The human IgE repertoire

Unique allergen-specific human IgE monoclonal antibodies derived from patients with allergic disease

Introduction

Allergic reactions are mediated by human IgE antibodies that bind to and cross-link allergen molecules. The sites on allergens that are recognized by IgE antibodies have been difficult to investigate because of the paucity of IgE antibodies in a human serum. Here, we report the production of unique human IgE monoclonal antibodies to major inhaled allergens and food allergens that can be produced at scale in perpetuity.

Materials and methods

The IgE antibodies were derived from peripheral blood mononuclear cells of symptomatic allergic patients, mostly children aged 3-18 years, using hybridoma fusion technology. Total IgE and allergen-specific IgE was measured by ImmunoCAP. Their specificity was confirmed through ELISA and immunoblotting. Allergenic potency measurements were determined by ImmunoCAP inhibition. Biological activity was determined in vitro by comparing β-hexosaminidase release from a humanized rat basophilic cell line.

Results

Human IgE monoclonal antibodies (n = 33) were derived from 17 allergic patients with symptoms of allergic rhinitis, asthma, atopic dermatitis, food allergy, eosinophilic esophagitis, or red meat allergy. The antibodies were specific for five inhaled allergens, nine food allergens, and alpha-gal and had high levels of IgE (53,450-1,702,500 kU/L) with ratios of specific IgE to total IgE ranging from <0.01 to 1.39. Sigmoidal allergen binding curves were obtained through ELISA, with low limits of detection (<1 kU/L). Allergen specificity was confirmed through immunoblotting. Pairs of IgE monoclonal antibodies to Ara h 6 were identified that cross-linked after allergen stimulation and induced release of significant levels of β-hexosaminidase (35%-80%) from a humanized rat basophilic cell line.

Conclusions

Human IgE monoclonal antibodies are unique antibody molecules with potential applications in allergy diagnosis, allergen standardization, and identification of allergenic epitopes for the development of allergy therapeutics. The IgE antibody probes will enable the unequivocal localization and validation of allergenic epitopes.

Evolutive emergence and divergence of an Ig regulatory node: An environmental sensor getting cues from the aryl hydrocarbon receptor?

One gene, the immunoglobulin heavy chain (IgH) gene, is responsible for the expression of all the different antibody isotypes. Transcriptional regulation of the IgH gene is complex and involves several regulatory elements including a large element at the 3' end of the IgH gene locus (3'RR). Animal models have demonstrated an essential role of the 3'RR in the ability of B cells to express high affinity antibodies and to express different antibody classes. Additionally, environmental chemicals such as aryl hydrocarbon receptor (AhR) ligands modulate mouse 3'RR activity that mirrors the effects of these chemicals on antibody production and immunocompetence in mouse models. Although first discovered as a mediator of the toxicity induced by the high affinity ligand 2,3,7,8-tetracholordibenzo-p-dioxin (dioxin), understanding of the AhR has expanded to a physiological role in preserving homeostasis and maintaining immunocompetence. We posit that the AhR also plays a role in human antibody production and that the 3'RR is not only an IgH regulatory node but also an environmental sensor receiving signals through intrinsic and extrinsic pathways, including the AhR. This review will 1) highlight the emerging role of the AhR as a key transducer between environmental signals and altered immune function; 2) examine the current state of knowledge regarding IgH gene regulation and the role of the AhR in modulation of Ig production; 3) describe the evolution of the IgH gene that resulted in species and population differences; and 4) explore the evidence supporting the environmental sensing capacity of the 3'RR and the AhR as a transducer of these cues. This review will also underscore the need for studies focused on human models due to the premise that understanding genetic differences in the human population and the signaling pathways that converge at the 3'RR will provide valuable insight into individual sensitivities to environmental factors and antibody-mediated disease conditions, including emerging infections such as SARS-CoV-2.

Human Monoclonal IgE Antibodies-a Major Milestone in Allergy

PURPOSE OF REVIEW

Bound to its high affinity receptor on mast cells and basophils, the IgE antibody molecule plays an integral role in the allergic reaction. Through interactions with the allergen, it provides the sensitivity and specificity parameters for cell activation and mediator release that produce allergic symptoms. Advancements in human hybridoma technologies allow for the generation and molecular definition of naturally occurring allergen-specific human IgE monoclonal antibodies.

RECENT FINDINGS

A high-resolution structure of dust mite allergen Der p 2 in complex with Fab of the human IgE mAb 2F10 was recently determined using X-ray crystallography. The structure reveals the fine molecular details of IgE 2F10 binding its 750 Å2 conformational epitope on Der p 2. This review provides an overview of this major milestone in allergy, the first atomic resolution structure of an authentic human IgE epitope. The molecular insights that IgE epitopes provide will allow for structure-based design approaches to the development of novel diagnostics, antibody therapeutics, and immunotherapies.

The Allergen: Sources, Extracts, and Molecules for Diagnosis of Allergic Disease

Allergenic source materials include pollen, molds, animal dander, and insects; food allergens from nuts, grains, and animals; venoms; and salivary proteins from insects and ticks. Clinical diagnostic tests have used heterogeneous extracts from allergen source materials for skin prick tests (SPTs). In vitro laboratory methods using immunoassays or microarrays can detect serum IgE directed against allergenic proteins where clinical testing may not be suitable. Clinicians rely primarily on licensed commercial extracts of allergens for SPTs. Manufacturers and regulatory agencies have standardized selected extracts for identity, composition, and potency. Allergen sources contain multiple proteins. The IgE antibody responses to these proteins vary between allergic subjects as does the quantity of specific IgE. Component-resolved molecular diagnostics can be used to improve the specificity of allergy testing and resolve clinical cross-reactivities that may affect treatment outcomes. This clinical commentary will review methods for the production, evaluation, and standardization of allergen extracts from the perspective of diagnostic testing that may be useful for allergists in practice.

Pharmacological Benefits of Triphala: A Perspective for Allergic Rhinitis

Allergic rhinitis (AR) is considered a major nasal condition impacting a large number of people around the world, and it is now becoming a global health problem. Because the underlying mechanisms of AR are complex, the development of single-drug treatment might not be enough to treat a wide spectrum of the disease. Although the standard guidelines classify and provide suitable diagnosis and treatment, the vast majority of people with AR are still without any means of controlling it. Moreover, the benefits of AR drugs are sometimes accompanied by undesirable side effects. Thus, it is becoming a significant challenge to find effective therapies with limited undesirable side effects for a majority of patients suffering from uncontrolled AR. Aller-7/NR-A2, a polyherbal formulation, has revealed promising results in patients by reducing nasal symptoms and eosinophil counts without serious adverse effects. Interestingly, three out of seven of the herbals in the Aller-7/NR-A2 formulation are also found in an Ayurvedic polyherbal formulation known as “Triphala,” which is a potential candidate for the treatment of AR. However, there are no current studies that have examined the effects of Triphala on the disease. This review aims to describe the complexity of AR pathophysiology, currently available treatments, and the effects of Triphala on AR in order to help develop it as a promising alternative treatment in the future.

Structural Aspects of the Allergen-Antibody Interaction

The development of allergic disease involves the production of IgE antibodies upon allergen exposure in a process called sensitization. IgE binds to receptors on the surface of mast cells and basophils, and subsequent allergen exposure leads to cross-linking of IgE antibodies and release of cell mediators that cause allergy symptoms. Although this process is quite well-understood, very little is known about the epitopes on the allergen recognized by IgE, despite the importance of the allergen-antibody interaction for the allergic response to occur. This review discusses efforts to analyze allergen-antibody interactions, from the original epitope mapping studies using linear peptides or recombinant allergen fragments, to more sophisticated technologies, such as X-ray crystallography and nuclear magnetic resonance. These state-of-the-art approaches, combined with site-directed mutagenesis, have led to the identification of conformational IgE epitopes. The first structures of an allergen (egg lysozyme) in complex with Fab fragments from IgG antibodies were determined in the 1980s. Since then, IgG has been used as surrogate for IgE, due to the difficulty of obtaining monoclonal IgE antibodies. Technical developments including phage display libraries have contributed to progress in epitope mapping thanks to the isolation of IgE antibody constructs from combinatorial libraries made from peripheral blood mononuclear cells of allergic donors. Most recently, single B cell antibody sequencing and human hybridomas are new breakthrough technologies for finally obtaining human IgE monoclonal antibodies, ideal for epitope mapping. The information on antigenic determinants will facilitate the design of hypoallergens for immunotherapy and the investigation of the fundamental mechanisms of the IgE response.

B-cell responses in allergen immunotherapy

PURPOSE OF REVIEW

The establishment of long-term clinical tolerance in AIT requires the involvement of basophils, mast cells, allergen-specific regulatory T and B cells, downregulation of effector type 2 responses, and increase in production of specific IgG, particularly immunglobulin G4 (IgG4) antibodies. This review aims to provide an overview of the role of B cells in AIT, their mechanism of action, and their potential for improving AIT.

RECENT FINDINGS

In-depth research of B cells has paved the way for improved diagnosis and research on allergic diseases. B cells play a central role in allergy and allergen tolerance through the production of immunglobulin E (IgE)-blocking antibodies. However, an increasing body of evidence has emerged supporting a role for B cells in regulating immune responses that extends beyond the production of antibodies. Regulatory B cells play an important role in immunosuppression, mediated by secretion of anti-inflammatory cytokines.

SUMMARY

Successful AIT establishes the reinstatement of immune tolerance toward allergens, reduces allergic symptoms, and improves clinical treatments in patients. B cells play a central role in this process through antibody-independent immune regulatory processes in addition to the production of IgE-blocking antibodies.

Aryl hydrocarbon receptor-induced activation of the human IGH hs1.2 enhancer: Mutational analysis of putative regulatory binding motifs

The human hs1.2 enhancer within the Ig heavy chain gene (IGH) is polymorphic and associated with a number of autoimmune diseases. The polymorphic region is characterized by tandem repeats of an ∼53-bp invariant sequence containing possible binding sites for several transcription factors. Our previous studies suggest the human hs1.2 enhancer is sensitive to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), an environmental toxicant and high affinity ligand of the aryl hydrocarbon receptor (AhR). TCDD induced hs1.2 enhancer activity in an AhR-dependent manner and the number of invariant sequences influenced the magnitude of activity. To better understand the regulation of human hs1.2 enhancer activity, the objective of the current study was to utilize mutational analysis and luciferase reporter constructs to evaluate the contribution of putative transcription factor binding sites to overall hs1.2 enhancer activity and modulation by TCDD. Basal and LPS-induced activity of the hs1.2 enhancer appeared to be most affected by mutation of sites outside of the invariant sequence or deletion of the entire invariant sequence; whereas sites influencing the effect of TCDD were dependent on the cellular activation state (i.e. unstimulated vs. LPS stimulation) and relatively independent of the putative AhR binding site within the invariant sequence. These results suggest that AhR activation affects human hs1.2 activity through an as yet undetermined non-canonical pathway. A better understanding regarding the role of the hs1.2 enhancer in human Ig expression and how AhR ligands modulate its activity may lead to insights into overall Ig regulation and mechanisms of dysfunction.

A Human IgE Antibody Binding Site on Der p 2 for the Design of a Recombinant Allergen for Immunotherapy

Der p 2 is one of the most important allergens from the house dust mite Dermatophagoides pteronyssinus Identification of human IgE Ab binding epitopes can be used for rational design of allergens with reduced IgE reactivity for therapy. Antigenic analysis of Der p 2 was performed by site-directed mutagenesis based on the x-ray crystal structure of the allergen in complex with a Fab from the murine IgG mAb 7A1 that binds an epitope overlapping with human IgE binding sites. Conformational changes upon Ab binding were confirmed by nuclear magnetic resonance using a 7A1-single-chain variable fragment. In addition, a human IgE Ab construct that interferes with mAb 7A1 binding was isolated from a combinatorial phage-display library constructed from a mite-allergic patient and expressed as two recombinant forms (single-chain Fab in Pichia pastoris and Fab in Escherichia coli). These two IgE Ab constructs and the mAb 7A1 failed to recognize two Der p 2 epitope double mutants designed to abolish the allergen-Ab interaction while preserving the fold necessary to bind Abs at other sites of the allergen surface. A 10-100-fold reduction in binding of IgE from allergic subjects to the mutants additionally showed that the residues mutated were involved in IgE Ab binding. In summary, mutagenesis of a Der p 2 epitope defined by x-ray crystallography revealed an IgE Ab binding site that will be considered for the design of hypoallergens for immunotherapy.

Peripheral IgE Repertoires of Healthy Donors Carry Moderate Mutation Loads and Do Not Overlap With Other Isotypes

IgE-mediated allergic disease represents an increasing health problem. Although numerous studies have investigated IgE sequences in allergic patients, little information is available on the healthy IgE repertoire. IgM, IgG, IgA, and IgE transcripts from peripheral blood B cells of five healthy, non-atopic individuals were amplified by unbiased, template-switching, isotype-specific PCR. Complete VDJ regions were sequenced to near-exhaustion on the PacBio platform. Sequences were analyzed for clonal relationships, degree of somatic hypermutation, IGHV gene usage, evidence of antigenic selection, and N-linked glycosylation motifs. IgE repertoires appeared to be highly oligoclonal with preferential usage of certain IGHV genes compared to the other isotypes. IgE sequences carried more somatic mutations than IgM, yet fewer than IgG and IgA. Many IgE sequences contained N-linked glycosylation motifs. IgE sequences had no clonal relationship with the other isotypes. The IgE repertoire in healthy individuals is derived from relatively few clonal expansions without apparent relations to immune reactions that give rise to IgG or IgA. The mutational burden of normal IgE suggests an origin through direct class-switching from the IgM repertoire with little evidence of antigenic drive, and hence presumably low affinity for specific antigens. These findings are compatible with a primary function of the healthy IgE repertoire to occupy Fcε receptors for competitive protection against mast cell degranulation induced by allergen-specific, high-affinity IgE. This background knowledge may help to elucidate pathogenic mechanisms in allergic disease and to design improved desensitization strategies.

Mast cells in mastocytosis and allergy - Important player in metabolic and immunological homeostasis

The role of mast cell (MC) activity in pathophysiology is complex and challenging and its clinical effects are difficult to predict. Apart from the known role of MCs in basic immunological processes and allergy, underlined is their importance in bone mineralization and in regulation of autoimmune reactions. Mast cell mediators, especially those released from mast cells in degranulation, but also those released constitutively, are important both in metabolic and immunological processes. Mastocytosis is a heterogeneous group of disorders characterized by accumulation of MC in one or more organs. There are scientific data indicating that mastocytosis patients are at increased risk of osteoporosis in the systemic form of the disease and children with cutaneous mastocytosis have a higher rate of hypogammaglobulinemia. Moreover, the origin of osteoporosis in patients with allergy is no longer considered as linked to steroid therapy only, but to the mast cell mediators' activity as well. There are indications that osteoporosis symptoms in this group of patients may develop independently of the cumulative steroids' dose. Thus, the influence of mast cells on metabolic and immunologic processes in allergic patients should be investigated. The assessment of mast cell activity and burden in mastocytosis may be used to guide clinical management of patients with allergy.

Investigation of the interaction of allergens of Glycine max with IgE-antibody for designing of peptidomimetics based anti-allergen

Allergen induced IgE dependent type I hypersensitivity is the main cause of the allergy, which would be a burden on medical setup in coming years. Allergens of Glycine max have been isolated, and their disease relationships are documented. Therefore, it becomes important to investigate the interaction of different allergens of Glycine max with IgE and also screen suitable therapeutics to prevent this interaction. The amino acid sequences of all allergens of Glycine max and their isoallergens have been taken, and 3D structure of allergens (Gly m 3, Gly m 4, Gly m 5, Gly m 6 and Gly m 8) and their isoallergens were generated using Modeller v9.17. The modeled structures were further validated using PSVS, ProSA, RAMPAGE, and PDBsum. HL domain of Fab region of human IgE (PDBID: 2R56) was generated using UCSFchimera. The HL domain was minimized by Schrodinger software using the OPLS_2005 force field. SiteMap identified epitope binding site of the minimized domain. All the predicted epitopes of different allergens were docked to the binding site of HL domain using the Patchdock server. We have also designed a peptidomimetics based inhibitor targeted at interaction interface of Gly m8 and IgE, using in-silico virtual screening, molecular mechanics, and molecular dynamics simulation studies. These studies identified BDE32166344 ((N-(1-{[1-(1-aminocyclopentanecarbonyl)-3-hydroxypyrrolidin-3-yl]methyl}piperidin-4-yl)acetamide) as a peptidomimetics based lead with binding energy of -72.77 kcal/mol. Therefore, the present study investigates the interaction between different Gly m allergens and IgE antibody and identifies peptidomimetics based lead that might be developed as a suitable therapeutics against allergy caused by allergen of Glycine max.

Molecular Aspects of Allergens and Allergy

Immunoglobulin E (IgE)-associated allergy is the most common immune disorder. More than 30% of the population suffer from symptoms of allergy which are often severe, disabling, and life threatening such as asthma and anaphylaxis. Population-based birth cohort studies show that up to 60% of the world population exhibit IgE sensitization to allergens, of which most are protein antigens. Thirty years ago the first allergen-encoding cDNAs have been isolated. In the meantime, the structures of most of the allergens relevant for disease in humans have been solved. Here we provide an update regarding what has been learned through the use of defined allergen molecules (i.e., molecular allergology) and about mechanisms of allergic disease in humans. We focus on new insights gained regarding the process of sensitization to allergens, allergen-specific secondary immune responses, and mechanisms underlying allergic inflammation and discuss open questions. We then show how molecular forms of diagnosis and specific immunotherapy are currently revolutionizing diagnosis and treatment of allergic patients and how allergen-specific approaches may be used for the preventive eradication of allergy.

Antibody Heavy Chain Variable Domains of Different Germline Gene Origins Diversify through Different Paths

B cells produce antibodies, key effector molecules in health and disease. They mature their properties, including their affinity for antigen, through hypermutation events; processes that involve, e.g., base substitution, codon insertion and deletion, often in association with an isotype switch. Investigations of antibody evolution define modes whereby particular antibody responses are able to form, and such studies provide insight important for instance for development of efficient vaccines. Antibody evolution is also used in vitro for the design of antibodies with improved properties. To better understand the basic concepts of antibody evolution, we analyzed the mutational paths, both in terms of amino acid substitution and insertions and deletions, taken by antibodies of the IgG isotype. The analysis focused on the evolution of the heavy chain variable domain of sets of antibodies, each with an origin in 1 of 11 different germline genes representing six human heavy chain germline gene subgroups. Investigated genes were isolated from cells of human bone marrow, a major site of antibody production, and characterized by next-generation sequencing and an in-house bioinformatics pipeline. Apart from substitutions within the complementarity determining regions, multiple framework residues including those in protein cores were targets of extensive diversification. Diversity, both in terms of substitutions, and insertions and deletions, in antibodies is focused to different positions in the sequence in a germline gene-unique manner. Altogether, our findings create a framework for understanding patterns of evolution of antibodies from defined germline genes.

The Association between Tobacco Smoke and Serum Immunoglobulin E Levels in Korean Adults

Objective Smoking is common in patients with allergic diseases. The aim of this study was to evaluate the cross-sectional association between the current smoking status and total and specific Immunoglobulin E (IgE) levels in Korean adults. Methods Data were obtained from the 2010 Korean National Health and Nutrition Examination Survey, a national cross-sectional study. We analyzed the data of subjects whose smoking status and serum IgE levels were of acceptable quality. Results A total of 1,963 subjects (1,118 never smokers, 340 ex-smokers, and 505 current smokers) were included. The total IgE levels and specific IgE levels to house dust mite Dermatophagoides farinae (Df), cockroach, and dog allergens in never smokers were significantly (p<0.0001) lower than in ex-smokers or current smokers. After adjusting for other variables, current smokers independently had significantly higher levels of total IgE and cockroach-specific IgE than ex-smokers or never smokers. The proportions of subjects with total IgE ≥150 kU/L and specific IgE ≥0.35 kU/L to Df-specific IgE were significantly (p value for trend <0.05) increased in ex-smokers and current smokers. The total IgE levels and IgE levels specific to Df, cockroaches, and dogs significantly (p value for trend <0.05) and proportionally increased with increasing numbers of cigarettes smoked daily. Conclusion Smoking was associated with elevated total IgE levels and IgE levels specific to Df, cockroach, and dog allergens in a cumulative, dose-dependent manner. Furthermore, current smoking status was an independent risk factor for elevated total IgE levels and IgE levels specific to cockroach allergen.

Piperine, a Pungent Alkaloid from Black Pepper, Inhibits B Lymphocyte Activation and Effector Functions

Piperine has several well-documented anti-inflammatory properties; however, little is known regarding its effect on humoral immunity. In this study, we describe the immunosuppressive effect of piperine on B lymphocytes, which are integral to the humoral immune response. Mouse B cells were cultured in the absence or presence of non-cytotoxic concentrations (25, 50, and 100 μM) of piperine during T-dependent or T-independent stimulation. Piperine inhibited B cell proliferation by causing G0/G1 phase cell cycle arrest in association with reduced expression of cyclin D2 and D3. The inhibitory effect of piperine was not mediated through transient receptor potential vanilloid-1 ion channel (TRPV1) because piperine also inhibited the proliferation of B cells from TRPV1-deficient mice. Expression of class II major histocompatibility complex molecules and costimulatory CD40 and CD86 on B lymphocytes was reduced in the presence of piperine, as was B cell-mediated antigen presentation to syngeneic T cells. In addition, piperine inhibited B cell synthesis of interleukin (IL)-6 and IL-10 cytokines, as well as IgM, IgG2b, and IgG3 immunoglobulins. The inhibitory effect of piperine on B lymphocyte activation and effector function warrants further investigation for possible application in the treatment of pathologies related to inappropriate humoral immune responses. Copyright © 2017 John Wiley & Sons, Ltd.

Unlike in Children with Allergic Asthma, IgE Transcripts from Preschool Children with Atopic Dermatitis Display Signs of Superantigen-Driven Activation

The IgE repertoire in children with asthma reflects an adaptive B cell response, indicative of Ag-driven selection. However, the same might not apply to atopic dermatitis, which is often the first manifestation of atopy. The objective of our present study was to characterize the IgE repertoire of preschool children with atopic dermatitis with regard to signs of superantigen-like activation, clonal relationship, and indications of Ag selection. Total RNA was isolated from PBMCs of five children with atopic dermatitis. IgE transcripts were amplified, cloned, and sequenced using RT-PCR. We obtained 200 functional IgE sequences, which were compared with 1140 sequences from 11 children with asthma. Whereas variable gene segment of the H Ig chain (VH) gene usage in asthma reflected germline distribution, IgE transcripts from children with atopic dermatitis displayed a dominance of the otherwise scarcely expressed VH2 and VH4 family. Whereas IgE transcripts from children with asthma were highly mutated (7.2%), somatic mutation rate in atopic dermatitis was less than half as high (3.4%). Moreover, the proportion of transcripts that were indicative of Ag selection was reduced to 11% in atopic dermatitis (24% in asthma). In summary, IgE repertoires vary significantly between children with different atopic diseases. Compared with children with asthma, IgE transcripts from preschool children with atopic dermatitis are significantly less mutated, clonally less focused, and less indicative of Ag selection. We consider our data reconcilable with the hypothesis that a superantigen-like activation contributes to the maturation and selection of the IgE repertoire in atopic dermatitis.

Persistence and evolution of allergen-specific IgE repertoires during subcutaneous specific immunotherapy

BACKGROUND

Specific immunotherapy (SIT) is the only treatment with proved long-term curative potential in patients with allergic disease. Allergen-specific IgE is the causative agent of allergic disease, and antibodies contribute to SIT, but the effects of SIT on aeroallergen-specific B-cell repertoires are not well understood.

OBJECTIVE

We sought to characterize the IgE sequences expressed by allergen-specific B cells and track the fate of these B-cell clones during SIT.

METHODS

We used high-throughput antibody gene sequencing and identification of allergen-specific IgE with combinatorial antibody fragment library technology to analyze immunoglobulin repertoires of blood and the nasal mucosa from aeroallergen-sensitized subjects before and during the first year of subcutaneous SIT.

RESULTS

Of 52 distinct allergen-specific IgE heavy chains from 8 allergic donors, 37 were also detected by using high-throughput antibody gene sequencing of blood samples, nasal mucosal samples, or both. The allergen-specific clones had increased persistence, higher likelihood of belonging to clones expressing other switched isotypes, and possibly larger clone size than the rest of the IgE repertoire. Clone members in nasal tissue showed close mutational relationships.

CONCLUSION

In the future, combining functional binding studies, deep antibody repertoire sequencing, and information on clinical outcomes in larger studies might aid assessment of SIT mechanisms and efficacy.

The Extracellular Domains of IgG1 and T Cell-Derived IL-4/IL-13 Are Critical for the Polyclonal Memory IgE Response In Vivo

IgE-mediated activation of mast cells and basophils contributes to protective immunity against helminths but also causes allergic responses. The development and persistence of IgE responses are poorly understood, which is in part due to the low number of IgE-producing cells. Here, we used next generation sequencing to uncover a striking overlap between the IgE and IgG1 repertoires in helminth-infected or OVA/alum-immunized wild-type BALB/c mice. The memory IgE response after secondary infection induced a strong increase of IgE⁺ plasma cells in spleen and lymph nodes. In contrast, germinal center B cells did not increase during secondary infection. Unexpectedly, the memory IgE response was lost in mice where the extracellular part of IgG1 had been replaced with IgE sequences. Adoptive transfer studies revealed that IgG1⁺ B cells were required and sufficient to constitute the memory IgE response in recipient mice. T cell-derived IL-4/IL-13 was required for the memory IgE response but not for expansion of B cells from memory mice. Together, our results reveal a close relationship between the IgE and IgG1 repertoires in vivo and demonstrate that the memory IgE response is mainly conserved at the level of memory IgG1⁺ B cells. Therefore, targeting the generation and survival of allergen-specific IgG1⁺ B cells could lead to development of new therapeutic strategies to treat chronic allergic disorders.

This study reveals that repertoires of IgE—the class of antibody that mediates allergic reactions—closely resemble those of IgG1, suggesting that the memory IgE response unfolds from IgG1-switched B cells (and not from IgM-expressing B cells) in response to T cell-derived cytokines.

Allergic inflammation is initiated when IgE antibodies bind to high-affinity receptors on the cell surface of mast cells and basophils, thereby triggering the release of proinflammatory mediators. The development and persistence of IgE responses in vivo is poorly characterized because of the low number of IgE-producing B cells and plasma cells. Naïve mature B cells produce IgM antibodies. Upon activation, they “switch” class to produce IgG, IgA, or IgE antibodies. It is currently highly debated whether IgE-expressing B cells are generated by direct switching from IgM-expressing B cells or by sequential switching via IgG1-expressing B cells. Using next generation sequencing, we compared thousands of IgE, IgG1, and IgM sequences after immunization of mice with parasitic worms and found a striking overlap between the IgE and IgG1 repertoires. We further show that the memory IgE response to a secondary encounter with the same parasitic worms was dependent on T cell-derived cytokines. Genetically modified mice and adoptive transfers of B cells revealed that the memory IgE response is conserved at the level of IgG1-expressing B cells. These results favor the concept that bona fide IgE-expressing B cells do not exist, and memory IgE responses unfold from IgG1-expressing B cells, which undergo a secondary switch reaction and differentiation to plasma cells.

Multiple independent IgE epitopes on the highly allergenic grass pollen allergen Phl p 5

Background

Group 5 allergens are small proteins that consist of two domains. They belong to the most potent respiratory allergens.

Objective

To determine the binding sites and to study allergic patients' IgE recognition of the group 5 allergen (Phl p 5) from timothy grass pollen using human monoclonal IgE antibodies that have been isolated from grass pollen allergic patients.

Methods

Using recombinant isoallergens, fragments, mutants and synthetic peptides of Phl p 5, as well as peptide-specific antibodies, the interaction of recombinant human monoclonal IgE and Phl p 5 was studied using direct binding and blocking assays. Cross-reactivity of monoclonal IgE with group 5 allergens in several grasses was studied and inhibition experiments with patients' polyclonal IgE were performed.

Results

Monoclonal human IgE showed extensive cross-reactivity with group 5 allergens in several grasses. Despite its small size of 29 kDa, four independent epitope clusters on isoallergen Phl p 5.0101, two in each domain, were recognized by human IgE. Isoallergen Phl p 5.0201 carried two of these epitopes. Inhibition studies with allergic patients' polyclonal IgE suggest the presence of additional IgE epitopes on Phl p 5.

Conclusions & Clinical Relevance

Our results reveal the presence of a large number of independent IgE epitopes on the Phl p 5 allergen explaining the high allergenic activity of this protein and its ability to induce severe allergic symptoms. High-density IgE recognition may be a general feature of many potent allergens and form a basis for the development of improved diagnostic and therapeutic procedures in allergic disease.

A folded and immunogenic IgE-hyporeactive variant of the major allergen Phl p 1 produced in Escherichia coli

BACKGROUND

Group 1 grass pollen allergens are a major cause of allergic disease. Specific immunotherapy involving controlled administration of allergens can be used as a disease-modifying treatment for such disease. Recombinant allergen variants with reduced IgE binding capacity may be used as component in such vaccines, as they may induce fewer treatment side effects than materials currently in use. A mutated variant of the immunodominant C-terminal domain of the group 1 grass pollen allergen Phl p 1 was recently established through an approach that used a set of human monoclonal IgE as a guide to identify mutations that disturbed IgE-allergen interactions. Further analysis of this domain is required to establish its potential for use in treatment.

METHODS

GST-tagged wild-type and mutated C-terminal domains of Phl p 1 were produced in Escherichia coli TUNER(DE3). The products were purified by affinity chromatography on immobilized glutathione. GST was removed by enzymatic cleavage and tag-free products were purified by size exclusion chromatography. Products were assessed by SDS-PAGE, circular dichroism spectroscopy, differential scanning fluorimetry and dynamic light scattering. Rats were immunized with GST-tagged and tag-free mutated C-terminal domain of Phl p 1. Antigen-binding properties of induced antibodies were assessed by immunochemical analysis.

RESULTS

The mutated domain has a structure very similar to that of the wild-type domain as determined by circular dichroism, but a reduced thermal stability. Immunization of rats demonstrates that this IgE-hyporeactive domain, despite its three sequence modifications (K8A, N11A, D55A), is able to induce antibodies that substantially block the binding of allergic subjects' IgE to the wild-type allergen.

CONCLUSIONS

It is concluded that this IgE-hyporeactive molecule can be produced in folded form and that it is able to induce an antibody response that efficiently competes with IgE recognition of Phl p 1. These findings suggest that it, or a further evolved variant thereof, is a candidate for use as a component in specific immunotherapy against grass pollen allergy.

High-density IgE recognition of the major grass pollen allergen Phl p 1 revealed with single-chain IgE antibody fragments obtained by combinatorial cloning

The timothy grass pollen allergen Phl p 1 belongs to the group 1 of highly cross-reactive grass pollen allergens with a molecular mass of ∼25-30 kDa. Group 1 allergens are recognized by >95% of grass pollen allergic patients. We investigated the IgE recognition of Phl p 1 using allergen-specific IgE-derived single-chain variable Ab fragments (IgE-ScFvs) isolated from a combinatorial library constructed from PBMCs of a grass pollen-allergic patient. IgE-ScFvs reacted with recombinant Phl p 1 and natural group 1 grass pollen allergens. Using synthetic Phl p 1-derived peptides, the binding sites of two ScFvs were mapped to the N terminus of the allergen. In surface plasmon resonance experiments they showed comparable high-affinity binding to Phl p 1 as a complete human IgE-derived Ab recognizing the allergens' C terminus. In a set of surface plasmon resonance experiments simultaneous allergen recognition of all three binders was demonstrated. Even in the presence of the three binders, allergic patients' polyclonal IgE reacted with Phl p 1, indicating high-density IgE recognition of the Phl p 1 allergen. Our results show that multiple IgE Abs can bind with high density to Phl p 1, which may explain the high allergenic activity and sensitizing capacity of this allergen.

Multiple IgE recognition on the major allergen of the Parietaria pollen Par j 2

The interaction between IgE antibodies and allergens is a key event in triggering an allergic reaction. The characterization of this region provides information of paramount importance for diagnosis and therapy. Par j 2 Lipid Transfer Protein is one of the most important allergens in southern Europe and a well-established marker of sensitization in Parietaria pollen allergy. The main aim of this study was to map the IgE binding regions of this allergen and to study the pattern of reactivity of individual Parietaria-allergic patients. By means of gene fragmentation, six overlapping peptides were expressed in Escherichia coli, and their IgE binding activity was evaluated by immunoblotting in a cohort of 79 Parietaria-allergic patients. Our results showed that Pj-allergic patients display a heterogeneous pattern of IgE binding to the different recombinant fragments, and that patients reacted simultaneously against several protein domains spread all the over the molecule, even in fragments which do not contain structural features resembling the native allergen. Our results reveal the presence of a large number of linear and conformational epitopes on the Par j 2 sequence, which probably explains the high allergenic activity of this allergen.

Possible therapeutic potential of a recombinant group 2 grass pollen allergen-specific antibody fragment

The induction of blocking IgG antibodies that compete with IgE for allergen binding is one important mechanism of allergen-specific immunotherapy. The application of blocking antibodies may be an alternative treatment strategy. A synthetic gene coding for a single-chain fragment (ScFv) specific for the major timothy grass pollen allergen Phl p 2 was inserted into plasmid pCANTAB 5 E, and the recombinant ScFv was expressed in Escherichia coli and purified by affinity chromatography. The ScFv was tested for allergen binding by ELISA, and its association and dissociation were measured by surface plasmon resonance (Biacore) technology. The ability of the ScFv to inhibit allergic patients' IgE binding to Phl p 2 and Phl p 2-induced basophil degranulation was studied by ELISA competition and basophil activation (CD203c) assays. We report the expression, purification, biochemical and immunological characterization of a monomeric single-chain fragment (ScFv) of human origin specific for the major timothy grass pollen allergen, Phl p 2. The Phl p 2-ScFv showed high affinity binding to the allergen and blocked the binding of allergic patients' polyclonal IgE to Phl p 2 up to 98%. Furthermore, it inhibited allergen-induced basophil activation. The Phl p 2-ScFv inhibited allergic patients' IgE binding to Phl p 2 as well as Phl p 2-induced basophil activation and might be useful for passive immunotherapy of grass pollen allergy.