S epsilon S mu and S epsilon S gamma switch circles in human nasal mucosa following ex vivo allergen challenge: evidence for direct as well as sequential class switch recombination

Local Immunoglobulin E in nasal polyps: Role and modulation

In the airway, IgE is traditionally regarded as a key mediator in allergic diseases, such as AR and allergic asthma. However, growing evidence demonstrates the importance of local IgE in airway inflammatory diseases, irrespective of the presence of allergy. In this review, we discuss the most recent evidence for IgE in chronic rhinosinusitis with nasal polyps(CRSwNP), including the local IgE’s characteristics, the modulation of its synthesis, and its function. The levels of local IgE are significantly elevated in polyps independently of IgE serum levels and atopic status. Local IgE, which is correlated with type 2 inflammation, is polyclonal and functional. IgE is produced by active B cells and is dependent on the class switch recombination(CSR). In NPs, this process is triggered by not only allergens but also microbial colonization, especially the superantigen- Staphylococcus aureus. The production of local IgE is modulated by lymphocytes(such as Tfh, ILC2s, iTreg), cytokines(such as IL-4, IL-13, IFN-γ, TGF-β, IL-2, IL-21), transcription factors, and B cell-intrinsic factor. Due to the central role of IgE in NPs, it is regarded as an ideal target for therapy and has been proved to be clinically successful. Based on this knowledge, we believe that exploring the trigger and regulatory factors for the activation of local B cells and CSR to IgE will provide more valuable information for us to recognize the pathological mechanisms of local IgE and offer the possible option for new therapeutic targets of nasal polyps.

Sequential class switch recombination to IgE and allergen-induced accumulation of IgE+ plasmablasts occur in the nasal mucosa of local allergic rhinitis patients

BACKGROUND

The involvement of allergen-specific (s)IgE in local allergic rhinitis (LAR) has been debated. Here, we investigate the effect of nasal allergen challenge with Dermatophagoides pteronyssinus (NAC-DP) in mucosal and peripheral B-cell subpopulations in LAR patients.

METHODS

Nine LAR, 5 allergic rhinitis (AR), and 5 non-atopic healthy control (HC) individuals were subjected to a 3-day NAC-DP protocol, and nasal biopsies and blood samples were collected before and after provocation. Nasal biopsies were used for immunohistochemistry and gene expression studies, whereas the frequency of lymphocyte subsets and basophil activation test (BAT) were analyzed in blood samples by flow cytometry. sIgG was measured in sera.

RESULTS

NAC-DP induced an increase in IgE⁺ CD38⁺ plasmablasts in the nasal mucosa of LAR patients, but not in AR or HC individuals. Markers of sequential recombination to IgE (εCSR) (from IgG) were observed in 33% of LAR, 20% of AR, and 0% of HC subjects. NAC-DP increased the proportion of peripheral CD19⁺ CD20⁺ CD38⁺ plasmablasts in AR and LAR patients, but not in HC. Expression of the mucosal homing receptor CXCR3 in peripheral CD19⁺ CD20⁺ CD38⁺ plasmablasts from LAR, AR, and HC individuals was 7%, 5%, and 0.5%, respectively. In vitro DP stimulation increased proliferating CD19⁺ CD20⁺ CD38⁺ plasmablasts in LAR and AR patients, but not in HC. Serum DP-sIgG was higher in LAR and AR patients as compared to HC. BAT was positive in 33%, 100%, and 0% of LAR, AR, and HC subjects, respectively.

CONCLUSION

These results suggest that allergen exposure induces the sequential εCSR of IgG⁺ CD19⁺ CD20⁺ CD38⁺ plasmablasts in the nasal mucosa of LAR patients.

A novel digital PCR-based method to quantify (switched) B cells reveals the extent of allelic involvement in different recombination processes in the IGH locus

B cells fulfill an important role in the adaptive immunity. Upon activation and immunoglobulin (IG) class switching, these cells function in the humoral immunity compartment as plasma cells. For clinical applications, it can be important to quantify (switched) B cells accurately in a variety of body fluids and tissues of benign, inflammatory and malignant origin. For decades, flow cytometry and immunohistochemistry (IHC) have been the preferred methods for quantification. Although these methods are widely used, both depend on the accessibility of B cell epitopes and therefore require intact (fixed) cells. Whenever samples are low in quantity and/or quality, accurate quantification can be difficult. By shifting the focus from epitopes to DNA markers, quantification of B cells remains achievable. During differentiation and maturation, B cells are subjected to programmed genetic recombination processes like VDJ rearrangements and class switch recombination (CSR), which result in deletion of specific sequences of the IGH locus. These cell type-specific DNA "scars" (loss of sequences) in IG genes can be exploited as B cell markers in digital PCR (dPCR) based quantification methods. Here, we describe a novel, specific and sensitive digital PCR-based method to quantify mature and switched B cells in DNA specimens of benign and (copy number unstable) malignant origin. We compared this novel way of B cell quantitation with flow cytometric and immunohistochemical methods. Through cross-validation with flow cytometric sorted B cell subpopulations, we gained quantitative insights into allelic involvement in different recombination processes in the IGH locus. Our newly developed method is accurate and independent of the cellular context, offering new possibilities for quantification, even for (limited) small samples like liquid biopsies.

The role of allergen-specific IgE, IgG and IgA in allergic disease

Immunoglobulin E (IgE)‐mediated allergy is the most common hypersensitivity disease affecting more than 30% of the population. Exposure to even minute quantities of allergens can lead to the production of IgE antibodies in atopic individuals. This is termed allergic sensitization, which occurs mainly in early childhood. Allergen‐specific IgE then binds to the high (FcεRI) and low‐affinity receptors (FcεRII, also called CD23) for IgE on effector cells and antigen‐presenting cells. Subsequent and repeated allergen exposure increases allergen‐specific IgE levels and, by receptor cross‐linking, triggers immediate release of inflammatory mediators from mast cells and basophils whereas IgE‐facilitated allergen presentation perpetuates T cell–mediated allergic inflammation. Due to engagement of receptors which are highly selective for IgE, even tiny amounts of allergens can induce massive inflammation. Naturally occurring allergen‐specific IgG and IgA antibodies usually recognize different epitopes on allergens compared with IgE and do not efficiently interfere with allergen‐induced inflammation. However, IgG and IgA antibodies to these important IgE epitopes can be induced by allergen‐specific immunotherapy or by passive immunization. These will lead to competition with IgE for binding with the allergen and prevent allergic responses. Similarly, anti‐IgE treatment does the same by preventing IgE from binding to its receptor on mast cells and basophils. Here, we review the complex interplay of allergen‐specific IgE, IgG and IgA and the corresponding cell receptors in allergic diseases and its relevance for diagnosis, treatment and prevention of allergy.

MicroRNA-directed pathway discovery elucidates an miR-221/222-mediated regulatory circuit in class switch recombination

MicroRNAs (miRNAs, miRs) regulate cell fate decisions by post-transcriptionally tuning networks of mRNA targets. We used miRNA-directed pathway discovery to reveal a regulatory circuit that influences Ig class switch recombination (CSR). We developed a system to deplete mature, activated B cells of miRNAs, and performed a rescue screen that identified the miR-221/222 family as a positive regulator of CSR. Endogenous miR-221/222 regulated B cell CSR to IgE and IgG1 in vitro, and miR-221/222-deficient mice exhibited defective IgE production in allergic airway challenge and polyclonal B cell activation models in vivo. We combined comparative Ago2-HITS-CLIP and gene expression analyses to identify mRNAs bound and regulated by miR-221/222 in primary B cells. Interrogation of these putative direct targets uncovered functionally relevant downstream genes. Genetic depletion or pharmacological inhibition of Foxp1 and Arid1a confirmed their roles as key modulators of CSR to IgE and IgG1.

Different B cell subpopulations show distinct patterns in their IgH repertoire metrics

Several human B cell subpopulations are recognised in the peripheral blood, which play distinct roles in the humoral immune response. These cells undergo developmental and maturational changes involving VDJ recombination, somatic hypermutation and class switch recombination, altogether shaping their immunoglobulin heavy chain (IgH) repertoire. Here, we sequenced the IgH repertoire of naïve, marginal zone, switched and plasma cells from 10 healthy adults along with matched unsorted and in silico separated CD19⁺ bulk B cells. Using advanced bioinformatic analysis and machine learning, we show that sorted B cell subpopulations are characterised by distinct repertoire characteristics on both the individual sequence and the repertoire level. Sorted subpopulations shared similar repertoire characteristics with their corresponding in silico separated subsets. Furthermore, certain IgH repertoire characteristics correlated with the position of the constant region on the IgH locus. Overall, this study provides unprecedented insight over mechanisms of B cell repertoire control in peripherally circulating B cell subpopulations.

Extrafollicular IgD+ B cells generate IgE antibody secreting cells in the nasal mucosa

Increased IgE is a typical feature of allergic rhinitis. Local class-switch recombination has been intimated but B cell precursors and mechanisms remain elusive. Here we describe the dynamics underlying the generation of IgE-antibody secreting cells (ASC) in human nasal polyps (NP), mucosal tissues rich in ASC without germinal centers (GC). Using VH next generation sequencing, we identified an extrafollicular (EF) mucosal IgD+ naïve-like intermediate B cell population with high connectivity to the mucosal IgE ASC. Mucosal IgD+ B cells, express germline epsilon transcripts and predominantly co-express IgM. However, a small but significant fraction co-express IgG or IgA instead which also show connectivity to ASC IgE. Phenotypically, NP IgD+ B cells display an activated profile and molecular evidence of BCR engagement. Transcriptionally, mucosal IgD+ B cells reveal an intermediate profile between naïve B cells and ASC. Single cell IgE ASC analysis demonstrates lower mutational frequencies relative to IgG, IgA, and IgD ASC consistent with IgE ASC derivation from mucosal IgD+ B cell with low mutational load. In conclusion, we describe a novel mechanism of GC-independent, extrafollicular IgE ASC formation at the nasal mucosa whereby activated IgD+ naïve B cells locally undergo direct and indirect (through IgG and IgA), IgE class switch.

Atractylon Treatment Attenuates Pulmonary Fibrosis via Regulation of the mmu_circ_0000981/miR-211-5p/TGFBR2 Axis in an Ovalbumin-Induced Asthma Mouse Model

Asthma-induced pulmonary fibrosis (PF) is an important public health concern that has few treatment options given its poorly understood etiology; however, the epithelial to mesenchymal transition (EMT) of pulmonary epithelial cells has been implicated to play an important role in inducing PF. Although previous studies have found atractylon (Atr) to have anti-inflammatory effects, whether Atr has anti-PF abilities remains unknown. The purpose of the current study was to validate the protective efficiency of Atr in both an animal model of ovalbumin (OVA)-induced asthma and an EMT model induced by transforming growth factor-β1 (TGF-β1) using TC-1 cells. The results of this study revealed that Atr treatment suppressed OVA-induced PF via fibrosis-related protein expression. Atr treatment suppressed OVA-induced circRNA-0000981 and TGFBR2 expression but promoted miR-211-5p expression. In vivo studies revealed that Atr suppressed TGF-β1-induced EMT and fibrosis-related protein expression via suppressing circRNA-0000981 and TGFBR2 expression. The results also suggested that the downregulation of circRNA-0000981 expression suppressed TGFBR2 by sponging miR-211-5p, which was validated by a luciferase reporter assay. Collectively, the findings of the present study suggest that Atr treatment attenuates PF by regulating the mmu_circ_0000981/miR-211-5p/TGFBR2 axis in an OVA-induced asthma mouse model.

Local immunoglobulin production in nasal tissues: A key to pathogenesis in chronic rhinosinusitis with nasal polyps and aspirin-exacerbated respiratory disease

OBJECTIVE

Local activation of B cells and antibody production are important for protective and pathogenic immune responses. Furthermore, there is evidence that local activation of B cells and antibody production are important for pathogenesis of chronic rhinosinusitis with nasal polyps (CRSwNP) and a severe subset of CRSwNP, aspirin-exacerbated respiratory disease (AERD). This review summarizes these findings and the potential role of B cells and antibodies in disease pathogenesis.

DATA SOURCES

Published literature from PubMed searches.

STUDY SELECTIONS

Studies relevant to B cell development and the roles of B cells and antibodies in the pathogenesis of CRSwNP and AERD.

RESULTS

Formation of tertiary lymphoid structures plays a key role in the local activation of B cells and antibody production. This process is important for fighting infections, but it also contributes to autoimmune disease. Furthermore, there is evidence to support a role for local B cell activation and antibody production in a variety of allergic diseases. Nasal polyp tissues from patients with CRSwNP and AERD have elevated levels of activated B cell subsets and locally produced antibodies. These locally produced antibodies may contribute to disease pathogenesis in a variety of ways, including activation of innate effector cells, whereas locally activated B cells may contribute to pathogenesis through the activation of T cells.

CONCLUSION

More studies are needed to determine the role of B cells and antibodies in driving disease in these patients. However, targeting the processes that drive local B cell activation and antibody production may provide new therapeutic approaches and could help to reduce chronic inflammation.

B Cell Responses in the Development of Mammalian Meat Allergy

Studies of meat allergic patients have shown that eating meat poses a serious acute health risk that can induce severe cutaneous, gastrointestinal, and respiratory reactions. Allergic reactions in affected individuals following meat consumption are mediated predominantly by IgE antibodies specific for galactose-α-1,3-galactose (α-gal), a blood group antigen of non-primate mammals and therefore present in dietary meat. α-gal is also found within certain tick species and tick bites are strongly linked to meat allergy. Thus, it is thought that exposure to tick bites promotes cutaneous sensitization to tick antigens such as α-gal, leading to the development of IgE-mediated meat allergy. The underlying immune mechanisms by which skin exposure to ticks leads to the production of α-gal-specific IgE are poorly understood and are key to identifying novel treatments for this disease. In this review, we summarize the evidence of cutaneous exposure to tick bites and the development of mammalian meat allergy. We then provide recent insights into the role of B cells in IgE production in human patients with mammalian meat allergy and in a novel mouse model of meat allergy. Finally, we discuss existing data more generally focused on tick-mediated immunomodulation, and highlight possible mechanisms for how cutaneous exposure to tick bites might affect B cell responses in the skin and gut that contribute to loss of oral tolerance.

Tracing IgE-Producing Cells in Allergic Patients

Immunoglobulin E (IgE) is the key immunoglobulin in the pathogenesis of IgE associated allergic diseases affecting 30% of the world population. Recent data suggest that allergen-specific IgE levels in serum of allergic patients are sustained by two different mechanisms: inducible IgE production through allergen exposure, and continuous IgE production occurring even in the absence of allergen stimulus that maintains IgE levels. This assumption is supported by two observations. First, allergen exposure induces transient increases of systemic IgE production. Second, reduction in IgE levels upon depletion of IgE from the blood of allergic patients using immunoapheresis is only temporary and IgE levels quickly return to pre-treatment levels even in the absence of allergen exposure. Though IgE production has been observed in the peripheral blood and locally in various human tissues (e.g., nose, lung, spleen, bone marrow), the origin and main sites of IgE production in humans remain unknown. Furthermore, IgE-producing cells in humans have yet to be fully characterized. Capturing IgE-producing cells is challenging not only because current staining technologies are inadequate, but also because the cells are rare, they are difficult to discriminate from cells bearing IgE bound to IgE-receptors, and plasma cells express little IgE on their surface. However, due to the central role in mediating both the early and late phases of allergy, free IgE, IgE-bearing effector cells and IgE-producing cells are important therapeutic targets. Here, we discuss current knowledge and unanswered questions regarding IgE production in allergic patients as well as possible therapeutic approaches targeting IgE.

Possibility of Local Allergic Rhinitis in Japan

Background

The concept of local allergic rhinitis (LAR) has been advocated recently. Allergic rhinitis in Japan is characterized by house dust mites (HDMs) and Japanese cedar pollen (JCP). To investigate LAR in Japan, total IgE and antigen-specific IgE (sIgE) were measured in inferior turbinate mucosa and their relationships with skin test (ST) and nasal allergen provocation test (NAPT) and as well as serum IgE levels were examined.

Methods

Subjects were 50 rhinosinusitis patients for surgery. ST was performed and serum total IgE and sIgE levels were measured preoperatively. Patients with class-0 serum anti-HDM or anti-JCP sIgE levels were subjected to NAPT with HDM or JCP, respectively, or both. In all patients, inferior turbinate mucosa was weighed and mashed, and total IgE and sIgE levels were then measured as local mucosal date per gram and per milligram. Because there is no clinical consensus how to evaluate nasal sIgE yet, both positive NAPT and detectable sIgE in obtained nasal mucosa were adopted as the diagnostic criteria of LAR in order to strictly elucidate the possibility of presence of LAR in Japan.

Results

JCP LAR was definitely diagnosed in 2 of 14 patients (14.3%) and HDM LAR in 5 of 21 (23.8%) in cases with rhinosinusitis symptoms in the absence of positive ST nor serum sIgE.

Conclusion

The present results positively support LAR by HDM or JCP being present in Japan.

IgE repertoire and immunological memory: compartmental regulation and antibody function

It is now generally recognized that bone marrow is the survival niche for antigen-specific plasma cells with long-term immunological memory. These cells release antibodies into the circulation, needed to prime effector cells in the secondary immune response. These antibodies participate in the surveillance for antigen and afford immune defence against pathogens and toxins previously encountered in the primary immune response. IgE antibodies function together with their effector cells, mast cells, to exert 'immediate hypersensitivity' in mucosal tissues at the front line of immune defence. The constant supply of IgE antibodies from bone marrow plasma cells allows the rapid 'recall response' by mast cells upon re-exposure to antigen even after periods of antigen absence. The speed and sensitivity of the IgE recall response and potency of the effector cell functions are advantageous in the early detection and elimination of pathogens and toxins at the sites of attack. Local antigen provocation also stimulates de novo synthesis of IgE or its precursors of other isotypes that undergo IgE switching in the mucosa. This process, however, introduces a delay before mast cells can be sensitized and resume activity; this is terminated shortly after the antigen is eliminated. Recent results from adaptive immune receptor repertoire sequencing of immunoglobulin genes suggest that the mucosal IgE+ plasmablasts, which have undergone affinity maturation in the course of their evolution in vivo, are a source of long-lived IgE+ plasma cells in the bone marrow that are already fully functional.

Mucosal IgE immune responses in respiratory diseases

IgE is the less abundant immunoglobulin isotype in serum and displays higher affinity for its cognate Fc receptor (FcεRI) than the rest of antibody isotypes. Moreover, the class switch recombination and the generation of memory responses remarkably differ between IgE and other isotypes. Importantly, class switch recombination to IgE can occur in the mucosae, preferentially through the sequential switching from IgG. Therefore, resident effector cells get rapidly sensitized, and free IgE can be found in mucosal secretions. All these aspects explain the involvement of IgE in respiratory diseases. In allergic rhinitis and allergic asthma, the IgE-sensitization to environmental allergens triggers an eosinophilic inflammation of the airway mucosa of atopic patients. In recent years, growing evidence indicates that some non-atopic patients with nasal reactivity to allergens display nasal eosinophilic inflammation, which could be triggered by the local production of allergen-specific IgE. This phenotype has been termed local allergic rhinitis. Mucosal IgE is also implicated in the pathophysiology of chronic rhinosinusitis with nasal polyps, even though the mechanisms for IgE synthesis might differ in this case. The role of IgE as mediator of airway diseases identify this marker as a therapeutic target. Some biologicals antagonize IgE-mediated inflammation of the airway mucosa, but they have not shown a beneficial long-term effect after discontinuation. In contrast, allergen immunotherapy does not only control the symptoms of airway allergy, but it also induces a long-lasting effect after discontinuation, thus modifying the natural course of the disease.

Non-classical B Cell Memory of Allergic IgE Responses

The long-term effectiveness of antibody responses relies on the development of humoral immune memory. Humoral immunity is maintained by long-lived plasma cells that secrete antigen-specific antibodies, and memory B cells that rapidly respond to antigen re-exposure by generating new plasma cells and memory B cells. Developing effective immunological memory is essential for protection against pathogens, and is the basis of successful vaccinations. IgE responses have evolved for protection against helminth parasites infections and against toxins, but IgE is also a potent mediator of allergic diseases. There has been a dramatic increase in the incidence of allergic diseases in recent decades and this has provided the impetus to study the nature of IgE antibody responses. As will be discussed in depth in this review, the IgE memory response has unique features that distinguish it from classical B cell memory.

Human adaptive immune receptor repertoire analysis-Past, present, and future

The genes encoding adaptive immune antigen receptors, namely the immunoglobulins expressed in membrane-bound or secreted forms by B cells, and the cell surface T cell receptors, are unique in human biology because they are generated by combinatorial rearrangement of the genomic DNA. The diversity of receptors so generated in populations of lymphocytes enables the human immune system to recognize antigens expressed by pathogens, but also underlies the pathological specificity of autoimmune diseases and the mistargeted immunity in allergies. Several recent technological developments, foremost among them the invention of high-throughput DNA sequencing instruments, have enabled much deeper and thorough evaluation of clones of human B cells and T cells and the antigen receptors they express during physiological and pathogenic immune responses. The evolutionary struggles between host adaptive immune responses and populations of pathogens are now open to greater scrutiny, elucidation of the underlying reasons for successful or failed immunity, and potential predictive modeling, than ever before. Here we give an overview of the foundations, recent progress, and future prospects in this dynamic area of research.

Turbinate-Specific IgE in Normal and Rhinitic Patients

BACKGROUND

Specific immunoglobulin E (sIgE) within the nasal airway is likely to be the most ideal marker of allergic status, but little is known of the normative values in asymptomatic patients and those with rhinitis.

OBJECTIVE

The aim of this study was to assess the diagnostic characteristics of inferior turbinate tissue biopsy sIgE in asymptomatic and rhinitic patients.

METHODS

A diagnostic cross-sectional study was undertaken, involving patients who underwent inferior turbinate surgery with or without other surgical interventions. Inferior turbinate tissue biopsy was performed during surgery and was assessed for allergen sIgE (dust mite, grass [temperate or subtropical], and animal epithelium) using an automated immunoassay. Tissue sIgE was assessed among asymptomatic patients and those with nasal symptoms. Data were presented as median (interquartile range). A receiver operating curve was used to predict the diagnostic utility of turbinate tissue sIgE in determining allergic rhinitis.

RESULTS

A total of 160 patients (41.89 ± 14.65 years, 36.9% females) were included. The median tissue sIgE concentration among the asymptomatic nonatopic group of patients was 0.09 (0.08-0.10) kUA/L and tissue sIgE > 0.10 kUA/L was determined as a positive threshold. Inferior turbinate tissue sIgE was shown to be a predictive test for allergic rhinitis (area under curve: 0.87, 95% confidence interval: 0.84-0.90) with 90% sensitivity and 89% negative predictive value.

CONCLUSION

Inferior turbinate tissue biopsy sIgE is a sensitive tool to predict allergic rhinitis. The threshold value of 0.1 kUA/L corresponded well with the asymptomatic nonatopic group of patients. This method detects sIgE in the nasal mucosa and may be a useful test for allergic rhinitis in future research.

IgE Test in Secretions of Patients with Respiratory Allergy

PURPOSE OF REVIEW

IgE is a key player in multiple inflammatory airway diseases. Ample literature demonstrates its presence in mucosa of patients with allergic rhinitis (AR), local allergic rhinitis (LAR), asthma, or chronic rhinosinusitis with nasal polyposis (CRSwNP).

RECENT FINDINGS

Current evidence shows that high-affinity IgE in blood stream of allergic individuals derives mainly from the mucosae. Also, mucosal synthesis of IgE can occur in the absence of systemic atopy, and may be relevant in atopic and non-atopic phenotypes of rhinitis as demonstrated in LAR. Specific IgE (sIgE) detection varies depending on technique used for sample collection and its measurement. sIgE detection is highly specific for diagnosis of LAR. Moreover, measurement of sIgE in secretions could be useful in monitoring response to allergen-specific immunotherapy in both AR and LAR phenotypes. This review will focus on recent developments in the role of IgE in respiratory diseases, and the clinical implications of its measurement in secretions.

Structure of a patient-derived antibody in complex with allergen reveals simultaneous conventional and superantigen-like recognition

Antibodies classically bind antigens via their complementarity-determining regions, but an alternative mode of interaction involving V-domain framework regions has been observed for some B cell "superantigens." We report the crystal structure of an antibody employing both modes of interaction simultaneously and binding two antigen molecules. This human antibody from an allergic individual binds to the grass pollen allergen Phl p 7. Not only are two allergen molecules bound to each antibody fragment (Fab) but also each allergen molecule is bound by two Fabs: One epitope is recognized classically, the other in a superantigen-like manner. A single allergen molecule thus cross-links two identical Fabs, contrary to the one-antibody-one-epitope dogma, which dictates that a dimeric allergen at least is required for this to occur. Allergens trigger immediate hypersensitivity reactions by cross-linking receptor-bound IgE molecules on effector cells. We found that monomeric Phl p 7 induced degranulation of basophils sensitized solely with this monoclonal antibody expressed as an IgE, demonstrating that the dual specificity has functional consequences. The monomeric state of Phl p 7 and two structurally related allergens was confirmed by size-exclusion chromatography and multiangle laser light scattering, and the results were supported by degranulation studies with the related allergens, a second patient-derived allergen-specific antibody lacking the nonclassical binding site, and mutagenesis of the nonclassically recognized allergen epitope. The antibody dual reactivity and cross-linking mechanism not only have implications for understanding allergenicity and allergen potency but, importantly, also have broader relevance to antigen recognition by membrane Ig and cross-linking of the B cell receptor.

The impact of allergen exposure and specific immunotherapy on circulating blood cells in allergic rhinitis

Allergic rhinitis (AR) is an IgE-mediated inflammatory disease of the nasal mucosa with well described local immune responses during allergen exposure. The frequent association of AR with general extra-nasal symptoms and other allergic conditions, such as conjunctivitis and asthma, however, support a more systemic disease impact. In addition to acute elevation of soluble inflammatory mediators in periphery blood, a growing number of studies have reported changes in circulating blood cells after specific nasal allergen challenge or environmental allergen exposure. These findings imply an involvement of specific blood leukocyte subsets, thrombocytes and recently, erythrocytes. This review summarizes the circulating blood cell dynamics associated with allergen exposure in AR subjects reported so far. Additionally, the impact of therapy, particularly allergen-specific immunotherapy (AIT), the only currently available causal treatment reducing AR-related symptoms, is further considered in this context.

Intranasal administration of allergen increases specific IgE whereas intranasal omalizumab does not increase serum IgE levels-A pilot study

Background

Administration of the therapeutic anti‐IgE antibody omalizumab to patients induces strong increases in IgE antibody levels.

Objective

To investigate the effect of intranasal administration of major birch pollen allergen Bet v 1, omalizumab or placebo on the levels of total and allergen‐specific IgE in patients with birch pollen allergy.

Methods

Based on the fact that intranasal allergen application induces rises of systemic allergen‐specific IgE, we performed a double‐blind placebo‐controlled pilot trial in which birch pollen allergic subjects were challenged intranasally with omalizumab, placebo or birch pollen allergen Bet v 1. Total and allergen‐specific IgE, IgG and basophil sensitivity were measured before and 8 weeks after challenge. For control purposes, total, allergen‐specific IgE levels and omalizumab‐IgE complexes as well as specific IgG levels were studied in subjects treated subcutaneously with either omalizumab or placebo. Effects of omalizumab on IgE production by IL‐4/anti‐CD40‐treated PBMCs from allergic patients were studied in vitro.

Results

Intranasal challenge with Bet v 1 induced increases in Bet v 1‐specific IgE levels by a median of 59.2%, and this change differed significantly from the other treatment groups (P = .016). No relevant change in allergen‐specific and total IgE levels was observed in subjects challenged with omalizumab. Addition of omalizumab did not enhance IL‐4/anti‐CD40‐induced IgE production in vitro. Significant rises in total IgE (mean IgE before: 131.83 kU/L to mean IgE after: 505.23 kU/L) and the presence of IgE‐omalizumab complexes were observed after subcutaneous administration of omalizumab.

Conclusion

Intranasal administration of allergen induced rises of allergen‐specific IgE levels, whereas intranasal administration of omalizumab did not enhance systemic total or allergen‐specific IgE levels.

International Consensus Statement on Allergy and Rhinology: Allergic Rhinitis

BACKGROUND

Critical examination of the quality and validity of available allergic rhinitis (AR) literature is necessary to improve understanding and to appropriately translate this knowledge to clinical care of the AR patient. To evaluate the existing AR literature, international multidisciplinary experts with an interest in AR have produced the International Consensus statement on Allergy and Rhinology: Allergic Rhinitis (ICAR:AR).

METHODS

Using previously described methodology, specific topics were developed relating to AR. Each topic was assigned a literature review, evidence-based review (EBR), or evidence-based review with recommendations (EBRR) format as dictated by available evidence and purpose within the ICAR:AR document. Following iterative reviews of each topic, the ICAR:AR document was synthesized and reviewed by all authors for consensus.

RESULTS

The ICAR:AR document addresses over 100 individual topics related to AR, including diagnosis, pathophysiology, epidemiology, disease burden, risk factors for the development of AR, allergy testing modalities, treatment, and other conditions/comorbidities associated with AR.

CONCLUSION

This critical review of the AR literature has identified several strengths; providers can be confident that treatment decisions are supported by rigorous studies. However, there are also substantial gaps in the AR literature. These knowledge gaps should be viewed as opportunities for improvement, as often the things that we teach and the medicine that we practice are not based on the best quality evidence. This document aims to highlight the strengths and weaknesses of the AR literature to identify areas for future AR research and improved understanding.

The mast cell stabilizing activity of Chaga mushroom critical for its therapeutic effect on food allergy is derived from inotodiol

While an anti-allergic effect of Chaga mushroom (Inonotus obliquus) has been indicated, its therapeutic effect on allergy and immunoregulatory mechanisms and chemical constituents directly responsible for that are hardly known. We examined the effect of 70% ethanol extract of Chaga mushroom (EE) and its dichloromethane (DF) and aqueous (AF) fractions using a mouse model of chicken ovalbumin (cOVA)-induced food allergy, and found that only EE and DF ameliorated allergy symptoms to a significant extent. The in vivo mast cell-stabilizing activity was also found only in EE and DF whereas the activities to suppress Th2 and Th17 immune responses and cOVA-specific IgE production in the small intestine were observed in all three treatment regimens, implying that inhibition of the mast cell function by lipophilic compounds was vital for the therapeutic effect. Results also indicated that inotodiol, a triterpenoid predominantly present in DF, played an active role as a mast cell stabilizer.

Local Allergic Rhinitis in Pediatric Patients: Is IgE Dosage in Nasal Lavage Fluid a Useful Diagnostic Method in Children?

Local Allergic Rhinitis (LAR) is an emerging disease. However, its incidence in the pediatric popolution has not yet been studied. The gold standard for the diagnosis is the nasal provocation test that is not everywhere avalaible and difficult to apply in children. The aim of our study was to evaluate the nasal lavage fluid IgE as a biomarker of LAR in children. 54 pediatric patients [IQR 4.0-12.0 years] were divided into 3 groups: study group (26 children with rhinitis symptoms and without evidence of systemic atopy); allergic rhinitis (AR) group (15 children) and 13 healty controls (HC). Every child was subjected to nasal lavage using 2 ml/nostril of physiologic saline solution, that was therefore analyzed by ImmunoCAP to obtain the IgE concentration. Rhinofibroscopy and nasal cytology were performed. Our data showed the presence of higher value of nasal lavage fluid IgE (average of 6.005 UI/ml; range: 4.47-7.74 UI/ml) in 16 out of 26 patients of the study group who therefore may be classified as affected by LAR. We observed a statistically significant difference (P< 0.0001) between NAR/HC group and LAR group, identifying a cut-off of 3.85 UI/ml. Finally, we found a better response to previous AR therapy in the LAR group than in the NAR group. Our data showed the high incidence of LAR in pediatric patients previously classified as NAR. The measurment of IgE in nasal lavage fluid may be considered an easy and rapid method for the diagnosis of LAR in children. Besides, our data add confirmatory evidence about the good response of LAR children to the classic AR therapy.

IgG1 memory B cells keep the memory of IgE responses

The unique differentiation of IgE cells suggests unconventional mechanisms of IgE memory. IgE germinal centre cells are transient, most IgE cells are plasma cells, and high affinity IgE is produced by the switching of IgG1 cells to IgE. Here we investigate the function of subsets of IgG1 memory B cells in IgE production and find that two subsets of IgG1 memory B cells, CD80+CD73+ and CD80-CD73-, contribute distinctively to the repertoires of high affinity pathogenic IgE and low affinity non-pathogenic IgE. Furthermore, repertoire analysis indicates that high affinity IgE and IgG1 plasma cells differentiate from rare CD80+CD73+ high affinity memory clones without undergoing further mutagenesis. By identifying the cellular origin of high affinity IgE and the clonal selection of high affinity memory B cells into the plasma cell fate, our findings provide fundamental insights into the pathogenesis of allergies, and on the mechanisms of antibody production in memory B cell responses.IgE is an important mediator of protective immunity as well as allergic reaction, but how high affinity IgE antibodies are produced in memory responses is not clear. Here the authors show that IgE can be generated via class-switch recombination in IgG1 memory B cells without additional somatic hypermutation.

Fifty years later: Emerging functions of IgE antibodies in host defense, immune regulation, and allergic diseases

Fifty years ago, after a long search, IgE emerged as the circulating factor responsible for triggering allergic reactions. Its extremely low concentration in plasma created significant hurdles for scientists working to reveal its identity. We now know that IgE levels are invariably increased in patients affected by atopic conditions and that IgE provides the critical link between the antigen recognition role of the adaptive immune system and the effector functions of mast cells and basophils at mucosal and cutaneous sites of environmental exposure. This review discusses the established mechanisms of action of IgE in pathologic immediate hypersensitivity, as well as its multifaceted roles in protective immunity, control of mast cell homeostasis, and its more recently revealed immunomodulatory functions.

Nonallergic rhinitis and lower airway disease

In the past years, several investigators have demonstrated the existence of local nasal responses in some patients with typical allergic rhinitis symptoms but without atopy and have defined a new phenotype called local allergic rhinitis (LAR) or 'entopy'. In a percentage of LAR subjects, the upper airway disease is also associated with lower airway symptoms. After the description of this phenotype, the differential diagnosis between LAR and nonallergic rhinitis (NAR) has become a challenge for the clinician. To correctly identify LAR patients is of high importance for treatment and management of these patients, and for an appropriate inclusion of patients in clinical trials and genetics studies. The treatment of LAR patients, in contrast with NAR, is oriented to allergen avoidance and specific treatment. Allergen immunotherapy, the aetiological treatment for allergic respiratory diseases, has demonstrated to be an effective and safe treatment in LAR, increasing immunological tolerance, and reducing the clinical symptoms and the use of medication. In this article, the important and novel aspects of LAR in terms of mechanisms, diagnosis and treatment will be discussed. Also, the involvement of the lower airway and the potential role of IgE in the bronchial disease will be also reviewed.

Direct versus sequential immunoglobulin switch in allergy and antiviral responses

Allergy is characterized by IgE production to innocuous antigens. The question whether the switch to IgE synthesis occurs via direct or sequential pathways is still unresolved. The aim of this work was to analyze the distribution of immunoglobulins (Ig) to house dust mite D. farinae and A. alternata fungus in allergic children with primarily established diagnosis and compare it to Epstein-Barr antiviral (EBV) response in the same patients. In allergy patients the only significant difference was found in allergen specific IgE, likely mediated by a direct isotype switch, while antiviral response was dominated by EBV specific IgG and low level of concordant IgA and IgG4 production consistent with a minor sequential Ig switches. Taken collectively, we concluded that sequential isotype switch is likely to be a much rarer event than a direct one.

Follicular helper T cells are responsible for IgE responses to Der p 1 following house dust mite sensitization in mice

BACKGROUND

Th2 cells have long been considered responsible for the switching of B cells to production of IgE during cognate interaction, primarily due to their expression of CD40L and secretion of IL-4. This concept has been challenged by the more recent definition of follicular helper T cells (Tfh) as the key T cell subset in B cell isotype switching, due to their physical location at the boundary of T cell:B cell areas in lymphoid follicles and ability to express IL-4 and CD40L.

OBJECTIVE

To determine whether Tfh cells are responsible for IgE responses to Der p 1 allergen after house dust mite (HDM)-induced allergic sensitization.

METHODS

Mice deficient in Tfh cells were sensitized to HDM and Der p 1-specific IgE measured by ELISA.

RESULTS

Mice with a mutation in T cell-expressed IL-6R were unable to expand Tfh populations after HDM sensitization, and their anti-Der p 1 IgE, IgG1 and total IgE responses were reduced by 80-90% compared with wild-type mice. These animals displayed unaltered lung Th2 and eosinophilic responses after intranasal HDM challenge and normal IL-4 production, but B cell infiltration of the airways was abrogated.

CONCLUSIONS AND CLINICAL RELEVANCE

Our data indicate that Tfh cells are largely responsible for switching B cells to IgE synthesis, most likely via an IgG1(+) intermediate. However, Th2 cells are the major source of IL-4 during HDM sensitization and this might contribute to IgE synthesis at a stage distal to Tfh-mediated isotype switching. The IL-6/follicular helper T cell pathway is a potential therapeutic target in allergic disease.

[Local allergic rhinitis to Alternaria alternata : Evidence for local IgE production exclusively in the nasal mucosa]

In a subgroup of patients with symptoms of allergic rhinitis (AR), no systemic sensitization can be detected in skin tests or serum. These patients are considered to be afflicted with so-called "local allergic rhinitis" (LAR) with IgE-production exclusively at the site of the nasal mucosa. Patients without any positive allergy test results but seasonal (intermittent) or perennial (persistent) allergic symptoms were often misdiagnosed as having "non-allergic rhinitis" (NAR) in the past.However, there is evidence for a specific IgE-production in the nasal mucosa in these patients without systemic sensitization. The diagnosis of LAR is confirmed by clinical symptoms, the detection of specific IgE production in the nasal mucosa and/or nasal provocation tests.We report on two cases of LAR to Alternaria alternata with symptoms of persistent allergic rhinitis that have been diagnosed by positive allergenspecific nasal challenge tests and specific IgE determinations in nasal secretions.According to an actual literature research, this is the second report published on LAR caused by Alternaria alternata.

Local IgE in non-allergic rhinitis

Local allergic rhinitis (LAR) is characterized by the presence of a nasal Th2 inflammatory response with local production of specific IgE antibodies and a positive response to a nasal allergen provocation test (NAPT) without evidence of systemic atopy. The prevalence has been shown to be up to 25% in subjects affected with rhinitis with persistence, comorbidity and evolution similar to allergic rhinitis. LAR is a consistent entity that does not evolve to allergic rhinitis with systemic atopy over time although patients have significant impairment in quality of life and increase in the severity of nasal symptoms over time. Lower airways can be also involved. The diagnosis of LAR is based mostly on demonstration of positive response to NAPT and/or local synthesis of specific IgE. Allergens involved include seasonal or perennial such as house dusts mites, pollens, animal epithelia, moulds (alternaria) and others. Basophils from peripheral blood may be activated by the involved allergens suggesting the spill over of locally synthesized specific IgE to the circulation. LAR patients will benefit from the same treatment as allergic patients using antihistamines, inhaled corticosteroids and IgE antagonists. Studies on immunotherapy are ongoing and will determine its efficacy in LAR in terms of symptoms improvement and evolution of the natural course of the disease.

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.

Intrinsic properties of germinal center-derived B cells promote their enhanced class switching to IgE

Background

Research on the origins and development of human IgE‐expressing (IgE⁺) cells is required for understanding the pathogenesis of allergy and asthma. These studies have been thwarted by the rarity of IgE⁺ cells in vivo and the low frequency of class switch recombination (CSR) to IgE ex vivo. To determine the main source of IgE⁺ cells, we investigated the relation between the phenotypic composition of tonsil B cells and the CSR to IgE ex vivo.

Methods

Human tonsil B cells were analyzed by flow cytometry (FACS) and cultured with IL‐4 and anti‐CD40 to induce CSR to IgE. Naïve, germinal center (GC), early GC (eGC), and memory tonsil B cells were isolated by FACS, and their capacities for IL‐4 and anti‐CD40 signaling, cell proliferation, and de novo class switching to IgE were analyzed by RT‐PCR and FACS.

Results

B cells from different tonsils exhibited varying capacities for CSR to IgE ex vivo. This was correlated with the percentage of eGC B cells in the tonsil at the outset of the culture. Despite relatively poor cell viability, eGC and GC B‐cell cultures produced the highest yields of IgE⁺ cells compared to naïve and memory B‐cell cultures. The main factors accounting for this result were the strength of IL‐4R and CD40 signaling and relative rates of cell proliferation.

Conclusions

This study shows that the maturation state of tonsil B cells determines their capacity to undergo class switching to IgE ex vivo, with the GC‐derived B cells yielding the highest percentage of IgE⁺ cells.

Poor association of allergen-specific antibody, T- and B-cell responses revealed with recombinant allergens and a CFSE dilution-based assay

BACKGROUND

The adaptive immunity underlying allergy comprises two components, the allergen-specific antibody (i.e. IgE, IgG) and the T-cell response. These two components are responsible for different disease manifestations and can be targeted by different therapeutic approaches. Here, we investigated the association of allergen-specific antibody and T- as well as B-cell responses in pollen-allergic patients using recombinant (r) major birch pollen allergen rBet v 1 and major timothy grass pollen allergen rPhl p 5 as defined antigens.

METHODS

Allergen-specific IgE and IgG antibody responses were determined by ELISA, and allergen-specific T- and B-cell responses were measured in peripheral blood mononuclear cells using a carboxyfluorescein-diacetate-succinimidylester (CFSE) dilution assay.

RESULTS

CFSE staining in combination with T-cell- and B-cell-specific gating allowed discriminating between allergen-specific T-cell and B-cell responses. Interestingly, we identified patients where mainly T cells and others where mainly B cells proliferated in response to allergen stimulation. No association between the level of allergen-specific Ig responses and B- or T-cell proliferation was observed.

CONCLUSION

Purified recombinant allergens in conjunction with CFSE staining allow the dissection of allergen-specific B- and T-cell responses. The dissociation of allergen-specific antibody, and B- and T-cell responses may explain the occurrence of selective IgE- and T-cell-mediated manifestations of allergic inflammation and may be important for the development of diagnostic and therapeutic strategies selectively targeting B cells and T cells.

Human B-cell isotype switching origins of IgE

BACKGROUND

B cells expressing IgE contribute to immunity against parasites and venoms and are the source of antigen specificity in allergic patients, yet the developmental pathways producing these B cells in human subjects remain a subject of debate. Much of our knowledge of IgE lineage development derives from model studies in mice rather than from human subjects.

OBJECTIVE

We evaluate models for isotype switching to IgE in human subjects using immunoglobulin heavy chain (IGH) mutational lineage data.

METHODS

We analyzed IGH repertoires in 9 allergic and 24 healthy adults using high-throughput DNA sequencing of 15,843,270 IGH rearrangements to identify clonal lineages of B cells containing members expressing IgE. Somatic mutations in IGH inherited from common ancestors within the clonal lineage are used to infer the relationships between B cells.

RESULTS

Data from 613,641 multi-isotype B-cell clonal lineages, of which 592 include an IgE member, are consistent with indirect switching to IgE from IgG- or IgA-expressing lineage members in human subjects. We also find that these inferred isotype switching frequencies are similar in healthy and allergic subjects.

CONCLUSIONS

We found evidence that secondary isotype switching of mutated IgG1-expressing B cells is the primary source of IgE in human subjects, with lesser contributions from precursors expressing other switched isotypes and rarely IgM or IgD, suggesting that IgE is derived from previously antigen-experienced B cells rather than naive B cells that typically express low-affinity unmutated antibodies. These data provide a basis from which to evaluate allergen-specific human antibody repertoires in healthy and diseased subjects.

Local immunoglobulin e in the nasal mucosa: clinical implications

Immunoglobulin E (IgE) can be highly elevated in the airway mucosa independently of IgE serum levels and atopic status. Mostly, systemic markers are assessed to investigate inflammation in airway disease for research or clinical practice. A more accurate but more cumbersome approach to determine inflammation at the target organ would be to evaluate markers locally. We review evidence for local production of IgE in allergic rhinitis (AR) and chronic rhinosinusitis with nasal polyps (CRSwNP). Diagnostic and therapeutic consequences in clinical practice are discussed. We describe that the airway mucosa has the intrinsic capability to produce IgE. Moreover, not only do IgE-positive B cells reside within the mucosa, but all tools are present locally for affinity maturation by somatic hypermutation (SHM), clonal expansion, and class switch recombination to IgE. Recognizing local IgE in the absence of systemic IgE has diagnostic and therapeutic consequences. Therefore, we emphasize the importance of local IgE in patients with a history of AR or CRSwNP.

Influence of seasonal exposure to grass pollen on local and peripheral blood IgE repertoires in patients with allergic rhinitis

Background

Previous studies of immunoglobulin gene sequences in patients with allergic diseases using low-throughput Sanger sequencing have limited the analytic depth for characterization of IgE repertoires.

Objectives

We used a high-throughput, next-generation sequencing approach to characterize immunoglobulin heavy-chain gene (IGH) repertoires in patients with seasonal allergic rhinitis (AR) with the aim of better understanding the underlying disease mechanisms.

Methods

IGH sequences in matched peripheral blood and nasal biopsy specimens from nonallergic healthy control subjects (n = 3) and patients with grass pollen–related AR taken in season (n = 3) or out of season (n = 4) were amplified and pyrosequenced on the 454 GS FLX+ System.

Results

A total of 97,610 IGH (including 8,135 IgE) sequences were analyzed. Use of immunoglobulin heavy-chain variable region gene families 1 (IGHV1) and 5 (IGHV5) was higher in IgE clonotypic repertoires compared with other antibody classes independent of atopic status. IgE repertoires measured inside the grass pollen season were more diverse and more mutated (particularly in the biopsy specimens) and had more evidence of antigen-driven selection compared with those taken outside of the pollen season or from healthy control subjects. Clonal relatedness was observed for IgE between the blood and nasal biopsy specimens. Furthermore in patients with AR, but not healthy control subjects, we found clonal relatedness between IgE and IgG classes.

Conclusion

This is the first report that exploits next-generation sequencing to determine local and peripheral blood IGH repertoires in patients with respiratory allergic disease. We demonstrate that natural pollen exposure was associated with changes in IgE repertoires that were suggestive of ongoing germinal center reactions. Furthermore, these changes were more often apparent in nasal biopsy specimens compared with peripheral blood and in patients with AR compared with healthy control subjects.

Biology of IgE production: IgE cell differentiation and the memory of IgE responses

The generation of long-lived plasma cells and memory B cells producing high-affinity antibodies depends on the maturation of B cell responses in germinal centers. These processes are essential for long-lasting antibody-mediated protection against infections. IgE antibodies are important for defense against parasites and toxins and can also mediate anti-tumor immunity. However, high-affinity IgE is also the main culprit responsible for the manifestations of allergic disease, including life-threatening anaphylaxisAnaphylaxis . Thus, generation of high-affinity IgE must be tightly regulated. Recent studies of IgE B cell biology have unveiled two mechanisms that limit high-affinity IgE memory responses: First, B cells that have recently switched to IgE production are programmed to rapidly differentiate into plasma cells,Plasma cells and second, IgE germinal centerGerminal center cells are transient and highly apoptotic. Opposing these processes, we now know that germinal center-derived IgG B cells can switch to IgE production, effectively becoming IgE-producing plasma cells. In this chapter, we will discuss the unique molecular and cellular pathways involved in the generation of IgE antibodies.

Alterations on peripheral blood B cell subsets induced by allergic rhinitis

OBJECTIVES AND DESIGN

Here we evaluated whether allergic rhinitis to Dermatophagoides pteronyssinus induces alterations on circulating B cell subsets.

MATERIALS AND METHODS

Circulating B cell subsets and isotype expression on antigen-experienced B cells from allergic patients under conventional pharmacological treatment (NO-SIT, n = 15) and under subcutaneous immunotherapy (SCIT, n = 33), and non-allergic subjects (NC, n = 25) were analyzed by flow cytometry.

RESULTS

In allergic patients, we found a significant decrease in IgM(+) and IgG(+) memory B cells and an increase in IgA(+) memory B cells. Additionally, the numbers of circulating IgA(+) plasmablasts in allergic patients were also increased, while those cells expressing IgM were reduced.

CONCLUSIONS

Allergic patients have a disturbed B cell subsets distribution which seems to underlie rhinitis pathogenesis and remain unchanged after SCIT.

IgE responses in mouse and man and the persistence of IgE memory

Rapid and robust recall or 'memory' responses are an essential feature of adaptive immunity. They constitute a defense against reinfection by pathogens, yet arguably do more harm than good in allergic disease. Immunoglobulin (Ig)E antibodies mediate the allergic reaction characterized by immediate hypersensitivity, a manifestation of IgE memory. The origin of IgE memory remains obscure, mainly due to the low proportion of IgE-expressing B cells in the total B cell population. The recent development of ultrasensitive methods for tracking these cells in vivo has overcome this obstacle, and their use has revealed unexpected pathways to IgE memory in the mouse. Here, we review these findings and consider their bearing on our understanding of IgE memory and allergic disease in man.

Local increase in IgE and class switch recombination to IgE in nasal polyps in chronic rhinosinusitis

BACKGROUND

Chronic rhinosinusitis with nasal polyps is generally characterized by local Th2 inflammation and is categorized into two subtypes in Japan: eosinophilic chronic rhinosinusitis (similar to chronic rhinosinusitis with nasal polyps in western countries) and non-eosinophilic chronic rhinosinusitis (characterized by Th1-dominant inflammation).

OBJECTIVE

To investigate local IgE production and class switch recombination to IgE in these two subtypes of chronic rhinosinusitis with nasal polyps.

METHODS

The identity of IgE-positive cells was determined using double-immunofluorescent staining for IgE and cell-type-specific molecular markers. To investigate the local class switch recombination to IgE and IgE synthesis in the mucosa, we performed real-time polymerase chain reaction to examine the mRNA expression of Th2 cytokines and class-switch-related molecules, including IL-4, IL-5, IL-13, ε germline gene transcripts, IgE mature transcript, IgG mature transcript, RAG1, RAG2 and activation-induced cytidine deaminase in eosinophilic polyps, non-eosinophilic polyps and controls.

RESULTS

The concentrations of total IgE and number of IgE-positive cells were significantly higher in the eosinophilic polyps compared with control and non-eosinophilic polyps. IgE-positive cells were predominantly mast cells in eosinophilic polyps and significantly correlated with the number of FcεR1-positive cells in the subepithelial layer. IL-5 and IL-13 mRNA and ε germline gene transcripts expression levels were significantly higher in eosinophilic polyps compared with control and non-eosinophilic polyps. In contrast, the number of plasma cells and the expression of IgG mature transcripts were increased in non-eosinophilic polyps compared with eosinophilic polyps. RAG2 mRNA was significantly increased in both eosinophilic and non-eosinophilic polyps compared with control mucosa.

CONCLUSION AND CLINICAL RELEVANCE

The current study suggests local class switching to IgE, production of IgE and IgE localization to the surface of mast cells in eosinophilic chronic rhinosinusitis in the Japanese population. The difference in the IgE-related profiles between eosinophilic chronic rhinosinusitis and non-eosinophilic chronic rhinosinusitis suggests heterogeneity in the pathogenesis of chronic rhinosinusitis with nasal polyps.

[Local (exclusive) IgE production in the nasal mucosa. Evidence for local allergic rhinitis]

BACKGROUND

IgE production at the site of the nasal mucosa without systemic allergic sensitization in skin tests or in serum represents so-called "local allergic rhinitis (LAR)" as a subgroup of patients with symptoms of allergic rhinitis (AR). Formerly, in case of negative allergological test results, seasonal (intermittent) or perennial (persistent) allergic symptoms have been diagnosed as "non-allergic rhinitis" (NAR). However, there is evidence for specific Th2 cytokine, tryptase, and ECP (eosinophil catonic protein) production in the nasal secretion after allergen exposure in these patients without systemic sensitization.

DIAGNOSIS

Taking this into account, we recommend performing an allergen-specific nasal challenge and measuring the (local) nasal IgE-levels in addition to standard allergy tests in clinical routine in this subgroup of patients. These tests should be perfomed while or shortly after allergen exposure. In addition, an update of the allergy testing should be performed after a time interval since it has been demonstrated that patients formerly diagnosed with NAR may develop LAR or AR, or patients with LAR may develop AR in the future.

TREATMENT

The pharmacological therapeutic options in LAR are in line with the treatment of AR. If and to what extent this subgroup of AR patients benefit from allergen-specific immunotherapy (SIT) is currently being evaluated in clinical trials.

What is the source of serum allergen-specific IgE?

Immunoglobulin E (IgE), the key effector element in the induction and propagation of allergic diseases, is the least abundant antibody class. In allergic patients, class switch recombination to IgE in B cells is induced by allergen contact in conjunction with T cell interaction and a Th2 cytokine environment. With regard to future therapeutic approaches, the sites of IgE production in human subjects and the nature and characteristics of IgE-producing cells are of great interest. In this context, it has been shown that allergen-specific IgE levels can be boosted by contact with allergens via the respiratory mucosa of the nose. Also, it has been proposed that allergy effector organs (e.g., the nasal mucosa and the lung) may be important sites of IgE production in allergic patients. IgE-producing cells have also been found in the blood, but their numbers are extremely low. Transfer of specific sensitization during bone marrow transplantation indicates the presence of IgE-producing B memory cells or plasma cells also in the bone marrow. This review summarizes data on the induction of IgE production, IgE memory and the sites of IgE production in human allergic patients.

Chronic rhinosinusitis with nasal polyps is characterized by B-cell inflammation and EBV-induced protein 2 expression

BACKGROUND

Despite the high prevalence and morbidity of chronic rhinosinusitis (CRS), little is known about the mechanisms that underlie its pathogenesis. Recent studies have suggested that B cells might play an important role in CRS.

OBJECTIVE

We sought to thoroughly characterize B lineage cells within sinus tissues of patients with CRS and healthy control subjects and to determine whether levels of EBV-induced protein 2, which is known to play an important role in the development of B-cell responses, were increased in patients with CRS.

METHODS

Cells isolated from sinus tissues of patients with CRS and healthy control subjects were characterized by means of flow cytometry and immunohistochemistry. Local production of antibodies was measured in tissue extracts, nasal lavage fluid, and sera by using multiplex bead arrays and ELISA. Quantitative RT-PCR, ELISA, and Western blotting were used to assess gene and protein expression from tissue extracts.

RESULTS

Nasal polyps (NPs) from patients with CRS had increased levels of both B cells and plasma cells compared with uncinate tissue from healthy control subjects (P<.05). NPs also contained significantly increased levels of several antibody isotypes compared with normal uncinate tissue (P<.05), but no differences in circulating antibody levels were found. Interestingly, levels of EBV-induced protein 2 were also increased in NPs (P<.05) and were positively correlated with expression of plasma cell markers (CD138 and B lymphocyte-induced maturation protein) in sinus tissue.

CONCLUSION

B cells and plasma cells are enriched in NPs, actively produce antibodies locally, and might contribute to chronic inflammation in patients with CRS. Elucidating the mechanisms that underlie this excessive local B-cell response might provide novel insights for the development of improved therapeutic strategies.

Local receptor revision and class switching to IgE in chronic rhinosinusitis with nasal polyps

BACKGROUND

Chronic rhinosinusitis with nasal polyps (NP) and allergic rhinitis (AR) is characterized by local Th2 inflammation and up-regulation of IgE; however, IgE in NP is 'polyclonal' and allergen specific, whereas IgE in AR is 'oligoclonal' and allergen specific. Germinal center (GC) reactions occur in AR, while only the formation of GC-like structures in NP is described. The aim of this study was to investigate the involvement of local IgE production, class switch recombination, and receptor revision in NP.

METHODS

We compared the levels of local IgE, germline gene transcripts, and mature Ig mRNA expression, recombination activating gene (RAG1 and RAG2), key markers of Th2 inflammation, and GC reactions in NP tissue vs AR and control tissue. Nasal mucosa was immunostained for the co-expression of RAG1 and RAG2 in B cells, plasma cells, and T cells, using dual or triple immunofluorescence (IF).

RESULTS

In NP, local IgE level and key markers of local class switching are increased compared with AR and normal controls (NC). In NP, switch circle transcripts reveal ongoing local class switch recombination to IgE. Up to 30% of B cells, plasma cells, and T cells in nasal polyps re-express both RAG1 and RAG2, required for receptor revision. RAG1 and RAG2 mRNA concentrations are increased in NP and correlated with the magnitude of inflammation and the presence of S. aureus enterotoxin (superantigen)-specific IgE in the nasal polyp mucosa.

CONCLUSION

Our results provide the first evidence of local receptor revision and class switching to IgE, and B-cell differentiation into IgE-secreting plasma cells in NP.