway hyperresponsiveness. There is a profound reduction in circulating IgE, which may be due to switching-off IgE production from B cells. In patients with severe asthma who require oral steroids there is a significant reduction in oral steroid requirements, and several patients are able to completely withdraw oral steroids in comparison with a placebo. E25 may also reduce signalling through CD23 as IgE levels are lowered and this might explain its efficacy in chronic asthma, through an inhibitory effect on T lymphocytes, macrophages, eosinophils and airway smooth muscle.

Enhanced intestinal transepithelial antigen transport in allergic rats is mediated by IgE and CD23 (FcepsilonRII).

We previously reported that active sensitization of rats resulted in the appearance of a unique system for rapid and specific antigen uptake across intestinal epithelial cells. The current studies used rats sensitized to horseradish peroxidase (HRP) to define the essential components of this antigen transport system. Sensitization of rats to HRP stimulated increased HRP uptake into enterocytes (significantly larger area of HRP-containing endosomes) and more rapid transcellular transport compared with rats sensitized to an irrelevant protein or naive control rats. Whole serum but not IgE-depleted serum from sensitized rats was able to transfer the enhanced antigen transport phenomenon. Immunohistochemistry demonstrated that sensitization induced expression of CD23, the low-affinity IgE receptor (FcepsilonRII), on epithelial cells. The number of immunogold-labeled CD23 receptors on the enterocyte microvillous membrane was significantly increased in sensitized rats and was subsequently reduced after antigen challenge when CD23 and HRP were localized within the same endosomes. Finally, pretreatment of tissues with luminally added anti-CD23 antibody significantly inhibited both antigen transport and the hypersensitivity reaction. Our results provide evidence that IgE antibodies bound to low-affinity receptors on epithelial cells are responsible for the specific and rapid nature of this novel antigen transport system.

Expression of CD23 receptors on b chronic lymphocytic leukaemia cells

CD23, the low affinity receptor for IgE (FcϵRII), is a 45kDa cell surface glycoprotein which is proteolytically cleaved to form a range of soluble CD23 species (sCD23), which have cytokine-like activities and act via a number of cell surface receptors. The currently defined receptors are CD11b–CD18, CD11c–CD18, CD21 and the αvβ3 and αvβ5 vitronectin receptor isoforms. Elevated levels of serum sCD23 are often noted in B-CLL, with very high levels correlating with a poor prognosis, suggesting that sCD23 may play a role in B-CLL disease progression, possibly by inhibiting apoptosis. To address this hypothesis, we have determined patterns of expression of CD23 and its receptors on CLL B cells and normal B cells. FACS analysis showed low levels of expression of CD23 on normal, resting B cells, and consistently higher levels on CLL B cells. CD21 was present at low levels on both normal and CLL B cells, and CD11c was found on a proportion of B-CLL samples. No significant expression of CD11b, αvβ3 or αvβ5 was detected. Mild acid washing of the cells did not increase detection of CD23 receptors, indicating that the receptors were not masked by binding of CD23 or other ligand. The receptor expression patterns found by FACS analysis were reflected by RT-PCR of receptor transcripts. These results indicate that any possible effect of sCD23 in B-CLL is unlikely to be mediated via any of the known CD23 receptors with the exception of CD21. This does not, however, rule out the involvement of other, as yet unidentified receptors in B-CLL development.

Predictors of atopy in HIV-infected patients

Some studies have reported an increase of atopy in HIV-infected (HIV+) patients, but the cause still remains unclear. To determine the prevalence of atopy in HIV+ patients and to investigate its predictors. Seventy-four HIV+ hospitalized patients (46 of them with AIDS) were studied prospectively for the presence of atopy, based on immediate hypersensitivity to common allergens by prick test. Serum immunoglobulins, specific IgE, lymphocyte subsets, and the expression of low affinity IgE receptor (CD23) on B cells were determined. Thirty-one percent of patients presented IgE values greater than 150 ku/L (39% of patients without AIDS and 26% of AIDS patients; P = .23) and 47% showed an increase (> or = 2%) in the percentage of CD23+ B cells. Non-AIDS patients had higher IgE values than AIDS patients (346 +/- 605 versus 175 +/- 276; P = .16). Atopy prevalence was higher in non-AIDS than in AIDS patients (28% versus 11%; P = .06). Specific IgE agreed with positive prick test in 58% of cases. Multivariate analysis showed that a personal history suggestive of allergic disease and IgE > 150 ku/L were predictors of atopy, while gender, risk group, CD4+ T cells, CD23 expression on B cells, and AIDS were not associated. HIV+ patients present a higher prevalence of atopy in early stages of HIV infection than general population. Since allergic reactions could accelerate HIV-infection by increasing type 2 cytokines, it is important to evaluate the atopic state in HIV+ patients with IgE > 150 ku/L or with suggestive allergic history in order to prevent it.

The role of CD23 on allergen-induced IgE levels, pulmonary eosinophilia and bronchial hyperresponsiveness in mice.

The role of Immunoglobulin (Ig)E in inflammation is the subject of considerable study and a number of studies have shown conflicting evidence for its role in eosinophil recruitment and bronchial hyperresponsiveness in a number of murine models. The low affinity IgE receptor, CD23, is known to act as a negative regulator of IgE production and we have used knockout mice deficient in CD23 to investigate the role of IgE in eosinophil recruitment and bronchial hyperresponsiveness in a murine model of airway inflammation. To study the role of the low affinity FcepsilonII receptor, CD23 in IgE production, lung inflammation and bronchial hyperresponsiveness. Wild-type and CD23 knockout C57Bl/6 mice (CD23-/-) were immunized by intraperitoneal injection with ovalbumin on days 0 and 14 and challenged with aerosolized antigen on day 21 for a period of up to 1 week. Blood samples, bronchoalveolar lavage and lung tissue samples were obtained to determine serum IgE levels and inflammatory cell numbers, respectively. Furthermore, airway resistance was measured to increasing concentrations of aerosolized 5-hydroxytryptamine in order to evaluate the effect of CD23 deficiency on bronchial hyperresponsiveness to antigen challenge. Sensitization of wild-type C57Bl/6 mice to ovalbumin resulted in elevated levels of total serum IgE and ovalbumin-specific IgE, which was significantly augmented in CD23 knockout C57Bl/6 mice (CD23-/-). A significant increase in the percentage of eosinophils recovered in bronchoalveolar lavage fluid from wild-type and CD23-/- mice was observed 24 h following 3 or 7 days aerosol exposure with ovalbumin (10 mg/mL). At 3 days, the increase in the percentage of eosinophils was significantly greater in CD23-/- groups. Immunohistochemical analysis of lungs sections revealed the presence of CD3+, CD4+ and CD23+ cells in wild-type mice but a lack of immunofluorescence of CD23+ cells in CD23-/- mice. In wild-type ovalbumin-immunized mice, bronchial hyperresponsiveness to aerosolized 5-hydroxytryptamine was observed following a 3-day antigen challenge, which was significantly greater in CD23-/- ovalbumin-immunized mice. These studies demonstrate that CD23-/- mice have increased capacity to produce IgE consistent with the view of a negative feedback role for membrane-bound CD23 and under such conditions, may account for the greater numbers of eosinophils recruited to the airways and bronchial hyperresponsiveness observed following acute but not chronic antigen challenge.

Restoration of the antibody response to IgE/antigen complexes in CD23-deficient mice by CD23+ spleen or bone marrow cells.

Mice immunized with IgE/Ag complexes produce significantly more Ag-specific Abs than mice immunized with Ag alone. The enhancement is mediated via the low-affinity receptor for IgE (FcepsilonRII or CD23), as shown by its complete absence in mice pretreated with mAbs specific for CD23 and in CD23-deficient mice. Because the constitutive expression of murine CD23 is limited to B cells and follicular dendritic cells (FDCs), one of these cell types is likely to be involved. One of the suggested modes of action of IgE/CD23 is to increase the ability of B cells to present Ag to T cells, as demonstrated to take place in vitro. Another possibility is that FDCs capture the IgE/Ag complexes and present these directly to B cells. The purpose of the present study was to determine whether CD23+ B cells or FDCs are responsible for the IgE/CD23-mediated enhancement of specific Ab responses in vivo. We show that the enhancement is completely restored in irradiated CD23-deficient mice reconstituted with CD23+ spleen or bone marrow cells. In these mice, the B cells are CD23+ and the FDCs are presumably CD23- because the FDCs are radiation resistant and are reported not to be replaced by donor cells after this type of cell transfer. In contrast, enhancement was not restored in irradiated wild-type mice reconstituted with CD23- cells. These results indicate that CD23+ B cells, and not FDCs, are the cells that capture IgE/Ag complexes and induce enhancement of Ab responses in vivo.

Expression of a functional inducible nitric oxide synthase in hairy cell leukaemia and ESKOL cell line.

The expression of nitric oxide synthase (NOS) isoforms was investigated in the established ESKOL hairy cell line and in leukemic cells of patients with hairy cell leukemia (HCL). By reverse transcription-polymerase chain reaction (RT-PCR), these cells were found to spontaneously express inducible NOS (iNOS)-specific mRNA, but not endothelial constitutive NOS (ecNOS) mRNA. The iNOS protein was detected by immunofluorescence in the cytoplasm of permeabilized leukemic cells and ESKOL cells, using different anti-iNOS monoclonal antibodies. A protein of 135 kDa was identified by Western blotting in ESKOL and HCL lysates, confirming the presence of an iNOS in these cells. Cytosolic homogenates displayed NOS catalytic activity, as measured by the conversion of 14C-labelled L-arginine into 14C L-citrulline and by detection in situ using the DAF-2DA (diaminofluorescein diacetate) NO-sensitive fluorescent probe. Ligation of CD23 (low affinity IgE receptor) was found to increase iNOS expression in ESKOL and conversely to decrease the percentage of cells undergoing apoptosis, as measured by the percentage of cells expressing annexin V. These results indicate that, as in chronic B cell lymphocytic leukemia cells (B-CLL) a functional iNOS is expressed constitutively in hairy cells that contributes to protecting these tumoral cells from apoptosis.

Regulation of antibody responses via antibodies, complement, and Fc receptors.

Antibodies can completely suppress or enhance the antibody response to their specific antigen by several hundredfold. Immunoglobulin M (IgM) enhances antibody responses via the complement system, and complement activation by IgM probably starts the chain of events leading to antibody responses to suboptimal antigen doses. IgG can enhance primary antibody responses in the absence of the complement system and seems to be dependent on Fc receptors for IgG (FcgammaRs). IgE enhances antibody responses via the low-affinity receptor for IgE (FcepsilonRII/CD23). The precise effector mechanisms that cause enhancement are not known, but direct B-cell signaling, antigen presentation, and increased follicular localization are all possibilities. IgG, IgE, and IgM may also suppress antibody responses when used in certain immunization regimes, and it seems reasonable that an important mechanism behind suppression is the masking of antigenic epitopes by antibodies. In addition, FcgammaRIIB, which contains a cytoplasmic inhibitory motif, acts as a negative regulator of antibody responses. This receptor, however, may prevent the antibody responses from exceeding a certain level rather than causing complete suppression.

The novel human IgE epsilon heavy chain, epsilon tailpiece, is present in plasma as part of a covalent complex

Several splice variants of the secreted human epsilon heavy chain have previously been identified by reverse transcription-PCR. The heavy chain of one isoform, IgE tailpiece, differs from the originally identified IgE, IgE classic, by the replacement of the 2 carboxy-terminal amino acids by 8 novel amino acids including a carboxy-terminal cysteine residue. Recombinant human epsilon tailpiece and epsilon classic heavy chains were expressed and secreted as H 2L 2 monomers in Sp2/0 murine myeloma cells. We have investigated the in vitro function and in vivo occurrence of epsilon tailpiece heavy chains using receptor binding assays, granule release assays, flow cytometry, half-life studies, immunoprecipitation, SDS-PAGE, two-dimensional SDS-PAGE, and Western blotting. IgE tailpiece and IgE classic exhibited similar in vivo half-lives in BALB/c mice, bound the human high- and low-affinity IgE receptors with similar affinities and triggered equivalent levels of high affinity IgE receptor induced degranulation. In humans, IgE classic is present as a 190 kD circulating protein in vivo. In contrast, we found that in plasma epsilon tailpiece was primarily present as part of covalent complexes of approximately 300 and 338 kD. Dissociation of the complexes revealed that two species of epsilon tailpiece heavy chains were present therein and surprisingly, these in vivo derived epsilon tailpiece heavy chains were approximately 5 and 10 kD smaller than the recombinant expressed epsilon tailpiece or epsilon classic heavy chains. These results show that epsilon tailpiece is present in novel covalent complexes in humans.

Atopic dermatitis: from the genes to skin lesions.

Atopic dermatitis: from the genes to skin lesions.

Molecular cloning and sequencing of the low-affinity IgE receptor (CD23) for horse and cattle

Expression of the low-affinity IgE receptor (CD23) on the surface of mononuclear cells is a critical event in the development of IgE-mediated immunologic responses. Using PCR and cDNA library screening, a 2.7 kb cDNA encoding equine CD23 and a 627 bp PCR fragment of cattle CD23 were sequenced and characterized. The equine CD23 sequence encodes a complete and continuous open reading frame of 327 amino acids, while the shorter cattle fragment encodes 209 amino acids corresponding to nucleotides 325–1098 of the equine CD23 transcript. In addition to high identities in their nucleotides and translated amino acids with CD23 sequences published for other species, the translated equine CD23 protein also shares many of the structural features of this molecule described for human and rodents. Interestingly, an additional repetitive element of possible functional significance consisting of 18 amino acids, located between the transmembrane region and the carbohydrate-binding lectin domain of horse CD23, was also identified. Based on these sequences, molecular assays will be developed to measure CD23 mRNA in tissues and expression of recombinant proteins will be essential to the production of species-specific antibody reagents. These assays and reagents will be useful in future studies of allergic and lymphoproliferative diseases in horses and cattle.

In vitro IgE inhibition in B cells by anti-CD23 monoclonal antibodies is functionally dependent on the immunoglobulin Fc domain

CD23, the low affinity receptor for IgE (FcεRII), is involved in regulation of IgE synthesis by B-lymphocytes. Five monoclonal antibodies to human CD23 were generated from cynomolgus macaques immunized with purified soluble CD23 (sCD23). Four of the five primate antibodies blocked the binding of IgE complexes to CD23 positive cells and also inhibited the production of IgE in vitro by IL-4 induced human peripheral blood mononuclear cells (PBMC). The variable domains of several primate antibodies were utilized to construct chimeric macaque/human (PRIMATIZED ®) monoclonal antibodies. PRIMATIZED ® p5E8G1, containing human gamma 1 constant region, inhibited IgE production in vitro as efficiently as the parent primate antibody, but the human gamma 4 constant version, PRIMATIZED ® p5E8G4, was not as effective in IgE inhibition. An F(ab′) 2 of p5E8G1 did not inhibit IgE production but did interfere with IgE inhibition by the intact anti-CD23 antibody in a dose dependent fashion. The murine monoclonal antibody MHM6 recognizes human CD23 at a different epitope than primate antibody 5E8, and inhibits IgE production by IL-4 induced PBMC. As with the F(ab′) 2 of p5E8G1, the F(ab′) 2 of MHM6 also failed to inhibit IgE production. These data imply that the mechanism by which anti-CD23 antibodies inhibit IgE production requires cross-linking of CD23 to an IgG receptor. These data also imply that neither bivalent cross-linking of CD23 alone or inhibition of CD23 binding to its natural ligands is sufficient to inhibit IgE production.

Two Peptides from CD23, Including the Inverse RGD Sequence and Its Related Peptide, Interact with the MHC Class II Molecule

The human CD23 molecule (low affinity receptor for IgE) has a C-type lectin domain, a reversed Arg-Gly-Asp (RGD) sequence near the C-terminus, and an “RGD-binding inhibitory peptide” at the root of the N-sugar chain. Three peptides were synthesized to determine their functions, i.e., #1, including an inverse RGD sequence near the C-terminus; #2, RGD-binding inhibitory peptides in the gpIIIa chain of platelet integrin gpIIb/IIIa; and #3, the inverse sequence located at the root of the N-sugar chain of CD23 which has homology to peptide 2. Among the three peptide, only peptide 3 inhibited aggregation of L-KT9 cells. Isotope-labeled peptides 1 and 3 bound to MHC class II molecules but peptide 1 did not bind to CD23 molecules. Peptide 3 showed a higher affinity to MHC class II than did peptide 1. Both peptides in CD23, therefore, seem to have interesting and important functions in relation to MHC class II molecules and also to CD23 molecules when CD23 on EBV-transformed B cells acts as a lectin in homotypic cell aggregation. The physiological function of CD23 was discussed from an evolutional point of view.

The Clinical Significance of Serum CD23 and CD25 in Chronic Cough Patients

Background : Coughing is the most common complaint for which patients seek medical service. When caughing continues over 3 weeks in non-smokers who do not take cough-provoking drugs, they are classified as patients with chronic cough. Three well known main causes of chronic caugh are postnasal drip syndrome, bronchial asthma and gastroesophaseal reflux disease. Among them, postnasal drip syndrome is reported to be the most common cause of all in chronic cough diseases, and allergic inflammation plays an important role in the pathogenesis of postnasal drip syndrome. CD23 and CD25 which are low affinity receptor for IgE and IL-2 receptor alpha, respectively, are closely related to allergic inflammation and their roles were evaluated in chronic cough patients. Methods : We evaluated 105 patients with chronic cough and selected 56 patients for measurement of serum CD23 & CD25 levels. We selected 10 normal, medical students for comparison of serum CD23 & CD25 levels. Result : The postnasal drip syndrome was found to be the most common cause of chronic cough. Serum CD23 and CD25 did not increase in chronic cough patient compared to normal controls. However in bronchial asthma patient, serum CD23 level was increased relative to normal control (p

Selective inhibition of low affinity IgE receptor (CD23) processing: P 1′ bicyclomethyl substituents

Using a variety of α-hydroxy hydroxamic acid derivatives, the size and shape of the S 1′ pocket for the CD23 processing metalloprotease has been explored. It has been demonstrated that a P 1′ 2-naphthylmethyl group occupies most of the available space and gives excellent selectivity against fibroblast collagenase (matrix metalloproteinase-1, MMP-1) and other MMPs.