Different stabilities of the structurally related receptors for IgE and IgG on the cell surface are determined by length of the stalk region in their alpha-chains

Immunohistochemistry analyses of the abomasal mucosa show differences in cellular-mediated immune responses to Haemonchus contortus infection in resistant and susceptible young lambs

Haemonchus contortus is known for its high pathogenicity in sheep, and the uncontrolled use of anthelmintics resulted in the emergence of multiple drug-resistant populations. Breeding sheep for gastrointestinal nematode resistance is a sustainable alternative to reduce dependence of anthelmintic drugs, and differences in the degree of resistance between breeds have been reported. Here we compare two sheep breeds (Santa Ines and Ile de France), concerning the differences in innate and adaptive immune response involved in the resistance against H. contortus infection. Immunohistochemical analyses of the abomasum were conducted in naïve Santa Ines (n = 14) and Ile de France (n = 12) lambs randomized into four groups: infected Santa Ines (n = 8), non-infected control Santa Ines (n = 6), infected Ile de France (n = 8), and non-infected control Ile de France (n = 4). The infected lambs were initially infected with H. contortus infective larvae at 14 days of age, and multiple infections were conducted every second day until they reached 66 days of age. There was a significant effect (P < 0.001) of the infection with increase in numbers of CD3+ T; CD79α+ B; GATA3+ Th2/ILC2; POU2F3+ tuft cells; FOXP3+ T reg; and IgE + cells in the fundus of the abomasal mucosa in both Santa Ines and Ile de France lambs. Nevertheless, the infected Santa Ines lambs presented the highest averages for CD79α+ B; GATA3+ Th2/ILC; IgE + cells; and POU2F3+ tuft cells and there was a significant association of the breed and infection status with regards to POU2F3+ tuft cells, with the highest mean in the infected Santa Ines group. The infected Santa Ines group had three lambs with high degree of resistance and five lambs that showed a moderate infection. Our results suggest a mechanism of synergistic coordination between different immune-cell types in promoting resistance of suckling lambs under H. contortus infection.

What is the contribution of IgE to nasal polyposis?

Taking a novel approach, this narrative review collates knowledge about nasal polyposis and the biological functions of IgE in several diseases (allergic rhinitis, allergic asthma, nonsteroidal anti-inflammatory drugs-exacerbated respiratory disease, and chronic spontaneous urticaria) to consider which IgE-mediated mechanisms are relevant to nasal polyposis pathology. A type 2 eosinophil-dominated inflammatory signature is typical in nasal polyp tissue of European patients with nasal polyposis, with a shift toward this endotype observed in Asian populations in recent years. Elevated polyclonal IgE is present in the nasal tissue of patients with and without allergy. It is derived from many different B-cell clones and, importantly, is functional (proinflammatory). Staphylococcus aureus enterotoxins are thought to act as superantigens, inducing production of polyclonal IgE via B-cell and T-cell activation, and triggering release of inflammatory mediators. In some patients, exposure to antigens/triggers leads to production of high levels of antigen-specific IgE, which mediates cross-linking of the high-affinity IgE receptor on various cells, causing release of inflammatory mediators. The efficacy of omalizumab confirms IgE as an important inflammatory mediator in nasal polyposis. By blocking IgE, omalizumab targets the T2 inflammation in nasal polyposis, reduces nasal polyp score and improves symptoms.

Characterization of human FcεRIα chain expression and gene copy number in humanized rat basophilic leukaemia (RBL) reporter cell lines

Several laboratories have created rat basophil leukemia (RBL) cell lines stably transfected with the human high affinity IgE receptor (FcεRI_H). More recently, humanized RBL cell lines saw the introduction of reporter genes such as luciferase (RS-ATL8) and DsRed (RBL NFAT-DsRed). These reporters are more sensitive than their parental non-reporter humanized RBL cell lines. However, no studies so far have addressed the levels of FcεRI_H surface expression on humanized RBL cell lines. This is a critical parameter, as it determines the ability of these cells to be efficiently sensitized with human IgE, hence it should affect the sensitivity of the cell assay–a critical parameter for any diagnostic application. Our purpose was to assess and compare the levels of expression of the transfected FcεRI_H chain in humanized RBL cell lines. We compared surface levels of FcεRIα_H by flow cytometry, using a fluorescently labelled monoclonal antibody (CRA-1/AER-37) and determined receptor numbers using calibration microspheres. FcεRIα_H copy numbers were assessed by qPCR, and the sequence verified. Transfection with FcεRIγ_H cDNA was assessed for its ability to increase FcεRIα_H expression in the NFAT-DsRed reporter. While both SX-38 and RS-ATL8 expressed about 500.000 receptors/cell, RBL 703–21 and NFAT-DsRed had approximately 10- to 30-fold lower FcεRIα_H expression, respectively. This was neither related to FcεRI_H gene copy numbers, nor to differences in steady state mRNA levels, as determined by qPCR and RT-qPCR, respectively. Instead, FcεRIα_H surface expression appeared to correlate with the co-expression of FcεRIγ_H. Stable transfection of NFAT-DsRed cells with pBJ1 neo-huFcεRI gamma, which constitutively expresses FcεRIγ_H, increased FcεRIα_H chain expression levels. Levels of FcεRIα_H surface expression vary greatly between humanized RBL reporter cell lines. This difference will affect the sensitivity of the reporter system when used for diagnostic purposes.

Spontaneous food allergy in Was-/- mice occurs independent of FcεRI-mediated mast cell activation

BACKGROUND

Food allergies are a growing health problem, and the development of therapies that prevent disease onset is limited by the lack of adjuvant-free experimental animal models. We compared allergic sensitization in patients with food allergy or Wiskott-Aldrich syndrome (WAS) and defined whether spontaneous disease in Was^-/- mice recapitulates the pathology of a conventional disease model and/or human food allergy.

METHODS

Comparative ImmunoCAP ISAC microarray was performed in patients with food allergy or WAS. Spontaneous food allergy in Was^-/- mice was compared to an adjuvant-based model in wild-type mice (WT-OVA/alum). Intestinal and systemic anaphylaxis was assessed, and the role of the high-affinity IgE Fc receptor (FcεRI) in allergic sensitization was evaluated using Was^-/- Fcer1a^-/- mice.

RESULTS

Polysensitization to food was detected in both WAS and food-allergic patients which was recapitulated in the Was^-/- model. Oral administration of ovalbumin (OVA) in Was^-/- mice induced low titers of OVA-specific IgE compared to the WT-OVA/alum model. Irrespectively, 79% of Was^-/- mice developed allergic diarrhea following oral OVA challenge. Systemic anaphylaxis occurred in Was^-/- mice (95%) with a mortality rate >50%. Spontaneous sensitization and intestinal allergy occurred independent of FcεRI expression on mast cells (MCs) and basophils.

CONCLUSIONS

Was^-/- mice provide a model of food allergy with the advantage of mimicking polysensitization and low food-antigen IgE titers as observed in humans with clinical food allergy. This model will facilitate studies on aberrant immune responses during spontaneous disease development. Our results imply that therapeutic targeting of the IgE/FcεRI activation cascade will not affect sensitization to food.

Fc-epsilon-RI, the high affinity IgE-receptor, is robustly expressed in the upper gastrointestinal tract and modulated by mucosal inflammation

Background

The role of the high affinity IgE receptor, FcεRI, in IgE-mediated immune responses of the gastrointestinal (GI) mucosa is poorly understood. Currently, a detailed characterization of FcεRI expression throughout the human gut is lacking. The aim of this study was to define the expression pattern of FcεRI in the GI tract.

Methods/Principal Findings

We compared FcεRI expression in children with gastritis/esophagitis (n = 10), celiac disease (n = 10), inflammatory bowel disease (IBD) (n = 9), and normal mucosa (n = 5). The α–subunit of FcεRI (FcεRIα), detected by immunohistochemistry, was found on cells infiltrating the mucosa of the esophagus, the stomach, and the duodenum, but was rarely detected in more distal sections of the GI tract. Accordingly, quantitative RT-PCR analysis on esophagus, stomach, duodenum, colon, and rectum biopsies revealed that FcεRIα and -β expression levels decreased towards the distal intestine. mRNA transcripts of the common Fc-receptor-γ chain were present in the entire GI mucosa. Double-immunofluorescence staining of esophageal specimens confirmed that FcεRIα was expressed on intraepithelial mast cells and Langerhans cells. The mRNA expression levels of the α, β, and γ subunits of FcεRI did not correlate with total serum IgE but were associated with mucosal inflammation.

Conclusion/Significance

Our data define the upper GI tract as the main site for IgE-mediated immune activation via FcεRI. Tissue mRNA levels of FcεRIα are regulated by inflammatory conditions rather than serum IgE, indicating that FcεRI might also play a role in pathologies other than allergy.

Molecular mechanisms of IgE mediated food allergy

The purpose of this review is to collate current knowledge and recent advances in molecular mechanism behind the immediate type hypersensitivity of foods. Food allergy is a growing concern of human health in developed as well as developing countries now days. Food allergic reactions are mostly IgE mediated and also known as immediate type hypersensitivity or type I reaction. This review encompasses a wide range of molecular events during IgE mediated reactions like primary exposure of allergens, processing of allergens by antigen presenting cells, role of transcription factors like GATA-3, STAT-6, NF-AT, c-maf, c-kit and NF-κB, Treg cells, toll like receptors, cytokines and chemokines, class switch to IgE, FcεR1 receptor, priming of IgE on mast cells or basophils, signaling events followed by secondary exposure of allergens, degranulation and release of mediators like leukotrienes, histamines, prostaglandins, β-hexosaminidase and ultimately anaphylaxis. This review may be helpful to beginners as well as experts working in the field of allergy and immunology because of the stepwise explanations of molecular mechanisms involved in IgE mediated reactions.

How to connect an IgE-driven response with CTL activity?

One of the goals of cell-based immune therapy in cancer is the induction of tumor-specific cytotoxic T-lymphocyte (CTL) responses. To achieve this objective, the ability of dendritic cells (DC) to cross-present tumor antigens can be exploited. One of the most efficient pathways for the induction of CTLs by cross-presentation is mediated by immunoglobulins of the IgG class, which are used by DCs to sample antigen in the form of immune complexes via Fc-gamma receptors. Could DCs use an IgE-mediated cross-presentation mechanism in a comparable manner to induce CTLs? We here discuss the potential of two human IgE Fc receptors, FcεRI and FcεRII, to serve as antigen uptake receptors for IgE-mediated cross-presentation. We conclude that the existence of an IgE-mediated cross-presentation pathway would provide a direct link between IgE-driven immune responses and CTL activity.

Development and validation of a standardized ELISA for the detection of soluble Fc-epsilon-RI in human serum

The aim of this study was to develop a standardized enzyme-linked immunosorbent assay (ELISA) for detection of human soluble Fc-epsilon-RI (sFcεRI), a serum isoform of the high affinity IgE receptor. A recombinant version of sFcεRI was produced in baculovirus and used as standard. ELISA plates were coated with anti-mouse IgG followed by incubation with the monoclonal capture antibody CRA1. This FcεRI-alpha-specific antibody binds to the stalk region of the protein and does not inhibit IgE-binding. After incubation with standards or serum samples, plates were incubated with chimeric IgE followed by detection with horseradish peroxidase conjugated anti-human IgE. Enzymatic activity was visualized with (3,3',5,5')-tetramethylbenzidine. Specificity was demonstrated by omission of capture or detection reagents. Units (U) of detection were established and the dynamic range of the assay was defined as 10-640 U/ml for a 1/5 serum dilution. Parameters of linearity (R(2)>0.999), matrix interference test (recovery of 70-110%), intra-assay variability (coefficient of variation (CV) <20%) and inter-assay variability (CV <20%) met acceptance criteria for immunoassay validation. Correlation analysis of serum units of sFcεRI measured with the new ELISA and serum IgE levels confirmed earlier published data describing a weak correlation of the two parameters in patients with elevated serum IgE while no correlation in patients with normal serum IgE or the total patient group was found. In summary, we established and validated a standardized ELISA for the detection of sFcεRI. This novel method now allows for comparative analysis of sFcεRI levels in health and disease.

A soluble form of the high affinity IgE receptor, Fc-epsilon-RI, circulates in human serum

Soluble IgE receptors are potential in vivo modulators of IgE-mediated immune responses and are thus important for our basic understanding of allergic responses. We here characterize a novel soluble version of the IgE-binding alpha-chain of Fc-epsilon-RI (sFcεRI), the high affinity receptor for IgE. sFcεRI immunoprecipitates as a protein of ∼40 kDa and contains an intact IgE-binding site. In human serum, sFcεRI is found as a soluble free IgE receptor as well as a complex with IgE. Using a newly established ELISA, we show that serum sFcεRI levels correlate with serum IgE in patients with elevated IgE. We also show that serum of individuals with normal IgE levels can be found to contain high levels of sFcεRI. After IgE-antigen-mediated crosslinking of surface FcεRI, we detect sFcεRI in the exosome-depleted, soluble fraction of cell culture supernatants. We further show that sFcεRI can block binding of IgE to FcεRI expressed at the cell surface. In summary, we here describe the alpha-chain of FcεRI as a circulating soluble IgE receptor isoform in human serum.

Immunoglobulin E in health and disease

The discovery of immunoglobulin E (IgE) was a breakthrough in the field of Allergy and Immunology. Our understanding of mechanisms of allergic reactions and the role of IgE in these disorders has paralleled to the discovery of treatment modalities for patients with allergy. Apart from allergic diseases, IgE is involved in pathogenesis of other disorders. Much controversy exists about the control of total IgE (tIgE) levels and allergen-specific IgE (sIgE) profiles in allergic individuals. This review aims at giving a comprehensive overview of IgE molecule and discussing the issues related to its importance in clinical setting.

Relationships between levels of serum IgE, cell-bound IgE, and IgE-receptors on peripheral blood cells in a pediatric population

Background

Elevated serum immunoglobulin (Ig) E is a diagnostic marker of immediate-type allergic reactions. We hypothesize that serum IgE does not necessarily reflect total body IgE because in vivo IgE can be bound to cell surface receptors such as FcεRI and FcεRII (CD23). The aim of this study was to analyze the relationships between levels of serum IgE, cell-bound IgE, and IgE-receptors on peripheral blood cells in a pediatric population.

Methodology

Whole blood samples from 48 children (26 boys, 22 girls, mean age 10,3±5,4 years) were analyzed by flow cytometry for FcεRI, CD23, and cell-bound IgE on dendritic cells (CD11c+MHC class II+), monocytes (CD14+), basophils (CD123+MHC class II-) and neutrophils (myeloperoxidase+). Total serum IgE was measured by ELISA and converted into z-units to account for age-dependent normal ranges. Correlations were calculated using Spearman rank correlation test.

Principal Findings

Dendritic cells, monocytes, basophils, and neutrophils expressed the high affinity IgE-receptor FcεRI. Dendritic cells and monocytes also expressed the low affinity receptor CD23. The majority of IgE-receptor positive cells carried IgE on their surface. Expression of both IgE receptors was tightly correlated with cell-bound IgE. In general, cell-bound IgE on FcεRI+ cells correlated well with serum IgE. However, some patients carried high amounts of cell-bound IgE despite low total serum IgE levels.

Conclusion/Significance

In pediatric patients, levels of age-adjusted serum IgE, cell-bound IgE, and FcεRI correlate. Even in the absence of elevated levels of serum IgE, cell-bound IgE can be detected on peripheral blood cells in a subgroup of patients.

The signal peptide of the IgE receptor alpha-chain prevents surface expression of an immunoreceptor tyrosine-based activation motif-free receptor pool

The high affinity receptor for IgE, Fc epsilon receptor I (FcepsilonRI), is an activating immune receptor and key regulator of allergy. Antigen-mediated cross-linking of IgE-loaded FcepsilonRI alpha-chains induces cell activation via immunoreceptor tyrosine-based activation motifs in associated signaling subunits, such as FcepsilonRI gamma-chains. Here we show that the human FcepsilonRI alpha-chain can efficiently reach the cell surface by itself as an IgE-binding receptor in the absence of associated signaling subunits when the endogenous signal peptide is swapped for that of murine major histocompatibility complex class-I H2-K(b). This single-chain isoform of FcepsilonRI exited the endoplasmic reticulum (ER), trafficked to the Golgi and, subsequently, trafficked to the cell surface. Mutational analysis showed that the signal peptide regulates surface expression in concert with other described ER retention signals of FcepsilonRI-alpha. Once the FcepsilonRI alpha-chain reached the cell surface by itself, it formed a ligand-binding receptor that stabilized upon IgE contact. Independently of the FcepsilonRI gamma-chain, this single-chain FcepsilonRI was internalized after receptor cross-linking and trafficked into a LAMP-1-positive lysosomal compartment like multimeric FcepsilonRI. These data suggest that the single-chain isoform is capable of shuttling IgE-antigen complexes into antigen loading compartments, which plays an important physiologic role in the initiation of immune responses toward allergens. We propose that, in addition to cytosolic and transmembrane ER retention signals, the FcepsilonRI alpha-chain signal peptide contains a negative regulatory signal that prevents expression of an immunoreceptor tyrosine-based activation motif-free IgE receptor pool, which would fail to induce cell activation.

The role of the high-affinity IgE receptor, FcepsilonRI, in eosinophilic gastrointestinal diseases

Primary eosinophilic gastrointestinal diseases (EGIDs) are a heterogeneous group of diseases including eosinophilic esophagitis, eosinophilic gastritis, eosinophilic gastroenteritis, eosinophilic enteritis, and eosinophilic colitis. The unifying hallmark and diagnostic marker of EGIDs is an eosinophil-rich inflammatory infiltrate of the GI mucosa, in the absence of known causes for eosinophilia. The etiology of EGIDs is not yet fully understood. The pathogenesis however seems to involve a complex interplay of genetic predisposition, exposure to food- and environmental allergens and IgE-mediated activation of the immune system. Accumulating evidence relates EGIDs to the group of T-helper (Th) 2 mediated immune disorders, like IgE-mediated allergy. In this article we discuss a possible role of IgE-mediated immune-activation via the high affinity receptor for IgE, FcepsilonRI, in the pathogenesis of primary EGIDs. Beyond its defined role in type I allergic reactions, we here hypothesize that activation of tetrameric FcepsilonRI on mast cells and basophils as well as trimeric FcepsilonRI on human eosinophils and antigen presenting cells in the gastrointestinal mucosa is critically involved in the pathology of EGIDs. We also discuss how IgE-independent triggering of FcepsilonRI could be a mechanisms responsible for activation of the immune system in patients with EGID.

Endocytosis, recycling, and degradation of unoccupied FcepsilonRI in human basophils

Previous studies about basophils and mast cells identified the ability of IgE to up-regulate FcepsilonRI expression by a process that depends on stabilization of the surface receptor by IgE. However, the mechanism of loss from the cell surface, when unoccupied, is not known. The current studies have examined whether unoccupied FcepsilonRI on basophils is lost by shedding or endocytosis. IgE was dissociated partially from purified human basophils to augment loss of the unoccupied receptor, and comparisons were made between basophils +/- IgE resensitization prior to 1-day culture. Incubation did not result in a detectable receptor in culture supernatants. However, in the presence of IL-3, although total cell surface expression decreased by 30% (relative to resensitized cells), FcepsilonRI from whole cell lysates was not statistically different between the two conditions. Incubation for 18 h without IL-3 resulted in the same loss from the cell surface but equivalent loss in whole cell lysates. This degradation process was reversible with Bafilomycin A. There was also evidence that the internalized receptor could be recycled. After the initial 18-h down-regulation, the receptor could be found partially restored to the cell surface if IgE were added back to the culture +/- cycloheximide. Loss of the unoccupied receptor, as well as accumulation of the receptor under the influence of IgE, was found to be insensitive to the presence of a src-family kinase inhibitor, PP1. These studies establish that the unoccupied receptor is lost by a process of endocytosis, partially recycled to the cell surface, and ultimately degraded by a lysosomal mechanism.